Pisces Or Fishes: General Characters and Classification
According to Nature of Skeleton:
Nature of skeleton are of two types depending upon the spaces of fish.
Fish With Cartilage:
The Indus skeleton of the fishes are cartilage type means this bone is made up by calcium that is a correct bone or flexible type cartage bone.e.g. dog fish Shark fish shop fish is example of the cartage fishes.
Fish With Bone:
This types of fish has strong skeleton and well structured with bone sach type off fishes Bony fishes.e.g. Rohu, Catla, mrigal etc. are fish with bone.
On the Basis of Accommodation:
Fishes are of three types on the basis of their accommodation. Fish of Freshwater:
This types of fish lives in the pond, river, canal, fen etc. with freshwater.
Semi Saltwater Fish:
This types of fish lives in the estuary and bay with semi saltwater. Tangra, bhetki, gurjali etc. are saltwater fish.
Saltwater Fish:
This types of fishes lives in saltwater OBC and costal area. Hilsa (ilish), rupchanda, bele etc. are saltwater fish.
According to the Presence of Scales:
Fishes are of two types on the basis of their Scales:
Fish With Scales:
The fishes body is covered with scale is known as scale fishes . Rui, katla, mrigal, calbasu (kalabaus) etc. are fishes with scale.
Fish Without Scales:
The fishes which has no scale on the body is called without scale fishes. E.g. catfish, pabda, tangra, boal etc.
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Classification of fish is described below according to the modern Zoologist.
Phylum- Chordate
Subphylum- Vertebrate
Super series-
1.Agnatha- Circular oral sucker
2.Gnathostomata- jaws present (Upper/Lower)
Super Class/series -
1. Pisces OR Fishes
2. Tetrapoda
Class (1) Pterichthyes ▸ (Devonian)
Class (2) Coccostei (Arthrodira) (Up. Silurian-Up. Devonian) [Gk. Coccosteus, rough-like a berry bone;
Class (3) Acanthodii
(Upper Silurian to Devonian):
Class (4) Elasmobranchii
[Gk. Elasma = a flat plate; branchia = gills] (Plate-like gilled fishes) [Jurassic - Recent] Approx. 800 species:
Class (5) Holocephali
(Bradyodonti) (UP. Devonian- Recent) [Gk. Holos = whole; kephale = head].Lund (1977) used the term Bradyodonti instead of Holocephali. Approx. 30 living species.
Class (6) Dipnoi
(Dipneusta) [Middle Devonian - Recent] [Gk. Di = double; pnol = breath] [6 living species]
Class (7) Teleostomi
(Lower Devonian - Recent), About 20,994 living species:
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Class (1) Pterichthyes
(Devonian) (Antiarchi):
The members of this class lived in the Devonian period. These are fresh water forms and the fossils that are well-preserved reveal certain internal structures in the museum's.
General Characters:
(i) Head and thoracic part are provided with strong bony plates of skeleton.
(ii) The bony plates are arrangement of is strikingly similar to that of the Class Arthrodira.
(iii) The tail is heterocerecal with a ventral fold.
(iv) The pelvic fins are usually some species absent.
(v) The part of alimentary canal as intestine contains spiral valve.
(vi) lungs is present it is a sac like pouch.
(vii) On the dorsal side of head the eyes are closely placed.
(viii) The mouth is ventrally placed.
(ix) The jaws are poorly developed.
(x) The body is naked in some forms, but in Pterichthys the body and tail are covered with scales.
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Class (2) Coccostei
(Arthrodira) (Up. Silurian - Up. Devonian) [Gk. Coccosteus, rough-like a berry bone;
General Characters:
(i) The characterised by having strong cranial roof formed by the union of bony plates in fishes the members of this class .
(ii) These bony plates are sculptured by the presence of tubercles.
(iii) The skull is articulated by a pair of condyles.
(iv) The vertebrae lack centra but the neural and haemal arches are present.
(v) They are generally called 'joint- necked' fishes and flourished well during the Devonian period.
(vi) The whip-like tail are present posterior part of the body is prolonged into which may be covered by scales.
(vii) covering the branchial arches is quit an operculum.
(viii) a pair of small unmovable lobed structures situated one on each side of the body.The pectoral fins are greatly reduced .
(ix) The pelvic fins are paired structures located on the ventral side.
(x) A well-formed dorsal fin is present.
Class (3) Acanthodi
(Upper Silurian period to Devonian period)
This class the most primitive placoderms. The members are smaller in size and are regarded as 'needle-finned sharks' because of their superficial resemblance characters with the shark group .
The acanthodians were fresh water fishes and the geological history revealed their existence from the upper Silurian to the Permian periods, their maximum abundancy being in the Devonian periods.
General Characters:
(i) They head is elongated fusiform bodies (almost eel-like) with a anterior blunt snout.
(ii) The eyes were large and directed forward. The mouth was placed terminally. (iii) The tail was heterocercal.
(iv) There were two dorsal fins in species.one longer than second one.
(v) A single anal fin was present.
(vi) the pectoral and pelvic fins are paired fins . The pair fin to support a large spine like structures from origin up to the anterior most tip edge.
(vii) Pectoral girdle are present.
(viii) In the pectoral fins Traces of basal elements were present .
(ix) Small rhomboid scales covered on the body .The scales were dermal derivatives and it composed of bony type.
(x) On the head region, ganoid types of the scales present.
(xi)jaws and branchial arches are mostly cartilaginous .
(xii) The jaws were primitive and head four ossified bone, two in the lower and two in the upper jaws.
(xiii) The upper jaw is maxillary type palak quadrate is composed of two rows of pieces it was a toothless and lower jaw is a mandible is present in teeth.
(xiv) The teeth were modified scales.
(xv) The hyoid arch bone was an unmodified branchial arch of species.
(xvi) The mandibular, hyoidal and all the branchial arches in primitive forms, were provided with small opercular folds. But in the higher group forms the mandibular operculum highly developed cover the gills.
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Class (4) Elasmobranchii
[Gk. Elasma : a flat plate,branchia -gills] (Plate-like gilled fishes) [Jurassic period- Recent period] There are 800 species.
The Elasmobranchii group of the class includes a cartilagenous fishes such as sharks and rays.
The group of the class are also called Elasmobranchii or cartilagenous which signify the 'plate gilled' fishes.
General Characters:
1. The Elasmobranchii group of fishes is mostly marine water are surviving it is the mostly predacious or hunter of the fishes.
2. The body is covered by rough aur smooth skin origin on the body minute placoid scales .(denticles) and mucous glands.
3. The mouth is ventrally placed. Rows of teeth (specialised placoid scales) are pre sent in the mouth. The skeleton is cartilaginous in nature, but bone formation in the vertebrae has been recorded in small cat shark (Scyliorhinus canalicula).
4. The nostril may be one or two in number, but do not open into the mouth cavity.
5. The median and paired fins are present. In the mail the base of pelvic fins with claspers. The fins are supported by fin-rays. The caudal fin is mostly heterocercal around tail.
6. The notochord is persistent. The vertebrae are complete and separate.
7. The spiral valve is present in the intestine.
8. The swim-bladder is absent.
9. The heart possesses a contractile conus arteriosus with rows of valves.
10. There are 5 to 7 pairs of gill for the respiration in respiratory system. each Gil r form is separate milk there is upperculum is present on the gill as a cover.
11. The opisthonephros is present in the kidney there are the functional in adult fishes.
12. Jaw suspension is of hyostylic type.
13. On the head the Ampullae of lorenzini is a sensory organ it has a electroreceptor organ of the fishes.
Class (5) Holocephali
( Bradyodonti) (Upper Devonian period - Recent period) [Gk. Holos : whole; kephale - head]. This term used first by Lund (1977) as Bradyodonti instead of Holocephali. Approx. 30 living species of fishes.
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General Characters:
1. Body of fishes is somewhat compressed and naked in adult species.
2. Number of 5-gills arches are present. spiracles is absent.
3. There 4-gills openings are protected by a single fleshy gill cover.
4. In bucal cavity as a Bony plates on the jaws instead of teeth used in crushing.
5. Some species Cloaca is absent.
6. The Skull is holostylic inform.(palatoquadrate is often fused to cranium).
7.There is bone in the skeleton.It is a group of cartilaginous.
8. There is no bony fin rays and no bony plate scales on the bady.
9. Paired Pectoral fins are broad and leaf-shaped structure.
10. The upper jaw is made up of cartilage, palatoquadrate is fused with neurocranium (the base of cranium), a character which indicates the name (holos - whole,cephalos - head).
11. On the tail region Diphycercal caudal fin are form.
12. Two different types of dorsal fins are form. The first with a spine.
13. Extra claspers are present on head side of the mail it is a unknown function of spaces of the group.
14. The Tail is slender type and it's whip-like structure.
Class (6) Dipnoi (Dipneusta)
[Middle Devonian period-Recent period] [Gk. Di =-double, pnoi =-breath] 6 species of fishes are living in globe.
The Dipnoans or lung-fishes constitute this class. The position of the dipnoans amongst the fishes is quite mostly significant. They constitute a sort of transitional group between the Teleostei and the A animals.
General Characters:
1. External gill opening single cover and covered with a bony gill cover of operculum.
2. The Paired Pectoral and pelvic fins lobate type with a jointed median axis.
3. Peculiar grinding teeth usually present on the palatal regions in bucal cavity.
4.In bucal cavity absent of articulated tooth-bearing pre- maxillary and maxillary bones.
5. Presence of internal nasal is open into the mouth region.
6. Air bladder serving as a lung with special pulmonary circulation in the species.
7. A cloaca opening is present.
8. In cranium Autostylic skull (palatoquadrate is fused to the undivided cranium).
9. Median or single fins are fused around the posterior third of the body.
10. Braincase or skull and vertebral column are poorly ossified.
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Class (7) Teleostomi
(Lower Devonian period - Recent period), Group of 20,994 living species:
The representatives of the class Teleostomi constitute the highly developed and more species forms amongst the fishes. It constitute many diagnostic features which separate them from remaining classes of fishes. Despite the wide ranging of the adaptive features, they possess the following common features.
General Characters:
1. The body is covered with thin dermal cycloid, ctenoid or ganoid scales and many lack scales entirely, e.g., the members of the family Siluriidae and some bottom dwellers.
2. The unpaired median and paired fins are present on the bady. The fins are supported by bony fin-rays. The tail is homocercal.
3. The mouth of fishes is terminal and arrengeged of teeth row.
4. A External gill-opening is covered by a bony operculum On the body of fishes.
5. The jaw suspension is usually hyostylic.
6. Generally vertebrae are amphicoelous type.
7. Usually cloaca is absent.
8. Usually present an air bladder or swim bladder. sometimes acts as lung in some forms.
9. The heart is two chambered (one auricle and one ventricle) with sinus venosusand conus arteriorsus.
10. Forebrain is feebly developed.
(Presently-23500 species of fishes,
21000 species-90%-Bony fishes CI-Teleostomi,
2500species -10%- Cartilagenous Fishes Cl-Chondrychthys)
https://www.insearchofknowledge.org/2024/03/pisces-or-fishes-museum-specimens-1-1.html
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Pisces or Fishes: Museum Specimens-1
1. Chondrichthyes (Elasmobranchi-Cartilagenous) Fishes
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Pisces or Fishes: 2. Osteichthyes- Museum Specimens-2
2. Osteichthyes (Teleostomi-Bony fish) Fishes
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