3.2.2 Bony fishes

3.2.2 Bony fishes

Subclass Elasmobranchii

The subclass, Elasmobranchii includes the following superorders (Compagno, 1973):

  1. Galeomorphii
  2. Squatinomorphii
  3. Squalomorphii
  4. Batoidea  

Superorder Galeomorphii

Galeomorph sharks have varied shapes.  Some of the species differ markedly from the typical body shape of a shark.  This superoorder includes the following orders (living groups):

  1. Heterodontiformes
  2. Lamniformes  

Order Heterodontiformes

Popularly called as horn sharks and are considered to be ancestral group of living elasmobranchs (Moyle et al., 1982).  The members of this group are sluggish and are shallow water bottom dwellers.  This group contains a single family, Heterodontidae having 6 species.  

Order Lamniformes

This order includes seven families.  They are i) Orectolobidae (nurse sharks), ii) Odontaspididae (sand sharks), iii) Lamnidae (thresher sharks or mackerel sharks), iv) Scyliorhinidae (cat sharks), v) Carcharhinidae (smooth sharks), vi) Sphyrnidae (hammerhead sharks) and vii) Rhiniodontidae (whale sharks).  This order has 56 genera and 200 species.  

The typical sharks come under the family, Lamnidae and Carcharhinidae.  The sharks of this order are mostly pelagic forms, large with blade like teeth.  Most of the members of this group are highly predacious feeding on large fishes, squids, cuttlefishes and marine mammals.  Some of the sharks, Carcharodon carcharias, Isurus oxyrinchus and Galeocerdo cuvieri are the man eating sharks.    

The whale sharks (Rhiniodon typus) and the basking sharks (Cetorhinus maximus) are not capable of biting attacks on humans and have developed mechanisms for straining plankton.  The whale shark attaining a maximum length of 18 m is considered as world’s largest fish.  

Superoorder Squatinomorphii

The angel sharks are represented in this superorder.  This superorder includes a family Squatinidae.  The family includes one genus, Squatina having 11 species.  The members of this group appear to be intermediate between sharks and rays and shares many characters of sharks and rays, at the same time possess its own specifications.  Because of these features, Compagno (1973) placed the angel sharks in the superorder, Squatinomorphii.  However, Nelson (1978) placed this group under the superorder, Squalomorphii.  

Though morphologically these sharks look like a ray with flattened body, yet the large pectrol fins are not attached to head.  Large spiracles are located on top of head, the five gill openings are more laterally located with terminal mouth.  Two dorsal fins are located on the caudal region of the body and anal fins are wanting.

Superorder Squlomorphii

This superorder includes three orders namely, Hexanchiformes, Squaliformes and Pristophoriformes.  Six species are represented under the order, Hexanchiformes and are deep water forms (Moyle and Ceech, 1982).  Six or seven gill openings are seen.  This order includes two families namely, Chlamydoselachidae and Hexanchidae.  

Cow sharks coming under the order are rather flabby, bottom oriented sharks with weak jaws and have small teeth.  This group comes under the family, Hexanchidae.    

The order, Squaliformes contains two families viz. Squalidae (dog fish sharks) and Echinorhinidae (bramble sharks). The order, Pristiophoriformes, the saw sharks, have teeth attached to their snout and is extended as a long flat blade.  The pristiophorids have many ray like characters and are closely related to Batoidimorpha.  Two genera and four species are included in this family.   

Superorder Batoidea

This superorder includes rays and skates having the following characters:

  1. Gill openings ventral in position.
  2. The pectoral fins enlarged, attached to side of head anterior to the five gill openings.
  3. No anal fins.
  4. Eyes and spiracle located on the top of the head and pavement like teeth present.
  5. Nictitating membrane absent.   
  6. Rajiformes

The members of this group are primarily adapted for bottom living and are benthic in habitat.  This superorder includes the following orders:

Last modified: Tuesday, 24 January 2012, 9:20 AM