NEM 10V Lecture Notes - Lecture 34: Tube Feet, Sea Cucumber, Echinoderm
Nematology
Part 8 Echinodermata (Starfish):
• We need to differentiate between Protostomes and Deuterostomes.
• The roundworms, flatworms, annelids, mollusks and arthropods that we have already
studied are all protostomes.
• Echinoderms and Vertebrates are all Deuterostomes.
• This is a good time to look at Figure 1 because you cannot tell by looking at adult
animals which ones are protostomes, and which ones are deuterostomes.
• Both protostomes and deuterostomes have a three-layer embryo.
• When the embryo is just a ball of cells it forms two openings, one that becomes a mouth
and one that becomes an anus.
• In protostomes, the first opening that forms becomes the mouth. Proto– means first and
stoma means opening.
• Deutero means second and in deuterostomes, the second opening becomes the mouth.
• There are five main groups of echinoderms.
• The Asteroidea or sea stars and starfish, Echinoidea or sea urchins and sand dollars, the
Crinoidea which are the sea lilies and feather stars, the Ophiuroidea are the brittle stars,
and the Holothuroidea are the sea cucumbers.
• Echinoderms are radially symmetrical deuterostomes that have interlocking spiny plates
embedded in their skin to form an internal skeleton.
• Their bodies are based on 5-part symmetry.
• A unique feature of echinoderms is a water-vascular system that operates the tube feet,
which have suction disks that are used in locomotion and in capturing prey.
• Sea stars are the most familiar echinoderms.
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