428 



ECHINODERMS OF THE BRITISH ISLES 



consisting of 12 pieces (2 interradialia in right and left dorsal 

 interradius) ; radialia perforated. Genital opening in the point 

 of one of the tentacles (usually the uppermost to the right of the 

 dorsal mid-line). Anchor usually narrower than the anchor plate 

 (Fig. 262, 2) ; the outer, free part of the anchor plate with 6, 

 rarely 7, serrate holes round the central hole ; the outermost 



hole mostly, though not always, 

 distinctly larger than the others. 

 Often a few small, mostly smooth 

 holes are found along the outer 

 edge of some of the plates. Small 

 calcareous bodies are found in the 

 longitudinal muscles. Colour in 

 life a faint pinkish. Grows to a 

 size of ca. 30 cm. length, but a 

 length of 10-18 cm. is the more 

 usual. 



Lives buried in the ground, in 

 sand or mud, or among Zostera. 

 It is hermaphrodite. The eggs are 

 very small ; nevertheless it has not 

 a typical pelagic larva but direct 

 development. 



Numerous parasites or com- 

 mensals are found on or in this or 

 the other Synaptids of the European 

 coasts,^ e.g. the Gregarines Urospora 

 synaptce Cuenot and Gonospora 

 Mercieri Cuenot, the Infusorians 

 Urceolaria synaptce Cuenot and 

 Rhabdostyla arenaria Cuenot, var- 

 ious Cercarians and Planarians, the 

 Rotatorian Discopus synaptoe Zel- 

 inka, the Tardigrade Tetrakentron 

 synaptce Cuenot (among the tentacles, where also the Discopus 

 especially abounds), the Copepod Synaptiphilus luteus Canu and 

 Cuenot (in the oesophagus), the Polynoids Harmothoe lumdata 

 (D. Chiaje) and H. marphysa M'Intosh, the LamelUbranch Eyito- 

 valva Perrieri Malard (on the skin of L. inhcerens, found only at 

 St. Vaast la Hougue), and — the most remarkable of all — the 



1 See especially L. Cuenot, " Contributions a la Faune du bassin 

 d'Arcaehon. V. Echinodermes", Bull. Station Biol. (V Arcachon, xiv., 1912, 

 pp. 68-92. 



Fig. 261. — Leptosynapta inhce- 

 rens (to the left), Labidoplax 

 Buski (in the middle), Myrio- 

 trochus vitreus (to the right). 

 The curvature of the posterior 

 end of L. inhcerens accidental. 

 Nat. size. (From Danmark's 

 Fauna.) 



