Homalopoma linnei ( Dall, 1889 )

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 : 413

Homalopoma linnei ( Dall, 1889)

( Fig. 5 D–J)

Leptothyra linnei Dall, 1889: 353 , pl. 33, fig. 8 (9 in error, see below).

Leptothyra linnei var. limata Dall, 1889: 353 .

Homalopoma linnei: Poirier, 1954: 26 ; Abbott, 1974: 60; Rios, 1985: 26, pl. 11, fig. 110; Rios, 1994: 43, pl. 14, fig. 146; Miyaji, 2004: 79; Rios, 2009: 69 [in part]; Rosenberg et al. 2009: 624; Miloslavich et al., 2010: table S6; Welch, 2010: table S1.

Homalopoma sp.1: Leal, 1991: 58.

Type material. Syntypes: MCZ 7538 , Cuba, Havana, off Morro Light, Blake sta. 0 2, 23°14’N, 82°25’W, 1472 m, 1 sh (R/ V Blake leg., 1877) ; MCZ 7539 , Cuba, off Havana, 822 m, 1 sh (R/ V Blake leg., 1877) ; MCZ 7540 , Cuba, off Honda Bay , 23°2’30”N, 83°11’0”W, 402 m, 1 sh (R/ V Blake leg., i/1878) ; NMNH 94984 , Caribbean Sea , Barbados, 13°17’N, 59°53’W, 183 m, 5 sh (R/ V Blake leg.) ; NMNH 94985 , Caribbean Sea, St. Lucia, Blake sta. 220, 13.8375N, 61.0625W, 212 m, 1 sh (R/ V Blake leg., 16/ii/1879) .

Type locality. Saint Lucia, BLAKE sta. 0 2, 1472 m depth; BLAKE sta. 20, 402 m depth; sta. 220, 212 m depth. Cuba, off Havana, 823 m depth. Barbados, 183 m depth .

Distribution. Florida, USA to southern Brazil, 60–260 m (live specimens) down to 1472 m (shells only) ( Miyaji 2004; Rosenberg et al. 2009).

Habitat. Coralline and muddy bottoms.

Material examined. Brazil: Espírito Santo: off São Mateus, Abrolhos Slope , MD55 sta. DC73, 18°59’S, 37°48’W, 607–620 m, MNHN, 4 sh (27/v/1987); MD55 sta. CB77 , 19°40’S, 37°48’W, 790–940 m, MNHN, 1 sh (27/v/1987). Additional non-MD55 material: Caribbean: types . Brazil: Ceará: 120 miles off Fortaleza, Canopus Bank , MZSP 53726 , 60– 260 m, 24 sh (viii/2005); MZSP 55524 , 240– 260 m, 2 spm (xi/2005); MZSP 67309, 260 m, 5 sh (viii/2005); MZSP 70295, 260 m, 3 sh + 4 spm (xi/2005); MZSP 94229, 260 m, 4 sh (xi/2005) .

Measurements. 6 whorls, H= 6.26 mm, D= 5.07 mm (largest specimen).

Remarks. In the original description, Dall (1889) cited figure 9 on plate 33. That figure, however, corresponds to another taxon introduced in the same work ( Arene bairdii , p. 389). The correct figure is number 8, which perfectly agrees with the original description as well as the types examined herein. Due likely to a typographical error, the figure number was switched with figure 8 before the final printing; one can easily notice that by the obvious interruption in the logical sequence of numbers.

The specimens studied here compare exceedingly well with the original description and the examined syntypes in size, sculpture elements, and variation. Even so, most shells inspected have spiral cords sculptured by spiny nodules on nearly all teleoconch whorls, which produce an overall rougher surface and a “spiky” appearance ( Fig. 5 D–F). Dall (1889) already mentioned this variation, indicating it as rare, probably based on a syntype specimen examined herein (UNSM 04984). Nevertheless, based on the current assemblage, this variation seems to be more common than initially assumed. Leal (1991) described this variation as a probable distinct species based on MD55 material, tentatively naming it “ Homalopoma sp.1”.

This species is quite similar to the sympatric congener Homalopoma boffii Marini, 1975 , but differs in being small- er, exclusively cream/white colored, and usually more profusely sculptured. Regarding the sculpture elements, the spiral cords referred to as “costae” by Dall in the original (1889) description, are usually narrower (though the number of spiral cords per whorl is variable and overlaps in both species) and the nodules are more irregular, angular (spiky), smaller and numerous than in H. boffii . These nodules are usually more closely spaced in H. linnei , and are often overlain giving the shell a scaly appearance ( Fig. 5 G ) that is very distinct from the larger and more widely spaced nodules of H. boffii ( Fig. 5 N ). Nevertheless, both species display some degree of overlapping variation. The only unequivocal characters that distinguish H. linnei from H. boffii in the analyzed material is the smoother, more elevated and inflated protoconch of the former ( Fig. 5 H ), and the sculpture of the initial whorls, which lacks the large, sequential nodules found on the initial teleoconch whorls in H. boffii ( Fig. 5 M ). Furthermore, the deep, well-marked subsutural channel in H. linnei is not so pronounced in H. boffii . Most importantly, the operculum is also strikingly distinct, having 9–10 whorls in H. linnei ( Fig. 5 I-J), as opposed to 10–12 in H. boffii ( Fig. 5 K-L), and also presenting a prominent widening of the last whorl in H. linnei . This widening produces an almost squarish outline ( Fig. 5 I ), which is different from the almost circular operculum of H. boffii ( Fig. 5 K ).

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).