Transcript Echinoderms
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Echinoderms CHAPTER 14 22-1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Echinodermata: Diversity and Characteristics Characteristics • • • • All members have a calcareous skeleton Spiny endoskeleton consists of plates Unique water-vascular system radial symmetry in adults 22-3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Echinodermata: Diversity and Characteristics Diversity • Likely descended from bilateral ancestors – Larvae are bilateral • Perhaps evolved radiality as an adaptation to sessile existence • Body plan is derived from crinoid-like ancestors transformed into free-moving descendants • Lack ability to osmoregulate – Restricts them to marine environments 22-4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Echinodermata: Diversity and Characteristics • None are parasitic • Asteroids or sea stars – Mostly predators • Ophiuroids or brittle stars – Move by bending their jointed muscular arms – May be scavengers, browsers, or commensal • Holothurians or sea cucumbers – Mostly suspension or deposit feeders 22-6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Echinodermata: Diversity and Characteristics • Echinoids or sea urchins – Found on hard bottoms while sand dollars prefer sand substrate – Feed on detritus • Crinoids – Sessile and flower-like as young and detach as adults – Suspension feeders 22-8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Echinodermata: Diversity and Characteristics Ecology, Economics, and Research • Due to spiny structure, echinoderms are not often preyed upon • A few fish and otters are adapted to feed on sea urchins • Sea stars feed on molluscs, crustaceans, and other invertebrates – May damage oyster beds 22-9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Asteroidea Form and Function • External Features – Have a central disc with tapering arms extending outward – Body is flattened and flexible, with a pigmented and ciliated epidermis – Mouth is on the underside or oral surface – Usually there are 5 arms but there may be more • rows of tube feet 22-10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Asteroidea • Water-Vascular System – This system is another coelomic compartment and is unique to echinoderms – Functions in locomotion, food-gathering, respiration, and excretion – Opens to outside at madreporite on aboral side – Madreporite leads to stone canal, which joins ring (circular) canal that encircles the mouth – Radial canals diverge from ring canal and extend into each ray 22-13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Asteroidea • Feeding and Digestive System – Mouth leads through a short esophagus to large central stomach – Lower part of stomach can be everted through the mouth during feeding – Anus is inconspicuous – Consume a wide range of food • Sea urchins • Molluscs – Sea stars pull valves apart and evert stomach through crack • Small particles carried by tube feet to mouth 22-15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Asteroidea • Reproductive System, Regeneration, and Autonomy – – – – – Sexes separate in most sexes Pair of gonads Fertilization is external Eggs and sperm are shed into the water in early summer Regenerate lost parts • Cast off injured arms and regenerate new ones • An arm can regenerate a new sea star if at least onefifth of central disc is present 22-16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Asteroidea Sea Daisies • Diversity and Characteristics – Small, disc-shaped animals discovered in deep water off New Zealand – Described in 1986, only two species are known 22-17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Ophiuroidea Form and Function • Largest in number of species – Over 2000 extant species • Arms of brittle stars are slender and distinct from the central disc • Tube feet lack suckers • Biology – Brittle stars are secretive and live on hard or sandy bottoms where little light penetrates • Often under rocks or in kelp holdfasts – Browse on food or suspension feed – Basket stars perch on corals and extend branched arms to capture plankton 22-19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Echinoidea • Diversity – Approximately 950 species of living echinoids – Sea urchins lack arms but their tests show five-part symmetry – Most sea urchins have radial symmetry and long spines – Sand dollars and heart urchins (irregular echinoids) have become bilateral with short spines – Echinoids occur from intertidal regions to deep ocean • Reproduction – Sexes separate – Gametes are shed into sea for external fertilization 22-22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-24 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Holothuroidea • Diversity – Approximately 1150 species of holothuroids – As common name suggests, these animals resemble cucumbers – Greatly elongated in the oral-aboral axis – Ossicles are greatly reduced and body is soft – Some species crawl on the ocean bottom, others are found under rocks or burrow 22-25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-26 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Class Holothuroidea Reproduction – Sexes are separate in most – Fertilization is external – A few brood their young inside the body or on the body surface • Biology – Sea cucumbers use ventral tube feet and muscular body waves to move – Some trap particles on the mucus of tentacles, ingesting food particles in pharynx – Others graze sea bottom with tentacles – Cast out part of viscera when irritated • Must regenerate these tissues • Organs of Cuvier are expelled in direction of an enemy – Sticky and have toxins – One small fish, Carapus, uses the cloaca and respiratory tree of a sea cucumber for shelter 22-27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Crinoidea • Diversity – – – – – Crinoids include both sea lilies and feather stars Far more numerous in fossil record Unique in being attached for most of their life Sea lilies have a flower-shaped body at tip of a stalk Feather stars have long, many-branched arms • Adults are free-moving but may be sessile – Many crinoids are deep-water species – Feather stars are found in more shallow water 22-29 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-30 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22-31