Book : Zoology
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Posted by: CHELSEA
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Writer CHELSEA

Phylum Pisces

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General Features

Pisces is a Class in the Subphylum Vertebrata of the Phylum Chordata, so they have all of the characteristics of both of these groups in addition to the following: 1.Skin covered in scales 2.Ectothermic, cold blooded 3.Soft shelled eggs that must be laid in water 4.External fertilization 5.All members are fully aquatic 6.Limbs modified into fins 7.Gas exchange through gills

Classification

Include three classes. 1) Placodemi, .2) Elasmobronchi (Chondrichthyes), 3) Osteichthyes.

Class 1 Picodermi

1) It includes extinct fishes. 2) They are all armored fishes. Their exoskeleton Is in the form of bony plates or shields. 3) Their endoskeleton is bony: 4) The hyoidean gill-slits are complete. It is not reduced. 5) The autodiastylic jaw suspension is seen in these fishes.

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Class 2 Chondrlchthys or Elasmobranchi

1) These fishes are exclusively marine. 2) The exoskeleton in the form of placoid scales. 3) Their endoskeleton is cartilagenous and are called Cartilage 4) Jaw suspension is amphistylic or hyostylic. 5) 5-7 pairs of gills are present. The Class Elasmobranchi is divided into two sub-classes. 1. Sub-class Selachi :- In these fishes the pectoral fin has cartilagenous rods. Fins are well developed. The caudal fin is hetetocercal. This subclass has four orders in which only two are living. Order 1. Proto selachl 1) Jaws show many pointed teeth. 2) Nasal openings are paired. 3) Hyostylic or Axnphistylic jaw suspension. It is represented by few living species. Ex :Heteroloatas Order 2. Euselachi 1) Skin contains placoid scales. 2) These fishes are exclusively marine. 3) 5 pairs of gill slits. They open separately. It is divided into two A) Sub-order . Pleurotremata: 1) Gill slits on the lateral sides of the body. 2) Pectoral fins are distinct. 3) It includes sharks and dog fishes. Ex :- Scoliodon, Sphyrna (Hammer headed shark), Stegostoma (Tiger shark). B) Sub-order Hypotermata: 1) It includes skates And Rays. 2) The body is flattened dorso-ventrally. 3) Pectoral fins are enormously expanded anterio posteriorly and gill openings are ventral and five in number. 4) Dorsal fins, if present are seen on the tail. Ex :- Pristis (Saw fish), Rhinobatus (Guitar fish), Torpedo (Electric ray), Raja (Skates), Trygon (sling rays), Myliobatis (Eagle rays) Sub-Class 2; Bradyodonti It includes fossil and modern chimaeras. 1. Mouth is small and bounded by lips. 2. Holostylic jaw suspension is seen. 3. Gill opening are enclosed in boneless operculum. 4. Male possesses a frontal clasper on the head. It is divided into 2 orders. Order 1. Eubradyodonti ‘It includes Helodus’. order2. Holocephali It includes chimaera. These are called devil fishes. Chimaera also called king of Hernngs. Chimara

Class 3 Osteichthyses a Telostomi

1. These fishes are marine, fresh water. 2. Cycloid, ctenoid or ganoid scales will form the exoskeleton. 3. Endoskeleton bony. 4. Jaws suspension is autostylic 5. Operculum is present. 6. Claspers are absent. This class is divided Into two sub-classes. Sub-Class I. Crossopterygii, Sub-Class II. Actinopterygii, Sub-Class-III. Crossoptenygii In this sub-class bony fishes are Included which show lobed and massive fins. The sub-class includes two orders, Order - 1 Rhipidistia This order includes extinct fishes. But in 1938 one coelacanth fish was caught. This was identified as, Rhipidistian fish by Miss. Latimer. The fish is called Latimeria. It is the oldest living fossil. Ortler -2. Dipnoi This order Includes living fishes. In the present day only 3 genera are living. They show discontinuous distribution. Ex: Neoceratodus (Australian lung fish), Sub-class II Actinopterigii These fishes will live in fresh water or marine water. They not show internal nostrils. This subclass is divided into three super orders. Super order I: Chondrostei This super order includes 3 orders, only fishes of one order or surving Order polypterifonnes :- The fishes wtth ganoid scales Caudal fin is symmetrical. Dorsal fin has many peculiar fin-lets. Ex:Polypterus. Super order II: Holostel: This include 2 orders. Order 1. Amiiformes. Caudal fin is heterocercal. Ex Antia (Bowin). Order 2. Lepldoeteiformes: Nasal opening at the end of the much elongate snout. Caudal fin is abbreviate heterocercal. Ex: Lepidpsteus (Gar pike). Super order III. Telosteti : This is a very important super order. It includes nearly 25,000 species. They are divided into many orders. Order I. Clupelfonnee : Caudal fin is homocercàl. Ex: 1. Hilsa hisha (Herrings).2. Salmon. Order 2. Cypriniformes: Weberian ossicles connecting the ear with air bladder is present. Mr-bladder is connected with duct to the alimentary canaL Ex : - Carps. (Labeo, Cinhina, Barbus). Order 3. Anguilllformes. : Body eel like, air-bladder, If present connected with intestine by a duct. Ex:Anguilla. Order 4. Beloniformes :Physoclistic fishes in which fins are without spines. Ex : Exocoetus, (flying fish)., Cypsilurus Order-5. Syngnathlformes: Physoclistic fishes In which the first dorsal fin, If present, Is spinous. Ex Hippocampus (Sea horse). Syngnathus (Pipe-fish) Order 6: Syinbranehiformes: Eel like body, air-bladder is absent spines absent In fins. Ex Asnphinuous. Order 7. Psrciformes: Physoclistic fishes fins usually with spines. Usually two dorsal fins. Eg: Fierasfer, Anabas (Climbing perch). Order 8. Pleuronectiformes. Both eyes are situated on one side skull is asymmetilcal. Fins usually without spine. Adults without air bladder. Ex :Cynogiossus Order 9. Echenelformes The spinous dorsal fin is t into an adhesive disc placed on the head. Air bladder is absent. Ex: Echenis (Sucker fish). Order 10. Ophiocephaliformes: Physoclisfic fishes in which are Without spine, scales are cycloid, air bladder is very long. Ex Channa or opiocephalus. Order 11. Tefradontiformes : Gill openings restricted air bladder is present or absent. Ex: Tetrodon, Diodon (Porcupine fish). Order 12. Gadiformes Physoclistic fishes in which fins are without spines, scales cycloid. 


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