314 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



The most conspicuous element of the nervous 

 system is the circum-esophageal commissure or 

 nerve ring. From it six main nerves run forward 

 and innervate the cephaUc sensory organs. Four 

 or more nerves extend posteriad from the nerve 

 ring; of these, one is situated in the dorsal chord, 

 a purely motor nerve; one or more pairs of sensory 

 nerves are situated in the lateral chords; and a 

 single or partially paired nerve is situated in the 

 ventral chord. The latter is the chief nerve of 

 the body, contains ganglion cells, and serves as 

 both a motor and sensory nerve. It may also 

 act as an associational center. Various com- 

 missures connect the longitudinal nerves. Somatic 

 sensory organs and genital papillae are served by 

 the lateral nerves and connect with the ventral 

 nerve through the commissures. 



A more extensive account of nematode anatomy 

 in general and of the various groups in particular 

 can be obtained from An Introduction to Nema- 

 tology, by Chitwood and Chitwood (1950). 

 Identification of a large number of marine forms 

 can be had from the lengthy studies of Steklioven 

 (1935) and W. Schneider (1939). 



HISTORICAL RESUME 



Nematodes of the Gulf of Mexico have received 

 only scant attention. For this reason we have 

 included records of marine nematodes from waters 

 adjoining the Gulf. These total 103 species 

 representing most of the major groups of marine 

 nematodes but probably not over 5 percent of 

 existent forms in the Gulf area. The first report 

 of a nematode from the Gulf was that of Tricoma 

 major by Cobb (1912) from Jamaica. Thereafter, 

 Baylis (1915) reported 2 further species from 

 Jamaica, commensals of the land crab, Gecarcinus 

 ruricola; Cobb (1920) reported 13 species from 

 Jamaica and 29 species from the Florida coast; 

 Chitwood (1935) reported 3 species from Puerto 

 Rico; Allgen (1947a) reported 15 species from 

 Tobago, British West Indies; and Chitwood 

 (1951) reported 47 species from the Texas coast. 

 All the species reported by Cobb were new, 33 

 of the 47 species from Texas were new, and 7 of 

 the 15 species from Tobago were new. From 

 these figures it is quite obvious that the nematode 

 fauna of the Gulf of Mexico is quite unexplored. 

 The following checklist is a classified summary of 

 the species reported in the literature. 



CLASSIFIED LIST OF SPECIES REPORTED FROM THE GULF OF MEXICO AND ADJACENT 



WATERS 



Class Phasmidea 



Phasmids present; caudal and hypodermal glands 

 absent; lateral excretory canals present; terminal ex- 

 cretory duct sclerotized; amphids pore-like. 



Order RHABDITIDA 



Esophagus in three sections. 



Suborder Tylenchina 



Stylet present. 

 Superfamily 



TYLENCHOIDEA Chitwood and 

 wood, 1937 



Chit- 



Dorsal gland orifice near base of stylet. 



Family TYLENCHIDAE FiHpjev, 1934 



Cuticle usually thin, striation moderate to faint; stylet 

 not greatly enlarged; esophageal metacorpus not enlarged. 

 1. Halenchus mexicanus Chitwood, 1951 (fig. 63, A). 

 Jyocality: Aransas Bay, Tex. 



Class Aphasmidea 



Phasmids absent; caudal and hypodermal glands usually 

 present; lateral excretory canals absent; terminal ex- 

 cretory duct seldom sclerotized; amphids usually ex- 



ternally modified, pocket-like, circular, spiral, ellipsoid, 

 or vesiculate. 



Suborder Enoplina 



Stylet absent; cephalic sensory organs usually setose; 

 caudal glands generally present. 



Superfamily TRIPYLOIDEA Chitwood, 1937 



Cuticle of head not duplicate. Mostly fresh water. 



Family IRONIDAE de Man, 1876 

 Stoma cylindrical. 



Subfamily Irotiinae Micoletzky, 1922 



Esophageal gland orifices at stomatal region. 



2. Trissonchtdus oceanus Cobb, 1920. Locality: Miami, Fla. 



3. Trissonchulus reversus Chitwood, 1951 (fig. 63, F. G). 



Locality: Aransas Bay, Tex. 



Family ENOPLIDAE Baird, 1853 



Stomatal region surrounded by esophageal tissue; 

 stomatorhabdions weakly sclerotized ; no distinct stomatal 

 capsule. 



Subfamily Leptosomatinae Micoletzky, 1922 



Amphids pocket-like; mandibles absent; esophagus 

 usually cylindrical, rarely conoid; posterior part of 

 esophagus muscular. 



