Echinoderms

Question 1

What are the four defining features of echinoderms?

Answer 1

Water vascular system derived from coelom

Pentamerous symmetry in adults

Calcareous ossicles forming an endoskeleton

Mutable (catch) connective tissue

Question 2

How many echinoderm species exist today?

Answer 2

~7,000 living species and ~13,000 fossil species.

Question 3

Where are echinoderms found?

Answer 3

All marine environments; benthic and some pelagic species. None in freshwater or on land.

Question 4

Why are echinoderms not found in freshwater or terrestrial environments?

Answer 4

Lack of osmoregulatory structures and reliance on cutaneous gas exchange.

Question 5

What is the perivisceral coelom?

Answer 5

The main body cavity lined with ciliated peritoneum.

Question 6

What systems arise from coelom?

Answer 6

Water vascular system, gonads, and parts of the nervous system.

Question 7

What is the stereom?

Answer 7

A mesh-like single calcite crystal structure in ossicles filled with living tissue (stroma).

Question 8

How does the endoskeleton vary among echinoderms?

Answer 8

Sea urchins/sand dollars: ossicles fused into a test

Starfish: adjacent skeletal plates

Sea cucumbers: scattered dermal ossicles

Brittle stars/crinoids: central skeletal ossicles

Question 9

What are pedicellariae and their functions?

Answer 9

Pincer-like structures for defense, cleaning, camouflage, or prey capture.

Question 10

What symmetry do adult echinoderms show?

Answer 10

Pentamerous radial symmetry, derived secondarily from bilateral larvae.

Question 11

What defines the oral surface?

Answer 11

Presence of ambulacral grooves and podia.

Question 12

What is the evolutionary significance of pentaradial symmetry?

Answer 12

Likely a structural adaptation for skeletal efficiency during metamorphosis.

Question 13

What is the WVS?

Answer 13

A coelomic system of fluid-filled canals used for locomotion, respiration, circulation, and feeding.

Question 14

Name the key components of the WVS.

Answer 14

Madreporite

Stone canal

Ring canal

Radial canals

Tube feet (podia)

Ampullae

Question 15

What are Polian vesicles and Tiedemann’s bodies?

Answer 15

Polian vesicles: fluid reservoirs (absent in echinoids, crinoids)

Tiedemann’s bodies: secretory or immune-related function (exact function unclear)

Question 16

How do tube feet work?

Answer 16

Ampulla contracts → tube foot extends

Longitudinal muscles contract → fluid returns to ampulla

Tube feet attach via suction or duo-gland system (adhesive/releasing chemicals)

Question 17

Besides movement, what functions do tube feet serve?

Answer 17

Respiration, excretion, chemoreception, and feeding.

Question 18

What is mutable or catch connective tissue?

Answer 18

Collagenous tissue that can rapidly change stiffness under nervous control.

Question 19

Where is catch connective tissue used?

Answer 19

Autotomy (e.g., shedding arms)

Reversible stiffening (e.g., feeding posture)

Defense (e.g., rigid spines in sea urchins)

Structural support (e.g., sea cucumber body wall)

Question 20

What makes it unique among collagenous tissues?

Answer 20

Ability to change mechanical properties rapidly without ATP.

Question 21

What systems do echinoderms lack?

Answer 21

No excretory organs

No central brain

No head

Question 22

What systems do they have?

Answer 22

Complete gut

Haemal circulatory system (if present)

Nervous system = nerve net + nerve ring + radial nerves

Usually separate sexes; both direct and indirect development

Question 23

What kind of symmetry do echinoderm larvae have?

Answer 23

Bilateral symmetry with ciliary bands, distinct from trochophore larvae of protostomes.

Question 24

What are the five extant classes of Echinodermata?

Answer 24

Crinoidea (sea lilies, feather stars)

Ophiuroidea (brittle stars, basket stars)

Asteroidea (starfish)

Echinoidea (sea urchins, sand dollars)

Holothuroidea (sea cucumbers)

Question 25

Which echinoderm class is considered the most "primitive"?

Answer 25

Class Crinoidea (sea lilies and feather stars)

Question 26

What feeding method do crinoids use?

Answer 26

Suspension feeding using mucus-covered podia along pinnules.

Question 27

What is the key structural difference between brittle stars and starfish?

Answer 27

Brittle stars have distinct, flexible arms used in locomotion; starfish do not use their arms for locomotion but rely on tube feet.

Question 28

What is the function of bursae in ophiuroids (brittle stars)?

Answer 28

Gas exchange and brood chambers for embryos.

Question 29

What unique feeding adaptation is found in Echinoidea (sea urchins)?

Answer 29

Aristotle’s lantern – a jaw-like structure with five teeth used for scraping algae.

Question 30

How do sea cucumbers respire?

Answer 30

Using respiratory trees attached to the cloaca; water is pulsed in through the anus.

Question 31

What are Cuverian tubules and their function in Holothuroidea?

Answer 31

Defensive structures ejected through the anus; sticky and sometimes toxic.

Question 32

What makes echinoderm connective tissue unique?

Answer 32

It's mutable or “catch” connective tissue – can rapidly change stiffness under neural control.

Question 33

What are the two types of echinoderm larvae?

Answer 33

Planktotrophic – feed on plankton Lecithotrophic – rely on yolk, do not feed

Question 34

What echinoderm class lacks ampullae in its tube feet?

Answer 34

Crinoidea (sea lilies) and Ophiuroidea (brittle stars)

Question 35

What is the ambulacrum?

Answer 35

Area on echinoderms where tube feet (podia) are located; involved in locomotion and feeding.

Question 36

What are pedicellariae?

Answer 36

Pincer-like structures in some echinoderms (like sea urchins and starfish) used for defense, cleaning, and prey capture.