GENERAL HISTOLOGY

Detailed explanation-1: -1: Sea urchins: Sea urchins do not have arms, but have rows of tube feet that can be extended out of pores of the internal shell. Sea lilies and feather stars are examples of Crinoidea. Both of these species are suspension feeders. They live both in shallow water and in depths as great as 6, 000 meters.

Detailed explanation-2: -Crinoids are echinoderms in the phylum Echinodermata, which also includes the starfish, brittle stars, sea urchins and sea cucumbers.

Detailed explanation-3: -Feather stars are echinoderms, like the more familiar sea stars. They are also a type of crinoid, along with sea lilies (which have a stalk).

Detailed explanation-4: -Crinoids are marine animals belonging to the phylum Echinodermata and the class Crinoidea. They are an ancient fossil group that first appeared in the seas of the mid Cambrian, about 300 million years before dinosaurs. They flourished in the Palaeozoic and Mesozoic eras and some survive to the present day.

Detailed explanation-5: -The sea lilies and feather stars reside within the class Crinoidea (from the Greek root word crino meaning lily). Sea lilies are sessile organisms attached to the substrate by a flexible stalk (Figs. 3.96 A and B). The digestive organs are in a bud at the top of the stalk called the calyx.