Echinodermata Spiny Skin

Echinoderms, Deuterostomes Adults have pentaradial symmetry but are believed to have evolved from Bilateral ancestors Larval stages have bilateral symmetry, deuterostome characteristics, anus first Characterized by a calcium carbonate internal skeleton and a water vascular system

Characteristics Pentaradial symmetry- body parts arranged in fives or multiples of five around a oral-aboral axis Shape adapted to a sedentary or slow moving lifestyle Allows uniform distribution of organs- sensory, feeding Skeleton composed of calcium carbonate plates(ossicles), Joints do not line up with radial symmetry, better protection covered by an epidermal layer, spines may project thru skin

Sea Star

Ossicles

Echinoderm Characteristics Water Vascular System- a series of water filled canals and extensions called tube feet Started as a modification of the coelom Includes a ring canal that opens to the outside thru a stone canal and an opening called a medreporite Radial canals (5) branch off the ring canal and lateral canals branch further to tube feet Tube Feet emerge from ventral surface of arms, suction cup at distal end, creates vacuum with water canal system Tube feet also exchange gases and nitrogenous wastes with the environment, sensory function also

Echinoderm Characteristics Hemal system- strands of tissue (tubular) that shadow the water vascular system, oral and aboral side Circulates fluid with cilia lined tubes, distributes nutrients from digestive tract, aids in transport of large molecules, hormones and coelomocytes( transport wastes)

Water Vascular System

Asteroidea Sea Stars usually live on hard surfaces, some on sand or mud, Brightly colored Usually 5 arms radiate out from central disk Mouth usually oriented downward, movable oral spines surround it Movable and fixed spines protrude from ossicles and roughen the body surface Dermal Branchiae (papulae) thin folds in body wall extend out between ossicles for gas exchange

Asteroidea Pedicellariae- small pincher like structures on attached to spines or ossicles, used to clean the body Ambulacral Groove- runs length of oral surface of each arm, houses radial canal and pairs of tube feet extend out groove Alternate extension and contraction of tube feet allow a stepping motion locomotion

Sea Star Internal Anatomy

Sea Star

Tube Feet Pedicellariae

Sea Star Cross Section

Dermal Branchiae or Papulae

Asteroidea Maintenance Functions Sea stars feed on snails, bivalves crustaceans, polychaetes, corals, detritus and others Mouth connected to short esophagus then a large oral stomach (cardiac) joined to a smaller aboral stomach (pyloric), short intestine leads to anus (aboral surface) Pyloric Cecea, 2 each arm function in digestion and absorption, extend from aboral stomach Some prey ingested whole undigested wastes expelled thru mouth Wraps arms around Bivalve and forces shells open.1mm, everts oral stomach into shell, digestive enzymes released, digests clam, retracts stomach

Regeneration and Reproduction Sea stars can regenerate any part of a broken, missing arm Some will regrow entire body if arm has any portion of central disk attached Asexual reproduction involves involves division of central disk and regeneration of each half Most Dioecious but sexes are indistinguishable two gonads per arm, external fertilization Embryos planktonic

Class Ophiuroidea Basket Stars and Brittle stars, 2000 species most diverse group of echinoderms Most hide under rocks or in crevices Long slender arms set off from central disk, used to collect food, 5 triangular jaws for chewing Basket stars have arms branched repeatedly Madreporite on oral surface Muscles in arms used for locomotion, superficial ossicles cover arms, closed ambulacral groove

Brittle Star

Basket Star

Brittle Star Mouth 5 Jaws

Class Echinoidea Sea urchins, sand dollars, sea biscuits Sea urchins specialized for living on hard surfaces, between rocks or coral Sand Dollars burrow in sand, usually live in dense beds Sea urchins are rounded, their test (shell) is made of 10 sets of plates, 5 ambulacral plates with tube feet and 5 interambulacral with spines Move by using spines to push and tube feet to pull

Echinoidea Feed on Algae, Bryozoans, coral polyps and dead animals Oral tube feet surround mouth, manipulate food Aristotles Lantern- Chewing apparatus can be projected from mouth, made of 35 ossicles and muscles Gills surround mouth provide gas exchange along with tube feet

Sea Urchin Anatomy

Sea Urchin

Sea Urchin Test

Sea Urchins

Aristotle’s Lantern

Sand Dollars

Sea Biscuit

Class Holothuroidea Sea Cucumber- found at all depths in ocean, crawl over hard substrate or burrow in sediment Elongated along the oral- aboral axis, lie on their sides, bottom slightly flattened, No arms Enlarged tube feet surround mouth, modified into tentacles Body wall thick and muscular, embedded ossicles(microscopic), Larger ossicles surround mouth attach body wall muscles

Holothuroidea Body wall contains longitudinal and circular muscles, worm like locomotion, move slowly but some can swim Eat particulate organic matter using mucus covered tentacles, thrust tentacle into mouth to wipe off food Paired tubules called respiratory trees attach at anus, protrude into body Some have statocyst and photoreceptors in skin

Holothuroidea Defense Many cucumbers produce toxins in body wall Some evert respiratory trees (Cuverian Tubules) contain sticky secretions and toxins Contractions of the body wall can result in expulsion of both respiratory trees, digestive tract and the gonads thru the anus (evisceration) All body parts regenerated

Sea Cucumber Anatomy

Sea Cucumber

Modified Tube Feet Tentacles

Sea Cucumber Feeding

Class Crinoidea Sea Lillies and Feather Stars, most primitive of all living echinoderms, 630 living species Sea Lillies attach permanently to bottom with a stalk made of stacked ossicles, flattened disk at base provides attachment Feather stars can crawl or swim, usually hold onto bottom with hooked cirri Calyx forms main body arms extend up, ambulacral groove and mouth face up, tube feet capture plankton and cilia in groove carry down to mouth

Feather Star

Sea Lillies

Crinoidea from Permian Period