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Summary Fishes
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- University Of South Africa (Unisa)
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By: nitacarstens26 • 3 year ago
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FISHES:SUPERCLASS AGNATHA:
Living jawless fishes:
2 classes: Myxini and Petromyzontida Small brain, 10 pairs of cranial nerves
No jaws, internal ossification, scales or paired fins Poor eyes, semi-circular canals present
Pore-like gill openings and an eel-like body form Sexes separate
Fibrous and cartilaginous skeleton External fertilisation
Vertebrae reduced or absent 5-16 pairs of gills
No distinctive stomach Heart with a sinus venosus, atrium and ventricle
Myxini: hagfishes
Marine group
Feed on annelids, molluscs, crustaceans
and dead or dying animals. They enter a
dead or dying animal through by digging
into the body. Using toothed, keratinized
plates on its tongue that fold together in
a pincer-like action, they rasp bits of
flash from its prey. For extra leverage
they tie a knot in its tail and pass the
knot forward along its body
Almost completely blind. Well-developed
sense of smell and touch
Can generate large amounts of slime
when disturbed
Their body fluids are in osmotic
equilibrium with seawater
Low-pressure circulatory system served by 2 accessory hearts and a main heart positioned behind the gills
Females produce a few large yolky eggs which take 5 months to hatch. No larval stage
, Petromyzontida: lampreys
Some are parasitic
Swim up streams to spawn in spring/summer.
Males build a nest and are joined by females. At
spawning, with the female attached to a rock, a
male attaches to the dorsal side of her head. As
eggs are shed into the nest they are fertilised by
the male. Adults die after spawning. Eggs hatch
after 2 weeks, releasing small larvae called
ammocoetes
Sharp keratinized teeth rasp flesh
To promote the flow of blood they inject an
anticoagulant into the wound
CLASS CHONDRICHTHYES: (Cartilaginous fishes)
Characteristics of Chondrichthyes:
Body dorsoventrally compressed Well-developed brain, 10 pairs of cranial nerves
Caudal fin heterocercal or diphycercal Senses of smell, lateral-line, vision and
Paired pectoral and pelvic fins electroreception, 3 pairs of semi-circular canals
Skin with placoid scales or naked Sexes separate, internal fertilisation - claspers
Cartilaginous skeleton Oviparous or viviparous
Notochord reduced Excretory system of kidneys
Distinct vertebrae 5-7 pairs of gills
Jaws with polyphyodont teeth No swim bladder or lungs
Large stomach Heart with a sinus venosus, atrium, ventricle and
Intestine with spiral valve conus arteriosus. Single circulation
Large oil filled liver
Subclass Elasmobranchii: sharks, skates and rays Eg. Dogfish sharks
Heterocercal tail
Paired pectoral and pelvic fins supported by
appendicular skeletons, 1-2 median dorsal fins, a
median caudal fin. Some have a median anal fin
In males, medial part of pelvic fin modified to
form a clasper used in copulation
Paired nostrils are associated with olfaction
Lidless lateral eyes with a spiracle behind each
5-7 gill slits anterior to each pectoral fin
Tough leathery skin covered in toothlike dermal
placoid scales to reduce turbulence of water
Jaws with sharp teeth. The front row of functional
teeth on the edge of the jaw is backed by rows of
developing teeth that replace worn teeth
Mouth cavity opens into a large pharynx which
contains openings to gill slits and spiracles. A short, wide esophagus runs to the j-shaped stomach. A liver and
pancreas discharge into a short, straight intestine. Attached to a short rectum is a rectal gland which secretes a
colourless fluid containing sodium chloride
Chambers of the heart are arranged in tandem formation.
Internal fertilisation. Large yolky eggs are laid
Subclass Holocephali: Chimaeras Eg. Ratfishes
Jaws bear large flat plates
Upper jaw fused to cranium
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