52 



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



Material. 



Fig. 78 Yoldiella perplexa. Lateral view from the right side of the 

 internal morphology of a specimen from Sta. 299 Guyana Basin. 

 (Scale =1.0 mm). For identification of parts see Fig. 34. 



view with little external periostracal extension anterior and 

 posterior to the umbo. 



Prodissoconch length: 177 (xm. Maximum recorded shell 

 length: 3.11 mm. 



Internal morphology (Fig. 78). The combined siphons 

 are well-developed. There is a long thin siphonal tentacle 

 attached to the left ventral side of a moderately deep siphonal 

 embayment. The anterior sense organ is well-developed. The 

 adductor muscles are relatively large; the anterior is bean- 

 shaped and slightly larger than the posterior and which is 

 more round. 



The gills bear up to 16 alternating plates which are distant 

 from the internal limit of the siphons and to which they are 

 joined by long extended axes. The labial palps are relatively 

 small and extend approximately 1/4 distance across body. 

 There are up to 13 palp ridges on the inner face. The palp 

 proboscides are moderately well-developed. 



The foot is also well-developed and anterior in position in 

 preserved specimens. There is a small byssal gland and the 

 pedal ganglia dorsal to the gland are also small. The visceral 

 ganglia are slender and elongate while the cerebral ganglia 

 are slightly larger and more 'club'-shaped. The stomach and 

 style sac are large. The hind gut describes a shallow single 

 loop to the right side of the body. No gonads were seen in the 

 whole mounts. 



Y. perplexa is characterized by a rounded high shell which 

 has a slightly sinuous postero-ventral shell margin. Unlike 

 other high rounded species such a Y. americana and Y. 

 subcircularis it has a simple and not particularly extensive 

 hind gut loop to the right and thus has characters intermedi- 

 ate between Y. lucida or Y. obesa and species such as Y. 

 subcircularis. 



Yoldiella americana (new species) 



Type locality. R.V. Chain Sta. 84, North America Basin, 

 4.7.1965, 36°24.4'N, 67°56.0'W, Epibenthic Trawl, 4749 m. 



Type specimen. Holotype BM(NH) 1992032, Paratypes: in 

 collection held by J.A. Allen. 



Cruise 



Sta 



Depth 



No 



Lat 



Long 



Gear Date 







(m) 













NORTH AMERICA BASIN 











Atlantis II 



12 

 Chain 50 



70 



4680 



190 



36°23.0'N 



67°58.0'W 



ET 



23. 8.64 



77 



3806 



1 



38°00.7'N 



69°16.0'W 



ET 



30. 6.65 





80 



4970 



75 



34°49.8'N 



66°34.0'W 



ET 



2. 7.65 





81 



5042 



9 



34°41.0'N 



66°28.0'W 



ET 



2. 7.65 





83 



5000 



4 



34°46.5'N 



66°30.0'W 



ET 



3. 7.65 





84 



4749 



235 



36°24.4'N 



67°56.0'W 



ET 



4. 7.65 





85 



3834 



4 



37°59.2'N 



69°26.2'W 



ET 



5. 7.65 





86 



3843 



268 



37°59.0'N 



69°18.5'W 



ET 



5. 7.65 



Atlantis II 



92 



4694 



3 



36°20.0'N 



67°56.0'W 



ET 



13.12.65 



17 



93 



5003 



6 



34°39.0'N 



66°26.0"W 



ET 



14.12.65 



Atlantis II 



121 



4800 



66 



35°50.0'N 



65°H.0'W 



ET 



21. 8.66 



24 



122 



4833 



25 



34°50.0'N 

 35°52.0'N 



64°57.5'W 

 64°58.0'W 



ET 



21. 8.66 





123 



4853 



94 



37°29.0'N 



64°14.0'W 



ET 



22. 9.66 





124 



4862 



76 



37°26.0'N 

 37°25.0'N 



63°59.5'W 

 63°58.0"W 



ET 



22. 8.66 





125 



4825 



37 



37°24.0'N 

 37°26.0'N 



65°54.0'W 

 65°50.0'W 



ET 



23. 8.66 



Atlantis II 



175 



4667- 



145 



36°36.0'N 



68°29.0'W 



ES 



29.11.67 



40 





4693 





36°36.0'N 



68°31.0'W 







Chain 106 



330 



4632 



243 



50°43.5'N 

 50°43.4'N 



17°51.7'W 

 17°52.9'W 



ES 



24. 8.72 





331 



4793 



10 



41°13.0'N 

 41°13.2'N 



41°36.7'W 

 41°38.7'W 



ES 



29. 8.72 



ARGENTINE BASIN 













Atlantis II 



242 



4382- 



8 



38<T6.9'S 



51°56.1'W 



ES 



13. 3.71 



60 





4402 















247 



5208- 

 5223 



293 



43°33.0'S 



48°58.1'W 



ES 



17. 3.71 





252 



4435 



1 



38°29.8'S 



52°09.1'W 



ES 



22. 3.71 



GUYANA BASIN 













Knorr 25 



287 



4980- 



12 



13°16.0'N 



54°52.2'W 



ES 



24. 2.72 







4034 





13°15.8'N 



54°53.1'W 









288 



4417- 



45 



11°02.2'N 



55°05.5'W 



ES 



25. 2.72 







4429 





11°03.8'N 



55°04.8'W 







Biovema 



DS03 5150 



3 



10°47.1'N 



42°40.7'W 



DS 



16.11.77 











10°47.1'N 



42°40.3'W 









DS05 5 



28 



10°45.9'N 



42°40.2'W 



DS 



18.11.77 











10°46.8'N 



42°39.8'W 









CO04 510 



1 



10°45.9'N 



42°40.2'W 



CP 



18.11.77 









- 



10°45.9'N 



42°39.3'W 









DS09 5875 



1 



11°36.5'N 



32°51.8'W 



DS 



25.11.77 









- 



1T37.1'N 



32°51.3'W 









DS11 5867 



2 



11°37.5'N 



32°43.8'W 



DS 



26.11.77 









- 



11°37.6'N 



32°52.8"W 







SIERRA LEONE BASIN 













Atlantis II 



139 



2099- 



1 



10°33.0'N 



17°53.0'W 



ES 



4. 2.62 



31 





2187 













Y. americana is found mainly in the deep western Atlantic 

 with a few records to east of the Atlantic Ridge at the western 

 edge of the Sierra Leone Basin. Otherwise the species is 

 recorded from the North America, Guyana and Argentine 

 Basins. Depth range: 2099-5867 m. 



Shell description (Fig. 79). Shell small, ovate, moderately 

 inflated, approximately equilateral; umbos moderately 

 raised, inwardly directed; dorsal margin slightly convex, 

 antero-dorsal margin slopes evenly to join broad curve of 

 anterior margin, ventral margin more convex posteriorly, 



