![]() They have different forms of free-swimming and free-living larvae each related with different classes.ĭespite diversity of echinoderms observed above, most of them look very much alike and have related modes of life. Tube feet (podia) are offshoots of radial canals of water vascular system and suckers at their ends facilitate attachment to substrate and are also utilized for locomotion. They possess simple circulatory or haemal system which runs through system of coelomic compartments. Body wall is composed of ciliated epidermis underneath which is a dermis which contains calcareous ossicles that give rise to spines. Their nervous system is well grown but uncentralized. There are different forms of gut and it might not have anus. Their body surface has five fields with podia (ambulacra) alternating with 5 that do not have podia (interambulacra). They are not cephalized (without any distinguished head) but have oral - aboral axis. There are two major kinds of body form among adults: radiate and globular. Adult is secondarily radially symmetrical. The early larva exhibits evidence of metameric segmentation adults are unsegmented. There are approx 6,250 - 6,500 species of echinoderms distributed between 3 subphyl and 5 classes. It is thought that echinoderms branched from same deuterostome evolutionary stem as vertebrates. ![]() In protostomes conversely, blastopore of embryo gives rise to mouth of adult. Echinoderms and chordates are called as deuterostomes as in both groups, blastopore of embryo grows in anus and mouth forms at opposite end. ![]() The phylum Echinodermata is said to be a connection between invertebrates and chordates due to certain similarities that two phyla share. ![]()
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