Echinoderms and Hemichordates - General Zoology - Lecture Slides, Slides of Zoology

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Chaetognaths, Echinoderms,

and Hemichordates

Chapter 22

Deuterostomes

 Deuterostome characteristics:  Radial, indeterminate cleavage  Formation of the mouth from a second opening  Enterocoelous coelom development  Chaetognaths are placed outside both protostome & deuterostome groups.

Clade Ambulacraria

 Superphylum Ambulacraria contains

two deuterostome phyla

 Echinodermata and Hemichordata

 Members share a three-part (tripartite)

coelom, similar larval forms, and an axial

complex (specialized metaneprhidium).

 Xenoturbella is the sister taxon to

Ambulacraria.

Phylum Echinodermata

 Echinoderms include sea stars, brittle stars, sea urchins, crinoids, sea cucumbers.  Entirely marine  Lack ability to osmoregulate.  Almost entirely benthic.  Nonsegmented.

Phylum Echinodermata –

Characteristics

 Spiny endoskeleton of plates  Water vascular system  Pedicellariae  Dermal branchiae (skin gills)  Pentaradial symmetry in adults

Phylum Echinodermata - Symmetry

 Echinoderms are bilaterally symmetrical as larvae.  This means their ancestors were bilaterally symmetrical.

Phylum Echinodermata - Symmetry

 Today’s echinoderms are mostly motile.

 Many are still radial.  Some have again become superficially bilateral (skeletal & organ systems still pentaradial).  Sea cucumbers.  A few sea urchins.

 No well defined head or brain.

Phylum Echinodermata -

Deuterostomes

 Echinoderms have a true coelom with

deuterostome development.

 Radial, indeterminate cleavage.  Enterocoelous – the mesoderm lined coelom develops from outpocketing of the primitive gut.  Formation of the mouth at the end of the embryo opposite the blastopore.

Water Vascular System

 The water vascular system opens to the outside through small pores in the madreporite.

Water Vascular System

 Canals of the water vascular system lead to the tube feet.  Tube feet may have suckers, allowing the echinoderm to move while remaining firmly attached to the substrate – important in areas with lots of wave action.

Development

 Eggs (which may be brooded or laid as benthic egg masses) hatch into bilateral , free-swimming larvae.  The type of larva is specific to each echinoderm class.  Class Asteroidea  Bipinnaria  Brachiolaria  Class Ophiuroidea  Ophiopluteus  Class Echinoidea  Echinopluteus  Class Holothuroidea  Auricularia  Class Crinoidea  Doliolaria

Development

 Metamorphosis involves a reorganization into a radial juvenile.  Left/right becomes oral/aboral.