81. Sabatieria hilarula de Man, 1922 (fig. 65, G, H). Locality: Aransas Bay, Tex. Reported by: Chitwood, 1951. Other localities: Coasts of Holland, Germany, Norway, France, and North Carolina. Superfamily MONHYSTEROIDEA Stekhoven and de Coninck, 1933

Amphids circular; stoma very diverse; cephalic setae 4 (?), 6, 10, 12, 16, 18, or more; ends of esophageal radii convergent; esophago-intestinal valve usually spheroid to cylindrical; outstretched ovaries. Marine or fresh water.

Family MONHYSTERIDAE Oerley, 1880 Stoma not styletiform; radial muscles of esophagus diffuse, without cuticular attachment points; esophagus cylindrical, without bulb.

Subfamily Monhysterinae Micoletzky, 1922 Cuticle not ridged; stoma not sclerotized, usually conoid; three low lips; papilloid sensory organs of internal circle; usually one anterior outstretched ovary. Marine fresh water.

or

82. Diplolaimella ocellata Chitwood, 1951. Locality: Aransas Bay, Tex.

83. Cytolaimium exile Cobb, 1920. Locality: Biscayne Bay, Fla.

84. Monhystera parva Bastian, 1865. Locality: Cedar Bayou, Tex. Reported by: Chitwood, 1951. Other localities: Northern coast of Europe, Mediterranean and Red Seas.

85. Monhystera socialis Bütschli, 1874 (fig. 65, C, D). Locality: Cedar Bayou, Tex. Reported by: Chitwood, 1951. Other localities: Northern coast of Europe. 86. Monhystera tobagoensis Allgén, 1947. Locality: Tobago, Br. W. Indies.

87. Theristus bütschlioides Chitwood, 1951. Locality: Aransas Bay, Tex.

88. Theristus elaboratus Chitwood, 1951 (fig. 65, I–K). Locality: Copano Bay, Tex.

Subfamily Xyalinae Chitwood, 1951

Cuticle coarsely striated; stoma sometimes sclerotized; cephalic setae 6 plus 12; 6 or 3 (?) lips. Marine. 89. Xenolaimus striatus Cobb, 1920. Locality: Biscayne Bay, Fla.

Family LINHOMOEIDAE Filipjev, 1929

Stoma not styletiform; esophageal radial muscles concentered, often with cuticular attachment points; esophagus usually with distinct bulb. Esophago-intestinal valve usually very large; one or two outstretched ovaries. Usually marine.

Subfamily Linhomoeinae Filipjev, 1929

Cuticle almost smooth; stoma short with weak to moderate sclerotization. Marine.

90. Catanema exile Cobb, 1920. Locality: Port Royal, Jamaica.

91. Anticyathus tenuicaudatus Cobb, 1920. Locality: Miami, Fla.

92. Terschellingia longicaudata de Man, 1907. Locality. Copano Bay, Tex. Reported by: Chitwood, 1951. Other localities: Northern coast of Europe.

93. Monhystrium wilsoni (Baylis, 1915) Cobb, 1920. Locality: Jamaica and Puerto Rico on gills of Gecarcinus ruricola and G. lateralis. Reported by: Baylis, 1915; Cobb, 1920; and Chitwood, 1935. 94. Monhystrium transitans Cobb, 1920. Locality: Jamaica and Puerto Rico, on gills of Gecarcinus ruricola and G. lateralis. Reported by: Cobb, 1920 and Chitwood, 1935.

95. Halinema spinosum Cobb, 1920. Locality: Biscayne Bay, Fla.

96. Metalinhomoeus setosus Chitwood, 1951. Locality: Aransas Bay, Tex.

97. Synonemoides ochra Chitwood, 1951. Locality: Rockport Harbor, Tex.

98. Anticyclus exilis Cobb, 1920. Locality: Bath Tub Springs, Jamaica.

99. Crystallonema fuscacephalum Cobb, 1920. Locality: Miami, Fla.

100. Linhomoella exilis Cobb, 1920. Locality: Biscayne Bay, Fla.

Subfamily Sphaerolaiminae Filipjev, 1924 Stoma cylindrical to globoid, heavily sclerotized. 101. Tripylium carcinicolum (Baylis, 1915) Cobb, 1920. Locality: Jamaica, on gills of Gecarcinus ruricola and Cardisoma guanhumi. Reported by: Baylis, 1915 and Cobb, 1920.

102. Tripylium carcinicolum var. calkinsi Chitwood, 1935. Locality: Puerto Rico, gills of Gecarcinus lateralis. 103. Halanonchus macrurus Cobb, 1920 Locality: Biscayne Bay, Fla.

GEOGRAPHIC DISTRIBUTION

Very few of the species thus far described from the Gulf and adjoining areas have been encountered by more than one worker so that discussions of geographic distribution are liable to considerable error. Spilophorella paradoxa has been reported from numerous localities on the coast of northern Europe, the North American Atlantic coast from Massachusetts to North Carolina, as well as from Tobago, British West Indies, and Aransas Bay, Texas. Syringolaimus smarigdus has been reported from Massachusetts and Texas. Both feed on algae, and it may be that their distribution is governed by the movement of the algae in oceanic currents. Onchium ocellatum was reported from Massachusetts and Florida, and Alaimella cincta was reported from Florida and Texas. Two species were reported as associates of land crabs in Jamaica and Puerto Rico, though the species of hosts appear to differ in the two localities. Two species were reported from North Carolina and Texas, seven species from Europe and Texas and seven species from Europe and Tobago, British West Indies. A

single species was reported from Sumatra and Texas.

Due to the scarcity of qualified American workers the fauna of the European coasts is far better known than the Gulf fauna, and this probably explains the predominance of European forms among species recorded from more than one locality. Allgén (1947b) reported numerous species from the western coast of North America, and these differ from the eastern fauna, as would be expected.

ECOLOGY AND LIFE HABITS

Most marine nematodes are bottom dwellers or live in association with algae, sponges, colonial hydroids, bryozoa, mollusks, decapods, ascidians, and others. Because of their inability to swim freely for long periods of time, they are never typically planktonic (i. e. holoplanktonic). A few nematodes appear capable of directed movement; monhysterids in particular exhibit a very rapid vibratory motion in which the body may appear as an ellipse with two processes at each end, but the worms cannot sustain these swimming movements for more than several seconds. Most nematodes have a slow serpentine motion which is rather ineffective in locomotion without the aid of a substrate for leverage. In their true habitat, however, locomotion is quite efficient (e. g., oncholaims can move rapidly among filamentous algae). Bottom dwellers are usually confined to a sharply restricted local area.

Many European workers, notably Micoletzky and Stekhoven, have paid considerable attention to ecological considerations, e. g., the association of certain species with certain types of bottoms, the frequency of species in a certain habitat, etc. The largest nematode population is to be found in mud rich in organic debris. Stekhoven has estimated that 500-600 nematodes per cubic centimeter may be found in such a bottom. Saprophagous species, carnivores, and algivorous and diatomivorous species abound here. here. In highly aerated regions such as breakwaters or surf-beaten rocks there is a rich fauna of algivorous species.

There are numerous references in the literature to the food of nematodes among the genera reported from the Gulf of Mexico. Monhysterids and chromadorids in general feed on algae and diatoms; Monhystera and Euchromadora feed

especially on algae-unicellular and filamentous; and Theristus on diatoms. The diatoms may be almost half the diameter of the body. In the anterior of the intestine they are filled with bright green pigment, but when the shells are rejected through the anus they usually contain only a small amount of unabsorbed brownish yellow pigment, proving that the diatoms are actually being utilized as food. Chitwood (1951) presumes that Paranticoma longicaudata feeds on algae because of elongate, irregular, greenish masses in the lumen and similarly colored cell inclusions. Halichoanolaimus has been reported several times as predatory on other nematodes. The genus Halenchus belongs to a group primarily parasites of terrestrial angiosperms, but the species H. fucicola, first described by de Man (1892), is a parasite of the brown alga, Fucus. Such nematodes have a strictly liquid diet, inserting their hollow oral stylet into plant cells and predigesting the contents to some extent. It would be interesting to ascertain the host plant for H. mexicanus described from the Gulf of Mexico (Chitwood 1951).

Herbivorous species may usually be recognized as such by the pigments present either in the intestinal lumen or as cell inclusions. Timm (1951) has reinvestigated such cell inclusions in Syringolaimus smarigdus which Cobb (1928) first found associated with the common mud snail, Nassa obsoleta. Cobb had reported that Syringolaimus was feeding on an encrusting orange alga of the genus Ralfsia growing on the shell of the snail, but Timm showed by chemical tests of the cell inclusions and contents of the lumen that this worm feeds rather on the filamentous green alga which forms a thick felt mat on the shell of Nassa. The junior author has likewise observed the feeding of Chromadora quadralineoides obtained in the living state from Chesapeake Bay off Solomons Island, Maryland. This nematode was found in great abundance in association with the bright red sponge, Microciona prolifera. Some worms were apparently feeding off the epidermal substance of the sponge through the action of their three, fine teeth, because bright red, finely divided particles were observed in the intestinal lumen. After 2 months in an unaerated aquarium the sponges had died, but the chromadorids were still thriving on small algae trapped by the coarse skeleton of the sponge.

As a general rule, four molts occur in the development of the parasitic and terrestrial free-living nematodes thus far observed, but there has been no formal study on the life cycle of any of the marine nematodes. Neither has the embryology of any marine nematode been worked out. We have recently observed the first three cleavages of Euchromadora vulgaris collected at Woods Hole, Massachusetts. In this species the first two cleavages appear to be equal, while the third cleavage is quite unequal in the derivatives of one of the first two blastomeres. The few published illustrations of nemic embryos in aphasmideans would appear to indicate differences from the established pattern in the Phasmidea. This should be an interesting field of investigation. Most species produce relatively few eggs; 1 or 2 fully formed eggs per uterus is the rule in small forms such as Monhystera and Chromadora, but some of the larger forms such as Oncholaimus may contain up to 20 mature eggs per uterus. The number of eggs is characteristic of the species. Eggs may be deposited in the one cell condition or in various stages of development, and a few viviparous marine nematodes have been reported.

Saline content of the water in which the marine nematodes live must be an important factor in their life, since there is practically no overlapping between marine and fresh-water inhabitants. Attempts to acclimate marine nematodes to fresh water, and vice versa, have been unsuccessful. Rhabditis marina has recently been found on decaying seaweed along the beach at Woods Hole, Massachusetts. This form has been cultured with bacteria on nutrient agar made up with either sea water or tap water. Specimens taken from either substrate may be transferred directly to tap water or sea water. Both rhabditids and tylenchids are usually soil or fresh-water inhabitants. Study of their osmotic relations should prove interesting. In the Nematoda, as in the Protozoa and Turbellaria, the excretory system is best developed in fresh-water and soil groups (Phasmidea) and less well developed in the marine groups (Aphasmidea). A study of estuarine forms would probably be very helpful in determining the conditions of transition from a marine to a fresh-water biotope.

On the other hand, the influence of oxygen tension is probably not so important as has been surmised. Chitwood and Chitwood (1938) concluded that Chromadora quadralineoides and Oncho

laimium oxyure var. domesticum were highly oxygen loving, since they were found in abundance on an aquarium aerator. However, we have cultured the former species for 2 months and the latter for an entire year in small unaerated aquaria. Probably they are able to help satisfy their oxygen requirements from the green algae on which they feed. Few appear to be adapted to anaerobic life. LITERATURE CITED

ALLGEN, C. A.
1947a. Papers from Dr.

Th. Mortenson's Pacific Expedition, 1914-1916, on some free-living marine Vidensk. nematodes from Tobago (Br. W. I.). Medd. Dansk. Naturl. Foren-Copenhagen 110: 45–63. 1947b. Idem. West American marine nematodes. Ibid. 110: 65-219.

BAYLIS, H. A.

1915. Two new species of Monhystera (nematodes) Ann. inhabiting the gill-chambers of land crabs. & Mag. Nat. Hist., ser 8 (95), 16: 414-421, figs. 1-6. CHITWOOD, B. G. 1935. Nematodes parasitic in, and associated with Crustacea, and descriptions of some new species and a new variety. Proc. Helm. Soc. Washington 2 (2): 93-96, fig. 22.

1951. North American marine nematodes. Texas Jour. Sci. 3 (4): 617-672, figs. 1–15.

and CHITWOOD, M. B.

1938. Notes on the "culture" of aquatic nematodes. Jour. Washington Acad. Sci. 28 (10): 455–460. 1950. An introduction to nematology.

213 pp.

Совв, N. А.

Sec. J. Anatomy,

1912. Further notes on Tricoma. Jour. Washington Acad. Sci. 2 (20): 480–484, figs. 1-2.

1920. One hundred new nemas. Contr. Sci. Nematol. (9): 217-343, figs. 1-118c.

1928. A new species of the nemic genus Syringolaimus with a note on the fossorium of nemas. Jour. Washington Acad. Sci. 18 (9): 249–253, figs. 1-3. DE MAN, J. G.

1892. Ueber eine neue, in Gallen einer Meersalge lebende Art der Gattung Tylenchus Bast. Festschr. 70 Geburtst. R. Leuckarts, 121-125, 3 figs., pl. 16, figs. 1-14.