HOLOTHURIOIDEA 



425 



sulphate) in order to get them well preserved. The plates always 

 lie horizontally, parallel to the circular muscles, the anchor 

 lying outermost. The basal part of the anchor, the handle, is 

 a little widened, with the edge very finely serrate or ramified. 

 Above the handle the shaft is somewhat compressed and has on 

 the inner side an arched keel, which serves as an articular surface, 

 on which the anchor moves in relation to the anchor plate. The 

 arms of the anchor, which are usually somewhat thorny, are 

 directed slightly outwards. The anchor plate is usually somewhat 

 narrower in the basal part, where it is connected with the anchor 

 and is often provided with an outwardly curved bow. There are 

 no special anchor muscles, but the whole apparatus is surrounded 

 by connective fibrillse. Movement is caused only by the con- 

 traction of the body wall. When the 

 body wall is extended, the tissue sur- 

 rounding the anchor is tightened and 

 the anchor is pressed downwards on to 

 the plate (Fig. 259, b) ; the anchor arms 

 become erect, forming a projection on 

 the skin, which acts as a small foot. 

 The points of the anchor arms do not 

 pierce the skin ; they thus act in a 

 similar w^ay as the ribs of the snakes. 

 When the body wall relaxes, the anchor 

 rises from the anchor plate, the point of 

 the arms then being directed inwards 

 (Fig. 259, a). The holes in the anchor 

 plate are generally serrate along the edge ; they usually show a 

 very constant and regular arrangement, which is of importance 

 for classification. 



Two genera of the subfamily Synaptince are known from the 

 British seas, but two more are very likely to be represented 

 there also, viz., Protanhjra Ostergren, the species Pr. abijssicola 

 (Theel) (Synapta abyssicola Theel) ^ having been found in the Bay 

 of Biscay, 4870 m. (" Princesse Alice "), and off Senegal, 3200 m. 

 (" Talisman "), also known from the West Indies and the east 

 coast of N. America, 2259-4870 m. ; Bhabdomolgus Keferstein, 

 the only species known, Rh. ruber Keferstein, having been found 

 at Brittany and Heligoland, in ca. 20 m.^ 



Fig. 259. — Anchor and 

 anchor plate of a Syn- 

 aptic! in two different 

 positions, side view. In 

 A by relaxed, b by ex- 

 tended, body wall. Dia- 

 graminatic. (After 

 Ostergren ; from Da7i- 

 mark's Fauna.) 



^ For a description of this species see ''Challenger'''' Holoth., ii., p. 14, 

 PL I. 11 ; H. L. Clark, The Apodous Holothurians, p. 105, PI. IV. 8-11. 



2 Herouard (" Monaco'', Ixvi., p. 141 ) also records Synaj^ula hydriforniis 

 (Losueur) from the Azores, 1250 m., though with a question mark, as he had 



