Class Crinoidea
Stalked crinoid
= permanently attached with distinct, flexible stalk
Comatulid crinoid
= attached to a surface as a juvenile (how?) but freeswimming/temporarily attached as an adult
Antedon bifida – 10 thin, pinnate arms, 25 short cirri
arising around the central plate, mottled in color, lower
side of arms and pinnule joints with prominent cross
ridges.
=> How is the comatulid crinoid adapted to a free-living
life style and which features of the stalked crinoid would
get in the way of this lifestyle?
Class Ophiuroidea
= brittle and basket stars
= some superficially resemble true starfish, but always
with more slender arms distinct from the central disk,
plate articulation in arms = snake-like movement of arms
for locomotion and feeding, arms may be branched or
forked in basket stars
Gorgoncephalus eucnemis – Basket star Puget Sound
= arms branch dichotomous, central disk generally darker
than the rays, color may vary from orange-red to pink
and even almost white
 with a variety of different color morphs, why are
these not individual species? What is the advantage
of different color morphs?
Ophioderma brevispina – common brittle star
= in seagrasses between Cape Cod and Brazil, dark brittle
star with 7-8 spines projecting from each arm segment,
central disk = 10-15mm, arm length 40-60mm
Live Ophiuroids to observe snakelike movement of the
arms
 take a drop of carmine: seawater suspension and
place on the oral disk to test for ciliary movement
Class Asteroidea
Asterias rubens – Common sea star
External anatomy: five arms, ill defined central disk, oral
and aboral surface, mouth, ambulacral groove with
tubefeet (make a slide of tubefeet to visualize their
structure), madreporite (view under dissecting microscope
to observe fine structure, what is this structure possibly
used for?), spines, pedicellariae (try to remove and place
on a slide to view structure, what are these structures
used for?), eyespots
Internal anatomy: coelom, pyloric stomach, cardiac
stomach (difference), gonads (how many? can you
determine the gender?), (intestine and anus), ring canal,
radial canal, ampullae, Tiedemann’s bodies (dissecting
microscope)
Asterias rubens – models
View external and internal structures as marked
Asterias rubens – arm cs
Ossicles, body wall musculature, coelomic epithelium,
ampullae (with musculature, observe directionality of
musculature),
tubefoot (observe musculature
directionality), pedicellaria, dermal branchiae, gonads
Asterias rubens – development, bipinnaria and brachiolaria
larvae (compare to pluteus which you will be producing
yourself)
Oreaster reticulatus – Carribean cushion star
Large, non-delineated central disk, obvious dermal spines
Pisaster ochraceus – Pacific sea star
Brownish color, arm number may vary between 4-7,
movement through tubefeet not snake-like arm movements
as ophiuroids
Patirina miniata – Bat star
Webbed rays, commonly found with 5 rays (sometimes 49), of up to 10 cm in length, color from red to yellow
Class Echinoidea
Arbacia punctulata – purple urchin
External anatomy: test, ambulacra and interambulacra
(how do they differ and how many are there?), genital
plates, periprocts, madreporite, tubefeet (make a slide
preparation to see structure; buccal, ambulacral)
pedicellariae (make slide preparations), spines (view the
spine attachment), peristomial membrane, mouth (teeth
Aristotle’s lantern), gills
Internal anatomy: esophagus, stomach, intestine, gonads,
ampullae, ring canal with polian vesicles
Aristotle’s lantern: pyramid, rotule, epiphysis, compass
elevator muscle, lantern retractor muscle, lantern
protractor
Lytechinus variegatus – variegated sea urchins
Live animals were available the previous week for
embryology, you should have observed pluteus larva
Strongylocentrotus droebachiensis – green sea urchin
Test only, observe spine attachment and distinguish
between ambulacra and interambulacra
Encope emarginata – sand dollar
Observe petaloid ambulacra, genital pores, mouth, food
grooves
Melitta quinquiesperforata – key hole urchin
Petaloid ambulacra used as gills, 5 oval shaped holes (=
lunules), contain Aristotle’s lantern with teeth shaped like
“doves”
Spatangoid sea urchin = heart urchin
Petaloid ambulacra (= phyllode), mouth, periproct, anus
Class Holothuroidea
Cucumaria sp. – common sea cucumber
External anatomy: oral-aboral axis, branched tentacles
(buccal podia, how many?), introvert, podia, anus,
microscopic ossicles in the body wall are all that remains
of the typical echinoderm test (how does that suit the
animal’s lifestyle?)
Internal anatomy: ring canal, esophagus, stomach,
intestine, cloaca, respiratory tree, gonad, longitudinal
muscle bands, ampullae