BIOL360 Lecture Notes - Lecture 10: Cystoidea, Blastoid, Calcite
12 May 2018
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Echinoderms and Hemichordates
Both are deuterostomes, characterized by
• first opening in developing embryo is the anus and then later a mouth
• have a body cavity developed from the embryonic gut
Echinoderms
• 5-fold symmetry
• Mesodermal skeleton of calcite plates covered by a spiny skin
• Waster vascular sytem -> water is pumped by hydraulics through animal by
muscle action; must have constant salinity
• Modified tube feet for feeding, locomotion and respiration
• All are marine, no freshwater
• Examples -> sea urchins, starfish, sea cucumbers
Ancestral echnioderms -> had unusual asymmetrical body plan with 5 ambulacra
that led to 5 fold symmetry
• Ex: helcosystis moroccoensis
o Calcite lattice-like exoskeleton of plates
o Could change shaped (tall and thin, short and fat)
o Found in Cambrian rocks
Blastozoans
• Informal group but imp echinoderms
• All are extinct -> cystoids, blastoids, eocrinoids
• Had short stems and lacked arms (brachials)
Sea Urchins and Sand dollars
• Robust endoskeleton or test composed of 100 of interlocking calcite plates
coated with an outer skin of spines or bumps; 10 segments
• Mobile, found in benthos
• Globular, discoidal and heart-shaped
• Good record, appeared during Ordovician radiation
Document Summary
Both are deuterostomes, characterized by first opening in developing embryo is the anus and then later a mouth: have a body cavity developed from the embryonic gut. Ancestral echnioderms -> had unusual asymmetrical body plan with 5 ambulacra that led to 5 fold symmetry: ex: helcosystis moroccoensis, calcite lattice-like exoskeleton of plates, could change shaped (tall and thin, short and fat, found in cambrian rocks. Informal group but imp echinoderms: all are extinct -> cystoids, blastoids, eocrinoids, had short stems and lacked arms (brachials) Micraster -> evolutionary patterns in fossils example of ontogenetic and phylogenetic change in fossil record. Crinoid -> sea lilies but not a plant; have 1000s of species today: almost all fossils were stalked. Like stacked coins: major expansion in ordovician and continued through paleozoic. Pterobranchs -> resemble bryozoans b/c they have zooid w/ tentacles and ciliated arms.
