Lecture 7 RH Flashcards
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.
Deutrostomes:
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?
Gut
What are the features of echinoderms?
Loss of gill slits
pentaradiality
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?
Externally
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?
Bipinnaria
Brachiolaria
Ophioplutius
Echinopluteus
Auricularia
Dollolaria
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?
Forceps-type
Spinous
Scissors type
Tridactyl-type
Globiferous-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)
asteroids
crinoids
holothurians
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:
sea-urchins
heart-urchins
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)
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