Ambulacraria Lecture 11 Flashcards
(29 cards)
What two groups make up ambulacrarians?
Echinoderms and Hemichordates
Traits of Echinoderms
All marine living, benthic
Paleozoic forms: sessile Modern forms: motile
what are the extant classes of Echinoderms (5)
Holothuriodea Echinoidea Crinoidea Ophiuroidea Asteroidea
Traits of Crinoidea
Sea lilies and feather stars
most ancient class of living echinoderms
mainly deep-water, suspension feeders
Traits of Asteroidea
Seastars (all benthic and found at wide range of depths
5-fold symmetry
predators and scavengers
5 arms typical (multiples of 5)
Traits of Ophiuroidea
Brittle stars and basket stars
slender arms for locomotion
diverse feeding habits
soft bottom habitats (fragile arms, easily able to regenerate)
Traits of Echinoidea
Sea urchins and sand dollars
no arms
skeletal ossicles form the test
pentaradial symmetry
Irregular body form
short spines (locomotion and body clean of sediment) flattened (secondary bilateral symmetry) adaptation for burrowing
Regular body form
Long spines (locomotion) tube feet assist in movement Pedicellariae (pincers) cleaning and defense
Traits of Holothuroidea
secondary bilateral symmetry (extended on oral-aboral axis)
tentacles and mucous (suspension and deposit feeding)
tube feet for locomotion
Hemichordate classes (2)
Pterobranchs
Enteropneusta
Pterobranchia traits
tube-dwelling, colonial animals
clear tripartite body
Enteropneusta
Acorn worms (solitary) Sediment dwelling animals (clear tripartite body)
Ambulacraria Characteristics (3)
Tripartite body (three coeloms)
Similar larval forms
Axial Complex
Divisions of Tripartite coelom
Perivisceral coelom (surrounds visceral tissues) Hydrocoel- (forms water vacular system)- lost in all except Crinoids Hemal coelom
Hemichordate body plan
Proboscis
Collar
Stalk
Protocoel (coelom of the proboscis)
Axial complex in Echinoderms and Hemichordates
Junction of two coeloms and WVS in Echinoderms
Heart-kidney complex in Hemichordates
(homologous axial complexes used in circulation of fluid and excretory functions)
Similar larval forms
ciliated
free-swimming
bilateral
Uniting features of Echinoderms (6)
- Calcareous skeleton, of endoskeletal plates
(skeletal ossicles)- stereom collectively - Pedicellariae (pincers, dorsal side, base of spine)
- Dermal branchiae (Papulae) (thin folds between ossicles, gas exchange)
- Water Vascular System (tube-feet, podia)
- pentaradial symmetry in adults (linked to sessile lifestyle)
- Ambulacral grooves (discrete arms with ambulacra on oral surface)- radial canal and primary podia
Parts of WVS (4)
Primarily for feeding; locomotion arose later
a- madreporite (connected to water)
b-polian vesicles- maintain internal pressure
c- radial canals (5)- extend ambulacral grooves (tube feet rows)
d- lateral canals to tube feet
How do tube feet work
extended through hydrostatic pressure
retracted via longitudinal muscles
Bilateral larvae development
left side- into adult (becomes oral plate)
right side- reabsorbed
Types of adult body forms (2)
- Ambularcra on five arms, with clear pentaradial symmetry (Crinoids, asteroidea and Ophiuroidea)
- Ambulacra extend from oral-aboral pole, arms absent, variable degree of bilateral symmetry (Echinoidea, Holothuroidea)
Echinoderm fossil record
Bilateral ancestor
Evolved radial symmetry for sessile lifestyle
stem groups- deuterostome features (ie. gill slits)
