DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



LI ST 



29 



PG BG 



Fig. 34 Yoldiella sinuosa. Lateral view 

 from the right side of the internal 

 morphology of a specimen from Sta. 299 

 Guyana Basin. (Scale = 1.0 mm). 



orly on either side of the stomach, anterior to the lateral 

 pedal retractor muscles. It also pentrates the foot posterior to 

 the stomach. 



Only male specimens were observed in which the testes 

 were restricted to the anterior dorsal and ventral limits of the 

 viscera. 



Yoldiella sinuosa is characterized by its slightly sinuous 

 postero-ventral shell margin and the s-shaped course of the 

 hind gut (see p. ). 



Yoldiella blanda (new species) 



Type locality. R.V. Atlantis II, Cruise 60, Sta. 247, 

 Argentine Basin, 17.3.1971, 43°32.0'S, 48°58.1'W, 

 Epibenthic Trawl, 5208-5223 m. 



Type specimen. Holotype: BM(HM) 1992020, Paratypes: in 

 a collection held by J. A. Allen. 



Material. 



Cruise Sta Depth No Lat Long Gear Date 



(m) 



ARGENTINE BASIN 



Atlantis II 242 4382- 119 38°16.9'S 51°56.1'E ES 13.3.71 

 60 4402 



245 2707 1 36°55.7'S 53°01.1'E ES 14.3.71 

 247 5208- 106 43°33.0'S 48°58.1'E ES 17.3.71 



5523 

 252 4435 42 38°29.8'S 52°09.1'E ES 22.3.71 

 256 3906- 63 52°19.3'S 52°19.3'E ES 24.3.71 



3117 

 259 3305- 20 37 < T3.3'S 52°45.0'E ES 26.3.71 



3317 



50r 



W/L 



H/L 



40 



70 

 60 



60r- 

 PL/TL 



40 L 



• • «• 



. . / 





Length(mm) 



n 

 4 



j This species is restricted to abyssal depths in Argentine 

 I Basin. Depth range: 2707-5223 m. 



Shell description (Figs. 36 & 37). Shell ovate, laterally 



Fig. 35 Yoldiella sinuosa. Variation in the ratios of height H/L, 

 width W/L, and post-umbonal length PL/TL to length against 

 length of a subsample from Sta. 299 Guyana Basin. 



compressed, fragile, slightly inequilaterial; umbos small, not 

 markedly raised or inflated, slightly anterior to the mid line; 

 antero-dorsal, anterior and ventral margins, evenly curved, 

 postero-dorsal margin slopes in almost straight line from 

 umbo, anterior and posterior limits dorsal to mid horizontal 

 line; hinge plate moderately strong, parallel to dorsal margin, 

 anterior and posterior series of teeth equal in number; 

 ligament amphidetic and extends slightly below hinge plate 



