Lecture Notes 7: Annelida
Lecture Notes 7: Annelida
Lecture Notes 7: Annelida
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Oligochaeta<br />
3100 spp. (Barnes); most land & FW, 200 marine; primitively FW, secondarily to land and sea. Generally<br />
scavenger / deposit feeder, some FW carnivores. In FW usually burrow in bottom sediments, good indicators<br />
of pollution. Earthworms - feed on decomposing matter; aerate and mix soil greatly; very beneficial. Darwin -<br />
on vegetable mounds and earthworms. Giant australian earthworms to 1+m.<br />
Externally simpler than polychaetes: no parapodia; few chaetae - hence name; no head appendages (in a few<br />
genera prostomium drawn out into tentacle); small eversible pharynx in some FW forms; sucking pharynx in<br />
earthworms. Chaetae in 2 prd. bundles / sgm. presumed to be homologous to noto- & neuropodia.<br />
In earthworms middorsal coelomic pores w/ sphincters to wet skin in burrowing.<br />
Around intestine - chloragogen tissue - glycogen & fat synthesis & storage; fm. of NH4, urea, also has waste<br />
concretions (silicates...).<br />
Excr. by metanephridia - highly convoluted ducts to regain water - hyperosmotic urine, urea; many empty<br />
nephridia into gut to have more chance at water reabsorption.<br />
Resp.: The largest terrestrial animals w/o specialized respiratory structures are giant earthworms - complex<br />
capillaries under epidermis though.<br />
Asex. repr. very common. All hermaphroditic, w/ distinct gonads, few repr. sgm., clitellum. 1-2 male sgm., then 1<br />
female sgm. following it, ea. w/ prd. distinct gonad; release developing gametes into coelom, where held in<br />
specialized septal pockets: seminal vesicles and ovisacs. Then funnel w/ sperm duct, traverses several sgm.<br />
before emptying, unite if 2 testicular segments. Funnel w/ oviduct, opens into immediately posterior segment.<br />
Ant. to female sgm. are 1-many sgm. having blind ending seminal receptacles. Clitellum 2-60 sgm, 6-7 in<br />
Lumbricus; lies post. to genital sgm.s. Sgm. w/ greatly swollen epidermis, w/ abundant gland cells - which<br />
produce mucus for copulation, secrete cocoon wall & albumin for eggs. Copulation, places sperm in seminal<br />
receptacle. Few days later - tough cocoon secreted by clitellum, passed forward, first eggs, then sperm into it,<br />
then sealed as gets off worm.<br />
Hirudinea<br />
Q&D, Barnes<br />
Leeches, 500 spp., SW, FW, land; primitively FW. Derived from oligochaetes. 1-40cm.<br />
Protandric hermaphrodites, lack parapodia, chaetae, head appendages, similar repr. - clitellum.
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