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