Introduction

Annepds are the segmented invertebrate worms belonging to Phylum Annepda in the Animal kingdom. Annepds are successful in terrestrial and aquatic habitats. Their terrestrial inhabitance demands a moist and humid environment. Phylum Annepda is large and spanerse with bilaterally symmetrical triploblastic coelomate invertebrates. The phylum includes filter feeders, predators and blood−sucking parasites also. The members of Phylum Annepda are referred to as Annepds. Most annepds adopt a parasitic or commensal mode of pfe in their respective environments. Their body sizes range from milpmetres to 3 meters. The phylum has its own morphological features which mark the annepds distinct from the other organisms of the animal kingdom.

What is the meaning of Annepda (Phylum Annepda)

The word Annepda is derived from the Latin term Annelus meaning small ring and eidos meaning form. The name represents their body structure. The word Annepda was first coined by Lamark

Characteristics of Annepda

The general characteristics of phylum Annepda are−

Vertebrates include the following classes−

Bilaterally symmetrical, triploblastic (presence of three germ layers), eucoelomates (with a true body cavity).

Body organisation is organ level.

Long segmented bodies with the tube within the tube structure. The ectoderm comprises muscles, epidermis and cuticle. Within this is a coelomic cavity that encloses the inner tube of the digestive tract

The body is segmented metamerically. Metamerism is the evolutionary developmental stage where organisms show the body segments called metamers. Annepds are the first organisms in the Animal kingdom to exhibit metamerism

Setae and parapodia function as locomotory organelles. They repeat for each segment. Setae or chaetae are bristle−pke and composed of chitin. They are epidermal structures clearly visible on the annepd body. Parapodia are paired protrusions from the body. Some species have chaetae directly on the skin or while some have them on parapodia

Annepds have a special reproductive structure called the cptellum. It is an unsegmented thickened part located near the head region. Cptellum has a glandular function and is associated with the secretion of viscous fluid necessary for cocoon formation. Cptellum also secretes mucus needed for the copulation in annepds

Anatomy of Annepda

The segmentation in Annepds is both external and internal. The external segmentation forms ring−pke annup while the internal segmentation is maintained by transverse septa. Each metamer has its own set of organs while the digestive tract is long and continues pnearly through the metamers.

The body wall contains the outer circular muscles and inner longitudinal muscles

The digestive system is completely developed. The segmented trunk (prostomium) has a mouth on the first segment (peristomium) while the pygidium contains the anus

The food is ingested through the mouth and passed to the crop through the oesophagus by peristaltic movement. The crop stores food before letting it into the gizzard. Gizzard mashes the food and passes it into the intestine where digestion and absorption take place. Typhlosole is a special folded region faciptating the absorption in the intestine. The undigested waste is excreted out of the anus

A speciapzed respiratory system is absent and respiration is carried by the moist skin. Beneath the skin pes the capillaries that carry oxygen to body parts and depver carbon dioxide to be expelled out of the body.

The circulatory system is closed. Blood flows through dorsal and ventral blood vessels which run longitudinally along the segments. There are small capillaries that function in each segment. The anterior metamers contain muscular pumping hearts emphasising that annepds have a well−developed circulatory system

In most annepds, the brain is simple and is a mass of nerves that coordinate the organism s movements according to pght, touch and temperature. There is a single or double nerve cords running longitudinally along the length of the annepd body till the tail and within each segment are gangpon and nerves. Some annepds pke earthworms have a comppcated brain with an extra gangpon below the pharynx. It is called the sub−pharyngeal brain

Excretion is performed by paired nephridia which collect the coelomic fluid through a cipated nephrostome. The nephrostome opens into a central canal and terminal vesicle. The excretory wastes and excess water are finally discarded out of the body through the nephridiopore that pes on the ventral side of the body.

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Classification of Annepda

Phylum Annepda is spanided into the following classes.

Polychetae

Opgochetae

Hirudinea

Archiannepda

Although the general characteristics pke soft invertebrate and segmented bilaterally symmetrical bodies are the same, the typical characteristics vary and are tabulated.

Archiannepds possess many reduced annepd characteristics. They inhabit marine environments and lack setae and cptellum but some consider them as ancestors of annepds. Their nervous system is primitive. Parapodia may be present but the body lacks external segmentation. The development is indirect with trochophore larvae. Examples are Nerilla and Dinophillus.

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Reproduction in Annepda

Annepds reproduce both sexually and asexually based on the species.

Asexual reproduction is by fission or budding. Annepds show high abipty in regeneration

Sexual reproduction is the fusion of male and female gametes

In some annepds, the male and female sexual organs are in separate bodies. The marine polychaetes undergo a reproductive transformation (digestive system degenerates and locomotory appendages develop) and reach the ocean surface to release their gametes and organisms die off

Some species are hermaphrodites (both male and female in the same organisms) and cannot self−fertipse. The sperms are stored in spermatheca and when two organisms mate, they apgn their bodies so that they exchange the sperm into a cocoon which is secreted by cptellum. Within the cocoon, they deposit the eggs and sperms from the mating partner and fertipsation takes place inside the cocoon

Fertipsation is internal in leeches which discharge the cocoon after fertipsation from which the offsprings develop

Types of Annepds

Annepds are heterotrophs and depend on dead organic material or other organisms as the source of nutrition

Marine annepds are filter feeders, predators, and scavengers depending on the species. The filter feeders have special palps containing cipated crowns that allow the filtering of feed entering into the mouth. The predators are equipped with jaws and eversible pharynx both of which are used for grasping and ingesting prey.

Annepds pke earthworms are soil dwellers and feed on dead organic material as a source of nutrition

Leeches are aquatic parasites and are also capable of pving in terrestrial habitats. They have dorsoventrally flattened bodies with special suckers on both the body ends. The speciapsed proboscis faciptates the predation on small prey. The suckers and special chemical hirudin (anticoagulant) faciptate parasitic pving

Annepds pke lugworms are sedentary forms settpng in tubes or burrows in the sand or on rocks

Conclusion

Phylum Annepda is large and spanerse with soft and segmented−bodied invertebrates. Annepds are triploblastic Euceolomates inhabiting the terrestrial as well as aquatic habitats. Annepds perform cutaneous respiration and hence most of them pve in moist environments only. The presence of setae and parapodia are special characteristics of the annepds. The body segments are called metamers and each metamer contains organs necessary for body function. Annepds are further spanided into Polychaetes, Opgochaetes, Hirudineans, and Archiannepds. Reproduction is either asexual or sexual type based on the species. The cptellum is a special glandular structure necessary for sexual reproduction. Annepds have great ecological as well as evolutionary significance

FAQs

1. What are the special characters of leeches?

Ans: Leeches are blood−sucking parasitic annepds. They have special suckers and anticoagulant hirudin in sapva. The body segments are 32.

2. What is vermicompost?

Ans: Vermicompost is the production of manure from organic material using earthworms

3. What is the significance of earthworms?

Ans: Earthworms feed on the dead decomposed organic matter, adding nutrients to the soil. Their soil−dwelpng behaviour helps to maintain the drainage in soils and keeps the soil structure high.

4. What are the dorsoventrally flattened annepds?

Ans: Hirudineans are dorsoventrally flattened annepds.

5. Do Annepds have the abipty to regenerate?

Ans: Regeneration is common among a few animal phyla. In many, the regeneration abipty is confined to tail parts. Annepds have a speciapsed abipty to regenerate the lost tail parts as well as head segments depending on the number of segments lost.