Vasum Röding, 1798

Vermeij, Geerat J., 2024, Shell-based genus-level reclassification of the Family Vasidae (Mollusca: Neogastropoda), Zootaxa 5405 (4), pp. 526-544 : 536-537

Genus Vasum Röding, 1798

Type species. Murex ceramicus Linnaeus, 1758 ; subsequent designation by Wenz 1943 (see also Vokes 1966), Recent, Indo-West Pacific ( Fig. 6 ).

Diagnosis. Shell solid, thick-walled, with low to high spire; maximum length 149 mm ( V. ceramicum ); axial sculpture consisting of short ribs on upper part of last whorl, each bearing two spiral rows of tubercles or spines; two spiral rows of shorter tubercles or spines at base of last whorl; central sector of shell with two primary cords bearing short nodes; umbilicus absent; aperture narrow, not forming channel or lobe posteriorly; outer lip polished at edge and on abapertural side; inner side of outer lip with or without brief or long paired lirae; columella with three or four folds; adapical-most fold just posterior to most adapical spine row at base; siphonal canal short, its tip dorsally recurved.

Included species. Vasum armatum ( Broderip, 1833) , southeast Polynesia; V.ceramicum ( Linnaeus, 1758) , Indian and western Pacific Oceans; V. turbinellus ( Linnaeus, 1758) , Indian Ocean and Red Sea to western Polynesia.

Material examined. Vasum armatum : CAS Fanning Island; Rangiroa Atoll. V. ceramicum : CAS Ras Kandaya, Dar Es Salaam, Tanzania; Militi, Kenya; Vermeij collection: Puntan Laguna, Pagan, Northern Marianas; Agat, Guam; Brumner Island, southeastern Papua New Guinea; Obi, Maluku, Indonesia. V. turbinellus : 74 lots from throughout the species range.

Remarks. The genus Vasum as restricted here is an Indo-West Pacific group of common reef-associated species. It differs from most other vasids by lacking an umbilicus, having the outer lip glazed on its edge and abapertural side, a very narrow aperture without posterior channel, and spines or nodes on all primary spiral cords. The only other similar vasid genus without an umbilicus is Aristovasum , which differs from Vasum by having a posteriorly lobate extension of the aperture and a row of subsutural spines. Vasum lacks the adaperturally directed scales on the spiral cords of Altivasum , Aristovasum , Florivasum and Hystrivasum . The outer-lip glaze extending to the abapertural side is a feature shared with the other Indo-West Pacific genera: Florivasum , Rhinovasum , and Tudivasum , as well as with the Australian Altivasum .

As understood here, Vasum comprises two groups of species: the first including V. armatum and V. turbinellus , the second being V. ceramicum . V. turbinellus as reviewed by Abbott (1959) extends from the Red Sea and East Africa to Queensland, Western Australia, the Ryukyu Islands east to the southern Marianas, Marshall Islands, Johnston Atoll, Fiji, Samoa and Raroia. V. turbinellus is replaced in southeast Polynesia by the smaller, spinier V. armatum .

Morphologically, V. turbinellus exhibits substantial geographic variation, pointing to the possibility that this species is in fact a species complex. The typical form corresponding to the type from eastern Indonesia have seven or eight very high spines on the shoulder angulation, followed below on the last whorl by a spiral row of much shorter spines. I have seen this form ( Fig. 6 ) from localities throughout the Indian Ocean and Red Sea, where it is in fact the only form of the species. It also occurs as the single morph of the species in the Philippines, Palau, Vanuatu, Western Australia, and the Marshall Islands. A second morph is characterized by eight or nine short tubercles at the shoulder angulation followed below by a row of spines of somewhat shorter tubercles, giving a bituberculate effect. This is the only morph I have found at Guam and Saipan in the Southern Marianas, as well as at Johnston Atoll (USNM 699671), the Great Barrier Reef in Queensland, Okinawa in the Ryukyu Islands, New Caledonia, and islands east of Fiji. The Polynesian V. armatum closely resembles this second morph except that the spines in V. armatum are sharper and even shorter.

Whether the geographic variation represents species-level differentiation or environmental effects is presently unknown. It is possible that the second morph of V. turbinellus , with a generally oceanic distribution, lives in more oligotrophic habitats than the form with longer shoulder spines, and that it therefore grows more slowly both in the spiral direction and at resting stages when the spines form and grow. There is a striking parallel with the situation in the rapanine muricid genus Sistrum ; the oceanic S. albolabris (Blainville) has shorter spines than S. ricinus (Linnaeus) from more continental coasts and the shores of large high islands ( Vermeij 2023). As in V. turbinellus , the long-spined forms of Sistrum are the only ones present in the Indian Ocean and Red Sea ( Vermeij 2023).

Vasum ceramicum , type species of Cynodonta Schumacher 1817 , differs from V. turbinellus and V. armatum by having a consistently lirate inner side of the outer lip, a much higher spire, and four strongly protruding crenulations on the outer lip immediately adapical to the row of basal spines. At a maximum length of 149 mm (a specimen from Agat Bay, Guam, in the Vermeij collection), V. ceramicum is the largest species in the genus. At least for now, I agree with Abbott (1959) and Vokes (1966) that the differences between the V. turbinellus group and V. ceramicum are insufficient to recognize Cynodonta as a genus.

Figures

FIGURE 6. Vasum tirbinellus (Linnaeus, 1758) in dorsal (A) and apertural (B) views. Andui Village, Halmahera, Maluku, Indonesia, Vermeij Collection.