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Flashcards in Lecture 7 RH Deck (76)

What distinguishes echinoderms from other invertebrates?

embryology (deutrostome rather than protostome)


What is the difference between protostomes and deutrostomes?

type of cleavage

fate of blastopore

ontogeny of coelom


What is the difference between cleavage of protostomes and deutrostomes?

Protostomes: Spiral and determinate.

Developmental fate of embryonic cells is rigidly determined early.

Each cell from a 4-cell embryo could form a quarter of a non-viable organism.


Cleavage is radial and indeterminate.

Planes of cell division parallel or perpendicular to vertical axis of embryo

Each cell of early embryo can develop into a complete embryo


What does determinate cleavage mean?

particular types of cells can only become particular types of organs


Which organisms undergo schizocely? What is it?

Protostomes, separation of solid mass of mesodermal cells


Which organisms undergo enterocely? What is it?

Deutrostomes, mesoderm buds from wall of embryonic archenteron and hollows to become coelomic cavities


What is an archenteron?



What are the features of echinoderms?

Loss of gill slits


Major group of invertebrate deutrostomes

Homogenous species of 7k living and 20k extinct species,

All are marine

endoskeleton of stereom ossicles and calcareous plates

Unique mutable connective tissue

Water vascular system; unique system of hydraulic canals branching into extensions called tube feet/podia


What are the classes of living echinoderms?

Asteroidea (sea-stars)

Ophiurodea (brittle stars)

Echinoidea (sea-urchins)

Crinoidea (comatulids and sea lilies)

Holothuroidea (sea cucumbers)

Concentricycloidea (sea daisies)


What is the type of symmetry that echinoderms exhibit?

pentamerous radial symmetry in postmetamorphic echinoderms

Premetamorphic echinoderms are generally bilaterally symmetrical

Several fossil species are asymmetric bilateral or even trimerous


What is the composition of the calcareous skeleton?

High Mg Calcite developing from mesoderm (unique in invertebrates) and thus located in body wall.

Ossicles are totally different from shells. Actually, the skelton of an echinoderm is covered by epidermis and cuticle


What is the water vascular system like?

Formed by canals located in or close to the body wall

Lined with ciliated epithelium and filled with fluid

Entire W.V.S filled with fluid similar to sea-waterbut contains coelomocytes, proteins, and high K+ concentrations

Ring canal surrounds oesophagus and mouth

2 types of organs may be attached to ring canal: Tiedmann's bodies
Polian vesicles


Where does the water come from in the water vascular system?

Sieve plate opens to the sea water and fluid of Water Vascular System flows in through here


What is the function of Tiedmann's bodies?

Defence function


What is the function of Polian

fluid storage in ampulla


What are the components of the water vascular system?

Vertical canal extends from ring to aboral ossicle

5 radial canals extend from ring canal to tips of arms

Lateral canals arise from radial canals on each side in an alternating fashion. Lateral canals have valves which terminate in an ampulla and a podium.


Where is the ampulla located?

Within the general coelom


Where are muscles located?

Muscle fibers lie in the wall of podia and ampulla


What is the function of muscles in echinoderms?

Ampulla contracts and podium relaxes to extend

Podium contracts and ampulla relaxes to force internal fluid back into ampulla to retract


What is the function of podia in echinoderms?

Podia take part in feeding, burrowing, locomotion, sensory perception, and respiration

In some phyla a single type of podium fulfills different function in others different types of podia coexist each with their own function


What is meant when it is said that echinoderms have mutable connective tissue?

Connective tissue have a unique ability to change stuffness according to conditions

Transition from rigid to flexible state is dramatic and has functional importance

Softening of tissue in some parts of an arm makes its loss easy when seized by a predator while the rest of the animal escapes (depolymerization in tissue)


Are echinoderms mono or dioecious?

Most echinoderms have separate sexes

Some brittle stars and sea cucumbers are hermaphroditic

All have external fertilization


How does echinoderm fertilization occur?



How do echinoderms develop?

Homolecithal egg undergoes radial and indeterminate cleavage. Blastula is ciliated and contains a large blastocoel. Cells from vegetal pole divide before invagination from blastocoel.


What are the types of larvae of echinoderms?

Plantotrophic larvae (feed on plankton)

Lecitotrophic larvae (use yolk as a source of nutrition)

Brooded larvae (Pre-metamporphic development in invagination of mother's body wall)


How many echinoderm species have lecitotrophic larvae?

About 50% of echinoderm species have lecitotrophic larvae


What do lecitotrophic larvae feed on?

Nothing they develop to metamorphosis. They depend on yolk to grow.


What is the consequence of having lecitotrophic larvae?

Dispersion is limited


What is planktotrophic larval development like?

Gastrula hatches from fertilisation membrane

Diplopleura is bilateral

Ciliated band surrounds mouth and captures food particles

Different types of larval development occurs in different echinoderm classes


What are the types of echinoderm larvae?








What do echinoid and ophiuroid larvae develop into?

Long slender projections each containing a skeletal rod (pluteus larvae)


What kind of larvae do asteroid and holothuroid produce?

short armed larvae


What kind of larvae do crinoids produce?

No projections and it is lecitotrophic


What is metamorphosis?

Dramatic change in morphology


What is the metamorphosis of echinoderms like?

Bilateral larva into radial juvenile

Juvenile structures develop from left side of larvae

Primary podia of juvenile protrude from left side, test substratum with chemoreceptor cells on podia

Animal detaches from a stalk and begins a separate life


What is the diversity of class crinoida like?

Most ancient forms

Attached stalked crinoids were abundant in paleozoic era; 80 species exist today

Free-living crinoids (order comatulida) are more abundant with 550 species in indo-pacific and polar waters


What features does the external structure of crinoidea have?

Main body structure (cuplike) with 5 (often branched) arms. On sides of arms is a row of jointed appendages called pinnules.

Aboral side contains a calyx

Stands on stalk connected to calyx in sea lilies and on cirri


How do crinoidea move around?

Flexion via flexor muscles which change connective tissue to soft state.

Extension undergoes the opposite changes

Bending is not the only motion that crinoids do

Stalked crinoids crawl on cirri


What do crinoids eat?

Suspension feeders using a filtration fan formed by pinnules of arms oriented generally at right angle to current, they increase available area.

Podia on pinnules bear mucus-secreting papillae

Oral surface directed upward, anus opens on same surface of mouth on top of anal cone

5 ambulacral grooves extend peripherally from mouth and extend into arms

Podia are located on each side of pinnules


How do crinoids develop?

Either brooders (antarctica) or lecitotrophic

Gametes are produced in the arms

Non-feeding doliolaria is barrel-shaped with apical sensory tuft and ciliary girdles

Attaches by adhesive gland

Metamorphosis forms stalked crinoid

In cromatulids cirri develop and the crown breaks free in water column


What are features of class asteroidea?

Star-shaped species that have become a symbol of sea life

Body composed of arms projecting from central disk

Usually 5 arms but some have many more


What are the features of external asteroid structures?

Mouth in center of underside disk

Wide furrow (ambulacral groove) extends from mouth radially to each arm

Each groove contains 2/4 rows of podia

Podia on tip of each arm: sensory podia

Pigment spot (light sensitive)


What are pedicellariae and what is their function?

Catching jaw-like appendages of 2 important orders of asteroids

Consist of a stalk surmounted by ossicles arranged to form forceps or scissors

Can be used for protection against larvae settlement or to catch prey


What is the function of papulae in asteroids?

Evaginations of epithelium and mesothelium

Increase respiratory surface made up of podia


What types of pedicellariae are there?



Scissors type




How do asteroids move around?

Water vascular system plays a major role

Asteroids walk n their podia that attach to substratum

Adhesion is largely chemical but physical adhesion (suckers) is also used by some species

Podia of some species lack suckers


How do asteroids feed?

Mouth opens in center of oral face

Mouth leads to stomach divided into cardiac and pyloric chambers

Pyloric chamber opens into 2 pylorice caeca in each arm

Short intestine opens into 2 intestinal caeca

Digested material


How does digestion happen in primitive asteroids?

Prey is swallowed whole and indigestible material is cast out of the mouth


What are the adaptations of soft-bottom asteroids?

Podia designed to bury

To locate buried prey they dig down into substratum


How do modern asteroids digest prey?

Extra orally. Muscles push the stomach out using pressure of coelomic fluid and the stomach moves through mouth to the outside. The stomach is then retracted with digested material


What is the role of asteroids in benthic ecosystems?

Predator asteroids moderate competitions among preys thereby increasing diversity

Predation reduces density of a strong competitor allowing weaker competitors to persist in a community


What does the crown of thorns starfish feed on?

Coral polyps.


How are algal blooms related to the crown of thorns starfish?

When dry period of several years is followed by heavy rain algal blooms result from runoff of nutrients. Blooms coincide with high crown of thorn population densities


What are the modes of reproduction of asteroids?

Arm can form a complete organism (asexual reproduction)

Sexual reproduction maintains diversity.

Dioecious with 2 gonads each arm


What are the features of sea daisies?

They are asteroids

Less than 1cm

Pentaradial without arms

Podia lie around the margin not along the ambulacral grooves


What are the features of class ophiuroids?

Brittle stars and basket stars

5 long, slender, sometimes spiny, or branched arms

Arms more sharply set off central disk than asteroids

No ambulacral groove

Arms have a solid construction by presence of vertebrae


How do ophiuroids move?

Central canal protected by oral shield

Podia without suckers

Center oral disk occupied by modified ossicles that form jaw teeth

Madreporite on oral face no anus

Podia play little role in locomotion

Ophiuroids move by pulling themselves along with 2 arms

Ophiuroids can coil their arms


How do ophiuroids feed?

Filter feeding: particles are trapped into bolus by podia and transferred to mid-oral line of arm and mouth via podia.

Deposit feeding: particles collected on sea bottom are collected by podia and transferred to mouth

Scavengers, carnivores: Large particles swept into mouth by looping motion of arm

Browsing on algae using teeth


Which echinoderms are bioluminescent?

ophiuroids (extensively studied)





How is bio-luminescence controlled?

Under nervous control in response to external stimuli. research suggest that acetylcholine and neuropeptides specific to echinoderms are involved as neurotransmitters in the control of bioluminescence


What are the features of class echinoids?

no arms, body shape is circular or oval

Movable spines

Radial symmetry modified to secondary bilateral symmetry in burrowing species

Ossicles are flattened and sutured together into a solid case, the test


Examples of class echinoidea:



sand dollars


What are the features of sand dollars?

Flattened body displaying circular circumference

Adaptation to burrowing and covering and has modified spines

Mouth located centrally

Periproct on oral face

Some species with opening in test: lunules


What is aristotle's lantern of sea-urchins and sand dollars?

scraping structure which has 5 calcareous plates and 5 teeth.

It is moved by muscles, lantern protruded and retracted through the mouth

Teeth can be opened and closed by muscle contraction

Graze on algae and sea grasses as well as other organic material

inferior part of lantern contains the pharynx


What are the features of heart urchins?

Small spines adapted for locomotion and burrowing in sediments.

Oval-sha[ed body, oral surface flattened, aboral surface complex

Several species harbour symbiotic sulfide-oxidizing bacteria in digestive tract to allow for burrowing under ocean floor despite the high H2S composition


What are features of class holothuroidea?

No arms

Elongated shape

Lie with side of the body, rather than oral pole, against substratum. hence only 3 rows of feet are developed

Skeleton reduced to microscopic ossicles

Buccal podia modified into tentacles


What is the type of symmetry of holothuridians?

Secondary bilateral


How do holothuridians move?

Contraction of longitudinal and circular muscles in the body wall


What does the coelom do in holothuridians?

fluid-filled and acts as a hydrostatic skeleton


What are the oral tentacles of holothuridians modified into?

Modified tube feet


What organism has a respiratory tree and what is its function?

sea cucumbers, respiratory tree functions in both respiration and excretion


What do holothuridians eat?

Suspended particles or deposits on deep-sea ocean floor


How do holothuridians reproduce?

Sexes are separate some are hermaphroditic


What are adaptations that some echinoderms have to their environment?

Bottom dwelling

Filter-feeding, deposit feeding, scavenging, herbivorous feeding, carnivorous feeding

Predatory success is due to their use of hydraulic mechanism of feet


What are the subphyla of phylum chordata?

urochordata (have a tail)

cephalochordata (head like structure)

vertebra (craniata)