Umbilia hesitata f. portlandensis

The extreme western Umbilia hesitata - a new subspecies?

by Felix Lorenz

Among the top twenty of the cowry-collector's favorites is certainly Umbilia hesitata and related taxa. Therefore, anything new that can be reported should be reported. In this case, I would like to discuss a set of shells I have obtained from Portland, Victoria. That area is the western limit of the species' distribution from what I know (see map 1), and the shells all show a set of consistent morphological characteristics that are noteworthy.

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Map 1: the distribution of U. hesitata along the coast of Victoria and NSW. "A" points at Portland, Victoria at the western extreme of the species' distribution.

Because different shells should have different names, and also because we have all agreed that  all this internet-dribbling has no scientific relevance (opposed to printed word), I am herewith proposing the following preliminary status:

Umbilis hesitata f. portlandensis nov.

Material: four shells trawled at unknown depth off Portland, Victoria (Fig. 4).

Compared to typical U. hesitata from the adjacent Bass Strait and Tasmania, the Portland shells have the following features separating them:

1) the posterior extremity is unproportionally short (Fig. 1 arrow 1)
2) the anterior dorsal depression is much deeper than in typical hesitata (Fig. 1 arrow 2) and the canal is shorter.
3) the general outline is different: in typical hesitata, there is a distinct step between the dorsal dome and the anterior extremity, in hesitata f. portlandensis the transition dorsum-extremity is gradual. The base is more convex in f. portlandensis (Fig. 2)
4) the spire is flattened and the protoconch is situated just above the posterior extremity in f. portlandensis, whereas in typical hesitata it is larger, perfectly circular and the protoconch is situated higher above the extremity (Fig. 3)
5) the four specimens of f. portlandensis are dramatically more heavy than any typical hesitata available for study.

These differences are consistent when typical hesitata of similar size from Bass Strait and Tasmania are compared. Very small hesitata (var. beddomei) tend to have shorter extremities resembling the f. portlandensis shells, but the features 2, 3 and 4 are rather obvious still, apart from the size.

Certainly, more shells with ascertained locality data are needed to clarify if U. hesitata can be split in a western and eastern subspecies.

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Fig. 1: On left: Umbilia hesitata typical from Bass Strait. Right: U. hesitata f. portlandensis

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Fig. 2: Shell profiles.  Top: hesitata f. portlandensis, bottom: typical hesitata.

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Fig. 3: Spire-position. On left: Umbilia hesitata typical. Right: U. hesitata f. portlandensis

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Fig. 4: Umbilia hesitata f. portlandensis nov.
Top: 94,6 mm. Middle: 82,8 mm. Bottom: 78,3 mm

© Felix Lorenz 2010