Transcript echinoderms
KINGDOM ANIMALIA Phylum Echinodermata Members of the Phylum Echinodermata Date back 570 million years ago 13,000 fossil species Only 7,000 species today Most are marine and benthic (90%) Range in size (<1cm to 2 m) 5 Classes Common Body Plan Adults are pentaradially symmetrical 5 sets of body parts around an oral-aboral axis Common Body Plan However, larvae are bilaterally symmetrical Settle near adults of their species and attach to substrate Metamorphosis: left side becomes oral surface of the adult and right side becomes aboral Larval mouth/anus disappear, gut migrates to adult position, and new mouth/anus open Endoskeleton Unique system of calcareous plates (ossicles) Reduced in sea cucumbers Fused to form a solid test in sea urchins/sand dollars Endoskeleton Skeletal elements bear pincer-like structures called pedicellariae Use to rid body of debris, defense, grasp objects to hide, or capture/hold prey Water-vascular system Hydraulic system of canals and reservoirs controls the movement of tube feet (podia) Critical to locomotion, gas exchange, feeding, and sensory reception Water-vascular system Water enters sieve plate (madreporite) Flows from stone canal to radial canals in each arm Lateral canals perpendicular to the radial canal terminate in muscular bulb (ampulla) connected to a tube foot Water-vascular system Water enters bulb, it contracts and water forced into foot Extends foot, pressing terminal sucker onto substrate Foot contracts, forcing water back into bulb and raises center of sucker Creates a vacuum seal; only broken when bulb contracts water into foot again Classification There are 6 classes of echinoderms 5 classes are described on the following slides Class Crinoidea Most ancient/primitive 625 species Base of 5 or 10 arms that can branch up to 200 arms Suspension feeders Each arm bears suckerless podia that produce mucus to capture detritus and transport it to mouth Class Crinoidea Sessile sea lily Cup-like body attached to stalk Attached to substrate Can bend stalk and flex/extend arms Class Crinoidea Free-moving feather star Stalk lost during larval development Can crawl/swim Jointed appendages (cirri) help it regain balance Class Asteroidea 1500 species of sea stars 5 or more broad arms surround a central disk Crawl on rocks or live on sea bottom Most are scavengers or predators Each arm bears podia with suckers Evert stomach into prey and digest it Class Ophiuroidea 2000 species of brittle stars Usually concealed in sand or under objects Some live in sponges or other colonial organisms Only 5 arms that are usually highly branched Class Ophiuroidea Arms are distinct from central disk Can crawl/cling Predators, scavengers, or suspension feeders Flexible arms bear suckerless podia that secrete mucus to entrap food and transport it to mouth Class Echinoidea 1000 species of sea urchins/sand dollars Movable spines and podia surround body; used for locomotion Herbivorous, detrivorous, suspension feed, a few predators Class Echinoidea Unique feeding apparatus called Aristotle’s lantern Hard plates and muscles just inside mouth Possesses 5 calcareous teeth Teeth protract to scrape algae off rocks or tear chunks of kelp Class Holothuroidea 1150 species of sea cucumbers Mucus-covered oral tentacles trap on plankton or ingest sand organic matter Gut modified to produce respiratory trees used for gas exchange Expel portions of these trees as defense mechanism; regenerate