. Bulletin of the Natural History Museum Zoology. 20 The subspecies has been long confused with Y. lucida (Waren, 1989) and there is little doubt that records of the latter species from deeper than 1000 m are of Y. obesa incala. In large specimens in particular, elongation and narrowing of the posterior margin together with a slightly upturned distal end of the postero-dorsal margin, resembles Y. lucida. A population from Rockall although similar in outline is rela- tively smaller and less inflated than the Biscay populations. Prodissoconch length: 187-208 (Jim. Maximum recorded shell len
. Bulletin of the Natural History Museum Zoology. 20 The subspecies has been long confused with Y. lucida (Waren, 1989) and there is little doubt that records of the latter species from deeper than 1000 m are of Y. obesa incala. In large specimens in particular, elongation and narrowing of the posterior margin together with a slightly upturned distal end of the postero-dorsal margin, resembles Y. lucida. A population from Rockall although similar in outline is rela- tively smaller and less inflated than the Biscay populations. Prodissoconch length: 187-208 (Jim. Maximum recorded shell length: mm. Internal morphology. Mantle structures are similar to those in Y. obesa , for example the ventral margin of the inhalent siphon is open ventrally, however the feeding aper- ture is not particularly well-developed. The posterior adduc- tor muscle is oval in shape and half the size of the crescent- shaped anterior muscle. There is a large stomach and style sac, and a single loop of the hind gut on the right side of the body. The byssus gland is moderately small. The palp probos- cides are long and palp ridges number up to 21. The gills are well-developed with up to 17 plates present. Points of distinction are as follows:- (1) The umbo in Y. obesa incala is slightly more medial than in Y. obesa (2) The posterior dorsal section of the hind gut loop takes a slightly more anterior course than in Y. obesa (3) The anterior adductor is relatively more ventral in position than in Y. obesa (4) Although the ligament is relatively short and, in many specimens rounded as it is in the North American subspecies, in some specimens the anterior and posterior ends are slightly swollen giving a 'dumb bell' appearance. In a specimen mm length, 281 ova were counted, with a maximum diameter 119 (im. In two specimens less mature, 240 and 387 ova were present in animals measuring mm and mm ALLEN, SANDERS AND F. HANNAH Yoldiella sim
Size: 1661px × 1505px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bhlconsortium, bookcentury1900, bookcollectionbiodiversity, bookl
