218 THE HOLOTHURIOIDEA 



CLASS I. HOLOTHURIOIDEA, C. T. v. SIEBOLD (1848) 1 



( = FISTULIDES, Lamarck, 1801 ; SCYTODERMATA, Burmeister, 1837; 

 ASCIDIASTELLA, T. & T. Austin, 1840 ; SCYTACTINOTA, Bronn, 

 1860). 



OKDER 1. Actinopoda. 

 2. Paractinopoda. 



Eleutherozoic Echinoderms normally elongate along the oro-anal 

 axis, which axis and the dorsal hydropore lie in the sagittal plane 

 of a secondary bilateral symmetry. The calcareous skeleton, which 

 may be entirely absent, is usually in the form of minute spicules. 

 sometimes of small irregular plates with no trace of a calycinal or 

 apical system ; to these is added a ring of pieces radiately arranged 

 round the oesophagus. Ambulacral appendages take the form of : 

 (1) circumoral tentacles, (2) sucking-feet, (3) papillae; of these (1) 

 alone is always present. The gonads are not radiately disposed. 



The Holothurians have long been known to man. Many of 

 the common v/rms are large and conspicuous animals, which are 

 frequently caught in the dredge or thrown up on our shores. It 

 is generally supposed that these are the marine animals to which 

 Aristotle gave the name of oXoOovpiov, from which their present 

 scientific name has been derived. Pliny, mentioning a species of 

 Citcumaria, calls it Cucumis marinus, or sea-cucumber, a name often 

 applied to Holothurians at the present day. 



Belon, in 1553, first described a Holothurian, recognising some of 

 its affinities to the starfish and sea-urchins ; and Rondelet, two years 

 later, gave some figures of two species. Bohadsch, Pallas, Fabricius, 

 Cuvier, and others increased our systematic and anatomical know- 

 ledge of this group during the later part of the eighteenth century. 



In 1816 Tiedemann published an excellent account of the 

 anatomy of Holothuria tubulosa, C4mel. (12), and since then the 

 study of the structure, development, and classification of the class 

 has been greatly extended by a large number of naturalists, amongst 

 whom one may mention A. Baur (1), Selenka (7), Semper (10), Joh. 

 Miiller, Metschnikoff, and Kowalevsky. Within recent years the 

 finer anatomy and histology of Holothurians have been studied by 

 O. Hamann (3), Herouard (4), Cue"not, and many others, and their 

 embryology by Selenka (7), Semon (9), and Bury (2). Our 

 knowledge of that most interesting group, the Elpidiidae, dates 

 almost entirely from the publication by Th4el of the Report on 

 the collections made during the Challenger Expedition (11). The 

 family Pelagothuriidae has only lately been described by H. 

 Ludwig (6) An admirable and comprehensive treatise on the 



1 By E. S. Goodrich, M. A. 



