marine inverts exam 2

Metazoa

All multicellular animals.

Bilateria

Animals with bilateral symmetry and three tissue layers.

Protostomia / Protostome

Bilaterian group in which the mouth forms first in development. Includes Lophotrochozoa and Ecdysozoa.

Deuterostomia

The other bilaterian branch (echinoderms, hemichordates, chordates).

Lophotrochozoa

Protostome clade that includes molluscs, annelids, and the lophophorates. Named for the lophophore and the trochophore larva.

Ecdysozoa

Molting protostomes (nematodes, arthropods, etc.).

Platyzoa

Protostome group containing flatworms and rotifers.

Triploblastic

Having three tissue layers: ectoderm, endoderm, mesoderm.

Coelomate

Having a true body cavity lined by mesoderm.

Monophyletic

A group containing an ancestor and all of its descendants. Polychaeta is likely not monophyletic.

Synapomorphy

A shared, derived trait that unites a group.

Homologous

Similar because of shared ancestry (for example, the aplacophoran pedal pit may be homologous to the foot).

Cephalization

Concentration of nervous control and sense organs at the anterior end.

Sessile

Attached and non-moving as an adult.

Interstitial

Living in the spaces between sediment grains.

Extant

Still living (as opposed to known only from fossils).

Gonochoristic (dioecious)

Separate sexes.

Monoecious / hermaphroditic

One individual has both male and female function.

Hydrostatic skeleton

Body fluid under pressure that gives support and allows movement by muscle contraction.

Chemosynthesis

Making organic molecules from CO2 using energy from chemicals (such as oxidizing hydrogen sulfide) rather than light.

Symbiosis (obligate vs facultative)

A close association between species. Obligate means required for survival; facultative means optional.

Facultative heterotrophy

Normally feeding on other organisms but able to supplement or replace it with other energy sources (for example, the sea slug Elysia chlorotica living off stolen chloroplasts for months).

Countercurrent exchange

Blood and water flow in opposite directions across a gill, which maximizes oxygen uptake.

Epitoky

Reproductive strategy in some polychaetes where segments bud off asexually to form a highly active reproductive individual that then takes part in sexual reproduction.

Broadcast spawning

Releasing eggs and sperm into the water for external fertilization.

Fragmentation

Asexual reproduction by breaking into pieces that regenerate.

Parthenogenesis

Development of eggs without fertilization.

Trochophore larva

Free-swimming, ciliated larva typical of molluscs and annelids.

Mesopredator

A mid-level predator that is itself prey for larger predators.

Mantle

Dorsal epithelium (tissue fold) that secretes the shell or calcareous spicules and encloses the mantle cavity.

Shell

Calcareous protective covering secreted by the mantle. Absent or reduced in many groups.

Valve

One piece of a shell (chitons have 7-8 valves; bivalves have 2).

Periostracum

Outermost shell layer. An organic protein matrix that protects the mineral layers beneath.

Prismatic layer

Middle shell layer of calcium carbonate. Provides most of the strength and rigidity.

Nacreous layer

Innermost shell layer of calcium carbonate. Smooth, iridescent surface next to the animal (mother-of-pearl).

Spicules

Small calcareous needles secreted by the mantle (found in the chiton girdle and in aplacophorans).

Mantle cavity

Space between the mantle and body that holds the gills (ctenidia) and receives waste.

Ctenidium (pl. ctenidia)

Comb-like molluscan gill that works by countercurrent exchange.

Foot

Muscular structure for crawling and/or anchoring. Modified into arms and funnel in cephalopods.

Visceral mass

The body region above the foot containing the digestive, nervous, excretory, reproductive, and respiratory organs.

Hemocoel

Blood cavity that serves as a hydrostatic skeleton.

Pericardium

The very small coelomic cavity around the heart. Not used for locomotion.

Hemocyanin

Copper-based oxygen-carrying blood pigment found in many molluscs.

Radula

Firm ribbon of chitinous teeth used to scrape or grasp food.

Teeth (radular)

The individual chitinous teeth on the radula. In chitons they are hardened with iron oxides.

Odontophore

Cartilage-like structure that supports the radula.

Buccal mass

The odontophore and radula assembly together.

Veliger

A later larval stage that follows the trochophore, with a shell and ciliated swimming lobes (velum).

Hypothetical ancestral mollusc (H.A.M.)

The simple model body plan (mantle, shell, foot, visceral mass, radula, ctenidia) used to compare all classes.

Statocyst

Balance organ. Some scallops have them.

Statolith

Small mineral grain inside a statocyst that senses gravity and movement.

Polyplacophora (chitons)

7-8 overlapping shell plates and a thick girdle.

Girdle

Thickened lateral mantle of a chiton, often bearing calcareous spicules. Pressed against the substrate to create suction.

Pedal waves

Muscular waves in the foot that move a chiton.

Aesthetes

Tiny sensory structures in chiton shells that detect light, chemicals, and movement.

Aplacophora

Tiny, worm-like, shell-less molluscs from deep water. Nerve arrangement suggests the shell was secondarily lost.

Pedal pit

Ciliated pit used for movement in aplacophorans.

Monoplacophora

"Living fossils" with a single cap-shaped shell and multiple pairs of gills and other organs. Rediscovered in 1952.

Scaphopoda (tusk shells)

Shell open at both ends, with no heart, ctenidia, or circulatory system.

Captacula

100-200 thread-like tentacles (each with a bulb tip) used by scaphopods to catch food.

Torsion

Twisting of the visceral mass and nervous system by 90-180 degrees during development.

Detorsion

Partial reversal of torsion during larval metamorphosis (seen in heterobranchs such as nudibranchs).

Operculum (gastropod)

Proteinaceous plate on the foot that closes the shell opening.

Columella

Central axis of a coiled shell.

Columellar muscle

Muscle attaching the body to the columella. Responsible for most major movements.

Apex

The tip (oldest part) of a gastropod shell.

Aperture

The shell opening. Growth occurs along the aperture margin.

Dextral coiling

Shell twists to the right (most common).

Sinistral coiling

Shell twists to the left (rare).

Osphradium

Chemosensory organ near the gill that samples incoming water.

Proboscis (gastropod)

Extendable feeding structure (in gastropods, a tube housing the mouth and radula).

Heterobranchia

Informal clade ("gills behind the heart") that includes nudibranchs, with reduction or loss of shell, mantle cavity, and gills.

Nudibranch

Shell-less sea slug in Heterobranchia.

Cerata

Projections on the back of nudibranchs used for protection, respiration, and camouflage.

Rhinophores

Head structures used for chemoreception.

Parapodia (in sea slugs)

Lateral body flaps used for locomotion, respiration, etc.

Pulmonates

Mostly terrestrial and freshwater gastropods with a closed mantle cavity that acts like a lung.

Pneumostome

The opening to a pulmonate's lung-like mantle cavity.

Umbo

Oldest part of a bivalve shell, formed during the larval stage. Growth rings extend from it.

Hinge ligament

Springy structure on the dorsal side that opens the valves.

Adductor muscles

Muscles that hold the valves closed. Enlarged in scallops, allowing swimming.

Byssal threads

Strong protein threads that mussels use to attach to surfaces.

Bipectinate gills

Gills with filaments on both sides of the axis, modified in bivalves for feeding and respiration.

Interfilamental ciliary junctions

Structures that rigidly connect neighboring gill filaments.

Deposit feeding

Collecting food particles from soft sediment.

Protobranchs

Primitive bivalves that deposit-feed in soft sediment.

Palp proboscides

Extensions of the palps that probe sediment for food.

Labial palps

Flaps near the mouth that sort food from non-food. Rejected particles are expelled into the mantle cavity.

Lamellibranchs

Bivalves with sheet-like gills (no longer an accepted clade). Split into 4 subclasses based on hinge morphology.

Lamellae (W-shaped)

Continuous sheets of gill filaments, extended and folded into a W shape.

Incurrent / excurrent siphons

Tubular extensions of mantle tissue. Water enters through one and leaves through the other.

Crystalline style

Translucent rod of protein and digestive enzymes that rotates against the gastric shield to grind food.

Gastric shield

Hard patch in the stomach against which the style rotates.

Digestive gland (diverticula)

Site of digestion and absorption.

Shipworms

Wood-boring bivalves (not true worms). Valves are modified for rasping wood and symbiotic bacteria digest it.

Chemosynthetic gill symbionts

Some bivalves house chemosynthetic bacteria in their gills (at hydrothermal vents and in shallow water).

Arms (cephalopod)

Foot-derived limbs (8 in squid, cuttlefish, and octopodes).

Tentacles (feeding tentacles)

Two extra feeding limbs in squid and cuttlefish, originating near the mouth.

Suckers

Structures on the arms for gripping substrate and prey.

Funnel / siphon

Foot-derived tube that expels water from the mantle cavity for jet propulsion.