44 



J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



Fig. 65 Yoldiella inconspicua africana. 

 Outlines a, of a shell from the right side 

 and a left valve to show detail of the 

 hinge-plate from Sta. 8532 6 Cape Verde 

 Basin and b, two shells from the right 

 side from Sta. 201 Angola Basin. (Scale 

 = 1.0 mm). 



body. A large well-developed kidney extends anteriorly close 

 to the posterior limit of the diverticula. 



The sexes are separate. The gonads lie dorsal and ventral 

 to the viscera and anteriorly they occur internal to the 

 digestive diverticula. A female 2.8 mm in length collected in 

 July (Incal CP 07) contained 255 closely packed ova with a 

 maximum diameter of 132 u,m. 



Yoldiella inconspicua africana (new subspecies) 



Type locality. R.V. Atlantis II, Cruise 42, Sta. 201, 

 Angola Basin, 23.5.1968, 9°25'S, 11°35'E to 9°29'S, 11°34'E, 

 Epibenthic Trawl, 1964 m. 



Type specimen. Holotype BM(NH) 1992039, Paratypes: in 

 collection held by J.A. Allen. 



Material. 



Cruise 



Sta Depth 



No 



Lat 



Long 



Gear Date 





(m) 













SIERRA LEONE BASIN 













Atlantis II 



145 2185 



29 



10°36.0'N 



17°49.0'W 



ES 



6.2.67 



31 



147 3984 



5 



10°38.0'N 



17°52.0'W 



ES 



6.2.67 



CAPE BASIN 













Atlantis II 



192 2117- 



55 



23°02.5'S 



12°19.0'E 



ET 



17.5.68 



42 



2154 















194 2864 



28 



22°54.0'S 



11°55.0'E 



ET 



17.5.68 



ANGOLA BASIN 















201 1964 



109 



9°25.0'S 

 ■ 9°29.0'S 



11°35.0'E 

 11°34.0'E 



ET 



23.5.68 



CAPE VERDE BASIN 













Discovery 



8521 ' 3058- 



2 



20°46.9'N 



18°53.4'W 



WS 



25.6.74 





3053 





■ 20°47.6'N 



18°53.5'W 









8521 6 3070- 



1 



20°47.9'N 



18°53.4'W 



WS 



26.6.74 





3964 





• 20°48.6'N 



18°53.4'W 









8521 1 3113- 



34 



13°47.8'N 



18°14.0'W 



WS 



4.7.74 





3119 





13°48.0'N 



18°14.8'W 









8532 6 2958- 



12 



13°48.2'N 



18°08.0'W 



WS 



5.7.74 





2952 





■ 13°47.6'N 



18°07.5'W 







Walda 



DS20 2514 



5 



2°32.0'S 



8°18.1'W 



DS 





Y. inconspicua africana is found off the West coast of Africa 

 in the Sierra Leone, Cape Verde, Angola and Cape Basins at 

 lower slope to abyssal depths. Depth range: 1964-3119 m. 



Shell description (Fig. 65). Shell very small, short, rela- 

 tively compressed, ovate wedge-shape, very slightly inequi- 

 lateral, except for some very fine lines shell surface smooth, 

 periostracum pale yellow, iridescent; umbos just anterior to 

 midline, slightly raised; antero-dorsal margin slightly convex, 

 nearly horizontal close to umbos, then curving to slightly 

 pointed anterior margin, ventral margin broadly rounded, 

 often slightly swollen posteriorly, ascending steeply to poste- 

 rior supramedial angle, postero-dorsal margin nearly hori- 

 zontal close to umbo, then slightly convex, sloping gradually 

 to posterior margin; posterior hinge plate narrow; teeth 

 small, oblique v-shape, 4-5 on each hinge plate; ligament 

 short, amphidetic, relatively wide, yoke-shaped, slight exter- 

 nal extension on either side of umbo. 



Prodissoconch length: 166 u.m. Maximum recorded shell 

 length 2.56 mm (Discovery Sta. 8521 b ). 



Internal morphology (Fig. 66). The siphons are com- 

 bined but with a single lumen. The combined siphon is large 

 and long, with relatively thin muscular walls. The single 

 tentacle is large, attached to the right or the left at the base of 

 the siphonal embayment. The feeding aperture is moderately 

 well-developed with a small internal secondary fold. The 

 mantle epithelial in the area of the feeding aperture and 

 anterior to it is well supplied with gland cells, similar to those 

 present in Yoldiella curta (p. 47). The anterior sense organ 

 lies far anterior and is covered dorsally by an extended and 

 particularly well-developed hood derived from the middle 

 sensory lobe. The adductor muscles are slightly unequal in 

 size; the larger anterior muscle is bean-shaped and the 

 posterior is round in outline. The gills are well-developed 

 with up to 12 filaments. The labial palps are relatively large 

 with up to 15 broad ridges on the inner face. The palps extend 

 across approximately one third of the body. The palp probos- 

 cides are long and relatively slender. The foot is well- 

 developed with a deeply divided sole. The byssal gland is 

 moderately small. The ganglia are large. Both cerebral and 



