Benthobrookula Clarke, 1961

Herbert, David G., 2024, The Vetigastropoda (Mollusca) of Walters Shoal, with descriptions of two new genera and thirty new species, European Journal of Taxonomy 923, pp. 1-119 : 53-54

Genus Benthobrookula Clarke, 1961

Type species

Brookula (Benthobrookula) exquisita Clarke, 1961 (original designation), Recent, South Georgia.

Remarks

There is uncertainty regarding the status of Benthobrookula . Some authors have chosen to rank it as a full genus, distinct from Brookula Iredale, 1912 ( Zelaya et al. 2006), based on the shape and sculpture of the protoconch (exsert and globose with a microscopically pitted surface), whereas others (Schwabe & Engl 2008) considered such differences inconclusive and discouraged the use of Benthobrookula at generic level, pending clarification through further morphological or molecular studies. Accepting that this matter remains unresolved, I believe the illustrations of the shell and protoconch of the type species of Brookula ( B. stibarochila Iredale, 1912 ) provided by Warén (1992) exhibit features sufficiently distinct from those of Benthobrookula to justify their provisional separation. Such features include the much less globose, less exsert and apparently smooth protoconch in Brookula , and the absence of fine spiral lirae on the early portion of the first teleoconch whorl.

Brookula stibarochila is a shallow-water, subtropical species with a characteristic coarsely cancellate sculpture on the early teleoconch whorls, comprising subequal axial and spiral elements. In contrast, species of Benthobrookula occur in deeper water, mostly at higher latitudes and in general the axial sculpture on the apical whorls is much stronger than the spiral sculpture.

The above notwithstanding, Benthobrookula as interpreted by Zelaya et al. (2006) includes a range of species, which despite sharing a similar protoconch morphology, exhibit considerable diversity in shell shape and sculpture. Some, such as Be. pfefferi (Powell, 1951) , closely resemble material from Walters Shoal, yet the type species is somewhat distinct in having a much more depressed, more coarsely sculptured shell, with a wide umbilicus (holotype illustrated by Zelaya et al. 2006: fig. 2). Benthobrookula itself may thus ultimately prove to be composite. The genus Aequispirella Finlay, 1924 is also relevant in this context. This New Zealand taxon has been poorly illustrated in most modern literature, but a good scanning electron micrograph of the type species A. corula (Hutton, 1885) was provided by Kaim (2004), showing a shell with a distinctly elevated profile and a much narrower umbilicus. Resolution of the status and relationships of these taxa, and the species referable to each, will require more in-depth study involving molecular data.

Species of Benthobrookula from Walters Shoal occur primarily on the slopes of the seamount, but two also range into deeper water on the surrounding plain. The material available was mostly associated with sandy substrata, but no specimens were collected alive. The different species can be relatively easily distinguished based on characters associated with shell proportions, rib number and rib slope, as detailed in Table 2 .