Oceanology Vocab: Chapters 9.6, 10, 18

**nerve cord**

A long, compact bundle of neurons that is part of the central nervous system.

**pharyngeal slits**

Small openings along the anterior part of the gut; one of the four key characteristics of chordates.

**notochord**

A flexible rod that lies below the nerve cord of chordates.

**post-anal tail**

A tail that extends beyond the anus; one of the four key characteristics of chordates.

**backbone**

A series of articulating bones surrounding the nerve cord of vertebrates; a spine or vertebral column.

**tunic**

The outer covering of sea squirts.

**incurrent siphon**

The “mouth” of tunicates.

**excurrent siphon**

The secondary opening on a tunicate which expels water from the gut.

vertebrates

Chordates with a backbone.

vertebra

(pl. vertebrae) Each of the bones that make up the backbone.

cartilage

A rigid material that is still lighter and more flexible than bone that makes up the skeletons of sharks, rays, and skates.

placoid scales

Small rough scales that make up the skin of cartilaginous fishes.

caudal fin

The posterior, or tail, fin of fishes.

dorsal

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

pectoral fin

Each of the pair of fins just behind the head of fishes.

demersal fish

A bottom-dwelling fish.

cycloid

Overlapping smooth scales of bony fishes.

ctenoid

Overlapping spined scales of bony fishes.

operculum

The flap of bony plates that covers the gills of bony fishes.

fin ray

Each of the bony spines in the fins of bony fishes.

swim bladder

The gas-filled sac in the body cavity of bony fishes that is involved in the adjustment of buoyancy.

ichthyology

The scientific study of fishes.

pyloric caecum

Each of the slender tubes found in the intestines of many bony fishes.

spiral valve

A spiral portion in the intestine of cartilaginous fishes.

cloaca

The common opening for the intestine and the excretory and reproductive systems of cartilaginous fishes and other animals.

gas exchange

The movement of oxygen and other gases between the atmosphere and the ocean, or between the water or atmosphere and living organisms, in which case it is often called respiratory exchange.

spiracle

One of two openings behind the eyes of cartilaginous fishes.

lamella

Each of the many thin plates that make up the gill filaments of fish gills.

countercurrent system of flow

An adaptation of bony fishes where the blood in the gills flows in the opposite direction of the water passing over them, increasing the efficiency of gas exchange.

chloride cells

Cells in the gills of fishes that are involved in the excretion of excess salts.

urea

A toxic waste product of some vertebrates.

olfactory sacs

Structures on both sides of the head of fishes that are sensitive to chemical stimuli.

barbels

Whisker-like sensory organs near the mouth of some bottom feeding fishes.

otoliths

Calcareous ear stones that fishes use to detect change in body position.

lateral line

A system of canals and sensory cells on the sides of fishes that helps them detect vibrations in the water.

neuromasts

Sensory cells in bony fishes that are sensitive to vibrations.

ampulla of Lorenzini

One of several sensory structures in the head of sharks that detect weak electric fields.

simultaneous hermaphroditism

Animals that can produce eggs and sperm at the same time.

sequential hermaphroditism

An animal that changes from male to female (or female to male) over the course of its life.

chromatophore

specialized cell in the skin of bony fishes which contain colored pigments.

structural color

A color that results when light is reflected by a particular surface.

iridophore

A chromatophore with light-reflecting crystals which gives fishes their structural colors.

warning coloration

Coloration that allows organisms to escape from predators by advertising something harmful or distasteful.

cryptic coloration

A color pattern that allows an organism to blend with the surroundings.

disruptive coloration

A color pattern that helps break the outline of an organism.

countershading

A color pattern that results in a dark back and a light belly; most common in epipelagic fishes.

school

A well-defined group of fishes or cetaceans of the same species.

anadromous

Marine fishes that migrate to fresh water to breed.

catadromous

Freshwater fishes that migrate to sea to breed.

internal fertilization

Sperm is directly transferred from males to females through copulation.

external fertilization

The release of gametes into the water.

oviparous

An animal that releases eggs.

ovoviviparous

An animal that produces eggs that hatch inside the female immediately before birth.

viviparous

An animal whose eggs develop inside the female while the embryo derives nutrition from the mother directly from the womb (aplacental viviparity) or by a placenta (placental viviparity) as in most mammals.

parthenogenesis

Development of an egg into an embryo without fertilization by a sperm.

midwater

Pertaining to the mesopelagic zone.

photophore

An organ that produces bioluminescence.

bioluminescence

The production of light by living organisms.

deep scattering layer

(DSL) A sound- reflecting layer made up of many types of organisms that migrate daily from the mesopelagic zone to the epipelagic zone.

tubular eyes

Specialized eyes of many midwater animals that allow acute upward or downward vision.

retina

The light-sensitive part of an eye.

counterillumination

The emission of light by midwater animals to match the background light.

oxygen minimum zone

A layer of water at a depth of approximately 500 m where oxygen is depleted.

pheromone

A chemical that organisms use to communicate with other members of their species.

male parasitism

The permanent attachment of a male to a female in some deep-sea fishes.

benthic

Organisms that live on the bottom.