Echinoderms: Sea Stars Goals of the lab: to introduce general characteristics of the phylum Echinodermata to understand the embryological differences between protostomes and deuterostomes to observe initial stages of embryo development, using prepared slides of starfish embryos to examine external and internal features of the starfish, as a representative of the phylum Echinodermata
Phylum Echinodermata eumetazoan (true tissues) bilaterally symmetrical larvae; radially symmetrical adults eucoelomate deuterostome
Phylum Echinodermata Class Astroidae Class Ophiuroidae Class Echinoidae Class Holothuroidae Sea stars Brittle stars Sea urchins Sea cucumbers Class Crinoidae Crinoids
Phylum Echinodermata No circulatory system No respiratory system Excretion (N elimination) by diffusion Simple nervous system, no brain Water-vascular system
A Comparison of Early Development in Protostomes and Deuterostomes
Early Embryonic Development
After fertilization & 1st cleavage Starfish Development Unfertilized egg 2 blastomeres After fertilization & 1st cleavage 4 blastomeres 2nd cleavage 8 blastomeres 3rd cleavage 32 blastomeres 6th cleavage, next slide 5th cleavage 16 blastomeres 4th cleavage
Starfish Development (continued) 64 blastomeres Non-motile blastula Ciliated blastula * blastula is same size as unfertilized egg Gastrula: Beginning invagination blastopore Gastrula: Archenteron, no mesenchyme Next slide Gastrula: During invagination
Starfish Development (continued) Gastrula: Archenteron with mesenchyme Early bipinnaria larva, lateral view Late gastrula: lateral view Late bipinnaria larva, lateral view blastopore becomes anus 2nd opening becomes mouth Young starfish Brachiolaria larva
Phylum Echinodermata Water Vascular System Tube feet & associated plumbing Used for walking, clinging to substrate & holding food
Starfish water vascular system
Class Echinoidea: sea urchins Slate pencil urchin Collector urchin Echinometra mathaei Echinothrix calamaris Colobocentrotus atratus
Class Holothuroidea: Sea Cucumbers Polyplectana kerfersteninii Holothuria atra
Class Asteroidea: Sea Stars Linckia sp. Maui, Hawaii Acanthaster planci Pin cushion
Class Ophiuroidea: Brittle Stars
Class Crinoidea: Feather Stars
Starfish Dissection: Schematic View
Starfish: Oral View Mouth Tube feet Ambulacral groove Spines
Starfish Dissection: Skeleton Removed: Aboral View Pyloric stomach Stone canal Gonads Cardiac stomach Digestive glands
Starfish Arm: Digestive Glands Removed Cardiac Stomach Gonads Ampullae Ambulacral Plates