50 



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



Fig. 73 Yoldiella curta. Outlines of shells of a similar size to show 

 intrapopulation differences in shape. Specimens from Sta. BG IV 

 DS 86 West European Bain. (Scale =1.0 mm). 



5CH 



W/L 



3CH 

 80-1 



h/l . • /•..,•;• 



60 J 

 60- 

 50 



PL/TL 



.v: 



Length (mm) 



Fig. 74 Yoldiella curta. Variation in the ratios of height H/L, width 

 W/L and postero-umbonal length PL/TL to length against length 

 of a sample from Sta. INCAL CP 01 West European Basin. 



Fig. 75 Yoldiella curta. Outlines of shells from the right side to 

 show change in shape with growth. Specimens from Sta. BG I DS 

 13 West European Basin. (Scale = 1.0 mm). 



section of the mid dorsal margin of the body and from there 

 to the anus. A shallow typhlosole is present along the length 

 of the hind gut. Occasional aberrent specimens were 

 recorded with an extra length of gut being accommodated 

 within the general pattern (see Fig. 75). 



The kidney is well-developed. There is a large pericardial 

 cavity but the heart is relatively small with few muscle fibres 

 in the wall of the ventricle. Gonads occur dorsally from the 

 anterior adductor muscle to just posterior to the stomach and 

 in the anterior part of the body internal to the digestive 

 diverticula and hind gut. The sexes are separate. In one 

 sectioned female (2.3 mm) 27 ova were counted and in other 

 specimens (1.8 and 2.1 mm) 69 and 70 ova were recorded 

 respectively. The maximum dimension was 108 |xm. 



This is one of a few deep-water specimens which were 

 brought to the surface alive and from which it was posible to 

 make some observations on the ciliary currents of the mantle 

 and the contained organs. The ciliary sorting mechanisms of 

 the gills, palps, mantle and body were found to be similar to 



