موضوع تعبير بالانجليزية عن حيوان فقاري

موضوع انشائي قصير باللغة الانجليزية عن حيوان فقاري

English topics and essays

Vertebrates  are animals that are members of the subphylum Vertebrata . Vertebrates include the overwhelming majority of the phylumChordata, with currently about 64,000 species described. Vertebrates include the jawless fish and the jawed vertebrates, which includes the cartilaginous fish (sharks and rays) and thebony fish. A bony fish clade known as the lobe-finned fishes includes the tetrapods, which are divided into amphibians, reptiles, mammals, and birds. Extant vertebrates range in size from the frog species Paedophryne amauensis, at as little as 7.7 mm (0.3 inch), to the blue whale, at up to 33 m (110 ft). Vertebrates make up about 4% of all described animal species; the rest are invertebrates, which lack backbones.

The vertebrates traditionally include the hagfish, which do not have proper vertebrae, though their closest living relatives, the lampreys, do have vertebrae. Hagfish do, however, possess a cranium. For this reason, the vertebrate subphylum is sometimes referred to as "Craniata" when discussing morphology. Molecular analysis since 1992 has suggested that the hagfish are most closely related to lampreys, and so also are vertebrates in a monophyletic sense. Others consider them a sister group of vertebrates in the common taxon of Craniata.