FURTHER PHYLOGENETIC CONSIDERATIONS IN THE ECHINODERMS Most zoologists believe that echinoderms evolved from bilaterally symmetrical ancestors. Radial symmetry was evolved during the transition from active to more sedentary lifestyles. The…
CLASS CRINOIDEA (krinon, lil + oekks, in the form of) Class Crinoidea includes the sea lilies and the leather stars. They are the most primitive living echinodemis. Therefore, they are…
CLASS HOLOTHUROIDEA (holothourion, sea cucumber + cockles, in form of) 1. Habitat and size: The class Flolothuroidea has approximately 1.500 species. They are commonly called sea cucumbers. Most adults range…
CLASS ECHINOIDEA (Or. echinos, spiny + oeides, in the form of) 1. Habitat The class Echinoidea is composed of sea urchins, sand dollars and heart urchins. Echinoidea has one thousand…
CLASS OPHIUROIDEA (ophis, snake + ourn, tail + andes, in the form of) The class Ophiuroidea includes the basket stars and the brittle stars. It has two thousand species. Thus…
CLASS ASTEROIDEA (aster, star + oeides, in the form of) The class Asteroidea contains sea stars. It has about 1,500 species. They live on hard substrates in marine environments. Some…
CLASSIFICATION OF ECHINODERMS The Echinoderms are triploblastic, coelomate animals. They have pentaradial symmetry in adults. They possess a water-vascular system. Their endoskeleton is covered by epithellium. Pedicellariae are present. Phylum…
THE ECHINODERMS EVOLUTIONARY PERSPECTIVE (Echino, spiny + derma, skin +am, to beer) The 400-million year-old Paleozoic rocks have almost all the fossils of the animals up to echinoderms. Many fossils…
SECONDARY GROWTH IN STEM The stem increases in thickness In sccondary growth. Secondary growth increases the Vascular tissues. Therefore, it increases the thickness of flue stem. Secondary Growth is common…
Occurrence Polytrichum have worldwide distribution. They are very common in cool temperature and tropical regions. Plants live in cool and shady places. General structure The main plant body is gametophyte.…
saadia
sidra
abida