Sinetectula, Fraussen & Vermeij, 2021

Fraussen, Koen & Vermeij, Geerat J., 2021, Sinetectula gen. nov., a new genus of Pisaniidae (Gastropoda: Buccinoidea) from the tropical Indian and Pacific Oceans, European Journal of Taxonomy 748, pp. 155-176 : 157-159

Genus Sinetectula gen. nov.

urn:lsid:zoobank.org:act:945AA942-8D54-4869-B958-3B8F14A46D02

Type species

Triton egregius Reeve, 1844 .

Diagnosis

Shell small (maximum length to about 34 mm), sturdy, fusiform, basally constricted; whorls weakly convex, separated by appressed suture; sculpture cancellate, dense, consisting of narrow but high spiral cords and fine axial ribs, spiral cords covered with obscure axial lamellae, spiral interspaces with fine secondary spiral threads or traces of them; subsutural sinus present; outer-lip edge serrated, evenly convex in profile, with fine lirae extending into aperture; parietal knob at the adapical end of the inner lip prominent, accentuating anal notch; columella with two adapical knobs; columellar callus expanded towards base and along siphonal canal, edge slightly flaring, surface sculptured with tiny knobs; siphonal canal open, dorsally weakly recurved.

Radula (only examined for Sinetectula egregia gen. et comb. nov.) (see Fig. 1Q ) with tricuspid rachidian tooth; base rectangular, weakly arched; with minute cusps. Lateral teeth tricuspid; base protruding at inner side; outer cusp dominant, inner cusps close together, median cusp thin.

Etymology

Sinetectula gen. nov. is derived from the Latin ‘ sine ’, meaning ‘without’ in combination with ‘ tectula ’, meaning ‘little roof’, or, in other words, ‘little homeless’. This also conjures up the contrast with the appearance of these small shelled gastropods that have, in reality, their home always with them. It also conjures up the contradiction that appears by virtue of the etymology by turning the ‘little homeless’ into ‘not homeless’, now that the name comes into existence.

Included species

Triton egregius Reeve, 1844 , Buccinum cinis Reeve, 1846 , Buccinum (Pollia) farinosum Gould, 1850 , Pisania naevosa Martens, 1880 , Buccinum nigricostatum Reeve, 1846 and Pollia shepstonensis Tomlin, 1926 . In addition, we add one still undescribed species.

We did not study Tritonidea castanea Melvill, 1912 from the Persian Gulf or Pisania townsendi Melvill, 1918 from Pakistan, two species that share characteristics with Sinetectula gen. nov.

Remarks

Cernohorsky (1975: 191) tentatively placed Triton egregius and Buccinum (Pollia) farinosum , here assigned to Sinetectula gen. nov., in Engina . Species of Engina in the broad sense differ from Sinetectula gen. nov. in their usually broader shape with lower spire, denticles rather than lirae on the inner side of the outer lip, much weaker parietal (at the adapical end of the inner lip) and anal denticles and therefore a usually less obvious anal notch, the narrower columellar callus without flaring lip but with radial ridges on

the parietal part of the columella, much broader and fewer spiral cords with much narrower interspaces, fewer and much broader axial ribs, and a straight or weakly convex (rather than convex) outer lip.

Species of Clivipollia Iredale, 1929 differ from Sinetectula gen. nov. in their larger protoconch consisting of 3½ to 3¾ whorls, the fewer but much more prominent and more rounded axial ribs, the absence of a parietal denticle at the adapical end of the inner lip with a weaker but usually much broader anal notch, the well-defined outer-lip denticles that sometimes extend as lirae into the aperture, the broad and deep notch between the anal denticle and the outer-lip denticles and the usually more vivid colour ( Fraussen & Stahlschmidt 2016: 30–38).

The genus Engina differs from Sinetectula gen. nov. in its fewer but usually more prominent axial ribs, the usually stronger apertural sculpture with prominent knobs within the outer lip and radially orientated lirae on the columellar callus (instead of knobs). The radula of Engina turbinella Kiener, 1836 , the type species of Engina (originally cited as Engina zonata Gray, 1839 ), looks similar to the radula of Sinetectula egregia gen. et comb. nov. but differs by the presence of 5 pronounced cusps on the rachidian tooth ( Ponder 1972: 252, fig. 1–10).

The American genus Parviphos Sarasua, 1984 differs from Sinetectula gen. nov. in its strongly varicate outer lip, fewer axial ribs, and the more prominent parietal tooth at the adapical end of the inner lip ( Watters 2009: 265–270, figs 232–262).

The American genus Monostiolum differs from Sinetectula gen. nov. in its axial sculpture reduced or absent on the last whorl, the weak apertural sculpture, and the absence of lirae within the outer lip. The spiral sculpture tends to be much finer in Monostiolum, and the spire is typically much higher, making for a slenderer shell ( Watters 2009: 259–265, figs 197–223).

The East African genus Micrologus Fraussen & Rosado, 2011 looks very similar in shape but differs from Sinetectula gen. nov. in its finer spiral sculpture with broader interspaces and a higher amount of secondary spiral cords (especially on the base and the transition to the siphonal canal), the much narrower columellar callus, the absence of knobs or lirae on the columellar callus and the absence of a serrated edge along the outer lip ( Fraussen & Rosado 2011: 76–78, figs 1–6).

The West Pacific genus Cancellopollia Vermeij & Bouchet, 1998 looks similar but differs from Sinetectula gen. nov. in its smooth columellar callus, the stronger spiral sculpture without secondary spiral cords, the absence of a strong (bicarinate) subsutural cord and the stronger varix on the outer lip ( Vermeij & Bouchet 1998: 479).

When known, the protoconch of Sinetectula gen. nov. varies among species. In Sinetectula egregia gen. et comb. nov., it consists of 1¼ flattened whorls lacking sculpture. In S. farinosa gen. et comb. nov., the protoconch consists of about 2–2½ whorls and bears a cord just above the abapical suture. In S. shepstonensis gen. et comb. nov., the protoconch consists of 3 whorls. The protoconch of S. cinis gen. et comb. nov. is unknown. The protoconch of S. farinosa gen. et comb. nov. resembles the planktotrophictype protoconch of species of Clivipollia by the presence of a subsutural spiral, but has fewer whorls ( Fraussen & Stahlschmidt 2016: 30–31, 36, figs 1a–b, 4j–l). The protoconch of S. shepstonensis gen. et comb. nov. resembles the planktotrophic-type protoconch of species of most Indo-West Pacific Engina by the number of whorls (3) and the rather conical shape. Species of Monostiolum and Parviphos have a smooth paucispiral protoconch ( Watters & Finlay 1989: 57, fig. 7; Watters 2009: 259, 265).

The genus Pisania Bivona, 1832 differs from Sinetectula gen. nov. in its much smoother, usually glossy shell wihout axial sculpture and the smoother aperture. The radula of Pisania striata (Gmelin, 1791) , its type species (originally cited as Pisania striatula Bivona & Bernardi, 1832 ), looks similar to the radula of Sinetectula egregia gen. et comb. nov. but differs by the presence of 5 more pronounced cusps on the rachidian tooth, the slightly shorter outer cusp on the lateral teeth and the absence of a protrusion at the inner margin of its base ( Cernohorsky 1971: 138, fig. 17; Ponder 1972: 260, fig. 1-1).

As with the variation in protoconch morphology, shape and sculpture also vary quite considerably among species of Sinetectula gen. nov. This is not unusual within Pisaniidae , or Buccinidae Rafinesque, 1815 in the broad sense. Indeed, Sinetectula gen. nov. has a somewhat heterogenous appearance. The shape varies among the species, with an ovate shape of S. farinosa gen. et comb. nov., in contrast with the slender shape of S. egregia gen. et comb. nov. and others. The shape varies also within a single species, with slender and broad specimens occurring within, for example, S. cinis gen. et comb. nov. (according to their distribution, the broader ones from Galapagos, while the more slender ones usually from Costa Rica) and S. shepstonensis gen. et comb. nov. (the limited material we studied suggests a variation according to bathymetric distribution, if not latitudinal distribution: the slender ones from deeper water off Somalia, while the broad ones are from shallower water off Mozambique and South Africa). The convexity of the whorls is stable in all species except S. shepstonensis gen. et comb. nov., where the specimens with a broader shell have a more convex whorl compared to the slenderer specimens from deeper water. The sculpture is moderately constant within a single species. As a result, the differences between the species can be described in the strength of the spiral cords and the axial ribs as well as in their number.

Distribution

Sinetectula gen. nov. is known from the tropical Indo-West Pacific, from eastern Africa in the west to the American West Coast in the east. Yet, we have not detected any specimens or species from the Atlantic. Sinetectula gen. nov. joins the related genus Clivipollia in having representatives in both the Indo-West Pacific and tropical eastern Pacific. Shasky (1987: 30), and referred to by Skoglund (1992: 81), reported Clivipollia fragaria (Wood, 1828) from the western Pacific as well as from Isla del Coco, Costa Rica, where S. cinis gen. et comb. nov. also lives. While Pisania in the broad sense and Engina are distributed in all tropical seas (including the Atlantic and East Pacific), all living Sinetectula gen. nov. are, together with the Clivipollia group, as far as we know, restricted to the Indo-West Pacific.

Both Sinetectula farinosa gen. et comb. nov. and S. egregia gen. et comb. nov. have a wide range, reaching from eastern Africa to the Marshall Islands. These two species may have a similar mode of life, what is also reflected in the fact that both are syntopic at Kwajalein Atoll and in Western Samoa.

Sinetectula gen. nov. is so far not known from the fossil record. In the case of S. cinis gen. et comb. nov. and S. nigricostata gen. et comb. nov. it is likely that they, or their immediate ancestors, arrived in the eastern Pacific from the west no later than the Early Pleistocene ( Vermeij 1987).

Figures

Fig. 1. Sinetectula egregia (Reeve, 1844) gen. et comb. nov. A–E. Specimen from the Marshall Islands, Kwajalein Atoll, in cave at Oceanside of West reef, depth 12 m, 12.0 mm long (KF 4756). F–H. Specimen with same collection data as for preceding, 14.5 mm long (KF 4756). I–L. Specimen from Indonesia, Sulawesi, 1°08′ N, 121°51′ E, near Pulau Raja, depth 5–40 m, 16.9 mm long (KF 4854). M–O. Specimen from Mayotte, Pananzi Island, BENTHEDI 1977 stn 32, 12°45′ S, 45°18′ E, depth 15–20 m, 15.0 mm long (MNHN). P. Specimen from Papua New Guinea, Madang, Astrolabe Bay, PAPUA NIUGINI stn PB14, 5°13.8′ S, 145°48′ E, depth 15 m, 16.6 mm long (MNHN IM-2013-12540). Q. Radula of preceding specimen. A–P. Images courtesy of MNHN – Alexandre Lardeur. Q. Image courtesy of Yuri Kantor. Scale bars: D–E, L, O = 2.0 mm; Q = 100 µm.