March 14, 2016

posted Mar 14, 2016, 12:43 PM by Unknown user   [ updated Mar 14, 2016, 12:44 PM ]
Science: we started to talk about Echinoderms are characterized by radial symmetry, several arms (5 or more, mostly grouped 2 left - 1 middle - 2 right) radiating from a central body (= pentamerous). The body actually consists of five equal segments, each containing a duplicate set of various internal organs. They have no heart, brain, nor eyes, but some brittle stars seem to have light sensitive parts on their arms. Their mouth is situated on the underside and their anus on top (except feather stars, sea cucumbers and some urchins).

Echinoderms have tentacle-like structures called tube feet with suction pads situated at their extremities. These tube feet are hydraulically controlled by a remarkable vascular system. This system supplies water through canals of small muscular tubes to the tube feet (= ambulacral feet). As the tube feet press against a moving object, water is withdrawn from them, resulting in a suction effect. When water returns to the canals, suction is released. The resulting locomotion is generally very slow.

There are 5 related classes in the phylum Echinodermata (the Latin name means "spiny-skinned"). For a detailed list with all classifications:

Spanish: Keep practicing your vocabulary and verb conjugations. 1st draft of your Spanish Research Project is due on Friday.