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How did so many types of larvae become known as worms?

How did so many types of larvae become known as worms?


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How did it come to be that so many types of creatures typically known as worms are actually insect larvae? Silkworms are not actually worms at all, but larvae of a type of moth. Another example being the Maguey worm, which is supposedly the worm in some types of tequila and also not a worm, actually also a type of moth-larvae?

I find it curious that Wikipedia would have a creature with the word worm in its title, and then the first thing they tell you about it is that it is actually an insect. These are just the two examples I came across, there are probably more.


Excellent question. My zoology professor during biology undergrads explained this by clarifying that "worm" is a term that relates to one type of shape of animals. As such it does not carry any additional information on the relatedness of animals or their developmental stage.

This view also seems to align with wikipedia.


An addition to tsttst answer:

"Worm" can go to very abstract realms, in Neuroethology "Worm" can be a stimulus attribute:

horizontal movement implied:

▄▄▄▄▄▄ would be considered "Worm configuration"





▀ would be considered "antiworm" (ignore the white stripes)

at this level of abstraction underlying taxa would not matter at all, could be an eel, a snake or a branch , or a piece of cardboard. As long as it triggers the "worm " synapse


This isn't really a matter of biology so much as etymology.

The English word for "worm" was applied to any sort of slithering distasteful creature for centuries before we actually started get our taxonomies properly sorted out. Thus, the word "worm" ended up in the common names for lots of organisms without any real relationship to one another besides their generally cylindrical shape. It's also unsurprising that there are so many different things that have ended up with that shape, because it's a really simple one to grow and thus an easy case for convergent evolution.

In short: "worm" just describes a common shape and isn't really a biological term of art.


In common English, worm is not a precise biological term, and long predates even the idea of precise biological names. It's a generic descriptor for creatures that are long & skinny, without much in the way of legs. So we have earthworms, silkworms, tapeworms, &c. Even dragons can be called worms - or wurms, wyrms, &c, depending on your spelling preferences. For instance, Old English epic Beowulf https://en.wikipedia.org/wiki/Beowulf ends with Beowulf fighting & being slain by a wyrm or dragon.

PS: Worm is also applied to non-biological things, for instance the worm gear: https://en.wikipedia.org/wiki/Worm_drive


How Did Insect Metamorphosis Evolve?

In the 1830s a German naturalist named Renous was arrested in San Fernando, Chile for heresy. His claim? He could turn caterpillars into butterflies. A few years later, Renous recounted his tale to Charles Darwin, who noted it in The Voyage of the Beagle.

Imprisoning someone for asserting what today qualifies as common knowledge might seem extreme, but metamorphosis&mdashthe process through which some animals abruptly transform their bodies after birth&mdashhas long inspired misunderstanding and mysticism. People have known since at least the time of ancient Egypt that worms and grubs develop into adult insects, but the evolution of insect metamorphosis remains a genuine biological mystery even today. Some scientists have proposed outlandish origin tales, such as Donald Williamson's idea that butterfly metamorphosis resulted from an ancient and accidental mating between two different species&mdashone that wriggled along ground and one that flitted through the air.

Metamorphosis is a truly bizarre process, but an explanation of its evolution does not require such unsubstantiated theories (for a critique of Williamson's hypothesis, see this study). By combining evidence from the fossil record with studies on insect anatomy and development, biologists have established a plausible narrative about the origin of insect metamorphosis, which they continue to revise as new information surfaces. The earliest insects in Earth's history did not metamorphose they hatched from eggs, essentially as miniature adults. Between 280 million and 300 million years ago, however, some insects began to mature a little differently&mdashthey hatched in forms that neither looked nor behaved like their adult versions. This shift proved remarkably beneficial: young and old insects were no longer competing for the same resources. Metamorphosis was so successful that, today, as many as 65 percent of all animal species on the planet are metamorphosing insects.

The egg of an idea
In 1651 English physician William Harvey published a book in which he proposed that caterpillars and other insect larvas were free-living embryos that abandoned nutrient-poor "imperfect eggs" before they matured. Harvey further argued that the cocoon or chrysalis a caterpillar entered during its pupal stage was a second egg in which the prematurely hatched embryo was born again. He entertained the idea that a caterpillar was one creature and a butterfly was an entirely different beast.

Some of Harvey's ideas were prescient, but he mostly misinterpreted what he observed. In 1669 Dutch biologist Jan Swammerdam rejected Harvey's notion of the pupa as an egg and the butterfly as a different animal than the caterpillar. Swammerdam dissected all kinds of insects under a microscope, confirming that the larva, pupa and adult insect were phases in the development of a single individual, not distinct creatures. He showed that one could find immature moth and butterfly body parts inside a larva, even before it spun a cocoon or formed a chrysalis. In some demonstrations, for example, Swammerdam peeled the skin off silkworms&mdashthe larval stage of the domesticated silk moth (Bombyx mori)&mdashto reveal the rudimentary wings within.

Today, biologists know that these adult structures arise from clusters of cells called imaginal discs, which first form when an insect embryo develops in its egg. In some species, imaginal discs remain largely dormant until the pupal stage, during which they rapidly proliferate and grow into adult legs, wings and eyes, using dissolved larval cells as fuel and building blocks. In other species, imaginal discs begin to take the shape of adult body parts before the insect pupates (See Sidebar: How Does a Caterpillar Turn Into a Butterfly?)

Swammerdam also recognized that not all insects metamorphose in the same way. He proposed four kinds of metamorphosis, which biologists later distilled into three categories. Wingless ametabolous insects, such as silverfish and bristletails, undergo little or no metamorphosis. When they hatch from eggs, they already look like adults, albeit tiny ones, and simply grow larger over time through a series of molts in which they shed their exoskeletons. Hemimetaboly, or incomplete metamorphosis, describes insects such as cockroaches, grasshoppers and dragonflies that hatch as nymphs&mdashminiature versions of their adult forms that gradually develop wings and functional genitals as they molt and grow. Holometaboly, or complete metamorphosis, refers to insects such as beetles, flies, butterflies, moths and bees, which hatch as wormlike larvae that eventually enter a quiescent pupal stage before emerging as adults that look nothing like the larvae. Insects may account for between 80 and 90 percent of all animal species, which means 45 to 60 percent of all animal species on the planet are insects that undergo complete metamorphosis according to one estimate. Clearly, this lifestyle has its advantages.

A new generation
Complete metamorphosis likely evolved out of incomplete metamorphosis. The oldest fossilized insects developed much like modern ametabolous and hemimetabolous insects&mdashtheir young looked like adults. Fossils dating to 280 million years ago, however, record the emergence of a different developmental process. Around this time, some insects began to hatch from their eggs not as minuscule adults, but as wormlike critters with plump bodies and many tiny legs. In Illinois, for example, paleontologists unearthed a young insect that looks like a cross between a caterpillar and a cricket, with long hairs coating its body. It lived in a tropical environment and likely rummaged through leaf litter for food.

Biologists have not definitively determined how or why some insects began to hatch in a larval form, but Lynn Riddiford and James Truman, formerly of the University of Washington in Seattle, have constructed one of the most comprehensive theories. They point out that insects that mature through incomplete metamorphosis pass through a brief stage of life before becoming nymphs&mdashthe pro-nymphal stage, in which insects look and behave differently from their true nymphal forms. Some insects transition from pro-nymphs to nymphs while still in the egg others remain pro-nymphs for anywhere from mere minutes to a few days after hatching.

Perhaps this pro-nymphal stage, Riddiford and Truman suggest, evolved into the larval stage of complete metamorphosis. Perhaps 280 million years ago, through a chance mutation, some pro-nymphs failed to absorb all the yolk in their eggs, leaving a precious resource unused. In response to this unfavorable situation, some pro-nymphs gained a new talent: the ability to actively feed, to slurp up the extra yolk, while still inside the egg. If such pro-nymphs emerged from their eggs before they reached the nymphal stage, they would have been able to continue feeding themselves in the outside world. Over the generations, these infant insects may have remained in a protracted pro-nymphal stage for longer and longer periods of time, growing wormier all the while and specializing in diets that differed from those of their adult selves&mdashconsuming fruits and leaves, rather than nectar or other smaller insects. Eventually these prepubescent pro-nymphs became full-fledged larvae that resembled modern caterpillars. In this way, the larval stage of complete metamorphosis corresponds to the pro-nymphal stage of incomplete metamorphosis. The pupal stage arose later as a kind of condensed nymphal phase that catapulted the wriggly larvae into their sexually active winged adult forms.

Some anatomical, hormonal and genetic evidence supports this evolutionary scenario. Anatomically, pro-nymphs have a fair amount in common with the larvas of insects that undergo complete metamorphosis: they both have soft bodies, lack scaly armor and possess immature nervous systems. A gene named broad is essential for the pupal stage of complete metamorphosis. If you knock out this gene, a caterpillar never forms a pupa and fails to become a butterfly. The same gene is important for molting during the nymphal stage of incomplete metamorphosis, corroborating the equivalence of nymph and pupa. Likewise, both pro-nymphs and larvae have high levels of juvenile hormone, which is known to suppress the development of adult features. In insects that undergo incomplete metamorphosis, levels of juvenile hormone dip before the pro-nymph molts into the nymph in complete metamorphosis, however, juvenile hormone continues to flood the larva's body until just before it pupates. The evolution of incomplete metamorphosis into complete metamorphosis likely involved a genetic tweak that bathed the embryo in juvenile hormone sooner than usual and kept levels of the hormone high for an unusually long time.

However metamorphosis evolved, the enormous numbers of metamorphosing insects on the planet speak for its success as a reproductive strategy. The primary advantage of complete metamorphosis is eliminating competition between the young and old. Larval insects and adult insects occupy very different ecological niches. Whereas caterpillars are busy gorging themselves on leaves, completely disinterested in reproduction, butterflies are flitting from flower to flower in search of nectar and mates. Because larvas and adults do not compete with one another for space or resources, more of each can coexist relative to species in which the young and old live in the same places and eat the same things. Ultimately, the impetus for many of life's astounding transformations also explains insect metamorphosis: survival.

The Biology of the Translucent Jewel Caterpillar, the Nudibranch of the Forest


Fluke

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Fluke, also called blood fluke or trematode, any member of the invertebrate class Trematoda (phylum Platyhelminthes), a group of parasitic flatworms that probably evolved from free-living forms millions of years ago. There are more than 10,000 species of flukes. They occur worldwide and range in size from about 5 millimetres (0.2 inch) to several centimetres most do not exceed 100 millimetres (4 inches) in length.

Flukes parasitize members of all vertebrate classes but most commonly parasitize fish, frogs, and turtles they also parasitize humans, domestic animals, and invertebrates such as mollusks and crustaceans. Some are external parasites (ectoparasites) some attach themselves to internal organs (endoparasites) others are semi-external, attaching themselves to the lining of the mouth, to the gills, or to the cloaca (the end of the digestive tract). Some attack a single host, while others require two or more hosts.

The symmetrical body of a fluke is covered with a noncellular cuticle. Most are flattened and leaflike or ribbonlike, although some are stout and circular in cross section. Muscular suckers on the ventral (bottom) surface, hooks, and spines are used for attachment. The body is solid and filled with a spongy connective tissue (mesenchyme) that surrounds all the body organs. A circulatory system is absent. The digestive system consists of a simple sac with a mouth either at the anterior end or in the middle of the ventral surface. An anus is usually absent, but some species have one or two anal pores. The nervous system consists of a pair of anterior ganglia, or nerve centres, and usually three pairs of lengthwise nerve cords.

Most species are hermaphroditic i.e., functional reproductive organs of both sexes occur in the same individual. In some, however, the sexes are separate. Most species pass through egg, larval, and mature stages.

Blood flukes occur in most types of vertebrates three species attack humans: the urinary blood fluke (Schistosoma haematobium), the intestinal blood fluke (S. mansoni), and the Oriental blood fluke (S. japonicum). The human diseases caused by them are known as schistosomiasis (bilharziasis) they affect millions of persons, particularly in Africa and east Asia.

The urinary blood fluke (S. haematobium), which lives in the veins of the urinary bladder, occurs mainly in Africa, southern Europe, and the Middle East. Eggs, laid in the veins, break through the vein wall into the bladder and are voided during urination. The larval fluke develops in the body of a snail (chiefly of the genera Bulinus and Physopsis), the intermediate host. The mature larva makes its way into the body of the final host, man, through the skin or the mouth.

The intestinal blood fluke (S. mansoni), which lives in the veins around the large and small intestines, occurs primarily in Africa and in northern South America. The eggs pass from the host with the feces. The larva enters the body of a snail (any of several genera), the intermediate host, and returns to a human host through the skin.

The Oriental blood fluke, which occurs primarily in China, Japan, Taiwan, the East Indies, and the Philippine Islands, differs from S. mansoni and S. haematobium in that it may attack vertebrates other than man, including various domestic animals, rats, and mice. Snails of the genus Oncomelania are the intermediate host. The adult occurs in the veins of the small intestine. Some eggs are carried in the bloodstream to various organs and may cause a variety of symptoms, including enlargement of the liver. Human hosts may die from severe infestations.

Flukes of detrimental economic significance to man include the widely occurring giant liver fluke of cattle (Fasciola hepatica) and the Chinese, or Oriental, liver fluke ( Opisthorchis sinensis, or Clonorchis sinensis). F. hepatica causes the highly destructive “liver rot” in sheep and other domestic animals. Man may become infested with this fluke by eating uncooked vegetables.

The Chinese liver fluke infests a variety of mammals, including man. In addition to the snail as an intermediate host, the Chinese liver fluke infests fish as a second intermediate host before passing to the final host. The cat liver fluke, Opisthorchis felineus, which may also infest man as the final host, also requires a freshwater snail (Bithynia leachii) and a carp as its secondary intermediate hosts.

This article was most recently revised and updated by John P. Rafferty, Editor.


Swimming heads

After spending months perfecting the rearing and breeding techniques needed to study these worms, the researchers were eventually able to sequence the RNA from various stages of the worm’s development. They did this in order to see where specific genes are turned on or off in an embryo.

They found that in the worms, activity of certain genes that would lead to the development of a trunk are delayed. So, during the larval stage, the worms are basically swimming heads.

“When you look at a larva, it’s like you’re looking at an acorn worm that decided to delay development of its trunk, inflate its body to be balloon-shaped and float around in the plankton to feed on delicious algae,” said Gonzalez. “Delayed trunk development is probably very important to evolve a body shape that is different from that of a worm, and more suitable for life in the water column.”

As they continue to grow, the acorn worms eventually undergo a metamorphosis to their adult body plan. At this point, the genes that regulate the development of the trunk activate and the worms begin to develop the long body found in adults, which eventually grows to about 40 cm (15.8 inches) over the span of several years.


Bio 11 Annelida Gap Notes

Name: ________________ __________________ Date: ________________ Block: __________

Phylum Annelida (Latin: anellus = “little ring”)

The “Segmented” worms

  • 2 Major Classes: (Really there are 4 classes)
  • Though there are truly 4 classes of Annelids we will only look at 2 of the classes, and 2 of the sublclasses found within the Phylum Annelida
    1. Class ________________________: (Means “Many Bristles”)
    2. Class ________________________:
      • Subclass ________________________________: The Earthworms (Means “Few Bristles”)
      • Subclass ________________________________: The Leeches

      DID YOU KNOW. The giant Australian Earthworm can grow to be up to 3 meters in length

      • The Annelids demonstrate a ____________________________ symmetrical body plan
      • They have the three true germ layers:
        • ____________________________
        • ____________________________
        • ____________________________
        • Just underneath the _____________________ lays a _____________________ which helps stop the Annelids from ______________________________ in terrestrial habitats
        • Annelids have a true _________________________ with a _______________ and ______________ connected by ______________________________
        • The mouth is controlled by a muscular _________________________and is connected to the ___________________________ by an ____________________________
        • After the ___________________________ is a sac-like part of the intestines called a _________________
        • Just after the ____________________ is the _________________ which aids in digestion
        • Annelids have large ___________________ on the ___________________ side of the their anterior end which acts as a primitive brain
        • The _______________________are connected to a ________________________ which runs down the ________________________ side of the body
        • Annelids are the first organisms we will look at that possess a true __________________ that is lined with ___________________________
        • The Annelids have both _____________________ and ____________________ muscles
        • Annelids are the first group of organisms that we will look at which have a ________________________________________________. Their circulatory system is made up of two _______________________________ which run along the length of the body on the ________________and __________________ sides. There are also a series of “______________” in the _____________________ end which pump the blood through the circulatory system. These “hearts” are called the ________________________.
        • Annelids are ____________________________ and contain both male and female reproductive organs.
        • These organs are found just anterior to a special structure called a ______________________ which is a swollen segment near the _______________ end of their body.
        • They are also the first organisms we will study that demonstrate true ___________________________:
          • Each segment of the Annelid worms contains similar structures to the next segment
          • Each segment is called a _______________________ and is separated from the next by a ______________________(plural = ________________). This is formed from of a double layer of __________________________
          • Annelid worms contain little bristles on their exterior called _________________ which aid in locomotion. The setae can be found in four pairs per segment and are made out of ___________________
          • Each segment of an Annelid contains a pair of _____________________ which are used for excretion
          • Each segment of Annelids have a _________________muscle which lays just beneath the ______________________

          III. Feeding:

          • The Annelids are very diverse in the way that they feed.
          • Some are __________________________ and live off of theirs host’s blood such as the leeches (Hirudinea)
          • Others are __________________________ and hunt their prey such as the marine Polychaetes
          • Other Polychaetes such as the Christmas tree worms, the fan worms and other tube worms are ______________________________________
          • We will focus on the Earthworm (Oligochaeta) feeding:
            • Most Earthworms are called ____________________________ which means that they eat decomposing organic matter
            • As Earthworms travel through the dirt they suck the dirt into their mouth using their muscular _________________________
            • The Earthworm sends the dirt through the ________________________ and into the _________________ by muscle contractions
            • The dirt is stored in the ______________ until the worm is ready for digestion
            • Using muscle contractions the dirt moves into the ___________________________ which acts much like a _______________________________
            • The ___________________ mechanically digests the dirt and organic material by mixing it. The sand in the dirt aids to grind the organic material into small pieces
            • The organic material and dirt continues along the ___________________ by muscle contractions
            • As it travels through the intestines the organic material is absorbed into the ______________ in the _______________ and ________________ blood vessels
            • The remaining inorganic dirt travels through the ___________________ to the __________________
            • Again, we will focus on the Earthworm for respiration
            • The circulatory system of Earthworms contains _______________________ which contains ___________________________.
            • ______________________ is taken into the Earthworm directly through the ______________________ by the process of _____________________
            • The oxygen enters the blood and is held by the _________________________ in the __________________ which carries the oxygen to the body cells of the Earthworm
            • _____________________________ exits the circulatory system directly through the ectoderm and into the Earthworm’s surroundings by the process of __________________
            • All Annelids have _______________ circulatory systems which contain ______________ which in turn contains ___________________________
            • The _________________________ in the blood gives the blood its red colour
            • The haemoglobin in the blood transports __________________ throughout the Annelid
            • The circulatory system of Annelids is made up of the ______________________________ which are a series of muscular “______________” in their __________________ end, and a _______________ of blood vessels which run along the _______________ and ___________________sides of the worm
            • The _______________________________ pump the blood through the ________________ blood vessel and collect blood from the _____________blood vessel
            • The blood vessels branch into ________________________________that are found along the _____________________ and the ______________________
            • These capillary beds are sites of ________________________, both for __________________________ at the ectoderm and ______________/___________ exchange at intestine
            • The blood transports ____________ , ____________________ and ________________ throughout the Annelid body
            • One form of excretion in Earthworms is directly out of the _______________
            • Undigested inorganic and organic food particles are expelled out of the anus
            • These mishmashes of inorganic and organic material are called _____________________
            • Another form of excretion in Earthworms uses structures found in every segment called ______________________:
              • There are two _________________ in each segment and they have two openings: the first opening opens into the _________________ cavity of one segement, then the ___________________ pass through the __________________ into the next ______________________ segment where they open into the surroundings of the Earthworm
              • Wastes are excreted by the body cells, circulatory system and intestines into the ______________________ cavity
              • The _____________________ collect the waste material from the ______________________ cavity of one segment and transport it out of the earthworm in the next _______________________ segment.

              VII. Response:

              • Earthworms are able to sense and respond to the following stimuli:
                • ____________________
                • ____________________
                • ____________________

                VIII. Movement:

                • Earthworms move by a process known as _______________________:
                  • Earthworms are unique in that they are made of individual segments that act together in unison
                  • Earthworms have both _____________________________ muscles which run down the entire body as well as ___________________ muscles in each segment
                  • Starting at the _____________________ end the ____________________ muscles contract while the ___________________________ muscles relax. This causes the anterior end to become ___________________ and elongate.
                  • After “stretching” the __________________________ muscles contract while the ____________________muscles relax. This causes the anterior end to become fat again
                  • As the body stretches the __________________ extend from the sides of the body to anchor into the soil
                  • As the _________________________ muscles contract the Earthworm drags itself forward
                  • If this process of contracting and relaxing of the longitudinal and circular muscles is done in sequence along the entire body it allows for easier motion and is called peristalsis

                  DID YOU KNOW. Human beings also perform peristalsis, however, we use the process to

                  swallow our food. Try eating or drinking upside down one time and see what happens.

                  • Asexual reproduction:
                    • Annelid worms can undergo the process of _________________ to produce two genetically identical worms
                    • Annelids can also _______________________ after they have been cut

                    DID YOU KNOW. Earthworms can be cut up to 1/13 their size and still regenerate.


                    Mulberry Silkworm: History, Habitat and Life Cycle

                    In this article we will discuss about Mulberry Silkworm:- 1. History of Mulberry Silkworm 2. Habit and Habitat of Mulberry Silkworm 3. External Features 4. Life Cycle 5. Economic Importance 6. Diseases 7. Other Silkworm Moths.

                    History of Mulberry Silkworm:

                    Bombyx mori is popularly called the Chinese silkworm or Mulberry silkworm moth. It is well known for genuine silk. The importance of silkworm in silk production was known in China during 3500 B.C. The Chinese people knew the methods for cultivating silk and of preparing cloth from it for more than 2000 years. The rearing of silk moth and production of raw silk is known as sericulture.

                    The art of sericulture was held by Chinese a very close secret, so much so, that the leakage of any information or attempt to export eggs or living cocoons was punishable with death. Even then silk was after all introduced in Europe by two monks, who were sent to China as spies.

                    They studied the nature, source and art of silkworm rearing and stealthily carried some eggs in their pilgrim’s staff to Constantinople in 555 A.D.

                    From this place the silkworm-rearing was spread into the Mediterranean and Asiatic countries including India, Burma, Thailand and Japan. The insect breeders have produced many races of silkworm moth by hybridisation to meet the requirements of climate, rapidity of reproduction, quality, colour and yield of silk.

                    Habit and Habitat of Mulberry Silkworm:

                    Bombyx mori or the Mulberry silkworm is completely domesticated organism and is never found wild. The adult moths seldom eat and are primarily concerned with reproduction.

                    Their larvae are voracious eaters. They feed on the leaves of mulberry trees. Some moths are single brooded or univoltine and others are many brooded or multivoltine. Owing to domestication, a large number of strains have evolved out, which produce cocoons of various shapes, sizes, weights and colours ranging from white to yellow.

                    Only one generation is produced in one year by worms in Europe and other countries where the length of winters far exceeds the duration of summers. Some strains pass through two to seven broods and are cultivated in warm climates. In South India, particularly Mysore, Coimbatore and Salem, a strain which produces several generations, extensively utilised to produce silk.

                    External Features of Mulberry Silkworm:

                    The adult moth is about 25.00 mm long with a wing-span of 40.00 to 50.00 mm. The female silk moths are larger than the males. The moth is quite robust and creamy-white in colour. The body is distinctly divisible into three regions, namely head, thorax and abdomen.

                    The head bears a pair of compound eyes, a pair of branched or feathery antennae and the mouth parts. The thorax bears three pairs of legs and two pairs of wings. The cream-coloured wings are about 25.00 mm long and are marked by several faint or brown lines. The entire body is covered by minute scales.

                    Life Cycle of Mulberry Silkworm:

                    The silk moth is dioecious, i.e., the sexes are separate. Fertilisation is internal, preceded by copulation. The development includes a complicated metamorphosis.

                    Eggs:

                    After fertilisation, each female moth lays about 300 to 400 eggs. These eggs are placed in clusters on the leaves of mulberry tree. The female covers the eggs by a gelatinous secretion which glues them to the surface of the leaves. The eggs are small, oval and usually slightly yellowish in colour. The egg contains a good amount of yolk and is covered by a smooth hard chitinous shell.

                    After laying the eggs the female moth does not take any food and dies within 4-5 days. In the univoltine (a single brood per year) they may take months because overwintering takes place in this stage but the multivoltine broods come out after 10-12 days. From the egg hatches out a larva called the caterpillar.

                    Larva:

                    The larva of silkworm moth is called caterpillar larva. The newly hatched larva is about 4.00 to 6.00 mm in length. It has a rough, wrinkled, hairless and yellowish white or greyish worm-like body. The full grown larva is about 6.00 to 8.00 cm in length. The body of larva is distinguishable into a prominent head, distinctly segmented thorax and an elongated abdomen. The head bears mandibulate mouth and three pairs of ocelli.

                    A distinct hook-like structure, the spinneret, is present for the extrusion of silk from the inner silk-gland. The thorax forms a hump and consists of three segments. Each of the three thoracic segments bears pair of jointed true legs. The tip of each leg has a recurved hook for locomotion and ingestion of leaves.

                    The abdomen consists of ten segments of which first nine are clearly marked, while the tenth one is indistinct. The third, fourth, fifth, sixth and ninth abdominal segments bear ventrally a pair of un-jointed stumpy appendages each.

                    These are called pro-legs or pseudo-legs. Each leg is retractile and more or less cylindrical. The eighth segment carries a short dorsal anal horn. A series of respiratory spiracles or ostia are present on either lateral side of the abdomen.

                    The larva is a voracious eater and strongly gregarious. In the beginning chopped young mulberry leaves are given as food but with the advancement of age entire and matured leaves are provided as food. The caterpillar moves in a characteristic looping manner. The larval life lasts for 2-3 weeks. During this period the larva moults four times.

                    After each moult, the larva grows rapidly. A full-grown larva is about 8.00 cm long and becomes transparent and golden brown in appearance. A pair of long sac-like silk-glands now develops into the lateral side of the body. These are modified salivary glands.

                    Pupa:

                    The full-grown larva now stops feeding and hides itself in a corner under the leaves. It now begins to secrete the clear and sticky fluid of its salivary glands through a narrow pore called the spinneret situated on the hypo pharynx. The sticky substance turns into a fine, long and solid thread or filament of silk into the air.

                    The thread becomes wrapped around the body of the caterpillar larva forming a complete covering or pupal case called the cocoon. The cocoon-formation takes about 3-4 days. The cocoon serves a comfortable house for the protection of the caterpillar larva for further development.

                    The cocoon is a white or yellow, thick, oval capsule which is slightly narrow in the middle.

                    It is formed of a single long continuous thread. The outer threads, which are initial filaments of the cocoon, are irregular but the inner ones forming later the actual bed of the pupa, is one long continuous thread about 300 metres in length, wound round in concentric rings by constant motion of the head from one side to the other about 65 times per minute.

                    The irregular surface threads are secreted first and the inner continuous thread later. The silk thread is secreted at the rate of 150 mm per minute. Within a fortnight the caterpillar larva transforms into a conical brownish creature called the pupa or the chrysalis.

                    The pupa lies dormant, but undergoes very important active changes which are referred to as metamorphosis. The larval organs such as abdominal pro-legs, anal horn and mouth parts are lost. The adult organs such as antennae, wings and copulatory apparatus develop. The pupa finally metamorphoses into the imago or adult in about 2-3 weeks time.

                    Imago or Adult:

                    The adult moth emerges out through an opening at the end of the cocoon in about 2 to 3 weeks time, if allowed to live. Immediately before emergence, the pupa secretes an alkaline fluid, that softens one end of the cocoon and after breaking its silk strands, a feeble crumpled adult squeezes its way out. Soon after emergence, the adult silk moths mate, lay eggs and die.

                    Economic Importance of Mulberry Silkworm:

                    The mulberry silkworm moth is a very useful and valuable insect. It provides two very important products such as silk and gut to the mankind.

                    1. Silk:

                    The true silk of commerce is the secretion of the caterpillars of silkworm moth. Silk is a secretion in the form of fine threads, produced by caterpillars in preparing cocoons for their pupae. Long sac-like silk- glands, which are, in fact, modified salivary glands, secrete a thick pasty substance, which is passed out through a pair of fine ducts that open on the lower lip.

                    This secretion is spun by the caterpillar into fine threads which harden on exposure to air to form fairly strong and pliable silk-strands. The caterpillar larva prepares silk filaments several thousand metre in length at the rate of 15.00 cm per minute.

                    2. Gut:

                    Another economic value of the silkworm is the preparation of gut used for surgical and fishing purposes. For preparing the gut, the intestines of silkworms are extracted, made into strings, dried, treated and packed. This industry has good prospects and is growing in Italy, Spain, Formosa, Japan and India.

                    Diseases in Silkworms:

                    Silkworms suffer form several diseases. Chief of these is pebrine caused by a protozoan parasite Nosema bombycis of the microsporidian group.

                    In this disease the caterpillars turn pale brown and later on shrink and die. This disease is highly infectious, transmittable through eggs and responsible for very heavy economic losses. The control is brought about by a microscopic examination of the body fluids of the female, in which the parasites (pebrine corpuscles) are met with.

                    The eggs may be discarded or retained according to the presence or absence of parasites. Other diseases are fletcherie and grasserie but of minor importance. Sometimes caterpillars exhibit symptoms like jaundice disease, i.e., losing appetite, showing irregular growths, etc.

                    Other Silkworm Moths:

                    There are two other silkworm moths which also yield silk. These are Attacus receni, B, the Eri silkworm moth and Antherea paphia, B, the tassar silkworm moth. Both these moths belong to the family Saturnidae are large-sized and their caterpillars are also considerably monstrous, stout and about 10.00 cm long.

                    The Eri silkworm which lives upon castor, is a domesticated form, cultivated in warm damp places. It is found in South-East Asia. Its life history resembles that of the mulberry worm. Its cocoon has loose texture and silk is not reliable, hence, this is carded and spun. The gloss on the thread is inferior. Adults are stout dark moths with dark brown white spotted and striped wings.

                    The tassar silkworm resembles the Eri but the caterpillars feed upon Dalbergia, Shorea, and Terminalia, etc. The cocoon is hard shell-like of the size of a hen’s egg and is generally found attached to a plant by a stalk.

                    The moth has yellowish or deep brown wings with an eye-spot on each one. It is found in China, India and Sri Lanka. Cocoon has reelable silk. This is a wild variety but can be domesticated. The silk produced by Eri silkworm and tassar silkworm is not of very good quality.

                    Other silkworms, viz., Moon moth, Atlas moth, Cashew caterpillars and Ficus worm, although produce silk cocoons but the quality of filament produced is inferior and weak, hence, they have no economic value.


                    Roundworms

                    Roundworms make up the phylum Nematoda. This is a very diverse animal phyla. It has more than 80,000 known species.

                    Structure and Function of Roundworms

                    Roundworms range in length from less than 1 millimeter to over 7 meters (23 feet) in length. As their name suggests, they have a round body. This is because they have a pseudocoelom. This is one way they differ from flatworms. Another way is their complete digestive system. It allows them to take in food, digest food, and eliminate wastes all at the same time.

                    Roundworms have a tough covering of cuticle on the surface of their body. It prevents their body from expanding. This allows the buildup of fluid pressure in the pseudocoelom. As a result, roundworms have a hydrostatic skeleton. This provides a counterforce for the contraction of muscles lining the pseudocoelom. This allows the worms to move efficiently along solid surfaces.

                    Roundworm Reproduction

                    Roundworms reproduce sexually. Sperm and eggs are produced by separate male and female adults. Fertilization takes place inside the female organism. Females lay huge numbers of eggs, sometimes as many as 100,000 per day! The eggs hatch into larvae, which develop into adults. Then the cycle repeats.

                    Ecology of Roundworms

                    Roundworms may be free-living or parasitic. Free-living worms are found mainly in freshwater habitats. Some live in soil. They generally feed on bacteria, fungi, protozoans, or decaying organic matter. By breaking down organic matter, they play an important role in the carbon cycle.

                    Parasitic roundworms may have plant, vertebrate, or invertebrate hosts. Several species have human hosts. For example, hookworms, like the one in Figure below, are human parasites. They infect the human intestine. They are named for the hooks they use to grab onto the host&rsquos tissues. Hookworm larvae enter the host through the skin. They migrate to the intestine, where they mature into adults. Adults lay eggs, which pass out of the host in feces. Then the cycle repeats.


                    Worms

                    Authors: Riftia tube worm colony, NOAA, Public Domain
                    Jen Hammock, National Museum of Natural History, Smithsonian Institution
                    Gisele Kawauchi, Museum of Comparative Zoology, Harvard University
                    Jon Norenburg, National Museum of Natural History, Smithsonian Institution
                    Ashleigh Smythe, Hamilton College
                    Seth Tyler, University of Maine

                    What is a worm? Of the thirty-odd phyla in the animal kingdom, at least a third are generally referred to as worms. If you include the more exotic, lesser-known phyla described as “worm-like,” it’s well over half. So, evolutionarily speaking, it might be easier to narrow down what’s not a worm.

                    If you think worms are relatively “primitive” or simple animals, consider Riftia pachyptila, the hydrothermal vent worm. Discovered in 1977 at the Galapagos Rift (Jones 1981), adults are nourished entirely by symbiotic bacteria that feed on sulfur compounds found at hydrothermal vents. The Siboglinidae (beard worms), the group to which Riftia belongs, are closely related to earthworms and the other segmented worms. Yet earthworms and vent worms have evolved strikingly different feeding strategies, anatomies, and physiologies. Earthworms have colonized dry land and have mouthparts, a digestive tract, and the capability to move around in search of food. Riftia lacks (as an adult) a mouth and gut, is sessile, and has acquired a chemosynthetic partner—all traits that enable Riftia to thrive in what seems to be an unimaginably hostile environment. That’s just one example.

                    Ecologically, worms have the whole range covered. Name any habitat—there’s almost certainly a worm there. Tropical rainforest, polar ocean, the digestive tract of an insect or a mammal—they’re all worm habitats. Worms also observe an array of different feeding strategies. Parasites, predators, grazers, detritivores, filter-feeders— there are worms enjoying every menu in nature. How big are worms? Worms in the phylum Nemertea (ribbonworms) can be 1 mm or up to 50 meters long (among the longest, though not the most massive, of living species of animals). What color are worms? Well… green: Eulalia myriacyclum, Paddleworm, Robin Agarwal, CC-BY-NC red and white: Bearded fireworm, Nick Hobgood, CC-BY-SA blue: Christmas tree worm, Arthur Chapman, CC-BY-NC yellow: Tetrastemma, Ribbon Worm, Malin Strand, CC-BY-NC-SA

                    And then there are the bioluminescent worms, like the Green bomber, Swima bombiviridis, a pelagic worm which, when disturbed, drops glowing green spheres from a cache conveniently attached behind its head- a handy distraction for potential predators. There are many arrow worms, ribbon worms and segmented worms that glow using a variety of chemicals (Haddock et al., 2010).


                    Insect Order Trichoptera (Caddisflies)

                    Some say caddisflies are even more important than mayflies, and they are probably right. The angling world has taken a while to come to terms with this blasphemy. Caddis imitations are close to receiving their fare share of time on the end of the tippet, but too many anglers still assume all caddisflies are pretty much the same.

                    Caddis species actually provide as much incentive to learn their specifics as the mayflies do. There is just as much variety in their emergence and egg-laying behaviors, and as many patterns and techniques are needed to match them. Anglers are hampered only by the relative lack of information about caddisfly behavior and identification.

                    In many species, the pupae become very active just before emergence and drift along the bottom of the river, sometimes for hours. The "deep sparkle pupa" patterns introduced by Gary LaFontaine in Caddisflies are the most popular of many imitations inspired by this behavior. It is a deep nymph fisherman's dream. Sometimes they drift similarly just below the surface for a long time before trying to break through.


                      Most species rise to the surface and struggle through. They usually take flight quickly once they're out of the water, but slow species first struggle and drift long distances half-submerged as they wriggle free from their pupal shucks (

                    After emerging, caddisfly adults live for a long time compared to mayflies, in part because they are able to drink to avoid dehydration (mayfly adults cannot eat or drink). This flight period ( Flight period: The span of time that the adults of an adult aquatic insect species are active and flying around, in between emergence and death. It may refer to the average adult lifespan of the individuals of that species, or to the total length of time for which at least some of them are active. ) lasts anywhere from a few days to a few months, depending on the species, so mating adults may be seen on or over the water long after emergence is complete.

                    Many caddisfly females dive underwater to lay their eggs on the stream bottom. Some crawl down objects to do this but most swim right down through the water column. The latter are responsible for my fastest trout fishing action ever -- days when trout raced each other to attack my flies the moment they hit the water, cast after cast.

                    Others lay their eggs on the surface in various ways. They may fly low over the water, periodically dipping their abdomens to lay eggs. Others land on the surface repeatedly, fussing and fluttering in enticing commotion. Less active species may fall spent ( Spent: The wing position of many aquatic insects when they fall on the water after mating. The wings of both sides lay flat on the water. The word may be used to describe insects with their wings in that position, as well as the position itself. ) to the surface with all four wings spread out. Others ride the water serenely while laying their eggs, and they are the easiest to match with the dead-drift ( Dead-drift: The manner in which a fly drifts on the water when not moving by itself or by the influence of a line. Trout often prefer dead-drifting prey and imitating the dead-drift in tricky currents is a major challenge of fly fishing. ) techniques of mayfly fishermen.

                    Some egg-laying methods keep the adult females safe from trout altogether. They may drop their eggs into the water from overhanging plants, or lay their eggs on the vegetation itself. That way the eggs don't enter the river until the next rain--an excellent drought survival strategy.

                    Most caddisfly larvae live in cases they build out of sand, rock, twigs, leaf pieces, and any other kind of underwater debris. Some even generate their own cases out of silk. There is tremendous variation in case style and also in the way the larvae manage their cases: whether they replace it as they grow or renovate their old one, and whether they carry it around or fix it to an object. Trout love to eat these larvae, case and all.

                    Other common caddis larvae build nets instead of cases. These are not residences but hunting traps, like tiny spider webs, designed to capture plankton and smaller aquatic insects the larvae eat. One larva may build more than one net and roam freely around the rocks and logs tending to each and ingesting the catch. The net-spinning families, in order of abundance, are Hydropsychidae, Philopotamidae, and Arctopsychidae.

                    One large and primitive family of caddisflies, Rhyacophilidae, needs neither cases nor nets. Most of its species are predators who stalk through rocky riffles killing other insect larvae and nymphs.

                    All of these types are especially prone to behavioral drift ( Behavioral drift: The nymphs and larvae of many aquatic insects sometimes release their grip on the bottom and drift downstream for a while with synchronized timing. This phenomenon increases their vulnerability to trout just like emergence, but it is invisible to the angler above the surface. In many species it occurs daily, most often just after dusk or just before dawn. ) , making them an important food source year-round for the trout in most rivers.

                    When caddis larvae are full-grown, they seek hiding places to pupate, either in their cases or in special cocoons. They are considered to be pupae throughout the radical reformation from grub-like larva into intricate winged adult. Some of the larva's body mass is consumed as energy for the development of the pupa, so the pupae and adults both have bodies one to three hook sizes smaller than their mature larvae. When pupation is complete, the insect which begins the emergence sequence is called a pharate adult ( Pharate adult: Caddisflies are considered to be pupae during their transformation from larva into adult. This transformation is complete before they're ready to emerge. The emerging insect we imitate with the "pupa" patterns we tie is technically called a pharate adult. It is a fully-formed adult caddisfly with one extra layer of exoskeleton surrounding it and restricting its wings. ) . It is no longer technically a pupa in the language of entomologists, but because anglers universally recognize the term "pupa" I use that convenional misnomer throughout this site.

                    Sometimes individuals within the same fall-emerging species mature at different rates. In some species, mature larvae compensate for this by entering an inactive phase called diapause ( Diapause: A state of complete dormancy deeper even than hibernation. While in diapause, an organism does not move around, eat, or even grow. Some caddisfly larvae enter diapause for a few weeks to several months. Some species of microscopic zooplankton can enter diapause for several hundred years. ) prior to pupation. Cool fall weather triggers the end of this phase for every individual within a few short weeks, synchronizing emergences that would otherwise be spread over several months. This boosts the quality of autumn caddisfly hatches like the giant western genus Dicosmoecus.

                    The presence of caddisfly adults in the air does not mean that the angler should immediately switch to an imitation. As Swisher and Richards put it in Selective Trout:


                    List of 11 Important Phylum | Animal Kingdom

                    Here is a list of eleven important phylum:- 1. Phylum Protozoa 2. Phyllum-Porifera 3. Phylum Cnidaria 4. Phylum Ctenophora 5. Phylum Platyhelminthes 6. Phylum Nemathelmlnthes 7. Phylum Annelida 8. Phylum Arthropoda 9. Phylum Mollusca 10. Phylum Echinodermata 11. Phylum Chordata.

                    1. Phylum Protozoa (Approximately 30,000 Known Species):

                    Unicellular Animals like Amoeba, Paramoecium, Monogystis and Malaria parasite. Protozoa are microscopic in size. Each individual consists of only one cell which has to carry on all the vital activities. They are abundantly found in water containing decaying organic matter. Some, such as the dysentery amoeba and the malaria parasite, live within other animals. Still others live in damp soil, or in fresh water, or in the sea.

                    The single-celled condition is an important feature which sets the protozoa apart from all other animals. These unicellular crea­tures have therefore been placed in the subkingdom protozoa, which includes only one phylum, the protozoa. The remaining phyla of animals, all of which are many-celled, comprise the sub- kingdom metazoa.

                    2. Phyllum-Porifera (Approximately 5000 Known Species):

                    These are pore-bearing sedentary animals found mostly in the sea. A few species occur in the fresh water but none on the land. The sponges, like plants, are attached to a substratum. The outer surface of the sponge is perforated by numerous pores and the body wall is supported by a framework which is composed of lime, or of silica or of an organic substance called spongin.

                    3. Phylum Cnidaria (Approximately 10,000 Known Species):

                    Hydra, Jelly-Fishes, Sea-Anemones and Corals.

                    Most of the cnidaria are marine but Hydra is found in fresh water. Some, such as the corals and sea-anemones, are attached to a substratum others are slow moving or adapted for drifting in the water. All are radially symmetrical. This means that the animal is the same all round, and has no right or left side. It is symmetrical around a median vertical axis, and can be divided into similar halves by a number of vertical planes.

                    Body wall is composed of two layers it encloses a central digestive cavity which communicates with the exterior by only one opening, the mouth. Thus, the cnidarian body is essentially a two-layered hollow sac opening by the month the sac may be tubular, as in hydra, or saucer-shaped, as in jelly fish. There are movable arm­ like structures near the mouth, called tentacles, which carry pecu­liar stinging cells for stunning the prey.

                    4. Phylum Ctenophora (Approximately 80 Species):

                    Beroe, Hormiphora, Pleurobrachia.

                    The phylum derives its name from two Greek words—Ktenos= comb, phoros= bearing. Ctenophores are all marine. They have bi-radially symmetrical bodies. They possess eight meridionally placed ciliated plates. They resemble the cnidarians on many counts but differ from them in not having the nematocysts. Their ectomesoderm is gelatinous and bear mesenchymal muscle cells. They possess a specialised aboral sense organ and the tentacles bear adhe­sive cells. All are planktonic.

                    5. Phylum Platyhelminthes (Approximately 6500 Known Species):

                    Flat-worms, Flukes and Tape-worms.

                    These are flat, un-segmented, worm-like creatures with soft and bilaterally symmetrical body. In a bilaterally symmetrical animal there is a right side and a left side, a fore end and a hind end, a dorsal or back surface and a ventral or front surface. There is only one plane of symmetry by which the body can be divided into two equal halves.

                    Leaf-like liver-flukes and ribbon-like tape­worms are parasites but there are several free-living species, marine as well as fresh-water. Digestive canal is incomplete, with only one opening, the mouth there is no anus. Excretion of waste products is effected by peculiar flame cells.

                    6. Phylum Nemathelmlnthes (Approximately 10,000 known Species):

                    These are cylindrical, un-segmented, worm-like animals with soft, bilaterally symmetrical body, tapering at both the ends. Diges­tive canal is complete, with two openings, a mouth in front and an anus behind it is a straight tube running through the body from end to end. Most of the group are aquatic. A few inhabits damp soil. Others, such as hook-worms, thread-worms and filaria worms are parasites of man and cattle.

                    7. Phylum Annelida (Approximately 7500 Know Species):

                    Earth-worms, Leeches and Sand-worms.

                    These are true worms with soft, elongated, bilaterally sym­metrical body, divided into a series of ring-like segments or meta- meres. The annelids are, therefore, known as the segmented worms. The annelidan body is built on the tube-within-a-tube plan.

                    The outer tube represents the body wall and the inner tube represents the digestive canal. The two tubes are separated from one another by a space called body cavity or coelom. Most of the annelids, such as the sand-worms, are marine others, like the leeches, are fresh-water but the earth-worm is sub-terrestrial.

                    8. Phylum Arthropoda (Approximately 750,000 Known Species):

                    Prawns, Crabs, Cockroaches, Centipedes, Millipedes, Scorpions, and Spiders.

                    Arthropods are bilaterally symmetrical, segmented animals with soft parts of the body protected by a hard chitinous external skeleton. Each segment of the body bears paired legs or appen­dages which are jointed. This phylum is the largest of the animal phyla and includes nearly three-fourths of all the known species of animals.

                    9. Phylum Mollusca (Approximately 90,000 Known Species):

                    Clams, Oysters, Snails, Cuttle-fishes and Octopus.

                    Molluscs are un-segmented and without appendages. The soft parts of the body are enclosed in a Hard calcareous shell, as in snails and oysters. A fleshy muscular foot for locomotion is often present. Many of the molluscs are marine, some are fresh-water, and a few like the garden snails are terrestrial.

                    10. Phylum Echinodermata (Approximately 6,000 Known Species):

                    Starfishes, Sea-urchins, Sea-cucumbers and Sea-lilies.

                    Echinoderms are characterised by spiny skin. All are marine, inhabiting the shore and bottom of the sea. A few such as the sea-lilies are attached but the majority are free to move about. Locomotion is very sluggish and effected by peculiar structures called tube-feet. This is the only phylum possessing a water- vascular system. The body is radially symmetrical and star-like as in starfishes, brittle-stars and basket-stars.

                    11. Phylum Chordata (Approximately 100,000 Known Species):

                    Balanoglossus, Ascidians, Amphioxus and Vertebrates.

                    The chordates possess a stiff supporting rod, called notochord. Leaving aside a few lower forms, such as balanoglossus, ascidians and amphioxus, all chordates are vertebrates. Vertebrates possess the backbone which forms the supporting skeleton for the long axis of the body.

                    Vertebrate body is bilaterally symmetrical and is typically composed of head, trunk and tail. There are two pairs of appendages, either in the form of paired fins or limbs, or wings. They comprise the highest animals and include man.

                    Vertebrates are divided into the following classes:

                    (1) The cyclostomata including lampreys and hag fishes which are round- mouthed and without a lower jaw

                    (2) The chondrichthyes or cartilaginous fishes such as sharks and electric rays

                    (3) The osteicthyes or body fishes like Bhetki and Rohu

                    (4) The amphibians such as toads, frogs and salamanders with moist, naked skin

                    (5) The reptiles including snakes, lizards, tortoises and crocodiles with scales on their outer surface

                    (6) The aves or birds with feathers and wings for flight

                    (7) The mammals including duck-billed mole, kangaroo, guinea-pig and man, with hairy skin and with young ones fed by the mother with her own breast-milk.


                    Watch the video: The Mutations Induced by the Devil Worm and Its Origins Explored. How the Worm Creates Nests 5 (December 2022).