Lecture Notes 7: Annelida

Dorso-ventrally flattened; Ant. and post. suckers modified from sgm.s. Suckers used in inch-worming locomotion;
elongate by contracting circ. muscles, reach out and attach. Fixed number of 34 sgm., though obscured by
secondary annulations. As expected for such fixety, no asex. repr. or regeneration.
Coelom-circ.: Well developed connective tissue and loss of distinct coelom; perhaps related to no need for it in
locomotion; or swimming - undulations. Acanthobdella retains 5 prd. coeloms anteriorly (& these sgm.s bear
chaetae); otherwise no septae, coelomic cavity reduced to interconnecting coelomic sinuses and channels -
developed into a new BVS. Original oligochaete BVS retained in some (Rhynchobdellida), but lost in many.
Coelomic fluid propelled by muscular contractions (unlike expected from Ruppert & Carle's division).
Dig.: 1/4 of spp. predacious on invert.s (but frog w/ me) and swallow prey whole, or some suck host dry (literally),
3/4 blood-sucking ectoparasites - mostly on vert.s, some on inverts; may associate w/ host temporarily or
permanently. Have either an eversible, muscular, sucking proboscis (Rhynchobdellida) which is trust into host
tissue; or a sucking pharynx w/ 3 jaws within the ant. sucker (Gnathobdellida) and a muscular pumping
pharynx. Pharyngobdellida, as Gnathobdellida but muscular folds instead of jaws. Great gut bacterial flora to
aid in digestion. Esophagus, stomach (=crop), intestine, rectum; stomach in most w/ 1-11 prs. of caeca;
intestine may also have 4 caeca.
Hirudo - still used in medicine, eats 2-5X body weight in blood infrequently, then piss blood-water out. hirudin =
anticoagulant
Nerv.: Brain, connectives, subesophageal ganglion + several segmental ganglia all en mass in sgm.s X-XII., prd. V.
cords w/ fused sgm.'l ganglia posteriorad. Neurons large – neurophysiologist’s toy.
Repr.: Sperm transfer by penis or hypodermic impregnation; internal fertilization - directly into female system
(unlike earthworms). Clitellum forms cocoon & albumin into it.