38 

 50 



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



30 

 80 



60 

 60 



40 



W\L 



H\L 



AA A 



•A A .A 



. .A A * 



PL\TL 



A A 



2 3 



Length (mm) 



Fig. 52 Yoldiella frigida. Variation in ratios of 

 height H/L, width W/L and postero-umbonal length 

 PL/TL to length against length of samples from; 

 open triangles, Sta. 105 North America Basin; 

 closed triangles, Sta. INCAL DS 03 Bay of Biscay; 

 closed circles Sta. 207 North America Basin. 



foot which tends to be largely hidden by palps is also 

 relatively large with well-developed retractor muscles. This is 

 particularly true of the anterior series. There is a moderate- 

 sized byssal gland. The pedal ganglia are elongate each with a 

 large statocyst dorsal to it. The visceral ganglia lie relatively 

 ventral in position, distant from the posterior section of the 

 hind gut. The visceral and the cerebral ganglia are not 

 particularly large. 



The gut describes a single loop on the right side of the 

 body. The size of the hind gut and the path it describes on the 

 right side of the body is highly characteristic of a species even 

 in those with a single loop and is particularly useful in 

 distinguishing, for instance, Y. frigida from Y. inconspicua 

 (Figs. 53 & 63). The oesophagus is particularly wide in 

 cross-section, the stomach is large with two sorting areas 

 clearly visible to the right side of the gastric tooth. The more 

 ventral of the two, which has not been observed in other 



Fig. 53 Yoldiella frigida. Outlines of shells 

 from the right side from three Stations to 

 show variation in shape within and between 

 populations and with increasing size. 

 Specimens from a, Sta. Ingolf 115 (det 

 Ockelmann); b, Sta. 105 North America 

 Basin; c, Sta. INCAL DS 03 Bay of Biscay. 

 (Scale = 1.0 mm). 



species, is broad and close to the aperture of the right 

 digestive duct. Ingested material was seen in the dorsal part 

 of the left digestive diverticulum. The duct to the right 

 digestive diverticulum overlies the dorsal section of the hind 

 gut. The kidney is well-developed and the pericardial cavity is 

 large . 



The sexes are separate. The developing gonads surround 

 the hindgut loop in the usual manner. In one sectioned 

 specimen (2.3 mm total length) 59 ova were present with a 

 maximum diameter of 120 u.m. The ova were present ventral 

 and internal to the digestive diverticula, with fewer numbers 

 overlying the viscera dorsally. 



