Title:
'Discovery' reports
image: of 509
ANTARCTIC AND SUBANTARCTIC MOLLUSCA
Family ASTARTIDAE Genus Astarte Sowerby, 1816 Type-species (subsequent designation, Stoliczka, 1871): Astarte lurida Sowerby Astarte longirostris Orbigny, 1846 (see p. 188, fig. 3, nos. 9-11)
187
A. magellanica Melvill & Standen, 1912, p. 362. A. longirostra Lamy, 1919, p. 90.
A. magellanica Lamy, 1919, p. 91.
A. longirostra Carcelles & Williamson, 1951, p. 333. A. magellanica Carcelles & Williamson, 1951, p. 333. A. longirostris magellanica Carcelles, 1953, p. 216. A. longirostre Powell, 1957, p. 121.
A. longirostra Soot-Ryen, 1959, p. 38.
A. longirostris Powell, 1960, p. 176.
A. magellanica Powell, 1960, p. 176.
Astarte longirostra Orbigny, 1846, p. 576, pi. 83,
figs. 19-22.
Crassina longirostra Chenu, 1862, p. 130, fig. 617.
Astarte magellanica Smith, 1881 a, p. 41, pi. 5, fig. 7.
A. longirostra Smith, 188ib, p. 227.
A. magellanica Smith, 1885, p. 209.
A. longirostris Rochebrune & Mabille, 1889, p. H. 110.
A. magellanica Rochebrune & Mabille, 1889,
p. H. 110.
A. longirostra Dall, 1903a, p. 943.
A. longirostra Dall, 1908, p. 411.
Occurrence: St. 159, South Georgia, 160 m; St. 388, South of Tierra del Fuego, 121 m; WS 85, Falkland Islands, 79 m; WS 88, Falkland Islands, 118 m; WS 228, Falkland Islands, 229-236 m; WS 237, Falkland Islands, 150-256 m; WS 245, Falkland Islands, 304-290 rn; WS 246, Falkland Islands, 267-208 m.
Distribution: Magellan Strait (type of magellanica)-, Tierra del Fuego; Falkland Islands (type of longirostris)-, Prince Edward Island (Smith); Marion Island (Smith); South Georgia; Kerguelen (Powell).
Dall (1908, p. 411) commented as follows: 'The variations of this shell [Astarte longirostris] are considerable. Orbigny figured one with exceptionally long umbones, and the more common mutation with shorter beaks has received the name of A. magellanica from E. A. Smith.' Lamy (1919, p. 91) noted that in both forms the interior borders of the valves are crenulated and not smooth as stated by Smith in his original description of magellanica. He accepted Dall's treatment of the two forms and evaluated magellanica as a variety. Carcelles & Williamson (1951, p. 333) listed magellanica as a subspecies of longirostra using the name trinominally. This would not appear to have been Lamy's intention; varietal usage would certainly fit the situation better as there is no evidence for geographical subspeciation. There is considerable variation in shape, development of sculpture and of interior crenulation in the 'Discovery' material. Some of the variants are figured here. The range of variation amongst shells from the Falkland Islands is such that it seems impossible to differentiate any geographic races on the material available. The earliest available name, longirostris Orbigny, is therefore used to cover all these forms.
A similar dimorphism as regards the crenulation of shell margins occurs in Astarte sulcata da Costa, the form with a smooth shell-margin being much less common. Ostroumoff (1900, p. 499) had postulated that this was a case of sexual dimorphism, but this was shown to be untrue by Sparck (1928), who observed that amongst crenulated specimens both males and females occurred. Sparck suggested that those with smooth margins might possibly be individuals which had grown unusually rapidly. Whatever the cause it seems that in Astarte the presence of smooth and crenulated specimens among the same populations cannot be taken as evidence for specific differentiation.
Facebook Twitter Stumbleupon Delicious Digg RSS