Chapter 16

• Echinoderms and Hemichordates are deuterostomes.
• Echinoderms and Hemichordates • Probably evolved from a filter-feeding ancestor.
• Echinoderms and Hemichordates are deuterostomes.• Enterocoelous coelom formation.
• Echinoderms and Hemichordates are deuterostomes.• Typically radially indeterminant cleavage.
• Echinoderms and Hemichordates are deuterostomes.• Blastopore becomes anus
• Echinoderms and Hemichordates are

  Form the deuterostome clade Ambulacraria
• Form the deuterostome clade Ambulacraria.• Common ancestry based on:• Hox genes.
• Form the deuterostome clade Ambulacraria.• Common ancestry based on:• rRNA genes.
• Form the deuterostome clade Ambulacraria.• Common ancestry based on:

  Mitochondrial DNA.
• Form the deuterostome clade Ambulacraria.• Common ancestry based on:

  Shared larval morphology
• Form the deuterostome clade Ambulacraria.• Common ancestry based on:

  Tripartite coelomic cavities
• Phylum Echinodermata The phylum of triploblastic. coelomate animals whose members are pentaradially symmetrical as adults and possess a water-vascular system and an endoskeleton covered by epithelium. Pedicellaria often present.
• Class Crinoidea Free living or attached by an aboral stalk of ossicles; flourished in the Paleozoic era. Sea lilies; feather stars. Approximately 630 living species.
• Class Asteroidea Rays not sharply set off from central disk; ambubcral grooves with tube feet; suction disks on tube feet; pedicellariae present. Sea stars. Approximately 1,800 species.
• Class Echinoidea Globular or disk shaped: no rays; movable spines; skeleton (test) of closely fitting plates. Sea urchins, sand dollars. Approximately 1,000 species.
• Class Ophiuroidea Arms sharply marked off from the central disk; tube feet without suction disks. Brittle stars. More than 2,000 species.
• Class Holothuroidea No rays; elongate along the oral-aboral axis; microscopic ossicics embedded in a muscular body wall; circumoral tentacles. Sea cucumbers. Approximately 1,700 species
• Phylum Hemichordata Widely distributed in shallow, marine, tropical waters and deep, cold waters; softbodied and worm-like; diffuse epidermal nervous system; most with pharyngeal slits.
• Class Enteropneusta Shallow-water. worm-like animals; inhabit burrows on sandy shore lines; body divided into three regions; proboscis, collar. and trunk. Acorn worms (Balanoglossus, and Saccoglossus). Approximately 100 species.
• Class Pterobranchia With or without pharyngeal slits; two or more arms; often colonial, living in an externally secreted encasement. Rhabdopleura. Approximately 30 species.
• Phylum Echinodermata Characteristics

  Calcareous endoskeleton in the form of ossicles from mesoderm.
• hylum Echinodermata charac

  Adults with pentaradial symmetry and larva with bilateral symmetry.
• Echinodermata charac

  Water-vascular system.
• Phylum Echinodermata Characteristics.

  Complete digestive tract

  . Hemal system.

  Nervous system consisting of nerve net, nerve ring, and radial nerves.
• Pentaradial symmetry.

  Body parts arranged in fives (or multiples of five) around an oral-aboral axis.

  Some secondarily bilateral.

  Evolution of the skeleton may account for pentaradial form
• Water vascular system.

  |Water-filled canals with tube feet extensions.

  Ring canal opens to outside via stone canal and madreporite.

  Polian vesicles function in water storage.

  Tube feet.

  Muscular ampulla.

  Often suction cup at distal end (may also be blunt or pointed).
• Functions.

  Locomotion.

  Attachment.

  Feeding.

  Exchanges of respiratory gases and wastes

  Sensory functions.
• Hemal system

  . Likely distributes nutrients and large molecules.
• Class Asteroidea

  Hard or sandy substrates in marine environments.

  Moveable and fixed spines roughen body surface.

  Dermal branchiae (papulae).

  Gas exchange.

  Pedicellariae.

  Pincerlike.

  Clean and protect body surface.

  Tube feet with suction disks.
• Class Asteroidea

  Maintenance Functions

  . Predators and detritus feeders

  . Ingest whole prey

  . Many are bivalve predators

  . Internal transport of gases, nutrients, and metabolic wastes by diffusion and hemal system

  . Gas exchange and excretion by diffusion across dermal branchiae
• asteroidea Asexual reproduction in some.

  Regeneration after division of central disk.
• asteroidea Regeneration.

  Broken arm replaced

  . Entire sea star from portion of central disk.
• Sexual reproduction. asteroidea

  Dioecious.

  Two gonads per arm .

  External fertilization and planktonic larval development
• Class Asteroidea

  Sea Daisies

  . Previously class Concentricycloidea.

  Highly modified member of Class
• Sea Daisies.

  Lack arms.

  1 cm diameter.

  Digestion and absorption of decaying organic matter.
• Class Ophiuroidea Basket stars and brittle (serpent) stars.
• Class Ophiuroidea Arms long, sharply set off from central disk (highly branched in basket stars).
• Class Ophiuroidea 1 No dermal branchiae or pedicellariae.
• Class Ophiuroidea Tube feet lack suction disks
• Class Ophiuroidea

  Muscles and articulating ossicles produce snake-like movements of arms.

  Water vascular system is not used in locomotion.