Zoology Test 3b Flashcards
What does Echinodermata literally mean?
“spiny skin” - endoskeleton of dermal ossicles with projecting spines
- made of calcium carbonate
Echinodermata diversity
- not particularly large (in term of species) about 6000 living species
- very important to ecology and evolution
- abundant in marine ecosystems
- humans are more closely related to echinoderms than to any other invertebrate group
symmetry of echinoderms
- radially symmetrical
- but have larval echinoderms have bilateral symmetry
- tells us that radial symmetry is secondarily derived
- secondary radial symmetry; evolved from bilateral ancestor, but evolved back to radial
nervous system in echinoderms
- cephalization is reduced or absent in this group
- nervous system is decentralized
- no brain
feeding habits of echinoderms
- feed on small organic particles or algae, small prey
- some however are efficient predators despite lack of central nervous system and cephalization
- most are active, mobile animals
water vascular system in echinoderms
- unique organ to echinoderms
- tube feet for locomotion
- functions in respiration, locomotion and excretion
- water flow: madreporite to internal system of canals to ampulla and tube feet
- stone canal > ring canal > radial canal > lateral canal > ampulla > tube foot
coelom in echinoderms
- functions in circulation, respiration and excretion
- fluid circulated by cilia on peritoneum lining eucoelom
excretion and gas exchange in echinoderms
- done via papulae and tube feet which project out between ossicles
endoskeleton of echinoderms
- dermal ossicles: little bony plates under skin, joined by connective tissue
- some project outward as spines
pedicillariae
- small pincers extending from skin
- clean skin of debris, protect papular, may aid in foo capture
- in sea stars and urchins only
osmoregulation in echinoderms
- no specialized structure
- restricted to marine ecosystems
- therefore at equilibrium all the time
reproduction in echinoderms
- mostly dioecious
- autotomy is common
- con regenerate complete organism with one arm and 1/5th of oral disc
autotomy
means that they loose a leg….
Crinoidea
- original, oldest
- only way to explain radial symmetry
- sea lilies and feather stars
characteristics of sea lilies and feather stars
- both start out attached to substrate via stalk, and continue much of life sessile, but adult feather stars detach and can swim
- arms are tentacle-like with leathery skin and small branched and mucus for trapping and eating suspended phytoplankton
Classes of Echinoderm
- Crinoidea
- Asteroidea
- Echinoidea
- Ophiuroidea
- Holothuroidea
types of Crinoidea
- sea lily
- feather star
types of Asteroidea
- starfish or sea star
types of Echinoidea
- sea urchin
- sand dollar
types of Ophiuroidea
- brittle stars
- basket stars
types of Holothuroidea
sea cucumbers
feeding in Asteroidea
- predators: feed on crustaceans, polychaetes, small fish and other sea stars
- eversible stomach: insert cardiac stomach into open bivalve shell to digest and absorb soft parts
tube feet in Asteroidea
- used for locomotion and gripping bivalve shells so that shells can be pulled open
major body modifications in Echinoidea - sea urchins
- oral surface has expanded around to the aboral side
- fused dermal ossicles form rigid test with long, movable spines, tube feet and pedicellariae
- can live up to 200 yo
feeding of Echinoidea
- grazers: feed on algae, detritus or small particles of food, although some feed on larger prey
- Aristotle’s lantern
body modifications and feeding in Echinoidea - sand dollars
- very small spines used to burrow just below sand
- fused dermal ossicles form rigid test, with tube feet, and pedicellariae
- organic particles settle on aboral surface, and cilia move them down to mouth
feeding in Ophiuroidea
- abundant in ocean, often covering sea bottom
- detritivores
- feeding done via moveable jaws
detritivores
feed on decaying matter and plankton
how do brittle stars differ from sea stars?
- locomotion by movable arms (no tube feet)
- incomplete digestive system
- no pedicellariae or papullae
- autotomy and regeneration even better developed than in sea stars - they lose arms easily and grow them back readily
papullae
peritoneum that sticks up through holes in ossicles
how do Holothuroidea differ from other echinoderms?
- greatly elongated on oral-aboral axis
- ossicles reduced so body is relatively soft, use a hydrostatic skeleton
- arrangement of tube feet modified for crawling
feeding in Holothuroidea
- feed by picking up food or trapping food on tentacles and stuffing them into mouth one by one
- to defend themselves, they expel parts of viscera which are sticky may contain toxins
- can “throw up” digestive system to distract predator while they get away - regenerates in 3 months
protostome
- Annelids, molluscs, arthropods
- blastula embryo, mouth forms first and then anus forms
- spiral cleavage occurs in development
- coeolom forms differently
- a mosaic embryo is formed
mosaic embryo
if a cell is taken away from the embryo, then that individual cell will die. needs entire embryo to survive
deuterostome
- echinoderms, hermichordates, chordates
- blastula embryo, anus forms first and then mouth forms
- radial cleavage occurs in development
- coeolom form differently
- a regulative embryo is formed
regulative embryo
if a cell is taken away, then that cell can continue to develop on its own without the embryo. forms its own embryo —-> twins
