Homalopoma boffii Marini, 1975

Cavallari, Daniel C., Salvador, Rodrigo B., Dornellas, Ana P. S. & Simone, Luiz R. L., 2019, Calliostomatidae, Colloniidae, Margaritidae, and Solariellidae (Gastropoda: Trochoidea) collected by the Marion Dufresne (MD 55) expedition in southeastern Brazil, with description of a new species of Calliostoma, Zootaxa 4609 (3), pp. 401-428 : 412

Homalopoma boffii Marini, 1975

( Fig. 5 K–N)

Homalopoma boffii Marini, 1975: 31 , figs 1–3. Rios, 1985: 26, pl. 11, fig. 109; Rios, 1994: 43, pl. 14, fig. 145; Rios, 2009: 69, text fig. (switched with preceding species entry in error). Homalopoma boffi [sic]: Leal, 1991: 58; Benkendorfer & Soares-Gomes, 2009: 151.

Type material. Holotype: MZSP 18772 . Paratype: MZSP 18773 , 1 spm, from type locality .

Type locality. Brazil, off Rio Grande do Sul state, 31°08’S, 49°31’W, 183–253 m, R/V “ W. Besnard ” sta. 1858 (6/viii/1972) .

Previously known distribution. Off southeastern Brazil, from São Paulo state to Rio Grande do Sul state ( Rios, 1994), including Trindade and Martim Vaz Islands, Montague and Columbia Seamounts ( Leal, 1991), 60–253 m (live specimens).

New records. Northeastern Brazil, off Ceará state, down to 260 m (shells only).

Habitat. Coralline and muddy bottoms.

Material examined. Brazil: São Paulo: off Santos , MZSP 36037 , 2 spm (local fishermen leg., xii/2002). Additional Non-MD55 material : Brazil: Ceará: 120 miles off Fortaleza, Canopus Bank , MZSP 53938 , 240– 260 m, 2 sh (viii/2005); MZSP 67303, 260 m, 7 sh (xi/2005); MZSP 70298, 260 m, 4 sh (xi/2005); MZSP 93535 , 60– 200 m, 2 sh (viii/2005); Rio Grande do Sul: types .

Measurements. 6–6½ whorls, H=8.7–10.0 mm, D=9.0– 10.4 mm (n=3).

Remarks. This seemingly rare species is usually characterized by its large, reddish shell, with strong rounded spiral cords and coarse nodulose sculpture starting on the teleoconch, but usually restricted to the first 3–4 whorls ( Marini 1975). The species, in fact, attains a larger size than reported in the original description (H=6.9, D=7.0 mm) and followed by the literature (e.g., Rios 1994, 2009; Rosenberg et al. 2009), reaching a shell height of 10.9 mm (MZSP 67303) and a maximum diameter of 10.8 mm (MZSP 36037) in non-MD 55 specimens we analyzed (from Canopus Bank, off northeastern Brazil).

Leal (1991) argued that the figures in the original description by Marini (1975: figs 1–3) were switched with those of another species, but the present examination of the type material showed that the holotype is the illustrated specimen: the proportions, sculpture and even the location of damaged areas are identical (MZSP 18772). Both type specimens are subadult shells, and the slight change in outline with age ( Fig. 5 N ) may have caused confusion.

With its known distribution restricted to southern-southeastern Brazilian waters in recent works ( Leal 1991; Rios 1994, 2009), Homalopoma boffii is here revealed as more widely distributed than initially assumed, ranging as far as northeastern Brazil. Part of this newly reported range overlaps with that of Homalopoma linnei ( Dall, 1889) , which has also been found in the MD55 material (see below). Marini (1975) pointed out the similarity of these species, arguing that the main differences resided in the shell’s ground color (reddish as opposed to pure white in H. linnei ), number of spiral cords (fewer in H. linnei ), and overall size (~25% larger than H. linnei ). Except for the discrepancy in size, which is strongly consistent (and even amplified) in the assemblage examined here, the remaining dissimilarities are not confirmed: some specimens of H. boffii from Canopus are almost pure white, and the number of spiral cords on the body whorl is variable from 12 to 16 in both species. Even so, there are additional differences to be noted. In H. boffii , the protoconch is much less inflated, nearly flattened ( Fig. 5 M ), and the very first teleoconch whorl already bears coarse, large nodules. The nodules themselves are always rounder and proportionally larger in H. boffii . Moreover, the shell of H. boffii has a more compact outline with a shorter spire, giving it a more globose profile ( Fig. 5 N ). The suture is shallower in H. boffii , lacking the prominent, deep subsutural channel present in H. linnei . The spiral cords in H. boffii are proportionally wider, as are the interspaces, which in turn are shallower and less prominent than in H. linnei . The operculum in H. boffii is roughly circular ( Fig. 5 K-L), as opposed to squarish in H. linnei ( Fig. 5 I-J).

Figures

FIGURE 5. Calliostomatidae and Colloniidae collected by the MD55 expedition, and specimens from Northeast Brazil. A–C. Falsimargarita terespira MNHN, sta. CB103 (H=10.5 mm, D=10.7 mm). A. apertural view. B. apical view. C. umbilical view. D–J. Homalopoma linnei. D–F. MNHN, sta. DC73 spm #1 (H=5.5 mm, D=4.7 mm). D. apertural view. E. apical view. F. umbilical view. G–I. MNHN, sta DC73 spm #2 (H=4.8, D=5.4 mm), under SEM. G. apical view. H. detail of apex. I–J. operculum of specimen from Canopus Bank, off Northeast Brazil, MZSP 70295. I. inner side (L=1.5 mm), J. outer side. K–N. Homalopoma boffii, specimen from Canopus Bank, off Northeast Brazil, MZSP 93535. K–L. operculum (L=1.2 mm). K. inner side. L. outer side. M. detail of apex under SEM, N. apertural view (H=7.3 mm, D=7.8 mm).