SUPER CLASS-PISCES
Super class—Pisces is considered as true fishes and
includes three main classes.
1. Class—Cyclostomata
Class—Cyclostomata(Cyklos — circular; stome —
mouth) includes the round mouthed fishes. They
are also called jawless fishes as they have sucking
mouth without jaws. They are marine, but show
migration to freshwater for spawning. Adult die
within few days after spawning but their larvae
return to the ocean.
The body of cyclostomes is elongated, smooth has
paired fins and are without scales. The cranium and
vertebral column are cartilaginous. Circulation is of
closed type. They have 6-15 pairs of gill slits for
respiration.
e.g., Petromyzon (lamprey), Myxine (hagfish).
Note
Petromyzon is sanguivorous as it sucks blood of fishes as
an ectoparasite. Myxine feeds on flesh of dead animals, so it
IS necrophagous.
2. Class—Chondrichthves
(Cartilaginous Fishes)
Class—Chondrichthyes (Chondros-cartilage; ichthys— fish) have over
600 species including sharks, rays and skates. They are called
cartilaginous fishes due to the presence of cartilaginous skeleton.
(i) They are mostly marine called poikilothermic animals.
They have the capacity to regulate their body temperature.
(ii) The body is laterally compressed and spindle-shaped.
(iii) Notochord is persistent throughout the life.
(iv) Mouth is ventral in position, skin is tough
containing minute placoid scales and teeth are
modified placoid scales. They have strong jaw and
are predaceous by nature.
(v) Gill slits are generally five pairs. The gill covering
operculum are absent.
(vi) Heart is two-chambered with one auricle and one
(vii) Air bladders are absent, so they swim constantly to
avoid sinking.
(viii) Some of them possess electric organs (e.g., Torpedo)
and some possess poison sting (e.g., Trygon).
(ix) Paired and unpaired fins are present, which are not
supported by fin rays. The tail fin is always
heterocercal (unequal lobes).
(x) They are called ureotelic animals as they secrete urea.
(xi) Sexes are separate and fertilisation is internal.
(xii) Males usually have claspers on pelvic fins, which
help in copulation.
(xiii) Many of them are viviparous.
e.g., Scoliodon (shark or dog fish), Carcharodon (great
white shark), Pristis (saw fish), Trygon (sting ray), Sphyrna
(hammer-headed shark).
3. Class -Osteichthyes (Bony Fishes)
Class—Osteichthyes (Osteon — bone; ichthys — fish) includes
bony fishes such as carps, catfishes, sardines, mackerels,
seahorse, etc. There are about 25000 species of bony fishes
found all over the world. They have a bony endoskeleton.
distinguished features of’ ()stcichthycs arc as follows
(i) “I hey are found in marine water as well as in
freshwater. They are cold-blooded animals.
(ii) The body is streamlined to facilitate swimming easily
through water.
(iii) Exoskeleton contains dermal scales like cycloid of
ctenoid scales.
(iv) Gills are covered with operculum (gill cover) and are
generally four pairs.
(v) Heart is two-chambered with one auricle and one
ventricle.
(vi) Air bladders are present. They are the hydrostatic organs.
(vii) Fins are paired and unpaired, which are supported by
fin rays.
(viii) Tail fin is always homocercal (equal lobes) or
diphycercal type.
(ix) These are ammonotelic animals that excrete ammonia
(x) Sexes are separate. Fertilisation is usually external
mostly viviparous and development is direct.
e.g.. I.abeo (rohu), Mrigal (carps), Catla (catla), Hippocampus
(seahorse), Exocoetus (flying fish), Remora (sucker fish”
Anabas (climbing perch), Protopterus (African lung fish).