PREVIOUSLY REPORTED HABITAT: 20 m; sand and broken shell. 



GULF OF MEXICO BLM-OCS OCCURRENCE: Two stations off Appalachicola , 



Florida, and one off southwestern Florida (Figure 30-53); 19-24 m; 



coarse to medium-fine sand, silty fine sand. 



DISTRIBUTION: North Carolina, Gulf of Mexico. 



Genus Opisthodonta Langerhans, 1879 



TYPE SPECIES: Opisthodonta morena Langerhans, 1879. 

 REFERENCES : 

 Fauvel, 1923:273. 

 Fauchald, 1977a:83. 



DIAGNOSIS: Prostomium with three antennae. Nuchal organs as large 

 ciliated ridges between prostomium and peristomium. Two pairs of ten- 

 tacular cirri. Antennae, tentacular, and dorsal cirri smooth and slen- 

 der. Pharynx armed with a large, dorsal, posterior tooth. 



Key to the Gulf of Mexico BLM-OCS Species of Opisthodonta 



la. Spiniger-like composite setae absent; terminal tooth of bidentate 

 composite falcigers nearly as large as subterminal tooth, blades 

 without hoods (Figure 30-56b,c). . . .Opisthodonta sp. A, p. 30-62 



lb. Spiniger-like composite setae present (Figure 30-58b); terminal 

 tooth of bidentate composite falcigers much smaller than subtermi- 

 nal tooth, blades with hoods (Figure 30-58c,d) 



Opisthodonta sp. B, p. 30-64 



Opisthodonta sp. A 

 Figures 30-55, 56a-f 



MATERIAL EXAMINED: 

 Gulf of Mexico BLM-OCS: 



MAFLA 2207D-7/76 (1 spec), 2207D-8/77 (1 spec), 2207F-11/77 (1 spec, 

 USNM 65679), 2211F-11/77 (1 spec), 2211K.-11/77 (1 spec), 2212G-7/76 (1 

 spec), 2315A-11/77 (2 spec), 2316C-11/77 (1 spec), 2422E-7/76 (1 

 spec), 2528D-8/77 (4 spec), 2533A-6/75 (1 spec), 2644D-9/75 (1 

 spec), 2645F-11/77 (3 spec). 

 DESCRIPTION: 



Length, 5.0+ mm; width, to 0.7 mm. Body stout anteriorly, slender 

 posteriorly; all specimens incomplete with up to 31 setigers. Prosto- 

 mium oval, with four lentigerous eyes, variable in size, in trapezoidal 

 arrangement; with or without two ocular spots at base of palps (Figure 

 30-56a). Antennae smooth, median antenna about twice as long as lateral 

 antennae. Palps large, directed ventrolaterally. Dorsal cirri slender, 

 alternating long and short. Ventral cirri auricular, extending beyond 

 parapodia anteriorly. Anterior parapodia with large setal fascicles. 

 Composite setae including 2-4 superior falcigers having moderately long 

 bidentate blades (Figure 30-56b), and numerous other falcigers having 

 shorter bidentate blades (Figure 30-56c). All falcigers with distal 

 teeth similar in size, and base of blades articulating in excavate 

 shaft-heads. Setae decreasing in number toward midbody region. Pos- 

 terior parapodia with slender, minutely bifid superior simple seta 



30-62 



