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

Class Crinoidae

Sea stars Brittle stars

Crinoids

Sea urchins Sea cucumbers

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

Unfertilized egg

Starfish Development

2 blastomeres

After fertilization

& 1st cleavage

4 blastomeres

2nd cleavage

8 blastomeres

3rd cleavage

16 blastomeres

4th cleavage

32 blastomeres

6th cleavage, next slide

5th cleavage

Starfish Development (continued)

64 blastomeres

Non-motile blastula Ciliated blastula

* blastula is same size as unfertilized

egg

Gastrula: Beginning invagination

blastopore

Gastrula: During invagination

Gastrula: Archenteron, no

mesenchyme

Next slide

Starfish Development (continued)

Gastrula: Archenteron with mesenchyme

Late gastrula: lateral view

Early bipinnaria larva, lateral view

Brachiolaria larvaYoung starfish

Late bipinnaria larva, lateral view

blastopore becomes

anus

2nd opening becomes

mouth

Phylum Echinodermata

Tube feet & associated plumbing

Used for walking, clinging to substrate & holding food

Water Vascular System

Starfish water vascular system

Class Echinoidea: sea urchins

Echinometra mathaei

Colobocentrotus atratus

Echinothrix calamaris

Slate pencil urchin

Collector urchin

Class Holothuroidea: Sea Cucumbers

Holothuria atra

Polyplectana kerfersteninii

Linckia sp.

Acanthaster planci

Class Asteroidea: Sea Stars

Maui, Hawaii

Pin cushion

Class Ophiuroidea: Brittle Stars

Class Crinoidea: Feather Stars

Starfish Dissection: Schematic View

Starfish: Oral View

Mouth

Ambulacral groove

Spines

Tube feet

Starfish Dissection: Skeleton Removed: Aboral View

Stone canal

Digestive glands

Gonads

Pyloric stomach

Cardiac stomach

Starfish Arm: Digestive Glands

Removed

Ambulacral Plates

Ampullae

Cardiac Stomach

Gonads