Phylum: Annelida

Characteristics

• segmented coelomate worms

• Thin, non-mounted cuticle and paired epidermal chateau

• Closed circulatory system with dorsal “hearts”

• hydroskeleton formed by coelom

• Teloblastic growth of segments from pygidium

• metameric segmentation derived from pygidia growth zone

• pygidium lies at the posterior end of the body and hence the most posterior segments are ht youngest

• circular and longitudinal muscle, ventral nerve cord, coelomoducts

• riploblastic

• protostomes

• bilateral symmetry

• etheric body

• circulatory, respiratory, nervous, excretory system

Classes

Polychaeta

Clitellata

Polychaeta

• marine annelids with paired segmental parapodia bearing numerous chatae

• nuchal - sensory organs on head

• 1mm-3mm

• wide variety of feeding and reproductive modes

• some lack parapodia and chateau

• bristle worms

• fancy appendiges released from head to filter feed

• t

chateau

bristle-like structures made of chitin, used for different functions

polycheata body segments

1. Head: the anterior, head region, consists of the prostomium, the presegmental part of the body that carries sensory antennae, and the peristomium, the first body segment forming the posterior part of the head.

The prostomium is bilateral and carries five sensory antennae. Behind the prostomium is the peristomium, which surrounds the mouth. The eversible pharynx, which is the anterior part of the gut, may partially protrude from the mouth. In Phyllodoce the pharynx is armed with a vertical pair of jaws or maxillae and a dorsal series of four to five toothed maxillary plates.

2. Segmental region: this region comprises the rest of the body. The segments are distinguished externally by annular rings and each segment carries a pair of appendages called parapodia.

The segments are demarcated by annular rings and each segment bears a pair of parapodia. Each parapodium consists of a dorso-lateral notopodium and a ventral neuropodium. From segments 16-30 onwards there are branchiae or gills attached to the notopodium. There are up to 4-7 filaments per gill containing fine blood vessels.

3. Pygidium: the tail (or pygidium) carries two elongated appendages. The pygidium is asegmental and includes the anus.

What’s this

polychata

Citellata

• freshwater, marine or terrestrial

• gonads and reproductive ducts limited to few segments

• clitellum produces a cocaoon for eggs and is synapomorphy for the taxon

• reduced chateau present in earthworms but absent in leeches

• citellum: thickening of the epidermis at teh female genital pores that secretes egg cocoon

• reduced setae

citellata subclass

oligochaete - paraphyletic group

hirudinea - fixed number of segments with a prosterior and usually anterior sucker

what’s this

Citellata, TS worm

What’s this

TS leech Citellata

locomotion

hydrostatic water pressure skeleton, fluid filled coelom , combined action of longitudinal and circular muscles, push liquid in a kind of fludi filled serum into the front of the worm and then pressure pulls the rest of the worm along with it and inch along