PHYLUM ANNELIDA
GENERAL CHARACTERISTICS
Overview p. 206
Are the segmented worms -- Include earthworms, sandworms, and leeches
DEVELOPMENT determinate, spiral cleavage, protostome, schizocoelous
PHYSICAL FEATURES
Basic features: worm-like (long skinny body) bilateral symmetry coelomate (true body cavity) metamerism present (repeating body segments no rigid skeletal structure
What is metamerism? Repeating body segments
1) Each body segment with: excretory, appendages, muscular
2) Systems going length of body: digestive, nervous, circulatory
3) Irregular systems: reproductive
Organ Systems
1) digestive: complete mouth, pharynx, esophagus, intestine, anus some (earthworm) with crop for grinding
2) skeletal/muscular: no rigid structures (bone or cartilage) segments partitioned off; w/ circular & longitudinal muscles short & fat -- long & skinny = hydrostatic skeleton each segment can function independently
3) nervous system: each segment with a cluster of nerves, ganglion branches out to muscles & other organs have an anterior supraesophogeal ganglion = brain
Phylum Annelida, p. 1

all have a series of sense organs
4) appendages: have hairs or pointed extension in each segment = setae others with flattened fin-like extension = parapodia
5) excretory system: in each body segment (less a few at the extremes) a pair of nephridia in each section series of small tubules to draw waste from vessel & coelom
6) circulatory system: closed with aortic arches, dorsal vessel and ventral vessel series of capillaries between dorsal & ventral earthworm with five pair aortic arches
CLASSIFICATION (p. 218)
Class Polychaeta (polychaetes) segments with parapodia & setae head distinct, some with eyes & tentacles sexes separate, organs transitory
Class Oligochaeta (oligochaetes & earthworms) segments with setae only head absent hermaphroditic (both organs present, but takes two)
Class Hirudinea (leeches) no parapodia or setae head absent hermaphroditic
Phylum Annelida, p. 2

Phylum Annelida, p. 3
CLASS POLYCHAETA (pp. 208-212
Largest annelid group with over 10,000 species most species 5-10 mm long, some over 3 m long most live in euryhaline environments brackish marshes with salinity changes common, burrow into sand or mud some are marine and part of plankton (move around)
Characteristics
1) commonly have well developed head or prostomium (fig. 11.2, p. 207) has eyes, tentacles (skinny), sensory palps (fatter)
2) segments with parapodia (fig. 11.2, p. 207) commonly also have many setae (this is why they are called poly-chaetes) parapodia used for swimming, crawling, anchoring also as main respiratory organs in some species
3) no clitellum (modified cocoon producing organ)
Body Structure
Nutrition – feeding related to where living, in tubes, feed on detritus active swimmers - scavengers or predatory
Reproduction - very unusual no permanent sex organs sexes are separate gonads are temporary swellings of the peritoneum reproductive cells secreted into coelom and out of body fertilization is external
Unusual or interesting species -
1) clam worms (sand worms) live in burrows near low-tide line active at night, crawling/swimming around feed on small animals
2) fan worms - live in tubes elongate out & have long crowns of tentacles

food caught on mucus carried by ciliated grooves to mouth
CLASS OLIGOCHAETA (pp. 212-216) most species live in water, the well known earthworms are terrestrial
Characteristics
1) Species characterized by presence of setae, not parapodia straight or curved setae longer in aquatic species
2) no well developed head still has a number of sense organs
3) clitellum present - cocoon producing structure
Earthworms burrow in rich moist soil, emerge at night or after heavy rain tropical species are largest at 4 meters & over 250 segments
No obvious head, anterior observed by prostomium (fig. 11.13, p. 213) hangs over mouth feed on soil - decaying organic matter, leaves food flow: mouth esophagus crop (storage) gizzard (grinding) intestine (digest & absorb)
Most body segments with four (4) pair setae (fig. 11.13 & 11.14, pp. 213-214) important in movement short/fat segments have protruding setae to anchor long/skinny segments may move freely setae also slightly oriented toward posterior
can tell as you run your hand along body length
Phylum Annelida, p. 4

Phylum Annelida, p. 5
Circulation is dual (fig. 11.13, p. 213)
1) fluid moving in coelom (within a unit)
2) circulatory system (through body) dorsal vessel is the pumping organ ("heart"), pumps blood forward five pairs aortic arches transfer blood ventrally, also maintains uniform pressure ventral vessel serves as the aorta
Excretion by a primitive nephridial system (fig 11.15, p. 214) nephridiostome (funnel) collects waste in coelom nephridial tubule intertwined with vessels, collects waste from blood nephridiopore (bladder-like) opens out of body
Nervous system is not as complex as in the polychaetes (fig 11.13, p. 213) brain (= supraesophogeal or cerebral ganglion), a pair of ganglia nerve cord is ventral pair of ganglia in each segment coordinates: movement, reflex response to stimuli
Reproduction: hermaphroditic (fig. 11.16, pp. 215) each individual with both testis & ovaries male: pair testis & sperm funnels leading to seminal vesicles (where sperm matures) female : pair ovaries to oviducts to pores copulation leads to mucus secretion by clitellum sperm deposited inside & slipped forward eggs picked up as slid off body as a cocoon fertilization occurs in cocoon
Other Oligochaetes (fig. 11.17, p. 216) freshwater species live in sediment most species are tube dwellers some live in mud which can become anaerobic, these species are indicators of rich organic pollution

CLASS HIRUDINEA (pp. 215-217)
Most are freshwater, few are marine size varies: 2-6 cm typically medicinal leech up to 20 cm (8 inches) – fig. 11.20, p. 217 largest in Amazon River - to 30 cm (a foot long!)
Habitat and nutrition varies, most species are fluid feeders a) are predatory on small invertebrates b) live on gills of fish c) parasitic on vertebrates - jaws to bite through skin very few are obligate parasites some can even climb trees to get to mammals & birds!
Morphology & anatomy (fig 11.19, p. 217) have a set number of segments, 17, 31, or 34 each segment with a groove, so number segments appear double segments do not have completely partitioned coelom no typical earthworm movement of segments independently lack setae -- have 2 suckers for attachment & movement move with suckers, one then other (creep)
Leeches are very smart! -- they have two brains
Anterior: 6 pair fused ganglia around the pharynx
Posterior: 7 pair fused ganglia they are very sensitive to odors (chemoreceptors)
Are hermaphroditic (fig 11.19, p. 217) require another individual for mating clitellum present only during mating season
Phylum Annelida, p. 6