Oceanology Vocab Chapters 9.2 - 9.3

**bilateral symmetry**

The arrangement of body parts in such a way that there are only two identical halves, with different anterior and posterior ends and dorsal and ventral surfaces.

**anterior**

The defined front end of a bilaterally symmetric animal.

**posterior**

The defined rear end of a bilaterally symmetric animal.

**dorsal**

The upper or back surface of an animal with bilateral symmetry.

**ventral**

The underside or belly surface of an animal with bilateral symmetry.

platyhelminthes

Phylum for flatworms; the structurally simplest bilaterally symmetrical body plan

**mesoderm**

The middle layer of embryonic tissue that gives rise to muscles, the reproductive system, and other organs.

turbellarians

most commonly seen marine flatworms; a group that consists mostly of free-living carnivores; most are small and have striking color patterns

flukes

(trematodes) largest group of flatworms, all are parasitic, many are marine

tapeworms

(cestodes) parasitic flatworms, with a few exceptions, have a long body consisting of repeated units

nemertea

phylum for ribbon worms; more complex degree of organization than flatworms

**proboscis**

An extension near the mouth that in some invertebrates helps in the capture or collection of food.

nematodes

phylum for roundworms, many are in sediments and rich organic matter

**hydrostatic skeleton**

A system that uses water pressure against the body wall to maintain body shape and aid in locomotion.

annelida

phylum for segmented worms

**segmentation**

A body consisting of similar compartments or segments.

**coelom**

The body cavity found in structurally complex animals.

polychaetes

almost all marine annelids are part of this class

**parapodium**

A usually flat lateral extension present on each of the body segments of polychaetes.

**seta**

(pl. setae) The bristles of polychaetes.

**morphology**

Body shape

**closed circulatory system**

A circulatory system where the blood or circulatory fluid is contained in distinct vessels.

**gill**

Thin-walled extensions of the body that are used in gas exchange.

**capillaries**

Thin blood vessels that allow for gas exchange.

**trochophore**

A planktonic larva found in polychaetes, some molluscs, and other invertebrates.

**mantle**

The outer layer of tissue that secretes the shell of molluscs.

**foot**

The muscular locomotory structure of molluscs.

**radula**

The ribbon-like band of teeth of molluscs.

**chitin**

The main component of the exoskeleton of many animals.

gastropods

largest, most common, and most varied group of molluscs Ex: snails, limpets, abalones, nudibranchs

nudibranchs

(sea slugs) gastropods that have lost the shell altogether

bivalves

the body is laterally compressed and enclosed in a shell with two parts Ex: clams, mussels, oysters, and similar mollusks

**valve**

Any of the two shells of bivalves and lamp shells.

**umbo**

The region around the hinge of a bivalve’s shell.

**siphon**

(funnel) The tube-like extension through which water flows in and out of the mantle cavity in bivalves and cephalopods, and in tunicates.

**byssal threads**

Strong fibers secreted by mussels for attachment.

cephalopods

adapt the molluscan body plan to an active way of life; agile swimmers; complex nervous system and a reduction or loss of the shell

Ex: octopuses, squids, cuttlefishes, and other fascinating creatures

**ink sac**

A gland found in some cephalopods that secretes a dark fluid used to discourage predators.

**pen**

The reduced, thin shell of squids.

monoplacophora

represented by a handful of species of limpet-like mollusks; only known from fossils until 1952; their gills and organs are repeated along the body which is reminiscent of the segmentation of annelids

**crystalline style**

An enzyme-releasing rod in the stomach of bivalves.

**open circulatory system**

A system where the blood or circulatory fluid is not contained in vessels and can flow into the body cavity.

**ganglia**

Clusters of nerve cells that serve as “local brains” in gastropods and bivalves.

**spermatophore**

A packet of sperm in cephalopods.

**veliger**

A planktonic larva in gastropods and bivalves.