Comprehensive Description

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Description

Trophon mawsoni n. sp., Pl. II, Figs. 6-8.

 

 

Trophon albolabratus: Hedley, 1916, p. 60 (not of Smith, 1875).

 

Zeatrophon "albolabratus Hedley 1916": Finlay, 1926, p. 424.

 

Trophon albolabratus: Tomlin, 1948, p. 228.

 

Trophon n. sp. (No. 1): Powell, 1955, p. 103.

 

When Hedley (1916, p. 60) recorded the Kerguelen Island Trophon albolabratus from Macquarie Island he compared the shells with the New Zealand ambiguus and this influenced Finlay (1926, p. 424) when he proposed Zeatrophon for the New Zealand shell to include in his genus the Macquarie Island "albolabratus" of Hedley, but in doing so he remarked that the Kerguelen shells are probably true Trophon.

 

Well-preserved B.A.N.Z.A.R.E. Macquarie material shows these shells to be true Trophon with a paucispiral asymmetrical protoconch. That of Zeatrophon is polygyrate and narrowly conical.

 

Although the Macquarie shell is now shown to be a true Trophon it is not identical with the Kerguelen albolabratus. Irrespective of length-breadth ratio, which is quite variable, Macquarie shells are always full-bodied whereas Kerguelen ones are deeply excavated basally which gives them a high-waisted appearance. This difference in build results in a relatively smaller aperture and a more prominent and more spirally twisted fasciole for the Macquarie species.

 

In sculpture both have 17 to 18 spiral cords on the body-whorl, but the axial lamellae vary within limits that are very distinctive for each species.

 

In albolabratus the axials are closely spaced, 46-50 on the body-whorl, and enclose rectilinear interspaces that are higher than they are wide, but in Macquarie shells the density of the axials is only about half that, 20-28 on the body-whorl, and this results in interspaces that are much wider than they are high.

 

Three closely related species combine to stretch across the Subantarctic from South Georgia to Macquarie Island. Namely distantelamellatus Strebel, 1908 (South Georgia), albolabratus Smith, 1875 (Kerguelen and Heard Islands) and now mawsoni n. sp. (Macquarie Island). The differences between them are sufficient to warrant full specific status for each.

 

 

Height 46.0 mm.; diameter 28.5 mm. (extra large dead shell).

 

Height 31.0 mm.; diameter 21.5 mm.

 

Height 28.5 mm.; diameter 17.5 mm. (Holotype).

 

 

Banzare Locality: Station 83.

 

 

There were many dead shells in the Station 83 haul, but only a few half-grown and juvenile ones that were in a living or fresh state. The holotype is a well-preserved half-grown shell with 21 axials on the body whorl; the larger figured paratype has 25. Normal adults range between 35 and 40 mm.”

 

 

(Powell, 1957: 142-143)

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© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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