Phylum Echinodermata
Echinoderms (Phylum Echinodermata) are a phylum of marine animals. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone. The phylum contains about 70,000 living species, making it the second-largest grouping of deuterostomes, after the chordates. Echinoderms are also the largest phylum that has no freshwater or terrestrial representatives.
Anatomy and physiology
Echinoderms evolved from animals with bilateral symmetry. Although adult echinoderms possess pentaradial, or five-sided, symmetry, echinoderm larvae are ciliated, free-swimming organisms that organize in a bilaterally symmetric fashion that makes them look like embryonic chordates. Later, the left side of the body grows at the expense of the right side, which is eventually absorbed. The left side then grows in a pentaradially symmetric fashion, in which the body is arranged in five parts around a central axis. Echinoderms exhibit fivefold radial symmetry in portions of their body at some stage of life, even if they have secondary bilateral symmetry. Many crinoids and some seastars exhibit symmetry in multiples of the basic five, with seastars such as Helicoilaster known to possess up to 50 arms, and the sea-lily Comanthina schlegelii boasting 200.
They have a few important aspects in common. They have bony ossicles in their body. They have a water-vascular system which pumps water through the madroporite. They also have small jaws that are supported by the water-vascular system. And they have tube feet which they use to attach to objects, for protection, as well as to obtain food. They have radial symmetry and most can regenerate lost limbs.
The following classes are types of echinoderms:
(1) Class Asteroidea--Starfish or Sea Stars (Six-rayed Starfish--Leptasterias hexactis)--sea stars have fairly developed senses of smell, touch, and taste. They also can respond to the presence of light. They normally eat small prey whole, but they have to extrude their stomachs to digest larger prey outside their bodies. Sometimes, sea stars will use their tube feet to help pry open bivalves, and then they will slip their stomachs in between the two shells.
(2) Class Ophiuroidea--Brittle Stars (Daisy Brittle Star--Ophiopholis aculeata)
Another picture of a Brittle Star (*)--found in all oceans (but mainly in the tropics). The group includes about 2000 species, varying in color. They eat decaying matter and microscopic organisms that are found on soft muddy bottoms.
(3) Class Echinoidea
Sea Urchins--they locomote using short to long, movable spines. Between their spines are small, pincerlike organs calledpedicellariae which they use to clean and defend themselves. The pedicellariae also contain a powerful toxin.
(4) Class Crinoidea--Feather Stars (Florometra serratissima)--feather stars will swim if they are disturbed.
(5) Class Holothuroidea--Sea Cucumbers
Class Chondrichthyes
It contains the cartilaginous fishes, those that have a skeleton of cartilage rather than bone. This includes all sharks, skates and rays. They also have five to seven gill slits on each side of the body. Sharks and rays reproduce by passing sperm from the male to the female, the male using modified fins called claspers. Some species produce large egg cases (usually those that live on the bottom) whilst others produce live young (usually those that swim in the water column) (http://www.woodbridge.tased.edu.au/mdc/Species%20Register/class_chondrichthyes.htm).
Taxonomy
Nelson's 2006 Fishes of the World arranges the class as follows:
§ Subclass Elasmobranchii
§ Order Plesioselachus
§ Order Squatinactiformes
§ Order Protacrodontiformes
§ Infraclass Cladoselachimorpha
§ Order Cladoselachiformes
§ Infraclass Xenacanthimorpha
§ Order Xenacanthiformes
§ Infraclass Euselachii (sharks and rays)
§ Order Ctenacanthiformes
§ Division Hybodonta
§ Order Hybodontiformes
§ Division Neoselachii
§ Subdivision Selachii (modern sharks)
§ Superorder Galeomorphi
§ Order Heterodontiformes (bullhead sharks)
§ Order Orectolobiformes (carpet sharks)
§ Order Lamniformes (mackerel sharks)
§ Order Carcharhiniformes (ground sharks)
§ Superorder Squalomorphi
§ Order Hexanchiformes (frilled and cow sharks)
§ Order Echinorhiniformes (bramble sharks)
§ Order Squaliformes (dogfish sharks)
§ †Order Protospinaciformes
§ Order Squatiniformes (angel sharks)
§ Order Pristiophoriformes (sawsharks)
§ Subdivision Batoidea (rays)
§ Order Torpediniformes (electric rays)
§ Order Pristiformes (sawfishes)
§ Order Rajiformes (skates and guitarfishes)
§ Order Myliobatiformes (stingrays and relatives)
§ Subclass Holocephali
§ Superorder Paraselachimorpha
§ Order Orodontiformes
§ Order Petalodontiformes
§ Order Helodontiformes
§ Order Iniopterygiformes
§ Order Debeeriiformes
§ Order Eugeneodontiformes*
§ Superorder Holocephalimorpha
§ Order Psammodontiformes*
§ Order Copodontiformes
§ Order Squalorajiformes
§ Order Chondrenchelyiformes
§ Order Menaspiformes
§ Order Coliodontiformes
§ Order Chimaeriformes (chimaeras)
Class Osteichthyes
It also called bony fish, are a taxonomic group of fish that have bones, as opposed to cartilaginous, skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of over 29,000 species. It is the largest class of vertebrates in existence today. Osteichthyes is divided into the ray-finned fish (Actinopterygii) and lobe-finned fish (Sarcopterygii). The oldest known fossils of bony fish are about 420 million years ago, which are also transitional fossils, showing a tooth pattern that is in between the tooth rows of sharks and bony fishes.
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
clade:
Craniata
Subphylum:
Vertebrata
Infraphylum:
Gnathostomata
Superclass*:
Osteichthyes
Huxley, 1880
Classes
Actinopterygii
Sarcopterygii
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