180 



LOWER INVERTEBRATES. 



Another very worm-like species, common in Labrador, is Chirodota Iceve. It is 



whitish-gray, with wheel-like plates, like the last species, showing as white spots. 

 The two last mentioned species belong to the family Synaptid^, in which the 



sexes are united in the same individual, the tentacles are finger-like, or lobulated, 



and the form elongated and worm-like. 



In Synapta the integument contains numerous perforated, flat, calcareous plates, 



to which are attached protruding anchor- 

 like hooks. Myriotrochus has a single 

 Polian vesicle, but, Synapta has several. 

 Synapta gbxuxKi is a common species upon 

 the Atlantic sea-coast, li\ing in sand at low 

 tide level. Its exceedingly attenuated body 

 breaks up into several pieces when the ani- 

 mal is disturbed. Synapta siniilis is said 

 to live in brackish water. Synaptula vivi- 

 para is one of those species in which the 

 young develop directly, and are protected 

 in a marsupium. 



Oligotrochiis vitreus is a sjjecies living 

 at depths of from fifty to two hundred 

 fathoms on the coast of Norway, less vermi- 

 form than Synajjta, since its length is only 

 about four times its thickness, and sluggish 

 in its motions on account of the slight con- 

 tractility and stiffness of its body, which 

 is transparent and colorless. The tentacles 

 are twelve in number, and are less devel- 

 oped than even in Chirodota. The cal- 

 careous plates, which ai'e wheel-like, are 



very few, and deeply sunk in the skin. The calcareous ring round the gullfit shines 



snow-white through the body-wall, which also allows the intestines, generative organs, 



etc., to be clearly seen. 



The next sub-order (Pneumophora) has a respiratory tree arising from the cloaca. 



Caicdijia is so called from the long, tail-like jjrolongation in which the body ends. 



The skin is rough externally, from the calcareous pieces imbedded in it. C. arenata, 



the only species, has fifteen four-pronged tentacles, and is a somewhat common object 



in Massachusetts Bay. 



Molpadia turgida, is a deep-water form that has been taken in over a hundred fathoms 



in the Gulf of Maine, and is known to range southward to Florida. It is a tailed si^ecies 



with fifteen tentacles and an anterior extremity shaped like the neck of a bottle. 



Most of the Apoda are natives of the cold seas of the Arctic regions, but some 



genera, as Synapta and Chirodota, are almost cosmopolitan. 



Fig. 158. — Synapta inhcerens, with anchors aud plates. 



Obdek III. — fed ATA. 



The Pedata, as their name implies, are always furnished with a greater or less 

 number of ambulacral feet; a respiratory tree is always present, and the sexes are 

 distinct. 



