Echinoderms

Question 1

Echinoderms - overview

Answer 1

-Echinoderm, Greek = spiny skinned
-Radially symmetrical, pentamerous (5-rayed),
dermal skeleton contains ossicles
-Varied ecological roles
~13,000 species, >15,000 in fossil record
-Important fishery in Asia + Europe
-Urchins/sea cucumbers are model organisms for
understanding fertilization/regeneration

Question 2

Echinoderms - classes

Answer 2

5 distinct classes
A) Crinoidea – feather stars
B) Ophiuroida – brittle star
C) Asteroidae – sea stars
D) Holothuoida – sea cucumbers
E) Echinoidea – sea urchins

Question 3

brittle stars

Answer 3

simple star shape, arms demarcated from central disc, move with whip like action

Question 4

sea stars

Answer 4

range from cushion to star-shaped, 5 or more arms

Question 5

sea urchins

Answer 5

globular test, pentaradiate

Question 6

criniodea

Answer 6

feather like profile, typically 5 radii

Question 7

Asteroidae - anatomy

Answer 7

-5-40 arms, covered in spines
-Water vascular system
-Sea water pumped in via a maderopite or sieve
plate
-Tube feet that extend from ambulacral grooves in
the sea star’s oral (bottom) surface
-Pedicellariae are pincer-like structures on the skin
of some sea star species
-Simple eyes, located on each arm

Question 8

Ossicles

Answer 8

-Ossicles are small calcareous elements embedded
in the dermis of the body wall of echinoderms
-They form part of the endoskeleton and provide
rigidity and protection
-Ossicles are found in different forms and
arrangements in sea urchins, starfish, brittle stars,
sea cucumbers, and crinoids

Question 9

Echinoidea - anatomy

Answer 9

-Skeleton plates are firmly bound together to form a
solid skeleton, called the test.
-Echinoids move by means of spines and climb and
cling on to hard substrata by means of their tubefeet
-Coiled digestive system which consists basically of a
tube joining the lower mouth to the anus on the
upper surface
-Feature a unique feeding apparatus called
Aristotle’s lantern

Question 10

Aristotle’s lantern

Answer 10

-Urchins have an intricate jaw apparatus called
Aristotle’s lantern
-This complex structure is composed of five jaws
made up of calcium plates
-The plates are connected by muscles.
-Urchins use this apparatus to scrape algae off rocks
and other surfaces, as well as biting/chewing prey

Question 11

Echinoderms : feet use

Answer 11

-Urchins don’t have any structure that people
recognise as an eye
-Yet, urchins display purposeful behaviour – they act
as if they can see
-Researchers have shown that possible light
receptors (red colour) are found across the entire
body of some urchins
-What it means to be an eye is so much broader than
we originally thought

Question 12

Holothurians - anatomy

Answer 12

-Elongated cylindrical body with the mouth
(surrounded by a crown of tentacles) and the anus
located at opposite ends of the body
-The body surface is thick, slimy in many species and
bears wart-like, conical or fleshy papillae
-The body wall contains calcareous of various shapes
-The digestive tube is very long, looped, and
occupies most of the main body cavity (somatocoel)
-Play an important role in bioturbation and release
of calcium carbonate – support coral growth

Question 13

Holothurians - gut regeneration

Answer 13

Sea cucumbers are known to practice one of the
most impressive forms of regeneration in the animal
kingdom — they can completely discard most of
their internal organs and then rapidly regrow them
-This is known as evisceration!
-Two types of evisceration:
- mainly just the intestine
- the whole anterior end discarded
-Able to regenerate entire digestive system using
specialised cells to dedifferentiate and rebuild the
lost structures