Heterocercal Tail - Encyclopedia.com
2018年5月8日 · The heterocercal tail is present in many fossil fish, in the sharks (Chondrichthyes), and in the more primitive bony fish, e.g. the families Acipenseridae and Polyodontidae. In the later, ray-finned fish ( Actinopterygii ) the homocercal tail developed, in which the vertebral column stops short of the tail fin, which is supported only by bony ...
Sturgeons - Encyclopedia.com
Sturgeons Sturgeons are large shark-like fish, with a heterocercal tail like that of a shark and a small ventral mouth behind an extended snout. The mouth has long barbells used for feeding on small animals on the bottom. Sturgeons feed on aquatic …
protocercal tail - Encyclopedia.com
protocercal tail Possibly the most primitive type of tail found in fish. The posterior end of the vertebral column is straight, dividing the tail fin into two equal lobes supported by fin rays. Source for information on protocercal tail: A Dictionary of Zoology dictionary.
Chondrostei - Encyclopedia.com
2018年5月8日 · *Chondrostei (*chondrostean fish*)* Group of bony fish [1] belonging to the subclass Actinopterygii [2]. Often ranked as a super-order, the chondrosteans have a partly cartilaginous skeleton (see CARTILAGE [3]), a heterocercal tail [4], a …
Cartilaginous Fishes - Encyclopedia.com
2018年5月11日 · Most cartilaginous fishes are marine carnivores with powerful jaws. Unlike bony fishes, they have no swim bladder, and therefore avoid sinking only by constant swimming with the aid of an asymmetrical (heterocercal) tail. There is no operculum covering the gill slits, the first of which is modified as a spiracle. Fertilization is internal so ...
Acipenseriformes | Encyclopedia.com
Acipenseriformes (subclass Actinopterygii, superorder Chondrostei) An order of rather primitive fish characterized by a cartilaginous skeleton, a heterocercal tail fin, and a head with a pointed, protruding rostrum and ventrally located mouth. Extant members of the order either have a naked skin or possess five rows of large, rhomboid, bony ...
Osteostraci - Encyclopedia.com
2018年5月8日 · The internal structure of the head resembled that of the extant lampreys. The body was enclosed in bony scales arranged in a series of vertical rows, and there were either one or two dorsal fins and a heterocercal tail. The internal skeleton was partly ossified.
Climatiiformes - Encyclopedia.com
2018年5月23日 · *Climatiiformes* One of the larger orders of fossil fish belonging to the class Acanthodii [1]. They possessed bony jaws and body skeleton, ganoid scales [2], a heterocercal tail [3], and stout spines located before the dorsal, anal, pectoral, and pelvic fins.
Fossil Fishes | Encyclopedia.com
Acanthodii Class of primitive, fossil fish that had a true bony skeleton, a heterocercal tail fin, a persistent notochord, ganoid scales, and stout spines in front of the fins. The acanthodians lived from the Silurian Period to the Permian Period and may be related to ancestors of the more modern bony fish.
Placodermi - Encyclopedia.com
2018年5月8日 · Placodermi Class of archaic, jawed (gnathostome), and heavily armoured fish, which appeared in the Devonian and which were virtually extinct by the end of that period.