312 



ECHINODERMATA— ECHINOZOA 



PHYLÜM IV 



Olass 2. HOLOTHURIOIDEA von Siebold.i 



The Holothurians, or Sea-cucumbers, difFer markedly from all other 

 Echinoderms in their elongated bodies with little or no skeleton. The mouth 

 and anus are with rare exceptions more or less nearly terminal at opposite 

 poles, and the former is always surrounded by a circle of tentacles, 8-30 in 

 number. The skeleton is represented by calcareous particles in the body 

 wall, which are commonly microscopic and dissociated, but are sometimes 

 several millimetres across, and in rare cases may even be closely united with 

 each other to form a rigid body wall. In some species skeletal particles are 

 nearly or quite wanting. 



The paleontological evidence bearing on the history of Holothurians is 

 very slight. Fossils occur in two forms, either as impressions or casts of the 



Fkj. 435 Ms. 



Eldonia ludwigi Walcott. Middle Cambrian (Burgess shale formation) ; British Columbia. Specimen 

 flattened in the shale and showing traces of internal organs. er and rc, Central ring and radial canals of 

 vascular System ; i, Intestine ; o, Oral aperture ; oc, Oral Chamber ; oe, Oesoijhagus ; s, Stomach ; t, 

 Tentacles ; ul, Umbrella lobes, crushed and macerated ; x-x, Junction - point of i stomach and intestine ; 

 a, Position of anus. Natural size (after Walcott). 



whole animal, or as dissociated skeletal particles preserved in very fine 

 limestones or shales. Of impressions or casts, the earliest described are 



^ Literature : Giebel, G., Zur Fauna des lithographischen Schiefers von Solenhofen. Holothu- 

 rienreste. Zeits. f. gesammt. Naturw., 1857, vol. ix. — Schlumherger, G., Note sur les Holothuridees 

 fossiles du Calcaire Grossier. Bull. Soc. Geol. France (3), 1888, vol. xvi. — Idem, Second Note 

 sur les Holothuridees fossiles. Bull. Soc. Geol. France (3), 1890, vol. xviii. — Ludwig, H., Die 

 Seewalzen. Bronn's Klassen und Ordnungen des Thierreichs, vol. ii., part 3, 1889-92. — Spandel, 

 E., Die Echinodermen des deutschen Zechsteins. Abh. Ges. Nürnberg, 1898, vol. xi. — Idem, Eine 

 fossile Holothurie. Dp. cit., 1900, vol. "xiii. — Wcdcott, G. D., Middle Canibrian Holothurians 

 and Medusae. Smiths. Mise. Coli., 1911, vol. Ivii., no. 3. — Glark, H. L., Fossil Holothurians. 

 Science, 1912, n.s. vol. xxxv. — Glark, A. H., Restoration of Eldonia. Zool. Anz., 1912, vol. xxxix. 



