150 



CLASS E C H I N O D E R M A T A. 



The following division was proposed by Mr. J. E. Gray, in the " Annals 

 of Philosophy" for 1826: 



I. Body globular, mouth and vent o|>].sit< . 



ILLUSTRATIVE EXAMPLES. 



PLATE 1. 



1. CIDARID*, containing the genera Diadema, Cidaris, and Astropyga. 

 Illustrations: Diadema fistularis, Cidaris imperialis, Astropyga radiata. 



2. EcHlNlDjE, which contain the genera Echinus and Echinometra. 

 Illustrations : Echinus miliaris, E. elegans, E. sardicus, Echinametra mam- 



millatus. 



II. Body variously-shaped, vent posterior. 



ILLUSTRATIVE EXAMPLES. 

 PLATE 2. 



3. ScuTELLiDjE, which includes the genera Echinanthus, EchinanKhnius, 

 Eschiiwdixus, Echinocyamus, and Cassidulus. 



Illustrations : Echinanthus subdepressa, Echinarachnius placenta, Echino- 

 discus digitata, Cassidulus Australis. 



4. GALERITID*, having the genera Galeritis, Discoidea, Echinonaus, 

 Echinocarys, Echindampas, Echinobrissus. 



Illustrations : Galerites albo-gaierus, Echinonaus minor, Echindampas 

 Koenigii, Echinocorys ovatus, Echinobrissus Breynii. 



5. S PAT ANG ii>., contain ing the genera Echinodardium,Spatangus, Brissus, 

 On,. 



Illustrations: Echinodardium atropos, Spatangus purpureus, Brissus uni- 

 color. 



The species of Echinoida have been described and figured by Klein and 

 Leske, in their Echinodermata ; and their figures have been mostly copied 

 into the French " Encyclopedic Methodique." 



The fossil species have been described by the same authors. 



Many of them are used as food by people resident on the sea-coast, who 

 generally reckon them delicacies, especially when their ovaries, which are 

 very large, and nearly occupy the whole body, are full of eggs. 



ORDER II. STELLERIDA. STAR-FISH. 



THE SteUerida, Asteroid, or Radiated Order (Radiata, on Plate 3), as the 

 name implies, is star-shaped ; the body or central part, containing the 

 stomach, having rays stretching out from its margin, of greater or less 

 length and number. Thus in one section of the genus Asterias, the body is 

 pentagonal, and the slightly hollowing out of its edges hardly produces 

 arms or rays, as in the Gibbous Star-fish, whilst in the other section of the 

 same genus, the body is deeply cleft, and the rays are of great length, as in 

 the Red Star-fish. In the Ophiwe, the arms are of great length, and in 

 Euryale, each arm, directly it stretches out beyond the body, divides into 

 two branches, and these again into others, which again and again divide, 

 assuming the appearance of interweaving branches of a tree, and which they 

 omploy for entangling their prey. 



The general characteristics of the Order are: Skin not irritable, but 

 mobile; body depressed and furnished with mobile angles or rays; diges- 

 tive cavity, with only one opening. Containing the genera Asterias, Opliium, 

 Euryale, and Cromatula. 



ILLUSTRATIVE EXAMPLES. 



PLATE 3. 



ASTERIAS. Body suborbicular, flattened, the circumference star-shaped, 

 either angulated, lobated, or divided into distinct rays. Under surface of 

 the division having a longitudinal sulcns, famished at each side with 

 moveable spines and numerous foramina for the passage of retractile tubular 

 tcntacula. Month below, central, placed at the union of the sulci. 



'1 ho animals of this genus are well known to our fishermen under the 

 names of Stir-fish and Sea-stars : and several species are excessively destruc- 



tive to Oyster-beds. They increase l>v the internal formation of a kind of 

 buds or gemma;, which when fully formed are cast forth by the jrent. 

 They possess the power of reproducing mutilated parts to a great degree, 

 so that not only a separated ]X>rtion is speedily re-supplied, but if an indi- 

 vidual be divided into as many parts as there are rays, provided a portion 

 of the mouth be attached to each, every ray will become a jjerfect Asterias. 

 The fishermen, by whom they are much dreaded, appear to be well aware 

 of this property, for if, in dredging for Oysters, any of these animals are 

 brought up, they immediately cut them into small pieces, and crush them 

 to atoms with thoir feet. The s[>ecies are numerous, and many of them 

 are natives of Britain. 



Illustration : Asterias pulchella, A. cylindrica. 



Oi'HiURA. Mouth simple, live-sided, placed beneath; body much de- 

 pressed, rounded, with five distinct, entire, squamous rays with very spinous 

 ridges, the latter with suckers; spines moveable. 



Type of the genus, Asterias mgra. 



Ten species, most of which are found on the sandy shores of Great 

 Britain. 



Illustrations : Ophiura mutica, 0. iMmarckii, O. Squamosa, 0. lineolata. 



EURYALE. Body orbicular, depressed, divided into five rays, separated 

 into two at the base, and repeatedly forked ; arms without any groove on 

 the lower surface, but furnished with a semilunar hole on each side of their 

 base, and a series of minute perforations on each edge. 



The singular form of these animals generally attracts attention ; they are 

 usually found, like the Ophiurce, with their much-divided arms clasping the 

 stems of the marine Algol and Corallines. There are seven species. 



The type of the genus is E. verrucosa, Lamarck the Asterias Euryale 

 and Asterias Caput Medusa of Gmelin; found in the Indian Seas. This 

 is larger than most of the other species, and it is studded externally with 

 granular warts. 



Illustration : Euryale simplex. 



ORDER III. HOLOTHURIA. 



THIS Order differs from either of the other Echinodermous Orders in the 

 skin being entirely devoid of any earthy contents, but it is very thick and 

 strong, consisting of a whitish fibrous tissue, which interweaves in various 

 directions, leaving apertures for the passage of the dorsal tubes, which pene- 

 trate through several wart-like projections on the back, and for the protru- 

 sion of the feet upon the belly, which are in great numbers. 



The characters of the restricted genus of this Order are : Body free, 

 cylindrical, thick, soft, and very contractile ; skin coriaceous, generally papil- 

 lary ; mouth ter- 

 minal, surrounded 

 by laterally divided, 

 rather branchy, or 

 pinnated gills.armed 

 with bony or calca- 

 reous teeth ; vent 

 near the hinder ex- 

 tremity. The ani- 

 mal is of a tubular 

 form, and upon its 



fore extremity is a Hnlutlmria. 



crown of twenty tentacules disposed ill two rows, and having the extensile 

 mouth in the centre, each tentacule being cylindrical, and having its expanded 

 end fringed. A longitudinal section of the external skin exhibits the appa- 

 ratus by which both tentacules and feet are moved, and which has a 

 resemblance to that of the other Orders, but rather more simple. 



They live on animal substances, which they draw to their mouth by theii 

 gills. Their stomachs are filled with pieces of coral, which are, perhaps, 

 useful in assisting digestion ; although not provided with lins. they swim 

 with great facility. 



