228 NEMATHELMINTHES 



C. morgani Montgomery (Fig, 364). Length 6 to 22 cm,; color 

 brown; head white: eastern states. 



Family 2. NECTONEMATIDAE. 



Marine worms with body faintly ringed externally 

 and with 2 rows of fine bristles on each side ; anus absent ; 

 tail of male curved ventrally and ends with 

 a conical projection: 1 genus and species, 

 which is found swimming at the surface of 

 il, I 'A the sea. 



[tlv Nectonema Verrill. With the char- 



Fig. .364 acters of the family, 



m'(?rr?.r,f/:' N. agile* Verr. (Fig. 365). Length of 



'^^te'mlK?'"' male 5 to 20 em.; of female 3 to 6 cm.; ^^o^!L 

 (Montgomery), thickness .3 to 1 mm.; color grayish-white: °^''^ ^^'^^^>- 

 marine, and pelagic at New^port, R. I., and Woods Hole; Naples; the 

 larval form parasitic in small crustaceans {Palcemonetes). 



Class 3. ACANTHOCEPHALA.f 



Elongated, parasitic worms which live as adults in the intestine of 

 vertebrates, to the walls of which they attach themselves by means of a 

 retractile proboscis armed with hook-like spines, and as larvae in the 

 bodies of small invertebrates, especially crustaceans. 



The body of the adult may be divided into three regions, the proboscis, 

 the neck, and the trunk. The proboscis is a more or less cylindrical struc- 

 ture at the front end of the body provided with several rows of recurved 

 spines. The neck is a continuation of the proboscis, but is without spines 

 and is sharply set off from the trunk. The trunk forms the principal 

 part of the body and is usually smooth, but may be annulated or spinose. 

 The integument consists of a cuticula and a subcuticula; in the latter is a 

 network of fibers and also large spaces of lacunae, and beneath it are 

 circular and longitudinal muscle fibers. A large body cavity is present. 

 Extending backwards from the base of the proboscis in most forms is the 

 proboscis sheath, a nuiscular sac into which the proboscis can be invagi- 

 nated and thus retracted. In certain forms, however, the sheath is inserted 

 near the middle or fonvard end of the proboscis, in which case it can be 

 only partially retracted or not at all. Extending backwards from the base 



* See "On Nectonema agile Verrill," by II. B. Ward, Bull. Mus. Comp. Zool., Vol. 

 2.'5, p. 1.3.^>, 1892. 



t See "Geschichte und Ergobnisse der Echinorhynsr-hen Forschung," etc., by M. 

 Liihe, Zool. Annalen, Vol. 1, p. 1.39. "Acanthocephalen," by M. Liihe, Siisswasser- 

 fauna Deutschlands, Ileft 16, 1911. 



