Echinoderms

Question 1

Deuterostomes

Answer 1

▪ Bilateral metazoans (Bilateria)
▪ Joined based on nature of larval growth
▪ Unity supported by molecular genetics
vertebrates, cephalocordada, echonidermenta, hemichordada

Question 2

Echinoderms

Answer 2

▪ Includes starfish, sand dollars, sea urchins, brittle
stars, sea cucumbers, crinoids
▪ About 7,000 living species and 13,000 described
fossil species
▪ All marine
“spiny skins”

Question 3

Features that join echinoderms into a clade

Answer 3

epidermal skeleton made up of ossicles, five fold radial symmetry, water vascular system,

Question 4

individual calcite crystals with a porous (”Swiss cheese”)

structure or stereom.

Answer 4

ossicles

– Can be loosely held together by liagments and muscles or fused

Question 5

Water vascular system

Answer 5

hydrostatic system of internal water-filled canals, which in many echinoderms form suckered “tube feet”, which are
sucker-like appendages that the echinoderm can use to move, grip the substrate, or manipulate objects

Question 6

Class Echinoidea

Answer 6

Sea urchins and sand dollars.
▪ Skeleton (test) made of closely interlocking plates, sometimes fused together -good fossil record!
▪ Test shape ranges from globose (urchins) to flat (sand dollars)
▪ Show near perfect five-fold symmetry (regular echinoids), presumed
primitive condition, or can be bilateral (irregular echinoids), presumed derived condition
▪ Jaw apparatus made of five hard teeth arranged in a circle -Aristotle’s lantern
▪ Regular echinoids mostly epifaunal grazers; some predators
▪ Irregular mostly infaunal deposit feeders
▪ Ordovician -Recent

Question 7

Class Holothuroidea

Answer 7

Sea Cucumbers
▪ Usually grouped with echinoids (no arms, stem, or tail)
▪ Generally soft-bodied; skeleton reduced to isolate
calcareous plates = ossicles
▪ calcareous ring encircles the pharynx or throat.
▪ Suspension feeders, deposit feeders
▪ Limited fossil record; Silurian? - Recent

Question 8

Class Asteroidea

Answer 8

True starfish
▪ Five arms (or multiples of five)
▪ Internal body parts, including water vascular system, extend into arms
▪ Tube feet line ambulacral grooves
▪ Highly mobile, use tube feet to move
▪ Predominantly predators
Ordovician-Recent

Question 9

Class Ophiuroidea

Answer 9

Brittle starfish and basket stars
▪ Well-defined central disk and separate arms
▪ Arms are flexible - move fairly rapidly by wriggling their
arms (rather than tube feet)
▪ Most are scavengers and deposit feeders, although they
also prey on small live animals such as small crustaceans
and worms. Some, in particular the basket stars, filter-feed
on plankton with their arms.
▪ Ordovician-Recent
▪ Presumed closely related Asteroidea

Question 10

Class Crinoidea

Answer 10

Crinoids
▪ Cup-like body carrying arms
▪ Arms have ambulacra and tube-feet
▪ May or may not have a stalk attaching to the substrate
▪ One living subclass
▪ Ordovician-Recent

Question 11

Small side branches on crinoids

Answer 11

pinnules

Question 12

Crinoids with stalk

Answer 12

Sea lillies

Question 13

Crinoids without stalk

Answer 13

feather stars

Question 14

Crinoids fossil record

Answer 14

▪ 3 subclasses of crinoids are known from the
Paleozoic
▪ Generally stalked
▪ Most abundant echinoderms from the
Ordovician -Permian
▪ Often major constituent Paleozoic limestones
▪ Nearly become extinct end Permian -only one
early Triassic genus!

Question 15

Blastozoans

Answer 15

Blastoids and “cystoids”

▪ Body covered by theca

Question 16

Blastozoans

Answer 16

Blastoids and “cystoids”
▪ Body covered by theca
▪ Brachioles extend out along ambulacra (not arms)
▪ Stalked filter feeders

Question 17

How do classes of blastoids differ?

Answer 17

From the arrangement of plates on theca

Question 18

theca

Answer 18

Covers the body of blastoids, made of interlocking plates with ambulacra

Question 19

Class Blastoidea

Answer 19

▸ Highly standardized arrangement of plates
▸ Complex internal folds of calcite below
ambulacra (hydrospires)
▸ Ordovician - Permian; very diverse in
Mississippian

Question 20

Class Edrioasteroidea

Answer 20

▪ Grouped with holuthurians and echinoids in subphylum Echinozoa
▪ Sessile suspension feeders
▪ Often found growing on brachiopod shells
▪ ambulacra grew in a curved, often spiral or nearly spiral pattern.

Question 21

Subphylum Homolozoa

Answer 21

▪ Flattened, bilateral to irregular - not pentaradial!
▪ Elongate extension of the body -tails??
▪ Questioned by some whether they are really
echinoderms -generally accepted that they are.
▪ Rare!
▪ Cambrian-Devonian

Question 22

First definite echinoderms appear in…

Answer 22

The early Cambrian. All are low diversity; suspension feeders

Question 23

primitive blastozoans (paracrinoids), ancestral crinoids, and homolozoa appear….

Answer 23

In the late cambrain. All are low diversity; suspension feeders.

Question 24

Echinoderm fossil record during the paleozoic

Answer 24

▸ Crinoids became dominant group - high tiering filter feeders
▸ Gradual loss of other classes

Question 25

Dominant group of modern echinoderms

Answer 25

echinoids

Question 26

Major expansion in the Echinoderm fossil record during…

Answer 26

Ordovician - 17 classes in Middle Ordovician! -nearly all

ways of life - many classes low diversity

Question 27

Paleontological problems with Echinoderms

Answer 27

▪ Origin of group and relations to some odd later Precambrian (Ediacaran) forms.
▪ Why such high diversity at the class level early on?
▪ Relationships of the classes to each other
▪ Relationships with chordates

Question 28

Symmetry in larval echinoderms

Answer 28

bilateral