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

Echinoderms, Hemichordates, Deuterostomes, Phylum Chaetognatha, Clade Ambulacraria, Water Vascular System, Endoskeleton, Calcareous Ossicles, Free Swimming Larvae. Above mentioned terms and points represent this lecture of general zoology course. A full series of lectures can be found in my documents.

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2011/2012

Uploaded on 11/19/2012

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Chaetognaths, Echinoderms,
and Hemichordates
Chapter 22
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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.