GENERAL CHHARACTERS AND CLASSIFICATION OF OSTEICHTHYES Subject – Zoology, Class - B.Sc. Part – II(Hons. and Subsi.) Paper – III(Hons.) & II(Subsi.) By:- KUNDAN PATEL Guest Faculty Department of Zoology, B.N. College, Patna INTRODUCTION The class Osteichthyes includes bony fishes with a wide range of variations in features. Fishes range from simple lobe-finned to ray- finned. They have certain common features but vary in certain characters like presence and types of scales. Size of fishes is also variable and some of the fishes are prominently known to us. Their abundance varies in different ecosystem depending upon their ecological needs. Let us see the general and identifying features of these fishes with the help of their classification. GENERAL CHARACTERS OF OSTEICHTHYES ● It includes both marine and fresh water fishes with bony endoskeleton ● The head and pectoral girdles are covered with large dermal bones ● Streamlined body with terminal mouth ● Have four pairs of gills which are covered by operculum on each side ● Skin is covered with cycloid or ctenoid scales ● They do not have placoid scales ● Heart is two-chambered and is cold-blooded GENERAL CHARACTERS OF OSTEICHTHYES ● The eyeball is supported by a sclerotic ring of four small bones ● The labyrinth in the inner ear contains large otoliths ● They have swim bladder which help the body to create a neutral balance between sinking and floating ● Sexes separate, fertilization usually external ● Mostly oviparous ● Development is direct ● E.g. – exocoetus(Flying fish), Hippocampus(Sea horse), Labeo(Rohu), Catla(Katla), Clarias(Magur), Betta(flying fish), Pterophyllum(Angel fish), etc. GENERAL CHARACTERS OF OSTEICHTHYES CLASSIFICATION OF OSTEICHTHYES The class Osteichthyes has bee classified into two subclasses as follows(Romer, 1966):- Subclass -1. Sarcopterygii:- ● Gr., sarcos = fleshy; pterygium = fin ● Paired fins leg-like or lobed, with a fleshy, bony central axis covered by scales ● Two dorsal fins, caudal fin heterocercal with an epichordal lobe ● Olfactory sacs usually connected to mouth cavity by internal nostrils or choanae ● Popularly called fleshy or lobe-finned or air breathing fish ● It has two orders:- CLASSIFICATION OF OSTEICHTHYES Order – 1. Crossopterygii:- ● Gr, crossoi = a fringe; pteryx = fin ● Paired fins lobed covered with scales. Pectoral fins are supported by a jointed median axis bearing radials. Caudal fin three-lobed ● Scales covered by a layer of cosmine ● Premaxillae, maxillae and squamosal bones present ● Internal nares may or may not be present ● Spiracles present ● Air-bladder vestigial ● E.g. – Latimeria, Coelacanths(extinct), etc. CLASSIFICATION OF OSTEICHTHYES CLASSIFICATION OF OSTEICHTHYES Order – 2. Dipnoi:- ● Gr, di=double; pnoe=breathing ● Cycloid scales covering the skin ● Single gill-slit on either side present and covered by operculum ● Paired fins lobed ● Tail fin symmetrical(diphycercal) with no trace of separate dorsal fins ● Internal nares present opening into mouth; spiracles absent ● Air-bladder single or paired, lung-like ● Notochord remain as an unconstructed rod, vertebrae cartilaginous arches ● Premaxillae and maxillae absent ● Lower jaw(palate-quadrate) firmly fused to neurocranium(skull autostylic) ● Stomach absent, intestine ciliated, no hepatic caeca, spiral valve present ● Auricle partly divided into two, ventricle completely divided by a ridge ● Ventral aorta shortenedinto a spirally twisted muscular bulbus cordis provided with valves ● Pulmonary and systemic circulation separate ● Cleavage holoblastic ● E.g. – lung fishes(Neoceratodus, Protopterus and Lepidosiren) CLASSIFICATION OF OSTEICHTHYES CLASSIFICATION OF OSTEICHTHYES Sublass – 2. Actinopterygii:- ● Gr, actis=ray; pteryx=fin ● Includes all ray-finned fishes ● Paired fins thin, broad, without fleshy basal lobes and supported by dermal fin-rays ● Radials of paired fins not arranged biradially ● One dorsal fin may be divided ● Caudal fin without epichordal lobe ● Tail generally homocercal, in a few heterocercal or semi- heterocercal ● Scales either ganoid or reduced to thin horny structure or completely absent in some ● Gill-slits covered by operculum. Spiracles absent ● Olfactory sacs not connected to mouth cavity. Internal nares absent ● Squamous bone absent ● It has been classified into three superorders:- CLASSIFICATION OF OSTEICHTHYES Superorder – 1. Chondrostei:- ● Primitive ray-finned fish or cartilaginous ganoids ● Tail fin heterocercal ● Scales usually ganoid ● Large mouth opening ● It has two orders:- Order – 1. Polypteriformes:- ● Typical rhomboid ganoid scales ● Dorsal fin of eight or more finlets ● Pectoral fins with a small prominent scale covered fleshy lobe ● Ossified skeleton ● Spiracles present ● Air-bladder bilobed opening into the intestine ventrally ● E.g. – Polypterus(Bichir) CLASSIFICATION OF OSTEICHTHYES CLASSIFICATION OF OSTEICHTHYES Order – 2. Acipenseriformes:- ● Body covered with five rows of bony scutes ● Snout elongated, having barbles on the ventral surface ● Caudal fin heterocercal ● Skeleton largely cartilaginous. Endocranium cartilaginous ● Jaws without teeth ● E.g. – Acipenser(Sturgeon), Polydon(Paddle-fish) Superorder – 2. Holostei:- ● Gr, holos=entire; osteon=bone ● Intermediate ray-finned fish, transitional between chondrostei and teleostei ● Ganoid or cycloid scales ● Tail fin heterocercal ● Mouth opening small CLASSIFICATION OF OSTEICHTHYES CLASSIFICATION OF OSOrdTEICHTHYEer – 1. Amiiformes:- S ● Thin, overlapping cycloid scales ● Caudal fin heterocercal ● Long dorsal fin ● Pectoral radials are attached to the scapulocoracoid cartilage ● Vertebral centra non-opisthocoelous ● Premaxillary not protractile, firmly articulated with the cranium ● Snout normal rounded ● Spiracles and clavicles are absent ● Presence of a single swim-bladder ● E.g. – Amia(Bowfin) Order – 2. Semionotiformes or Lepidosteiformes:- ● Scales rhomboidal ganoid and in oblique rows ● Body elongated ● Nasal opening at the end of much elongated snout ● Caudal fin heterocercal ● Vertebrae completely ossified and opisthocoelous ● Air-bladder cellular ● E.g. – Lepidosteus or Lepisosteus(Garpike) CLASSIFICATION OF OSTEICHTHYES CLASSIFICATION OF OSTEICHTHYES Superorder –3. Teleostei:- ● Gr., teleos=complete; ostgon=bone ● Scales cycloid, ctenoid or absent ● Mouth terminal, small ● Tail fin mostly heterocercal ● Endoskeleton bony ● Single external gill-slit on each side of the head covered by operculum ● Cloaca and claspers absent ● Air-bladder usually present ● Spiracle is lost ● Spiral valve in the intestine absent ● Conus arteriosus greatly reduced but there is an enlarged bulbus arteriosus ● Advanced or modern ray-finned fishes CLASSIFICATION OF OSTEICHTHYES Order – 1. Clupeiformes:- ● Scales cycloid and well developed ● Head and operculum not scaled ● Single dorsal and small ventral fin without spines ● Ventral fin may be absent ● Pelvic fins abdominal ● Caudal fin homocercal ● Air-bladder communicate with the pharynx ● Vertebral centra completely ossified ● Weberian apparatus absent ● E.g. – Clupea(herringer), Salmo(Atlantic salmon), Sardinops(Pacific sardine), Notopterus(Chital fish), Gadusia, Ilisha, etc. CLASSIFICATION OF OSTEICHTHYES CLASSIFICATION OF OSTEICHTHYES Order – 2. Scopeliformes:- ● Deep sea fishes having phosphorescent organs ● Dorsal and anal fins without spines. An adipose fin present ● Mouth wide and provided with numerous small teeth ● Air-bladder absent ● E.g. – Harpodon(Mumbai duck) Order– 3. Cypriniformes:- ● Fins either without spines or dorsal, anal and pectoral have a spine each ● Ventral(pelvic) fins abdominal ● Air-bladder connected with the pharynx by a duct ● A peculiar Weberian apparatus, connecting the internal ear with the air- bladder, present ● Body covered with scales or naked ● E.g. – Labeo(Rohu), Cirrhina, Botia, Cyprinus(Carp), Puntius, Tor, Heteropneustes(Singhi), Calrius(Magur), Wallago(Lachi), Mystus(Tengra), etc. CLASSIFICATION OF OSTEICHTHYES CLASSIFICATION OF OSTEICHTHYES CLASSIFICATION OF OSTEICHTHYES Order – 4. Anguiliformes:- ● Body elongated eel-like or snake-like ● Scales vestigial or absent ● Dorsal and anal fins long and confluent behind ● Pelvic fins, if present, abdominal ● Fins devoid of spines ● Air-bladder with duct ● E.g. – Anguilla(Freshwater eel), Muraena(Moray) Order – 5. Beloniformes:- ● Body elongated, covered with cycloid scales ● Fins without spines pectoral fins large and high on body ● Ventral(pelvic) fins abdominal ● Some of them are capable of jumping into the air and glide with the help of enlarged pectoral fins ● E.g. – Belone or Xenentodon(Garfish), Hemiramphus(Half beak), Exocoetus and Cypselurus(Flying fishes) CLASSIFICATION OF OSTEICHTHYES CLASSIFICATION OF OSTEICHTHYES CLASSIFICATION OF OSTEICHTHYES Order – 6. Syngnathiformes:- ● Body covered with protective layer of scales or bony rings ● Snout tubular with suctorial mouth ● Pectoral fins small, pelvics absent and a single dorsal fin present ● Fin-rays of dorsal, pectoral and pelvic fins not branched ● Tail prehensile in sea horse, but not in pipe fish ● Air-bladder closed ● Males possess brood pouch for the development of the young ● Physoclistic ● E.g. – Hippocampus(Sea horse), Fistularia(Flute fish), Syngnathus(Pipe fish) Order – 7. Ophiocephaliformes or Channiformes:- ● Body covered with cycloid scales ● Head depressed, covered with plate-like scales ● Fins without spines ● Air-bladder very long and without duct ● Accessory respiratory organs present ● Physoclistic ● E.g. – Ophiocephalus or Channa(Snake head fish) CLASSIFICATION