Echinoderms:
Phylum Echinodermata:
-strange
-free moving & radial symmetry.
-they probably evolved from a bilateral ancestor
-some have poison glands.
-Deuterostome, entrocoelous coelomates.
-other Phyla in this group, deuterostome are; Chaetognatha, Hemichordata, & Chordata.
-water-vascular system from coelomic compartment.
-endoskeleton made of calcareous ossicles.
-no other group with a complex organ system is radial symmetry.
-no ability to osmoregulate
-particle feeders such as sea stars, or predators
-unsegmented
-five or more radiating ambulacra
-no head or brain
-locomotion by tube feet.
-digestive system usually complete, anus absent in ophiuroids.
-extensive coelom
-blood-vascular system hemal system.
-excretory absent.
-sexes separate
-some mammals feed on them, sea otters.
-feed on molluscs, crustaceans
-egg can develop into adult without presence of sperm in special conditions.
Class Asteroidea
-sea stars, or starfishes.
-body covered with ciliated, pigmented epidermis
-mouth on oral side.
-Ambulacrum pl. ambulacra: runs from mouth to the tip of the arm on the oral side
-Ambulacral groove: is bordered by rows of tube feet (Podia)
-radial nerve is in center of each ambulacral groove.
-aboral surface is rough & spiny.
-Pedicellariae
-Papulae or dermal branchiae or skin gills lined with peritoneum.
-anus on aboral side.
-ossicles
-Coelom is filled with fluid.
-this fluid has amebocytes (coelomocytes)
-bath the internal organs & projects into the papulae.
Water-Vascular System:
-madreporite: small pores that open to outside.
-madreporites lead to stone canal ---> ring canal around mouth ---> radial canals
---> ambulacral groove of each ray.
-attached to ring canal are 4 or 5 pairs of Tiedemann's bodies which form the one
to 5 Polian vesicles.
-Polian vesicles absent in some sea stars. Asterias
.
-lateral canals connect the radial canal to cylindrical Podia or tube feet, along
the side of ambulacral groove in each ray.
-Ampulla lies within the body coelom & outer end of which that bears the suckers.
-Ampulla is the muscular portion of each podium.
-contraction of muscles in ampulla forces the water into podium, extending it.
Digestive system:
-mouth on oral side lead to esophagous ---> stomach ---> ceca
-digestion is mostly extracellular
-Anus in some star is inconspicuous & some lack intestine & anus.
Hemal System:
-has little or nothing to do with body fluid circulation.
-useful in distributing digestive material, specific function not known.
-it is a system of tissue strands enclosing unlined sinuses & it is enclosed in Coelomic
compartment.
Reproductive System:
-regeneration & autotomy
-separate sexes.
-external fertilization
- larva bipinnaria
-arms can regenerate easily even if all are lost.
-Autotomy
-development is direct.
-eggs are brooded
Ophiuroidea:
"brittle star"
-most species
-have five arms typically
-more slender
-no pedicellariae or papulae
-ambulacral grooves are closed & covered with arm ossicles
-no suckers on tube feet.
-tube feet for feeding but not much for locomotion.
-Madreporite on oral surface.
-vertebrae: each of the jointed arms consists of column of articulated ossicles connected
by muscles & covered by plates.
-locomotion is arm movement.
-five movable plates serve as jaws surround the mouth.
-no anus, indigestible material out thru mouth.
-skin is leathery, & no cilia on surface of body.
-visceral organs found in central disc only
-stomach but no intestine
-bursae
-water circulate in & out of these sacs for -exchange of gases.
- nocturnal
-sexes separate - some brood their young in the bursae
-larva is called ophiopluteus
-regeneration & autotomy.
Class Echinoidea:
-compact body in an endoskeletal test or shell.
-lack arms
-their test show a pentamerous plan of the echinoderms.
-have hemispherical shape, radial symmetry
-sand dollars, heart urchins
-five ambulacral rows are homologous to the five arms of the sea star & have pores.
-spines are moved by muscles around the base.
-Pedicellariae among spines bear poison glands & toxin paralyzes small prey.
-in some urchins the brancheal gills (modified Podia) encircle the Peristome.
-chewing mechanism called Aristotle's lantern.
-fine food get trap between spines & ciliated tracts on the oral side carry the particles
to the mouth.
- herbivorous
-hemal & nervous system similar to asteroids.
-sexes are separate
-external fertilization.
-echinopluteus larvae of nonbrooding.
Class Holothuroidea:
-greatly elongated in oral aboral axis
-ossicles are reduced so body wall is leathery.
-soft bodied animals
-body wall contain circular & longitudinal muscles along the ambulacra.
-because of no dermal ossicles the fluid-filled coelom act as hydrostatic skeleton.
-digestive waste empties to muscular cloaca
-gas exchange also occur thru skin & tube feet.
-sexes separate only sea cucumbers have single gonads
-fertilization is external & free swimming larva is auricularia
-some species brood the young either inside the body or somewhere on the body surface.
- self-mutilation
-sea cucumber cast out its visceral structures & lost parts are soon regenerated for
dense.
-some small fish Carapus
use sea cucumber as a shelter, commensalism
Class Crinoidea:
-sea lilies & feather stars.
- sessile
-body disc or calyx is covered with leathery skin (tegmen) contain calcareous plates.
-poor developed epidermis.
-Calyx and arms together is called crown.
-sessile forms have stalk which is attached to aboral side of the body.
-stalk have cirri.
-have anus, intestine, mouth, esophagous.
-ambulacral grooves are open & ciliated & serve to carry food to the mouth.
-sexes are separate
-larva is doliolaria, free swimming
Class Concentricycloidea:
-Pentaradial symmetry but have no arm.
-water-vascular system have 2 concentric ring canals,
-outer ring represent the radial canals
-hydropore homologous to madreporite connect the inner ring canal to aboral surface.
-no intestine or anus, shallow saclike stomach.
-one species has no digestive tract, have velum instead absorption thru velum.