P Echinodermata, SP Eleutherozoa LT PDF

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Description

Subphylum: Eleutherozoa Body shape: star, globular, discoidal or cucumber •Mouth located on 'ventral' side or oral-aboral axis parallel to substratum

4 major classes: Asteroidea- starfish Ophiuroidea- brittle stars Echinoidea - sea urchins, sand dollars, heart urchins Holothuroidea - sea cucumbers

SP: Eleutherozoa C: Asteroidea •Sea stars •~ 1,500 species •Star-shaped ('aster' = star) •Central disk from which the arms radiate •Arms broadly joined to central disk (c.f Ophiuroidea)

What type of symmetry do Asteroidea adults?

Pentaradial symmetry

What type of symmetry do Asteroidea larve have?

Bilateral symmetry

SP: Eleutherozoa C: Asteroidea anatomy • Typically pentamerous (5 arms) • Oral surface facing DOWN •Anus in the center of aboral disk •Each ambulacral groove contains 2-4 rows of tube feet •Tube feet short, stout, used for walking (c.f Echinoidea long slender TF to reach past spines) •Madreoirte (WVS opening) present.

SP: Eleutherozoa C: Asteroidea arms: -Every arm has 1pr of digestive glands -Every arm has a radial nerve sits along amblacral groove

-Every arm has 1pr of gonads -strong enough to pull apart live bivalve molluscs to get flesh inside (c.f phiuroids with fragile arms)

SP: Eleutherozoa C: Asteroidea feeding -Carnivores and scavengers -Some starfish are suspension feeders -Feed on polyps, snails, bivalves -Notorious pests on coral reefs and oyster beds - 2x stomachs: •Eversible cardiac stomach (large chamber with pouched walls) •The prey is engulfed by everted stomach •Partly digested prey soup is transferred to pyloric stomach and the caecae

SP: Eleutherozoa C: Asteroidea feeding on a bivalve •Inserts the stomach through minute openings between imperfectly sealed edges of the valves •Can pull the valves to produce the slight gap •0.1mm gap is enough for the starfish to digest the bivalve

Crown of thorns seastar (SP: Eleutherozoa C: Asteroidea) -Huge pest -No natrual predators -Eats corals -Divers inject them with vinegar which kills them.

SP: Eleutherozoa C: Asteroidea regeneration •Can regenerate lost arms and organs •Some species are able to regenerate entire body from one arm

SP: Eleutherozoa C: Asteroidea reproduction -Asexual reproduction common -Usually dioecious

•Few hermaphrodites (ecept Echinoidea) -10 gonads •2 in each arm •Gonopores open aborally on genital plates (surface opposite substrate - not crushing your babies) -External fertilization •no intermittent organs -Planktonic larvae -Some brood their young -> direct development

SP: Eleutherozoa C: Asteroidea development •Larvae bilaterally symmetrical •Left side of a larva becomes oral surface of a starfish

SP: Eleutherozoa C: Asteroidea Bipinnaria larva The first stage in larva development of most starfish, followed by brachiolaria stage. -Bilateral symmetry

SP: Eleutherozoa C: Asteroidea Brachiolaria larva These larva attach to the substrate and undergo metamorphosis. The sea star grows its arm. -Bilateral symmetry.

Young starfish (SP: Eleutherozoa C: Asteroidea) 1-2 months the baby sea stars metamorphosize into star-shaped creatures. They start growing a variety of tubes, which will eventually become their arms, in order to catch and feed on algae. -Radial symmetry.

SP: Eleutherozoa C: Ophiuroids -brittle stars

SP: Eleutherozoa C: Echinoidea -Sea urchins ('echin' = spiny) -Usually burrowers -Wide oral opening -ball and socket joint -Echinoderms have ossicles that are fused, forming a rigid skeletal shell, known as the 'test'.

SP: Eleutherozoa C: Echinoidea external anatomy -Oral surface: -ambulacral ossicles (narrow) •fine pr holes 4 tube feet -adambbulacral plates (wide) •5pr rows of both adam & ambu

-Apical disk =aboral surface =very small -Apical disk w. central periproct containing the anus •periproct surreounded by 5 genital & 5 radial plates •1 genital plate modified into madreporite -leads 2 WVS & axial sinus

SP: Eleutherozoa C: Echinoidea tube feet -Doubled Ampulla Canals •Tube feet and spines used in locomotion •tube feet = respiratory - exchange gasses b/tw inside & outside echinoderm. •each tube foot needs 2 holes in test to operate •Excretion organ

SP: Eleutherozoa C: Echinoidea respiration -tube feet -5 pr oral invaginations - peristomial gills -peripharyngeal coelom subdivision of perivisceral coelom •(Surrounds lantern)

•peri=surrounds •pharyngeal=mouth -Aristotles lantern uses muscles - needs extra O2, need extra gills -extra gills in peristomial membrane (surrounding lantern)

SP: Eleutherozoa C: Echinoidea Aristotle's Lantern -Muscles can open/close the lantern, move it up/down and sideways •Used for grazing •Teeth grow continuously •Surrounded by peristomial membrane

SP: Eleutherozoa C: Echinoidea Digestive system •Feed on plant material - low quality food •Therefore, long gut •Gut goes round and round the body (2 complete turns)

-Swallow a lot of water with food •Can weaken (dilute) digestive enzymes •The test does not allow for increase in volume

-Solution -a tubular siphon parallels the gut •Removes excess water

SP: Eleutherozoa C: Echinoidea Pedicellariae "pincers" -Several types are commonly present •Stalked •Often poisonous •Can produce painful sting -pedicellariae = highly mod spines arranged into a group of 3, act as jaws.

SP: Eleutherozoa C: Echinoidea Regeneration & reproduction

Limited regeneration •Dioecous •External fertilization •Planktonic echinopluteus larva •No brooding found so far

SP: Eleutherozoa C: Echinoidea ecological importance -Prey for sea otters and fish -Control algae growth •1983 Caribbean: in the absence of sea urchins the algal mats increased from 1-2mm to ~ 30mm -Sea urchin eggs (roe) are eaten •Especially in Japan - export commodity

SP: Eleutherozoa C: Echinoidea SC: Regularia •Notice large movable spines • Radial symmetry •Well-developed Aristotle's lantern •Central - peristome and periproct •Grazers - herbivores, scavengers, graze on encrusting animals

SP: Eleutherozoa C: Echinoidea SC: Irregularia Sand dollars, heart urchins, snapper biscuits •Notice short spines •Burrowers, therefore: - 2o bilaterally symmetrical •Deposit feeders (microphagous) - Aristotle's lantern often reduced •Peristomal gills reduced - Respiratory podia (tube feet)

SP: Eleutherozoa C: Echinoidea SC: Irregularia body & function -Small movable spines •locomotion, sorting of the food particles by size -Food particles are picked up by tube feet and transported to the mouth

-Specialized respiratory tube feet are arranged dorsally in petaloid -Mouth and feeding tube feet on the oral surface (toward substrate) -Anus moved posteriorly •to prevent feeding on own feaces -Respiratory tube feet dorsally in petaloid -Lunules (slots) -to reduce lift

SP: Eleutherozoa C: Ophiuroidea "ophio"= snake brittle stars, basket stars -No anus -No ambulacral groove -WVS & tube feet play little role in locomotion -good chemoreception -radial canal buried into middle of arm (uses muscles for movement) -Madreporite oral & hard to find -Vertebra-like ossicles in the arms •Muscles connect and operate the vertebrae •Vertebral ossicles are responsible for 'snaky' ophiuroid motion

SP: Eleutherozoa C: Ophiuroidea arms -brittle stars •arms sharply demarcated from disk •long and snakey arms •tueb feet on oral surface •arms used for movement more than tube feet •tube feed for feeding! -use thier arms fro propulsion across sea floor -arms are fragile

-basket stars

•arm split multiple times as they further from central disk

SP: Eleutherozoa C: Ophiuroidea locomotion -Most mobile echinoderms •Walk and 'run' •Tube feet are not used in locomotion •Vertebral ossicles have muscular connection •Spines provide traction

SP: Eleutherozoa C: Ophiuroidea feeding -Carnivores, scavengers, deposit feeders, suspension feeders •Most use several feeding modes with one predominant

-Suspension feeding •most common for basket stars bc big surface area •brittle stars = "fuzzy sea carpet" •Plankton & detritus adhere to tube feet & to mucus strands between adjacent arm spines •Remove collected plankton by wiping the arms through comb-like oral papillae

SP: Eleutherozoa C: Ophiuroidea regeneration & reproduction -Autotomy - cast off arms easily •Regenerate lost arms & organs •Sexual reproduction also •Asexual reproduction in some species (split central disk, form new animals) -Gonads attached to special pouches - bursae •Open orally on genital plates -Each gonad associated with 1 genital slit, 10 in all (5 arms, 2 slits per arm). •gammets released in slits, washed by h20 current and released by cilia SP: Eleutherozoa C: Ophiuroidea Development & reproduction •Usually dioecious (few hermaphrodites) •External fertilization

•Planktonic larvae - ophiopluteus •Many brood their young - direct development

SP: Eleutherozoa C: Ophiuroidea digestion -Digestive tract is simple •Mouth -> esophagus -> sac-like stomach •Stomach does not extend into the arms •Stomach is not eversible •No intestine, no anus •Digestion occurs within stomach

SP: Eleutherozoa C: Ophiuroidea Excretion -no anus •wastes get egested (c.f injested) out through mouth

SP: Eleutherozoa C:Holothuroidea • Sea cucumbers 'holothur' = polyp •~ 1200 species •Elongate, cucumber shaped •Ossicles microscopic •Flexible body wall •Spines absent •No arms -Ring of branched tentacles around the mouth •Mouth and anus at opposite ends

SP: Eleutherozoa C: Holothuroidea body plan •Elongated on aboral/oral axis -> have to lie on their side •2ndary (2o) bilateral symmetry - dorsal and ventral surface •3 ambulacral grooves on the ventral surface form sole, or trivium •Tube feet cover the sole

•2 ambulacral grooves on the dorsal surface - bivium •Tube feet often reduced or absent on bivium -the 5 ambulacral rows show evidence of the pentaradial symmetry even through they are bilaterally symmetrical

SP: Eleutherozoa C: Holothuroidea Anatomical Features •Simple stomach and long gut •Gas exchange via respiratory trees connected to cloaca (basically breathing from their butt) •Well developed hemal system - nutrient & gas transport •Only one gonad

SP: Eleutherozoa C: Holothuroidea WVS •Water vascular system: -Madreporite internal -Filled with coelomic fluid -Polian vesicles - maintain pressure in WVS (?)

SP: Eleutherozoa C: Holothuroidea nervous system & locomotion -Nerve ring around base of tentacles + 5 radial nerves along body (mouth location) -Organs of sense + sometimes statocysts -Locomotion: •slowly creep about on tube feet •worm-like burrowers use peristaltic movement •few pelagic

SP: Eleutherozoa C: Holothuroidea feeding Suspension feeding: -Tenticles are covered with adhesive papillae and mucus -Feathery tentacles catch plankton, the animal then licks them off one at a time (pic) Deposit feeding: -Swipe the sediment with mop-like tentacles, then lick them off

-non-discriminatory feeding

SP: Eleutherozoa C: Holothuroidea Reproduction -Possess a single gonad •located anteriorly •gonopore opens between the bases of tentacles •Dioecous, external fertilization •Planktonic auricularia larva •Brooding •only one gonad (c.f all other echinodermata) -Some have internal incubation •within coelom •young come out through the rupture of body wall

SP: Eleutherozoa C: Holothuroidea Mutable connective tissue • Thin cuticle, non-ciliated epidermis, thick dermis •Dermis contains microscopic ossicles •Internal to dermis - circular muscle and 5 bands of longitudinal muscle (evidence of pentaradial symmetry) •Dermis is mutable connective tissue

SP: Eleutherozoa C: Holothuroidea defense •Tubules of Cuvier - a mass of sticky tubules attached to bases of respiratory trees inside body •Expelled by forceful contraction and rupture of body wall •Defense chemicals are released in the process - many very toxic •Tubules regenerate after discharge •"Cuke nuke"

SP: Eleutherozoa C: Holothuroidea Ecology -Benthic dwellers, burrowers -Few deep-ocean species pelagic -Lodge themselves into tiny crevices

• mutable connective tissue -Many species are edible •50-60% protein! •Annual world trade of ~ 80,000 tonnes, at ~ US$20/kg

-Overfishing problems: •One of main income sources for 18,000 residents •> 4 million sea cucumbers harvested annually •Ban imposed unsuccessfully in 1995 and again in 2005 •Ban lifted after riots broke out...