DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



47 



Basin at shelf slope break and upper slope depths. Depth 

 range: 497-1679 m. 



Shell description (Fig. 69). Shell small, subovate, 

 approximately equilateral, relatively compressed, 'boat- 

 shaped' in outline except for fine concentric lines, smooth, 

 iridescent; umbos inflated, inwardly directed; anterior and 

 posterior dorsal margins concave proximal to umbo, distal to 

 umbo slightly convex, slope gradually to anterior and poste- 

 rior margins, anterior margin slightly produced, ventral mar- 

 gin broadly curved, more convex posteriorly to slightly 

 produced, posterior margin; horizontal axis supramedial; 

 hinge plate short, teeth small, 'V'-shaped, proximal teeth 

 very small, difficult to discern, 6 anterior and 6 posterior in 

 individual 3.66 mm long; ligament amphidetic, large with 

 long, narrow, secondary external anterior and posterior 

 extensions. 



Prodissoconch length: 150 u.m. Maximum recorded shell 

 length: 4.03 mm. 



The shape of the shell is similar to that of Yoldiella 

 inconspicua s.s. The main differences include the marked 

 proximal concavities of the dorsal margin, the more inflated 

 umbos and detail of the hinge. 



Internal morphology (Fig. 70). There is a wide combined 

 siphon with a single lumen. The siphonal tentactle lies to the 

 left side of the siphonal embayment. A feeding aperture is 

 present ventral to the combined siphon. The adductor 

 muscles are slightly unequal in size, in cross-section the 

 posterior is broadly oval in outline while the larger anterior 

 muscle is 'bean'-shaped. 



The foot is well-developed and there is a large byssal gland 

 in the heel. The gills are well-developed with between 10-17 

 alternating filaments (the number varying with the size of the 

 individual). The labial palps are of moderate size, extending 

 approximately one third across the body with between 10-18 

 internal ridges. The hind gut forms a single loop on the right 

 side of the body (Fig. 70). 



Yoldiella curta Verrill & Bush 1898 



Type locality. North America Basin, 40°16.5'N, 

 67°05.3'W. 1290 fm. Original specimens were taken from the 

 North America Basin between 41°11.5'N, 66°12.3'W and 



39°38'N - 70°22'W by U.S. Fish Commission Steamer Alba- 

 tross, 5.10.1883, Beam Trawl. 



Type specimen. Holotype U.S. Natl. Mus. No. 38457. 



Phaseolus ovatus Verrill 1884, p. 230. 



Yoldia jeffreysi Verrill 1884, p.229; Verrill 1885, p. 576. 



Yoldia curta Verrill & Bush 1898, p. 868, pi. 97, Fig. 8; 



Waren 1989, p. 244. 

 Yoldiella miniscula Verrill & Bush 1898, p. 870, pi. 79, Figs. 



2, 7; Waren 1989, p. 244, Figs. 14 A & B. 



Although a very well-defined species in that it is the only 

 known Yoldiella with the hind gut configuration described 

 below (p. 51), in its shell shape it is very similar to a number 

 of other species. We believe that Y. miniscula Verrill & Bush 

 is synonymous with it, indeed Verrill & Bush (1898) state this 

 latter very minute species may, with a larger series, prove to 

 be the young of one of the preceding species they describe. 

 These latter include Y. inconspicua, Y. pachia, Y. lucida, Y. 

 iris, Y. inflata, Y. subangulata, Y. lenticula and Y. curta. 

 Verrill & Bush (1898) were correct in their supposition and 

 here we illustrate specimens of Y. miniscula to show their 

 similarity (Fig. 71). 



Note. The holotype specimen of Y. miniscula (U.S. Natl. Mus. 

 No. 38415) is from the same Station as the holotype of Y. curta. 



Material. 



Fig. 70 Yoldiella argentinensis . Lateral view from the right side of 

 the internal morphology of a specimen from Sta. 237 Argentine 

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

 34. 



Cruise 



Sta DepthNo 

 (m) 



Lat 



Long 



Gear Date 



WEST EUROPEAN BASIN 











La Perlc 



DS06 



1 











(Biogas 1) 



DS07 



4 













DS12 2180 



1 



47°28.5'N 



8°35.5'W 



DS 



9. 8.72 





DS13 2165 



15 



47°33.7'N 



8°39.9'W 



DS 



9. 8.72 



Jean Charcot 













(Polygas) 



DS25 2096 



16+6v 44°08.2'N 



4°15.7'W 



DS 



1.11.72 





DS26 2076 



2 



44°08.2'N 



4°15.0'W 



DS 



1.11.72 





CV10 2108 



2v 



47°30.7'N 



8°40.6'W 



CV 



22.10.72 



(Biogas 11) 



DS32 2138 



4 



47°32.2'N 



8°05.3'W 



DS 



19.4.73 



(BiogasIII) 



DS36 2147 



5 

 (1 em 



47°32.7'N 

 )ty 4 dried) 



8°36.5'W 



DS 



24. 8.73 





DS38 2138 



7+2v 



47°32.5'N 



8°35.8'W 



DS 



25. 8.73 





DS49 1845 



4+4v 



44°05.9'N 



4°25.6'W 



DS 



1. 9.73 



(Biogas IV) 



DS52 2006 



2+4v 



44°06.3'N 



4°22.4'W 



DS 



18. 2.74 





DS61 2250 



1 



47°34.7'N 



8°38.8'W 



DS 



25. 2.74 





DS62 2175 



10 



47°32.8'N 



8°40.0'W 



DS 



26. 2.74 





DS63 2126 



19+2v 47°32.8'N 



8°35.0"W 



DS 



26. 2.74 





DS64 2156 



7+4v 



47°29.2'N 



8°30.7"W 



DS 



26. 2.74 



(Biogas V) 



CP07 2170 



3 



44°09.8'N 



4°16.4'W 



CP 



21. 6.74 



(Biogas VI) 



DS71 2194 



7 



47°34.3'N 



8°33.8'W 



DS 



20.10.74 





DS86 1950 



28 



44°04.8'N 



4<T8.7'W 



DS 



31.10.74 





DS87 1913 



7 



44°05.2'N 



4°19.4'W 



DS 



1.11.74 







(13+8v) 











DS88 1894 



5 



44°05.2'N 



4°15.4'W 



DS 



1.11.74 



Jean Charcot CP08 2177 



3 



44°33.2'N 



8°38.5'W 



CP 



20.10.74 



(Biogas VI) 



CP09 2171 



1 



47°33.0'N 



8°44.1'W 



CP 



20.10.74 



Jean Charcot CP01 2068- 



38 



57°57.7'N 



10°55.0'W 



CP 



16. 7.76 



(Incal) 



2040 





■ 57°56.0'N 



10°55.0'W 









CP02 2091 



4 



57°58.4'N 

 ■ 57°57.7'N 



10°42.8'W 

 10°44.6'W 



CP 



16. 7.76 





DS01 2091 



468 



57°59.7'N 

 ■ 57°59.2'N 



10°39.8'W 

 10°41.3"W 



DS 



15. 7.76 





DS02 2081 



544 



57°58.5'N 

 ■ 57°58.5'N 



10°48.5'W 

 10°49.2'W 



DS 



16. 7.76 





DS05 2503 



2 



56°28.1'N 

 ■ 56°27.6'N 



11°11.7'W 

 11°12.0'W 



DS 



18. 7.76 





DS06 2494 



6 



56°26.6'N 

 56°25.9'N 



11°10.5'W 

 11°10.7'W 



DS 



18. 7.76 



