NEET Biology Animal Kingdom Notes - Class-Pisces

Superclass Pisces

Superclass Pisces.

Class 1. Chondrichthyes (Cartilaginous Fishes)

         (i) General characters.

            (1) Mostly marine and predaceous.

            (2) Body fusiform or spindle shaped.

(3) Fins both median and paired, all supported by fin rays. Pelvic fins bear claspers in male. Tail heterocercal.

            (4) Skin tough containing minute placoid scales and mucous glands.

(5) Endoskeleton entirely cartilaginous, without true bones (Gr. chondros, cartilage + ichthys, fish). Notochord persistent. Vertebrae complete and separate. Pectoral and pelvic girdles present.

(6) Mouth ventral. Jaws present. Teeth are modified placoid scales. Stomach J-shaped. Intestine with spiral valve.

(7) Respiration by 5 to 7 pairs of gills. Gill-slits separate and uncovered. Operculum absent. No air bladder and lungs.

(8) Heart 2?chambered (1 auricle and 1 ventricle). Sinus venosus and conus arteriosus present. Both renal and portal systems present. Temperature variable (poikilothermous).

            (9) Kidneys opisthonephric. Excretion ureotelic. Cloaca present.

            (10) Brain with large olfactory lobes and cerebellum. Cranial nerves 10 pairs.

(11) Olfactory sacs do not open into pharynx. Membranous labyrinth with 3 semicircular canals. Lateral line system present.

(12) Sexes separate. Gonads paired. Gonoducts open into cloaca. Fertilization internal. Oviparous or ovoviviparous. Eggs large, yolky. Cleavage meroblastic. Development direct, without metamorphosis.

(ii) Classification of Chondrichthyes

            (a) Subclass I. Selachii : (Gr., selachos, a shark)

            (1) Multiple gill slits on either side protected by individual skin flaps.

            (2) A spiracle behind each eye.

            (3) Cloaca present.

Examples: True sharks. About 250 living species. Dogfishes (Scoliodon, Chiloscyllium, Mustelus, Carcharinus), spiny dogfish (squalus) seven gilled shark (Heptanchus), Zebra shark (stegostoma), hammer-headed (Sphyrna), whale shark (Rhineodon). Skates and rays. About 300 species. Skate (Raja), stingray (Trygon), electric ray (Tropedo), eagle ray (Myliobatis), guitar fish (Rhinobatus), sawfish (Pristis)

Electric organ are found in Torpedo

            (b) Subclass 2. Holocephali : (Gr., holos, entire + kephale, head)

            (1) Single gill opening on either side covered by a fleshy operculum.

            (2) No spiracles, cloaca and scales.

            (3) Jaws with tooth plates.

            (4) Single nasal opening.

            (5) Lateral line system with open groove.

            Examples : Rat fishes or chimaeras. About 25 species. Hydrolagus (= Chimaera).

Class 2. Osteichthyes (Bony fishes)

            (i) General Characters

            (1) Inhabit all sorts of water-fresh, brackish or salt; warm or cold.

            (2) Body spindle-shaped and streamlined.

            (3) Fins both median and paired, supported by fin rays of cartilage or bone. Tail usually homocercal.

(4) Skin with may mucous glands, usually with embedded dermal scales of 3 types; ganoid, cycloid or ctenoid. Some without scales. No placoid scales.

(5) Endoskeleton chiefly of bone (Gr., osteon, bone + ichthyes, fish). Cartilage in sturgeons and some other. Notochord replaced by distinct vertebrae Pelvic girdle usually small and simple or absent. Claspers absent.

            (6) Mouth terminal or sub terminal. Jaws usually with teeth. Cloaca lacking, anus present.

            (7) Respiration by 4 pairs of gill on body gill arches, covered by a common operculum on either side.

(8) An air (swim) bladder often present with or without duct connected to pharynx. Lung-like in some (Dipnoi).

(9) Ventral heart 2-chambered (1 auricle + 1 ventricle). Sinus venosus and conus arteriosus present. Aortic arches 4 pairs. Erythrocytes oval, nucleated. Temperature variable (poikilothermous).

            (10) Adult kidneys mesonephric. Excretion ureotelic.

(11) Brain with very small olfactory lobes, small cerebrum and well developed optic lobes and cerebellum. Cranial nerves 10 pairs.

            (12) Well developed lateral line system. Internal ear with 3 semicircular canals.

(13) Sexes separate. Gonads paired. Fertilization usually external. Mostly oviparous, rarely ovoviviparous or viviparous. Eggs minute to 12 mm. Cleavage meroblastic. Development direct, rarely with metamorphosis.

(ii) Classification of Osteichthyes

            (a) Subclass I. Sarcopterygii : (Gr., sarcos, fleshy + pterygium, fin)

            (1) Paired fins leg-like or lobed. With a fleshy, bony central axis covered by scales.

            (2) Dorsal fins 2. Caudal fin hreterocercal with an epichordal lobe.

(3) Olfactory sacs usually connected to mouth cavity by internal nostrils or choanae, hence the previous name of subclass, choanichthyes (Gr., choana, funnel + ichthyes, fish).

(4) Popularly called fleshy or lobe-finned, or air breathing fish. Divided into 2 superorders or orders: Crossopterygii and Dipnoi.

          Order 1. Crossopterygii ? (Gr., crossoi, a fringe + pteryx, fin)

            (1) Paired fins lobate. Caudal fin 3?lobed.

            (2) Premaxillae and maxillae present.

            (3) Internal nares present or absent. Spiracles present.

            (4) Air bladder vestigial.

            Example? Primitive fleshy-finned extinct fishes. Single living genus Latimeria.

            Order 2. Dipnoi ? (Gr., di, double + pnoe, breathing)

            (1) Median fins continuous to form diphycercal tail.

            (2) Premaxillae and maxillae absent.

            (3) Internal nares present and spiracles absent.

            (4) Air bladder single or paired, lung-like

            Examples ? Lung fishes. Only 3 living genera : Epiceratodus (Neoceratodus), Protopterus and Lepidosiren

(b) Subclass II. Actinopterygii ? (Gr., actis, ray + pteryx, fin)

            (1) Paired fins thin, broad, without fleshy basal lobes, and supported by dermal fin rays.

            (2) One dorsal fin, may be divided.

            (3) Caudal fin without epichordal lobe.

            (4) Olfactory sacs not connected to mouth cavity.

(5) Popularly called ray-finned fishes. Divided into 3 infaclasses or superorders: Chondrostei, Holostei and Teleostei.

          Superorder A. Chondrostei ? (Gr., chondros, cartilage + osteon, bone)

            (1) Mouth opening large.

            (2) Scales usually ganoid.

            (3) Tail fin heterocercal.

            (4) Primitive ray-finned fish or cartilaginous ganoids.

            Examples ? Acepenser (Sturgeon), Polyodon (paddlefish)

          Superorder B. Holostei ? (Gr., holos, entire + osteon, bone)

            (1) Mouth opening small.

            (2) Ganoid or cycloid scales.

            (3) Tail fin heterocercal.

            (4) Intermediate ray-finned fish, transitional between Chondrostei and Teleostei

            Examples ?Lepisosteus (garpike)

            Superorder C. Teleostei ? (Gr., teleos, complete + osteon, bone)

            (1) Mouth opening terminal, small.

            (2) Scales cycloid, ctenoid or absent.

            (3) Tail fin mostly homocercal.

            (4) A hydrostatic swim bladder usually present.

            (5) Advanced or modern ray-finned fishes

Examples ? Harpodon (Bombay duck) Cyprinus (carp), Labeo rohita (rohu), Catla, Botia, Carassius (Goldfish), Clarius (Magur), Heteropneustes or Saccobranchus (singhi), Wallago (lachi), Mystus (tengra), Electrophorus (electric eel) Anguilla (freshwater eel), Muraena (moray) Hemirhamphus (half beak), Belone (garfish), Hippocampus (sea horse), Syngnathus (pipe fish), Fistularia (flute fish) Ophiocephalus or channa (snake head) Amphipbnous, Symbranchus (eels). Mastacembelus, Macrognathus, Pterois (scorpion fish), Pleuronectes, Synaptura, Solea, Echeneis or Remora (sucker fish), (porcupine fish), Tetrodon (globe fish)