Echinodermata Flashcards
What are some types of echinoderms?
Sea stars, urchins, sea lilies, sand dollars, sea cucumbers.
When did echinoderms arise?
The start of the Cambrian
Crinoids were a dominant group in what era?
Paleozoic
Describe echinoderm larvae
They are ciliated, free-swimming organisms that organize in bilateral symmetry which makes them look like embryonic chordates
Describe an echinoderm skeleton
Echinoderms have a mesodermal skeleton composed of calcareous plates or ossicles. Each one of these, even the articulating spine of a sea urchin, is composed mineralogically of a crystal of calcite. Ossicles may be fused together, as in the test of sea urchins, or may articulate with each other as in the arms of sea stars, brittle stars and crinoids.
What is catch connective tissue?
Collagenous material can change its mechanical properties in a few seconds or minutes through nervous control rather than by muscular mean
Describe the echinoderm water vascular system
Its a network of fluid-filled canals derived from the coelom (body cavity) that function in gas exchange, feeding, sensory reception and locomotion. This system varies between different classes of echinoderm but typically opens to the exterior through a sieve-like pore on the surface of the animal.
The water vascular system assists with the distribution of nutrients throughout the animal’s body and is most obviously expressed in the tube feet which can be extended or contracted by the redistribution of fluid between the foot and the internal sac.
Describe the echinoderm digestive system
Echinoderms possess a simple digestive system which varies according to the animal’s diet. Starfish are mostly carnivorous and have a mouth, oesophagus, two-part stomach, intestine and rectum, with the anus located in the centre of the aboral body surface
How does gas exchange occur?
Gaseous exchange occurs via dermal branchae or papulae in starfish, genital bursae in brittle stars, peristominal gills in sea urchins and cloacal trees in sea cucumbers. Exchange of gases also takes place through the tube feet.
Describe echinoderm excretion
Echinoderms lack specialized excretory (waste disposal) organs and so nitrogenous waste, chiefly in the form of ammonia, diffuses out through the respiratory surfaces.[
Describe the echinoderm circulatory system
Haemal and perihaemal systems are derived from the coelom and form an open and reduced circulatory system. This usually consists of a central ring and five radial vessels. There is no true heart and the blood often lacks any respiratory pigment.
Echinoderms are an exception having both a coelomic circulatory system (i.e., the water vascular system) and a haemal circulatory system (i.e., the haemal and perihaemal systems)
Describe the echinoderm nervous system
Echinoderms have a simple radial nervous system that consists of a modified nerve net consisting of interconnecting neurons with no central brain, although some do possess ganglia. Nerves radiate from central rings around the mouth into each arm or along the body wall; the branches of these nerves coordinate the movements of the organism and the synchronisation of the tube feet. Starfish have sensory cells in the epithelium and have simple eyespots and touch-sensitive tentacle-like tube feet at the tips of their arms. Sea urchins have no particular sense organs but do have statocysts that assist in gravitational orientation, and they have sensory cells in their epidermis, particularly in the tube feet, spines and pedicellariae. Brittle stars, crinoids and sea cucumbers in general do not have sensory organs but some burrowing sea cucumbers of the order Apodida have a single statocyst adjoining each radial nerve and some have an eyespot at the base of each tentacle.[40]
Describe echinoderm reproduction
- reach maturity after ~2-3 years
- external fertilization
- both gamete types released into the water
- larvae swim free until they settle
- asexual reproduction through transverse fission
How do echinoderms move around?
Echinoderms primarily use their tube feet to move about but some sea urchins also use their spines. The tube feet typically have a tip shaped like a suction pad in which a vacuum can be created by contraction of muscles. This along with some stickiness provided by the secretion of mucus provides adhesion. Waves of tube feet contractions and relaxations move along the adherent surface and the animal moves slowly along
What role does burrowing play in ecological function?
The burrowing of sand dollars, sea cucumbers and some starfish stirs up the sediment and depletes the sea floor of nutrients. Their digging activities increases the depth to which oxygen can seep and allows a more complex ecological tier-system to develop.
