Echinodermata

What are the groups within Deuterostomes?

• echinoderms

• hemichordates

• chordates

what are the key features of echinoderms?

• Synapomorphies:

  • pentaradial symmetry as adults (bilateral symmetry as larvae)

  • endoskeleton of calcareous plates

  • water vascular system

• Epidermis: spines and/or pedicellariae

• No head/brain: have a diffuse neural net

how do echinoderms reproduce?

• separate sexes

• external fertilization, spawning behavior

• can reproduce asexually via regeneration

what environment do echinoderms live in and how do they feed?

• they are all marine

• predators, grazers, suspension feeders

oral vs aboral side of echinoderms

• oral side has the mouth

• aboral side

Water vascular system

• a hydraulic system used to control locomotion, feeding, waste transport, and respiration

• water enters through pores (madreporites) and circulates through canals that lead to tube feet (with suckers)

endoskeleton in echinoderms

• derived from mesoderm

• covered in epidermis

• calcareous plates connected by catch collagen

what is the function of catch collagen?

It is a special type of connective tissue that changes the rigidity of the body very quickly without using muscles (is controlled by the nervous system)

is pentaradial symmetry a derived or ancestral trait in echinoderms?

derived (MRCA had bilateral symmetry)

evertable stomach of echinoderms

sea stars can extend their stomach pushing it through very small openings during feeding

classes of echinoderms

• Crinoidea

• Asteroidea

• Ophiuroidea

• Echinodea

• Holothuroidea

Crinoidea

• sea lilies and feather stars

• oral surface: dorsal

• aboral surface: ventral

• common fossils

where do crinoidea live?

shallow water and deep trenches

sea lilies vs feather stars

• sea lilies are attached to a surface by a stalk, are sessile

• feather stars are more motile

Asteroidea

• sea stars

• predators, evertable stomach

• regeneration

• can have >5 limbs

where do asteroidea live?

shallow and deep waters

what type of symmetry do sand dollars and sea cucumbers have?

They have features of bilateral symmetry (how they move) and pentaradial symmetry, but are considered to be pentaradial

are echinoderms cephalized and/or segmented?

neither

how do echinoderms breathe

• they do not have a respiratory system

• use diffusion and water vascular system for respiration

what type of guts do echinoderms have?

• complete gut w/ specialized regions

do echinoderms have pharyngeal slits?

no (they were present in the MRCA, but lost)

Ophiuoridea

• brittle stars and basket stars

• long slender arms with spines

• secretive predators

• can be bioluminescent

brittle stars vs basket stars

• brittle stars are more mobile

• basket stars are sessile

Echinoidea

• sea urchins and sand dollars

• move slowly

• graze on algae

• have spines and calcareous exoskeleton for protection

Holothuroidea

• sea cucumbers

• scavengers and filter feeders

• soft-bodied

• catch collagen allows them to fit in tight places

• unique defense (evisceration), may be toxic