Bio 125 Exam 3 ch 16 echinoderms

Ch 16 echinoderms

key characteristics of echinoderms

pentamerous radial symmetry in adults and bilateral symmetry in larvae. water vascular system with tube feet for locomotion and feeding, skin gills for respiration. Brain is absent.

Sea Stars

Class Asteroidea, move with tube feet, have central disc in center of body surrounded by 5 arms, internal organs extend through entire body, have pedicellariae

pedicellariae

pincer like organs that keep skin clean

keystone species

A species that plays a greater than expected role in the composition and numbers of other species in the community.

External Anatomy of Sea Stars

Aboral surface (top): anus, madreporite, arm. Oral surface (bottom): mouth, ambulacral groove, tube feet.

Brittle Stars

Class Ophiuroidea, central disc surrounded by 5 thin flexible arms, internal organs are restricted to central disc, tube feet without suckers for feeding on detritus, no anus, move with arms

Sea Urchins, Sand Dollars

Class Echinoidea, conspicuous moveable spines, rigid plates fused into a solid test, move with tube feet, mouth on bottom, anus on top of body, biting mouth for grazing with Aristotle’s Lantern.

Aristotle’s Lantern

A feeding structure of jaws and muscles

Role Sea Urchins Play in Ecosystem

Sea Urchins eat kelp forests, but a population explosion of urchins can lead to a collapse of the ecosystem, creating urchin barrens where kelp forests and coral reefs are destroyed. They are preyed upon by sea stars, sea otters, and fish. Their population size is a direct indicator of the balance of the ecosystem.

Sea Cucumbers

Class Holothuroidea, worm-like with mouth and anus on opposite ends and 5 rows of tube feet restricted to 1 side, radially symmetrical, skin embedded with calcareous spicules, no spines, deposit feeders, evisceration.

Evisceration

Expulsion of the internal organs when disturbed, internal organs regenerate back. Creates distraction for predators and used for defense.

Crinoids

Class Crinoidea, 5 or more arms branch out for suspension feeding, sea lilies live attached in deep water, feather stars crawl on the bottom and live mostly in shallow water coral reefs.