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Phylum Echinodermata
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Lecture notes on echinoderms (part of echinoderms and chordates)
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Phylum EchinodermataThis is part of deuterostomia. It's divided into echinodermata and chordata.
Archenteron is an endoderm lined cavity at gastrulation that develops into a digestive tract. Coelom
is a body cavity lined with mesoderm. Blastopore is the opening in the archenteron.
Evolution of echinodermata based of the 'asterozoan hypothesis'
During the cambrian period.
Phylum echinodermata features
Adults have radial symmetry of 5
Open circulatory system, no heart
Dipleurula larvae
Slow moving or sessile
Nerves but no cephalisation
Water vascular system
They have a thin skin that covers an endoskeleton of hard calcareous plates, giving skeletal bumps
and spines with different functions.
Water vascular system is unique to echinoderms. It’s a network of hydraulic canals branching into
extensions called tube feet. These function in locomotion, feeding and gas exchange. The
madreporite is the opening of the water vascular system.
How it works is that the ampullary muscles extend and stick but the retractor muscles shorten.
Sexual reproduction in echinoderms usually involves release of gametes by separate males and
females into the seawater. Their ciliated, planktonic, dipleurula larvae are bilateral and even the
adults aren't truly radial.
Dipleurula larvae: a band of cilia encircles their mouth. The dipleurula type of larvae is only found in
echinoderms and hemichordates. The ciliated larvae of hemichordates are very similair to those of
echinoderms. This suggests that these 2 groups stem from a common ancestor. The trochophore
type of larvae found in many protostomes has a band of cilia encircling the body anterior to the
mouth.
There are 6 classes in the echinoderms:
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