Pseudocoelomates and coelomates

As a group, pseudoceolomates are:

Covered by a cuticle

No organs or gas exchange, internal transport or excretion

Poorly cephalised

Mouth and anus are seperate

Very small

Poorly cephalised

lack the body formation of a head (concentrated nerve and feeding organs)

Interstitial fauna

Animals that inhabit the spaces between individual sand grains

Nematoda

Found in interstitial spaces

Paratsites of plants and animals

Play a role in decomposition

Off-white or grey colour

Nematoda examples

Hookworms - burrow into feet and make way to stomach

Ascardis - eggs ingested through faecal contamination, malnutrition and intestinal blockage

Filarial nematodes - cause blockages of lymphatic system; elephantiaisis

Economic benefit of nematodes

entomopathogenic - kill ionsects and molluscs so can be used as pesticides

Rotifera

Mostly freshwater

Crown of cilia in two discs

Swim using cilia

Feed on protozoans and other rotifers

Only sexual reproduction except sometimes in favourable conditions

Gastrotricha

Body is bottle shaped and surface is ciliated

Marine and feshwater

Interstitial

Feed on bacteria, small protozoa and organic detritus

Nematomorpha

Freshwater

Long hair like bodies

Closely related to nematodes

Parasitic in juvenile stages, adult stage non-feeding

Acanthocephala

Endoparasites of marine freshwater and terestrial vertebrate digestive system

Anthropod are intermediate hosts

Kinorhyncha

Anterior end is spiny

Microscopic animals that burrow in marine sediments

Loricifera

Interstitial in marine sediments

abdomen has a cuticular girdle called lorica

spiny at anterior end

Priapulida

Unsegmented worm-like marine animals

burrow in sand and mud

teeth capture and pull in prey

Entoprocta

Unlike Bryozoa the anus is inside the ring of tentacles

Attached to rocks

Most colonial

Grow from a creeping stolon

Coelomate (eucoelomate)

fluid filled cavity completely lined with tissue derived from mesoderm

Peritoneum

layer of epithelial cells that makes up the tissue lining in eucoelomates

Retroperitoneal

located behind the peritoneum - organs buldging into the peritoneum

Mesentery

a fused double layer of the parietal peritoneum that attaches parts of the intestine to the interior abdominal wall

3 evolutionary lines of coelomates

Protostomes (molluscans, annelids, arthropods)

Deuterostomes (echinoderms, hemichordates, chordates)

Lophophorates (Bryozoa, phoronida, brachiopoda)

Annelida

Segmented worms

Segments are in a linear series, demarcated externally by grooves, internally seperated by septa

What does each segment of annelida worms contain?

Nervous system

Excretory system

Reproductive system

3 classes of Phylum annelida

Polychaetes, clitellata, sipuncula

Class Polychaeta

bristle worms

some swim amoung plankton, most burrow or build tubes in sediment

Prostomium and Peristoneum

Prostomiun - carries sense organs, eyes antennae

Peristomeum - carries tentacles, ventral mouth on proboscis

Two parts of biramous parapodia

dorsal notopod

ventral neuropod

Mobile and Immobile forms of polychaetes

Errant = mobile - well developed sense organs and jaws

Sedentary = immobile - specialised gills/tentacles

Class Clitellata

Oligochaeta -Earthworms, Hirudinea - leeches, branchiobdellida

Class Sipuncula

Peanut worms or sipunculids, live in soft sediment