Aristovasum, Vermeij, 2024

Vermeij, Geerat J., 2024, Shell-based genus-level reclassification of the Family Vasidae (Mollusca: Neogastropoda), Zootaxa 5405 (4), pp. 526-544 : 529-530

Genus Aristovasum gen. nov.

Type species. Turbinella cassiformis Kiener, 1840 ; Recent , Brazil ( Fig. 1 ).

Diagnosis. Shell large, up to a length of 105 mm, solid, spiny; spire one-quarter to one-third total shell length; axial sculpture consisting of short, high, rounded ribs on upper part of last whorl, each bearing one peripheral and one subsutural spine; base with three spiral rows of spines; upper and lower sets of spines separated by sector with thin, high spiral cords bearing adaperturally directed scales; umbilicus absent; aperture relatively broad; outer lip glazed at edge but not abaperturally; posterior end of outer lip with two glazed spines, forming an adult flare to aperture; inner side of outer lip with paired denticles near edge, smooth further within; columella with three or four folds; adapical columellar fold situated just posterior to adapical row of basal spines; tip of siphonal canal dorsally oriented.

Included species. Aristovasum cassiforme Kiener, 1840 (Rio Grande do Norte to Bahia, Brazil), A. chipolense Vokes, 1966 ) (Chipola Formation, Early Miocene, Florida).

Etymology. Greek aristo, best; and Vasum .

Material examined. Aristovasum cassiforme, Vermeij collection, Guarapari, Espirito Santo, Brazil.

Remarks. The new genus Aristovasum comprises a divergent group of tropical western Atlantic species, one ( A. chipolense ) from the Early Miocene of Florida, the other ( A. cassiforme ) from the Recent fauna of Brazil. Diagnostic characters include the posterior flaring of the aperture with two glazed subsutural spines, the present of adaperturally directed scales on central-sector spiral cords, the presence of subsutural spines, the absence of long spiral lirae inside the outer lip, and the absence of an umbilicus. The posterior flare of the aperture differs from the posterior extensions seen in Rhinovasum gen. nov., in which it is a lobe or smooth rounded platform, and Florivasum , in which the outer and inner lip merge seamlessly at the posterior end of the aperture. Volutella shares with Aristovasum a smooth inner side of the outer lip, but it lacks the posterior apertural extension and subsutural spines; moreover, Volutella has an open umbilicus, which is absent in Aristovasum . There are three basal rows of spines in Aristovasum and only one or two in Volutella .

In her monograph, Vokes (1966) recognized that Vasum chipolense (here Aristovasum ) differs from all other American vasids except its likely descendant, A. cassiforme . She also speculated that A. chipolense might be ancestral to Hystrivasum , which shares with Aristovasum the presence of adaperturally directed scales or spines. Hystrivasum differs from Aristovasum by having an open umbilicus and lacking the glazed posterior end of the aperture.

The only account of the biology of A. cassiforme is that of Matthews-Cascon (1985), who showed that the diet of this sand- and grassbed-dwelling species consists of polychaetes and bivalves. The species lives at a depth of three to five meters.

Figures

FIGURE 1. Aristovasum cassiforme (Kiener, 1840) in dorsal (A) and apertural (B) views. Guarapari, Espírito Santo, Vermeij Collection.