. Bulletin of the Natural History Museum Zoology. 38 50 ALLEN, 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 foot which tends to be largely hidden by palps is also relatively large with well-developed retractor muscles. This is particularly true of the a
. Bulletin of the Natural History Museum Zoology. 38 50 ALLEN, 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 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 = 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
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