Vertebral column may be cartilaginous in nature as is case in some fishes or bony as in most vertebrates. Unlike protochordates, vertebrates are the ones we come across more or less on the daily basis. Like animals include cats, horses, pigeons, chickens, dogs, etc. It should be emphasized that humans are chordates.
Characteristics of Subphylum Vertebrata:
Chordate subphylum, Vertebrata, is characterized by given features:
Vertebrates which evolved from fish pass through similar embryonic stages. The flexible notochord develops in back and blocks of tissue known as somites form along each side of it. Somites will become major structures, like muscle, connective tissue, vertebrae, and, later, larger glands of body.
Features of Superclass Agnatha:
Features of Members of superclass are given below:
Characteristics of the Class Cyclostomata (lampreys and hagfishes)
The class cyclostomata derived its name by having round or circular mouth. Class is characterized by given features:
Cyclostomes are extremely unique among vertebrates due to of their semi-parasitic nature. Lampreys, with exception of some small freshwater forms, join themselves to other fishes by their suctorial mouth and then rub off flesh through horny teeth carried by highly-developed tongue. Hagfishes are able to boring their way right in body of prey, consuming all soft parts and leaving skin behind as ordinary empty shell, held by the bones.
Class Cyclostomata comprises of 2 orders: Petromyzontia (or Hyperoartii) and Myxinoidea (or Hyperotreti).
Order: Petromyzontia (or Hyperoartii) E.g. lampreys - Petromyzon marinus.
The Petromyzontes are characterised by the following features:
The hagfishes are characterized by the following features:
Circular mouth fitted with rasping tongue surrounded by short tentacles, gill pouches attached to common external opening on either side, nasal opening at tip of snout rather than on top of head as in lampreys, completely marine, elongate (eel-like) body.
Features of Class Ostracodermi (Extinct):
This class is extinct but had features like: small fish-like animals (only few centimeters long), bottom dwellers, rudimentary fins and bony armor, poor swimmers, no lower jaw, filter feeders or deposit feeders, no teeth, and are marine.
Features of Superclass Gnathostomata (jaw- bearing animals):
Characteristics of Class Placodermi (Extinct):
The class Placodermi is considered as first set of fish with jaws but is now extinct. Members of the class had the given characteristics:
Cartilaginous fishes contain the given characteristics:
Class Chondrichthyes is separated in two extant subclasses:
Subclass: Elasmobranchii (sharks, rays and skates)
Subclass: Holocephali (chimaera, at times known as ghost sharks). Members of class Chondrichthyes contain backbone which is composed of cartilage. They are not fishes you come across frequently because of their marine.
Features of Class Osteichthyes (Bony fish)
Members of this class have the given features:
The Osteichthyes are characterized by endochondral ("spongy") bone in endoskeleton, dermal fin rays composed by lepidotrichiae (altered, tile-shaped scales), and 3 pairs of tooth-bearing dermal bones lining jaws (dentary, premaxillary and maxillary). Osteichthyes comprise 2 main subclasses, Actinopterygii and Sarcopterygii.
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