Deuterostomes 3: Fishes

Flashcards covering the characteristics, evolution, classification, and physiology of jawless, cartilaginous, and bony fishes.

Superclass Agnatha

A superclass of jawless fish that includes Class Myxini and Class Cephalaspidomorphi.

Class Myxini (Hagfish)

Jawless fish characterized by a lack of paired fins and scales, a biting mouth with two rows of teeth, slime production, and the absence of a cerebellum.

Class Cephalaspidomorphi (Lampreys)

Jawless fish that possess a complete cartilaginous skull and vertebrae, a sucker-like oral disk, and a tongue with keratinised teeth.

Placoderms

Armoured fishes that evolved jaws in the Late Ordovician and reached sizes over $30$ ft in length before becoming extinct by the end of the Devonian period.

Class Chondrichthyes

Cartilaginous fishes, such as sharks and rays, featuring a heterocercal tail, oily liver for buoyancy, internal fertilisation, and teeth that are not firmly anchored to the jaw.

Class Osteichthyes

Bony fishes characterized by a bony endoskeleton, a homocercal tail, a swim bladder for buoyancy, external fertilisation, and an operculum covering the gills.

Operculum

A hard flap found in Osteichthyes that covers the gills and improves respiratory efficiency through buccal pumping.

Heterocercal tail

A type of tail fin where the vertebral column extends into a typically larger upper lobe, characteristic of Class Chondrichthyes.

Homocercal tail

A symmetrical tail fin characteristic of Class Osteichthyes.

Swim bladder

A gas-filled sac in bony fishes used to control buoyancy without energy expenditure and sometimes involved in sound production.

Oval body

A muscular valve used by bony fishes to release gases from the swim bladder.

Class Actinopterygii (Ray-finned fishes)

The most species-rich group of Osteichthyes ($>30,000$ species) with fins supported by parallel bony rays and no internal fin muscles.

Class Sarcopterygii (Lobe-finned fishes)

Fishes with paired fins consisting of a muscular lobe supported by a central core of bones, including the coelacanth and six species of lungfish.

Countercurrent flow

An efficient gas exchange mechanism where blood flows through the secondary lamellae in the opposite direction of water flow.

Oviparous

A reproductive strategy involving the laying of eggs.

Ovoviviparous

A reproductive strategy where fertilised eggs are held within the uterus until they hatch.

Viviparous

A reproductive strategy involving placental development and live birth.

Lateral line

A mechanoreceptor system that senses low-frequency vibrations from relatively long distances.

Ampullae of Lorenzini

Electroreceptors that sense bioelectric fields surrounding prey, found in Chondrichthyes but lost in most bony fishes.

Dentine

The material inside fish teeth, which are thought to have evolved from modified scales on the skin.

Enameloid

The substance covering the dentine in the teeth of fish and amphibians.

Circulatory System

A system featuring a $2$-chambered heart and single-circuit circulation, which is the simplest among vertebrates.