GASTEOTEICHA 243 



CLASS 2. GASTROTRICHA.* 



Minute worms less than .5 mm. long with an elongated body, usually 

 forked behind, with a ciliated ventral surface and a dorsal surface either 

 bare or covered with bristles or scales arranged in longitudinal rows; 

 head end contains the mouth and usually bears a pair of eyes and 

 paired sensory bristles; digestive tract a straight tube with a long mus- 

 cular oesophagus, extending to the anus, which is in the dorsal surface at 

 the hinder end of the body ; a pair of long kidney tubules opens into the 

 intestine; a very large brain is present, dorsal to the oesophagus, from 

 which nerves radiate; animals hermaphroditic, paired ovaries and testes 

 being present in the hinder part of the body cavity ; no genital ducts are 

 present and it is not known how the very large eggs reach the outside; 

 development direct: fresh-water animals found among infusorians and 

 rotifers; about 32 species, of which 12 have been found in this country. 



FAMILY CH.ETONOTIDAE. 

 With the characters given above: several genera. 

 Key to the genera of Chcetonotidae here described: 

 Oj Posterior end forked. 

 &! Back covered with spines or scales. 



Cj Caudal forks short 1. CH^ETONOTUS 



c 2 Caudal forks very long and segmented 2. LEPIDODEBMA 



& 2 Back not covered with spines or scales 3. ICHTHYDIUM 



o 2 Posterior end not forked 4. DASYDYTES 



1. CHJETONOTUS Ehrenberg.f Gastrotricha with a short, unsegmented 

 forked tail and with dorsal spines or scales; 

 head formed of 3 lobes, usually with 2 pairs 



of tufts of sensory bristles and hi some species 



.,, _ ., Fig. 397 Chcetonotus 



with a pair of eyes; ventral side lams (Stokes). A, dorsal 

 ,, , 00 . aspect ; B, head, 



flat: 23 species. 



C. lams (0. F. Miiller) (Fig. 397). Back covered with 

 short conical spines, the posterior ones being usually the 

 larger; length .12 mm.: common. 



C. longispinosus Stokes (Fig. 398). Back with 2 



Fig. 398 transverse rows of lone: spines : often common. 



Chwtonotus *" 



longispinosus 2. IiEPiDODERMA Zeller. Back covered with scales; 



(Stokes). 



tail forks long and segmented: several species. 



L. rhomboides (Stokes) (Fig. 399). Forks of tail one-fourth the 

 length of the body and composed of 20 segments; a deep, transverse 

 depression back of the mouth ; length .3 mm. 



* See "Beitrage zur Systematic der Gastrotrichen," by T. Griinspan, Zool. Jahrb. 

 Syst, Vol. 26, 1908. "Die Siisswasserfauna Deutschlands," Heft 14, 1912. 

 t See "Aquatic Microscopy," etc., by A. C. Stokes, p. 185, 1896. 



