Cosmioconcha costorum, Simone & Monsecour, 2024

Simone, Luiz Ricardo L. & Monsecour, Kevin, 2024, Paratypes of Brazilian Cosmioconcha helenae (Gastropoda, Columbellidae) actually belong to a new species, Zootaxa 5406 (3), pp. 492-494 : 492-494

Cosmioconcha costorum new species

http://zoobank.org/ urn:lsid:zoobank.org:act:93A5AEB0-BDC9-4C84-8EE9-801E1E060F2C

( Figures. 1–6, 9–12 )

Types. Holotype MZSP 102539 , shell . Paratype: MZSP 102534 , 1 shell from type locality .

Type locality. BRAZIL. Amapá; off Amapá , ~ 3°00’N 49°28’W, 56 m [ RV Almirante Saldanha col., 1.05.1968] .

Diagnosis. Cosmioconcha species of small size, fusiform, protoconch of 3 whorls, small subsutural shoulder, axial cords on all whorls, small nodes on the intervals of the subsutural band and the axials, spiral liration on lower half of last whorl, outer lip simply arched, inner lip shallowly concave with thin callus, anal notch small, canal open.

Description. Shell of ~ 7 mm, fusiform; walls thick. Color white, with light yellow band in lower half in spire whorls, and in middle third in last whorl ( Figs. 2, 3, 5, 6 ). Apex relatively blunt; spire ~57% of shell length, spire angle ~40°. Protoconch of 3 smooth whorls, successive larger, width of 0.6 mm; transition with teleoconch clear-cut, orthocline, sigmoid ( Figs. 11, 12 ); occupying ~7% of shell length, ~19% of shell width. Teleoconch of ~5 whorls, each whorl with weakly convex, almost straight profile, with small subsutural shoulder, bearing small nodes in uniform intervals, 14 in penultimate whorl. Each subsutural node continuing inferiorly as axial, shallow rib, forming undulating sculpture; in spire, axial cords from suture to suture; in last whorl, axial ribs more nitid in superior half, in inferior half becoming lower, crossed by strong spiral liration, as ~15 spiral, narrow, smooth, uniform, crowded cords, covering entire inferior half, including canal ( Figs. 2, 3, 5, 6 ). Aperture elliptical, oblique, not deflected, ~length twice exceeding width; occupying ~38% of shell length, ~40% of shell width; outer lip simply arched, weakly prosocline; ~10° with shell longitudinal axis ( Figs. 2, 5 ); inner lip shallowly concave, callus thin; anal notch small, producing subsutural shoulder. Canal ~12% of shell length; ~25% of shell width; rather opened. No umbilicus.

Habitat. Dredged in 56 m.

Etymology. the epithet is in honor of both researchers that dealt with the species, Fabio H. A. Costa, who described C. helenae and designated the here studied paratypes ( Costa, 1983); and Paulo Marcio S. Costa, a Brazilian columbellid specialist who also have seen differences between southern and northern samples of previous concept of C. helenae , additionally who designated the present generic combination ( Costa, 2005).

Measurements (in mm). holotype MZSP 102539 ( Figs. 1–3 ): 6.9 by 3.0; paratype MZSP 102534 ( Figs. 4–6 ): 6.2 by 2.5.

Discussion. Cosmioconcha costorum is really very similar to C. helenae , so much that both specimens were comprehensibly designated paratypes of that species by its author. However, a series of details indicate that both represent different entities. One of the main differences is that C. costorum has a multispiral protoconch ( Figs. 11, 12 ), of 3 whorls, while in C. helenae the protoconch is paucispiral ( Fig. 13 ), with 1.5 whorl. The size of both is also different, C. costorum is up to 7 mm, while C. helenae usually is over 10 mm with equivalent number of shell whorls (compare Figs. 7–10 , shells in the same scale). The shell profile of C. costorum is slightly more elongated and straight, while that of C. helenae is slightly more globose, mainly in the last whorl, so much that the fist whorls have a slightly concave profile ( Figs. 7–8 ). The subsutural shoulder is much more pronounced in C. costorum , rendering the whorls profile flat. A shoulder is less developed in C. helenae , which has whorls more convex. However, its holotype has a vestigial subsutural shoulder, but this has been shown a rare feature, as most specimens shows this much less-developed. Additionally, the lirations highly developed in the inferior half of last whorl, are not detected at all in superior half of C. costorum , but it is barely present in C. helenae , overlying on axial sculpture. This discussion was enriched with examination of more specimens of C. helenae that, as referred above, have been often collected, in the MZSP collection, or photos of which were accessed at some conchological web sites (e.g., Femorale, 2023). Geographically, C. helenae appears to be restricted to Rio de Janeiro region, in shallow waters. Reported occurrences in other regions are apparently misidentifications, as the present reported one.

Pelorce (2017) reviewed the Columbellidae from French Guyana resulting in the description of several new species. He recognized six species of Cosmioconcha , of which four were introduced as new species: C. costorum differs from C. costattenuata Pelorce, 2017 in being smaller, in having multispiral protoconch (that species has a 1.5 whorl protoconch), by fewer teleoconch whorl (that species has 6 whorls), by more globose outline (that species is more elongated) and in having much more pronounced axial ribs. C. costorum differs from C. flammea Pelorce, 2017 in being slightly larger, by more elongated outline, by shorter protoconch (that species has a 4-whorl protoconch) lacking a clear subsutural spiral incision; additionally, C. flammea is distinct in only showing large quantity of axial ribs, close located from each other, on the last whorls, while earlier whorls lack axial sculpture. C. costorum differs from C. rikae Monsecour & Monsecour, 2006 , from the Caribbean Panama and French Guyana, in having a shorter outline, and fewer axial ribs in entire teleoconch, including in last whorl, where that species lacks sculpture; both species share the same size and protoconch features. C. costorum differs from C. coltrorum Monsecour & Monsecour (in press) in being smaller, more globose (that species is slender), fewer teleoconch whorls, more spaced and more pronounced axial ribs, and less pronounced color pattern.

Figures

FIGURES 1–13: Cosmioconcha spp type shells. 1–3. C. costorum holotype MZSP 102539 (L 6.9 mm), frontal, right and dorsal views, scale = 1 mm. 4–6. C. costorum paratype MZSP 102534 (L 6.2 mm), frontal, right and dorsal views, scale = 1 mm. 7–10. Types at same scale (= 3 mm). 7–8. Holotype of C. helenae MZSP 102531, frontal and dorsal views. 9. Holotype of C. costorum. 10. Paratype of C. costorum. 11–13. Shell apex, arrows showing protoconch-teleoconch transition, scales= 0.5 mm. 11. Holotype of C. costorum. 12. Paratype of C. costorum. 13. Holotype of C. helenae.