48 



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





OS01 2634 5 



Sarsia 



S-65 



1922 19 





33/2 



1537- 8 

 1830 





S-44 



1739 68 



Chain 106 



313 



1500- 106 

 1491 





316 



2173- 91 

 2209 



NORTH AMERICA BASIN 



Atlantis II 



73 



1470- 699 



12 





1330 



Chain 50 



87 



1102 354 



Chain 58 



103 



2202 303 



Atlantis II 



115 



2031- 249 



24 





2051 



Atlantis II 



128 



1254 8 



30 



131 



2178 53 



Chain 88 



207 



805- 239 

 811 





210 



2024- 4 

 1064 



ARGENTINE BASIN 



Atlantis II 



239 



1661- 36 



60 





1679 





240 



2195- 1 



240 



2195- 

 2323 



1 



264 



2041- 

 2048 



4 



GUYANA BASirv 



[ 





Knorr 25 293 



2456- 

 1518 



49 



295 



1000- 

 1022 



25 



SIERRA LEONE BASIN 





Atlantis II 142 



1124- 



45 



31 



1796 





145 



2185 



1 



BRAZIL BASIN 







159 



834- 

 939 



1 



167 



943- 

 1007 



4 



169 



587 



6 



CAPE BASIN 







Atlantis II 189 



11007-496 



42 



1014 





190 



974- 

 979 



7 



191 



1546- 

 1559 



2 



Walda DS10 1432 



1 



50°14.4'N 13°10.9'W OS 30. 7.76 



50°15.2'N 13°11.0'W 



46°15.0'N 4°50.0'W ED 25. 7.67 



43°41.0'N 3°36.0'W AD 13. 7.67 



43°40'8'N 3°35'2'W ED 16. 7.67 



51°32.2'N 12°35.9'W ES 17. 8.72 



50°58.7'N 13°01.6'W ES 18. 8.72 



50°57.7'N 13°01.3'W 



39°46.5'N 70°43.3'W ET 25. 8.64 



39°48.7'N 70°40.8'W ET 6. 7.65 



39°43.6'N 70°37.4'W ET 4. 5.66 



39°39.2'N 70°24.5'W ET 16. 8.66 



39°46.5'N 70°45.2'W ES 15.12.66 



39°38.5'N 70°36.5'W ES 18.12.66 



39°39.0'N 70°37.1'W 



39°51.3'N 70°54.3'W ES 21. 2.69 



39°51.0'N 70°56.4'W 



39°43.0'N 70°46.0'W ES 22/23.2.69 



39°43.2'N 70°49.5'W 



36°49.0'S 53°15.4'W ES 11. 3.71 



36°43.4'S 53°10.2'W ES 23. 3.71 



36°12.7'S 52°42.7'W ES 28. 3.71 



8°58.0'N 54°04.3'W ES 27. 2.72 



8°04.2'N 54°21.3'W ES 28. 2.72 



10°30.0'N 17°51.5'W ES 5. 2.67 



10°36.0'N 17°49.0'W ES 6. 2.67 



7°58.0'S 34°22.0'W ES 18. 2.67 



7°58.0'S 34°17.0'W ES 20. 2.67 



- 7°50.0'S 



8°03.0'S 34°23.0'W ES 21. 2.67 



- 8°02.0'S 34°25.0'W 



23°00.0'S 12°45.0'E ES 16. 5.68 



23°05.0'S 12°45.0'E AD 17. 5.68 



23°05.0'S 12°31.5'E ES 17. 5.68 



18°40.0'S 10°56.3'E DS 



Y. curta is probably the most widely distributed species of 

 Yoldiella. It occurs throughout the Atlantic at slope and 

 abyssal rise depths. Depth ranges: 



Brazil Basin 587-1007 m 



Cape Basin 974-1559 m 



Guyana Basin 1000-1518 m 



Argentine Basin 1661-2048 m 



Sierra Leone Basin 1624-2185 m 



North American Basin 805-2178 m 



West European Basin 1537-2634 m 



Shell description (Figs. 71 & 72). Verrill & Bush (1898) 

 give a full and accurate description of this species. Y. curta 

 has a small, smooth, ovate, semi-transparent shell through 

 which the characteristic, indeed unique, course of the hind 

 gut is usually visible. The latter is usually seen as a double 

 strand on the right side of the body with a single loop on the 

 left extending out from the posterior margin of the anterior 

 adductor. The hinge is short with a large internal ligament. 

 The outline of the shell is variable both within (Fig. 73) and 

 between populations. There is no lunule or escutcheon. The 

 hinge plate is very short and slender and does not reach to the 

 level of the inner margin of the adductor muscles. The 

 number of teeth on each hinge plate varies with size up to a 

 maximum of 7. There is usually one more tooth on the 

 posterior hinge plate. The shell may be confused with other 

 species e.g. Y. inconspicua, Y. lucida and Y. frigida, even 

 though the hinge and the hind gut configuration are charac- 

 teristic. 



In general, with increasing length, the height/length ratio 

 increases thus producing a more rounded outline (Figs. 74 & 

 75). The outlines of the anterior and posterior margins are 

 variable. The anterior margin may be smoothly rounded or 

 slightly angular, while the posterior margin is slightly 

 extended with the degree of curvature and the position of the 

 posterior limit in relation to the mid horizontal shell axis 

 somewhat variable. With increasing size shells become more 

 inequilateral with the posterior end slightly elongate. There is 

 also a gradual increase in the width to length ratio. 



Prodissoconch length: 170 u.m. Maximum recorded shell 

 length: 4.77 mm. 



Internal morphology (Figs. 76 a & b). As in other 

 Yoldiella species the mantle is little modified and for the most 

 part unfused. The inner muscular lobe is relatively broad and 

 somewhat folded in preserved specimens. Posteriorly the 

 inner muscular layer fuses to form a relatively wide, thin- 

 walled combined siphon with a single lumen. In one whole 

 mount several faecal pellets lying one on top of the other 

 were seen within the siphon and in one series of sections two 

 faecal pellets one in the dorsal half and one in the ventral half 

 of the siphonal lumen were seen. The gill axes attach laterally 

 close to the ventral margin of the siphon, thus any inhalent 

 componant is probably restricted to the ventral margin. A 

 large siphonal tentacle originates from a pocket in the sipho- 

 nal embay ment at the base of the siphon, usually on the left 

 side. A small secondary muscular mantle fold marks the inner 

 limit of the feeding aperture which in life must extend beyond 

 the shell margin as a pair of flaps. Here the inner mantle lobe 

 is increased in thickness and width and in the preserved 

 contracted state is much folded. The epithelium on the 

 ventral side of the secondary muscular fold, on the dorsal side 

 of the muscular fold, as well as the epithelium between the 

 two, is well supplied with acidophilic gland cells. The gland 

 cells within the epithelium between the folds extend anteri- 

 orly beyond the limit of the feeding aperture for a short 

 distance. The anterior sense organ is well-developed. Over it 

 the middle sensory lobe forms a long thin flap which is 

 well-supplied with glandular epithelial cells. The adductor 

 muscles are large, approximately equal in size with the 'quick' 

 and 'catch' parts clearly visible. The anterior adductor if 

 anything is slightly the larger, it is 'crescent'-shaped in cross 

 section while the posterior muscle is approximately circular. 

 The gills lie comparatively ventral in position within the 



