Notes: 30-1

Mollusks and Annelids

Both have a true coelom (body cavity)
Similar larval stage - trochophore
Bilateral Symmetry
Organ systems

Characteristics of Mollusks
· Visceral Mass (organs)
· Mantle (outer body layer)
· Foot (muscle, movement)
· Shell in most
· Radula - tongue-like structure, sharp
· Gills for respiration
· Most have separate sexes

Types of Mollusks
· Gastropods - snails, slugs, nudibranchs ("stomach foot")
· Bivalves - clams, oysters ("two doors")
· Cephalopods - nautilus, cuttlefish, squid, octopus ("head foot")

Characteristics of Annelids

· Segmented Body
· Coelom (body cavity)
· Organ Systems
· Bristles or Parapodia (appendages)
· Bilateral symmetry
· Cerebral Ganglion (brain)

Annelids are classified by their bristles or parapodia
Marine worms: have parapodia (ex. Nereis)
Earthworms: have setae
Leeches: have no setae or parapodia, feed on blood

Earthworm Anatomy (see page 673)

· "eat" soil
· hermaphrodites
· No eyes, but they can detect light and touch
· Movement occurs from elongating and contracting circular and longitudinal muscles - anchor with setae
· Hydrostatic Skeleton

Earthworms have a CLOSED CIRCULATORY SYSTEM

Blood is enclosed in two main vessels - the dorsal and ventral blood vessels. The heart consists of five arches in the anterior end of the worm - called the AORTIC ARCHES