Biodiversity and Conservation Chapters 10 & 11: Mollusca and Annelida

90,000

Number of living mollusc species

70,000

Number of mollusc fossil species

Ammonite

Extinct mollusc that is visually similar to the Nautilus, and could get very large

Sea

Location in which molluscs originated, according to fossil data

humidity, shelter, and calcium in the soil

Factors that limit the range of gastropods

Radula

Barbed, rough tongue of a mollusc; absent in bivalves

Head

Well developed organ with a mouth and some sensory organs, found in most molluscs

Foot

Ventral organ adapted for attachment to the substrate or for locomotion; secretes mucus that aids in adhesion or movement

Foot modifications

Attachment of a disc for limpets or the hatched foot of bivalves

Mantle

Present in all molluscs; a sheath of skin on each side of the body that secretes the shell and performs gas exchange where exposed

Periostracum

Outermost layer of the shell that serves as protection

Conchiolin

A protein that makes up the Periostracum

Prismatic layer

Internal layer of the shell that makes up most of the shell mass

Aragonite or calcite

Possible materials for what makes up the Prismatic layer

Nacre

Innermost layer of the shell that is next to the mantle and surrounds any material that comes between the shell and the mantle to reduce irritation

Open circulatory system

Circulatory system of most molluscs, excluding cephalopods

Metanephridia

Ducts that perform excretion and the discharge of sperm and eggs in molluscs

Pair of ganglia with connecting nerve cords

Nervous system in molluscs

Gastropoda

Class of Mollusc that is usually dioecious; aquatic species have free swimming trochophore and veliger larval stages

Dioecious

Having just one type of sex organ

Veliger

Larval stage that develops from the trochophore and has the beginning of a foot, mantle, and shell

Bivalvia

Class of Mollusc that has poorly developed sensory organs, no radula, an umbo, a folded mantle with siphons

Siphons

Excurrent and incurrent openings that form from the folding of the posterior edges of the mantle

Umbo

The location where the shell starts to develop for Bivalves; closer to the anterior end of the animal

Trochophore, veliger, and spat

Larval stages of marine Bivalves

Glochidia

Specialized veliger larva found in freshwater bivalves; they attach to the gills of passing fish where they live briefly as parasites before becoming sedentary adults in the substrate

Chromatophores

Cells in the skin of Cephalopoda that expand and contract to produce a color and/or texture change

Cephalopoda

Class of Molluscs that have arms/tentacles, some can change color, and some can produce ink

Ink production

Ink sac empties into the rectum when the animal is alarmed

Fertilization of Cephalopods

Internal fertilization via a specialized arm or tentacle

Phylum Annelida

Phylum of segmented worms that live in marine, freshwater, and moist terrestrial habitats

17,000

Number of species of Annelida, two thirds of which are marine

Metamerism

Segmentation in annelids; each section contains components of most organ systems

Benefits of metamerism

Increased burrowing efficiency, a more sophisticated nervous system, and redundancy

Pygidium

The location at which segments grow in marine annelids

Setae

Tiny chitinous bristles present on most annelids, excluding leeches

Short setae

Used to anchor segments in terrestrial annelids

Long setae

Used to help aquatic worms swim

Polychaetes

Marine annelids that have many setae on each segment; usually benthic

Benthic

Living in the substrate

Hydrostatic skeleton

Coelom filled with fluid that serves to provide movement in most annelids, excluding leeches

Longitudinal muscles

Muscles that are contracted to cause an annelid body to shorten and expand

Circular muscles

Muscles that are contracted to cause an annelid body to narrow and lengthen

Peristalsis

Alternate waves of muscle contraction in annelids; allows for efficient burrowing

Oligochaeta

Species of Annelid that have very few setae per segment, are hermaphrodites, breath through their skin, and eat on decayed matter and vegetation

Clitellum

Band on the earthworm that secretes mucus, which keeps two worms together during mating

Hermaphrodite

Having both sex organs