Themes > Science > Zoological Sciences > Animal classification > Polygenetic Tree of Kingdom Animalia > Protostome and Deuterostome Conditions > Introduction of Deuterostomes

The phylum Echinoderms are marine invertebrate animals that have an internal skeleton composed of pieces of calcium carbonate (calcite ossicles) and a special system of fluid-filled vessels (the water vascular system) that aids in locomotion, feeding, and sensory reception. The phylum includes starfish, as well as brittle starts, feather stars, sand dollars, sea cumbers, sea lillies, and sea urchines. Fossil echinoderms are from the lower Cambrian Period onward.

A feature of echinoderms is their excellent power of regeneration. They easily repair injured tissues and replace lost parts. Some sea cucumbers can eject their digestive system and associated organs when disturbed, and grow a new set within a few weeks.

The Chordate Branch of the animal family tree includes invertebrate and vertebrate species. All are bilateral animals with a supporting rod for the body (notochord), dorsal nerve cord, pharynx, and gill slits in the pharynx wall.

Tunicates , a subgroup of Chordata, have these features in their larval stage of development. In metamorphosing into adults they retain the pharynx but lose the notochord and nerve cord.

A second subgroup of Chordata, the Lancelets, retain all three chordate features throughout life.

Members of the only other subgroup of Chordata, the Vertebrata, are distinguished by a vertebral column. This anatomical structure is formed from cartilage or bony tissue, or both. The hagfish and lampresy are living descendants of some early jawless fishes. They latch onto prey with their specialized mouthparts.

Amphibians is a vertebrate that is somewhere between fishes and reptiles in body plan and reproductive mode. Most amphibians have a large bony endoskeleton and four legs. No matter how far they venture onto land, they have not fully escaped dependency on water.

Birds are the only animals that produce feathers, which they use in flight, heat conservation, and in socially significant visual displays.

Birds still resemble reptiles in many ways. They have horny beaks, scaly legs, and many have the same internal structures.

Reptiles evolved from certain amphibians during the late Carboniferous. The reptiles were the first vertebrates to escape dependency on standing water. They have scaly sking, rely on internal fertilization, and have amniote eggs.

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