Phylum Annelida

Phylum Annelida contains three classes: Polychaeta Oligochaeta Hirudinida Annelid characteristics include: Paired epidermal setae Bilateral Symmetry Coelom divided by septa Metamerism Circular and longitudinal muscles Nervous system with dorsal cerebral ganglia and ventral nerve cord Closed circulatory system Excretory system (paired nephridia in each segment)

Class Polychaeta Distinct head with eyes and tentacles Gr. polys, many, + chaite, long hair Distinct head with eyes and tentacles Most segments with parapodia Many setae present in tufts on parapodia Clitellum absent Usually dioecious Examples: Nereis

Fig. 17.5

Fig. 17.6

Fig. 17.7

Fig. 17.8

Figure: 16_30b Title: Annelids Caption: (b) The “fireworm” polychaete swims by using paddles on each segment. The bristles on each paddle can deliver a fiery sting.

CO 17

Fig. 17.9

Fig. 17.10

Fig. 17.11a

Fig. 17.4

Figure: 16_30a Title: Annelids Caption: (a) A polychaete annelid projects brightly spiraling gills from a tube, made by the worm and attached to rock. When the gills retract, the tube is covered by a “trap door” visible as a reddish collar encircling the top of the tube.

Fig. 17.12

Fig. 17.13

Fig. 17.15

Class Oligochaeta Head absent Segments without parapodia Gr. oligos, few, + chaite, long hair Head absent Segments without parapodia Few setae per segment Clitellum present Monoecious Examples: Lumbricus, Tubifex

Fig. 17.21

Fig. 17.22

Class Hirudinida Setae absent Body with 34 segments Anterior and posterior suckers Clitellum present only during breeding season Monoecious Examples: Hirudo

Figure: 16_30c Title: Annelids Caption: (c) This leech, a freshwater annelid, shows numerous segments. The whitish disk is a sucker encircling its mouth, allowing it to attach to its prey.

Fig. 17.25

Fig. 17.23