GASTROTRICHA 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 sensoi-y 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 veiy 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^TONOTIDAE. 

 With the characters given above : several genera. 

 Key to the genera of Chcetonotidae here described: 

 fli Posterior end forked. 

 6i Back covered with spines or scales. 



Ci Caudal forks short 1. Ch^tonotus 



Cj Caudal forks very long and segmented 2. Lepidodebma 



dz Back not covered with spines or scales 3. Ichthydium 



o. Posterior end not forked 4. Dasydytes 



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



forked tail and with dorsal spines or scales; ■, , s-.. „ __ Slagl 



head fomied of 3 lobes, usually with 2 pairs %**^i^i^^ ^^1 



of tufts of sensory bristles and in some species 



, . , Fig. 897 — Chwtonotus 



with a pair of eyes; ventral side larus (Stokes), a, dorsal 



. aspect ; B, head, 



flat: 23 species. 



hN| C. larus (0. F. Miiller) (Fig. 397). Back covered with 



sliort 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 long spines : often common. 



Chwtonotus r^ 1, -r. T • 1 1 



longispinosus 2. Lepidoderma Zeller. Back covered with scales; 



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. 



