Echinoderms

Are echinoderms deuterosomes or protosomes?

Deuterostomes (ass first). 

Deuterosomes are a part of the larger group …

Bilaterians. Sister group of protosomes. 

What are the Phylums includeded in Deuterostomes?

Phylum Echinodermata – sea stars, urchins, etc.

• Phylum Hemichordata – acorn worms, pterobranchs

• Phylum Chordata – tunicates, lancelets, vertebrates

Characteristics of Phylum Echinodermata

• all marine

• eucoelomate

• pentaradial symmetry

• endoskeleton (CaCO 3)

• water vascular system

• tube feet (in most)

• ring-like nervous system

• blood vascular system reduced or absent

• excretory organs absent

• monoecious

• typically free-swimming, bilaterally symmetric larval stage

Echinoderm Classes

Class Crinoidea – sea lilies

• Class Asteroidea – sea stars

• Class Ophiuroidea – brittle stars & basket stars

• Class Echinoidea – sea urchins

• Class Holothuroidea – sea cucumbers

Class Asteroidea – sea stars

• Rocky, sandy, or muddy substrates

• predators of esp. bivalves

• General Features:

  • 5 arms (rays)

  • oral/aboral surface

  • tube feet in ambulacral grooves

  • madreporite - allows water into water vascular system

Sea Star Water Vascular System

• Madreporite - allows water in

• Stone Canal - connects to

• Ring Canal - connects to 

• Radial Canals - connects to

• Lateral Canals - connects to

• Tube feet (podia) - with suckers, operated by ampullae

Sea Star Digestive System

• mouth

• esophagus

• stomach

  • cardiac

  • pyloric

• pyloric caecae (digestive glands)

• anus

Sea Star Body Wall

• Dermal ossicles

• “catch” connective tissue

• papulae (dermal gills) - respiration

• pedicellariae - keeps them clean (pincers)

• Spines

• muscles

Sea Star Structure - gut wall and hemal system

• coelom well developed

  • water vascular system derived from part of it

  • functions in respiration, circulation, excretion

• hemal system present

  • function unclear; likely distributes nutrients

Sea Star Nervous System and Sense Organs

• nervous system

  • nerve rings and radial nerves on both oral and aboral sides

• sense organs not well developed

Sea Star Regeneration

famous for ability to regenerate missing arms

• can autotomize (cast off) if injured

• can also regenerate central disc if part remains

Sea Star Reproduction and Development

Monoecious - external fertilization.

• Primitive pattern is indirect development

  • bipinnaria larva > brachiolaria larva > metamorphosis > juvenile sea star

• Many have Direct dev and eggs may be brooded.

Sea stars have larval types specific to classes of echinoderms - others:

• Ophiuroids: Ophiopluteus

• Echinoids: Echinopluteus

• Holothuroids: Auricularia

• Crinoids: Doliolaria

Sea Star Wasting Disease

Tissues disintegrate. Shown to be due to a bacterium

Class Ophiuroidea

• Brittle stars and basket stars

• 5 arms

• no pedicellariae, gills

• ambulacral grooves closed

• tube feet w/o suchers. Move via musculat action of arms

• Generally feed on small particles

Class Echinoidea

Sea urchins and sand dollars

• no arms

• dermal ossicles form solid shell → test

• Ambulacral grooves closed.

  • areas extend up sides

• spines present, often used for locomotion

• tube feet and pedicellariae well developed

• Mosly herbivores, some may be carniovores

Class Echinoidea - Aristotle’s Lantern

complicated mouthpart structure used for feeding.

Class Holothuroidea

Sea cucumbers

• elongated oral - aboral axis

• Reduced ossicles

• lie on side, tube feet typically dev on bottom side only

• Oral tentacles around mouth

• Respiratory tree off of cloaca

• Feed on small particles

• Can eject guts as defense mechanism

Class Crinoidea

• sea lilies & feather stars

• sessile (attached) for much of adult life, stalk present

• typically deep water, but may be in shallows

• arms with pinnules used for filter feeding

• ambulacral grooves present, used for feeding, transporting food caught on pinnules

• good fossil record

Phylum Hemichrodata

• acorn worms

  • (Class Enteropneusta)

• pterobranchs

  • (Class Pterobranchia)

• grouped with echinoderms as clade Ambulacraria

  • tornaria larva resembles sea star bipinnaria larva

• gill slits tie them to chordates (presumably lost in echinoderms)