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PHYLUM ECHINODERMATA. 



Sub-order 1. ASPIDOCHIROTAE. With 18-30 shield shaped tentacles 

 (except Molpadiidae). Ampullae of the tentacular canals, respiratory 

 trees, and cuvierian organs present or absent. Without retractor 

 muscles of the pharynx (present in Molpadia). 



Fam. 1. Holothuriidae. Body cylindroidal. Solelike ventral surface 

 usually but slightly developed. The ampullae of the tentacular canals 

 are well developed and project into the coelom. The calcareous ring is 

 formed of 5 radial and 5 interradial pieces. Otolithic vesicles are absent. 

 Stone-canals often numerous, opening into the body-cavity. Longitudinal 

 muscles usually divided ; retractor muscles absent. Respiratory trees 

 well developed, the left being usually covered by the plexus of the intes- 



. 



FIG. 184. Dorsal and ventral view of Deima atlanticum (after Herouard). 



tinal vascular system. Cuvierian organs present. Mainly in the indo- 

 pacific region and littoral. Mutteria Jager, anus with calcareous teeth ; 

 the other genera are without these. Holothiiria L., trepang, ambulacra! 

 appendages over whole body, not in rows, cosmopolitan ; Labidodemas 

 Selenka, with feet only which are confined to the radii ; Pseudostichopus 

 Theel ; Stichopus Brandt, trepang, with flat ventral surface on which 

 there are usually three rows of feet. 



British genus, Holothuria with species : 

 With pedicels only, H. intestinalis A. and R. 



,, pedicels and papillae, H. tremula Gunn. 



,, pedicels almost entirely ventral, H. nigra auct. 



,, two rows of pedicels on either side of body, H. aspera Bell. 

 Fam. '2. Synallactidae. Body rarely cylindrical, generally flattened 

 and with a ventral sole. Tentacular canals without ampullae. The stone- 



