Cheirodonta mizifio, Fernandes, Maurício R. & Pimenta, Alexandre D., 2015

Fernandes, Maurício R. & Pimenta, Alexandre D., 2015, Five new species and two records of Triphorinae (Caenogastropoda, Triphoridae) from Brazil, Zootaxa 4012 (3), pp. 493-513 : 496-498

Cheirodonta mizifio sp. nov.

( Figure 2 )

Type material. Holotype: MNRJ 18696. Paratypes: Brazil: Rio Grande do Norte state: MNRJ 31622, BPot 2- MR32 [1]. Bahia state: MNRJ 33082, 13º29’22”S, 38º48’43”W, vii/2008 [1]; MNRJ 32901, 13º29’43”S, 38º49’08”W, v/2007 [1]. Espírito Santo state: IBUFRJ 19688, Piúma [11]. Rio de Janeiro state: IBUFRJ 19691, Itaipú, Niterói [1]; MNRJ 32555, 23º05’S, 40º58’W, 100 m [1].

Other material examined. Brazil: Rio Grande do Norte state: MNRJ 31614 [3], MNRJ 31619 [1], BPot 1- MR41; MNRJ 31620, BPot 1-MR42 [2]; MNRJ 31621, BPot 1-MR43 [1]; MNRJ 31623, BPot 2-MR42 [1]; MNRJ 31624, BPot 2-MR44 [2]; MNRJ 32077, BPot 1-MR32 [1]. Bahia state: MNRJ 33805, 18º13’S, 38º20’W, 55 m, 21/ix/1995 [2]. Espírito Santo state: MNHN, Expedition MD55 sta. DC73, 18º59’S, 37º48’W, 607-620 m, 27/v/ 1987 [1]. Rio de Janeiro state: MNRJ 18591, HAB 13-H3 [1]; MNRJ 18624, HAB 16-H3 [1].

Type locality. Station HAB 13-H3 of Project Habitats: 21º43’06”S, 40º11’37”W, 73 m, Rio de Janeiro state, Brazil.

Etymology. The specific name alludes to the resemblance of the shell to the cigar used by “preto-velho”, an entity in the Afro-Brazilian religion of Umbanda; “ mizifio ” is a common expression of him, meaning “my son”. Epithet as a noun in apposition.

Diagnosis. Brown, elongated shell; median spiral cord emerges weakly in the beginning of sixth to eighth whorl, reaching same size than abapical cord after three to four whorls; little developed suture; three supranumerical cords.

Description. Shell sinistral, elongated, narrow, conical, profile rectilinear (juveniles) to slightly curvilinear (adults), reaching 7.76 mm in length, 2.07 mm in width. Color light to dark brown, almost homogeneous, with nodules slightly clearer than background of shell; some shells slightly orange. Protoconch conical, 0.46–0.55 mm in length, 0.35–0.42 mm in width, with 5–5.5 slightly convex whorls; embryonic shell dome-shaped, covered by hemispherical (top of embryonic shell) or arrowhead-shaped (mid and bottom) granules and small vesicles, these are more concentrated in its adapical and final portion, and coalesce into axial ribs; larval shell with two spiral cords, but adapical one disappears in some just before the transition to teleoconch; about 32 slightly sigmoid axial ribs. Teleoconch with up to 13 whorls; two spiral cords (adapical and abapical) on first whorl, abapical one continuous with that of protoconch; median spiral cord emerges weakly in the beginning of sixth to eighth whorl, reaching almost same size as abapical cord (adapical one often thicker than others) after three to four whorls; 20 to 23 opisthocline axial ribs; rounded nodules of medium size; little developed suture, with a small sutural cord; little nodulose to slightly wavy subperipheral cord and two smooth to slightly wavy basal cords; three small supranumerical cords may develop near the peristome, one between median and abapical spiral cords, another between abapical and subperipheral cords and the last between subperipheral and adapical basal cords; aperture elliptical; anterior canal curved backward, being long and open, but crossed in its base by projection of outer lip; posterior canal as an orifice almost detached from aperture.

Remarks. The shells of Cheirodonta mizifio sp. nov. vary, especially relating to the strength of the adapical spiral cord on the teleoconch (being little, Fig. 2 A or considerably more, Fig. 2 B developed than remaining cords) and the number of whorls in which the median spiral cord reaches the same size as the abapical one after its emergence. In addition, shells from Bahia ( Fig. 2 C) and Rio Grande do Norte ( Fig. 2 D) states have the median spiral cord emerging on the sixth teleoconch whorl, but it occurs usually in the seventh/eighth whorl in specimens from Espírito Santo and Rio de Janeiro states ( Fig. 2 A–B). Shells from Rio Grande do Norte are smaller and with fewer whorls than remaining shells.

This is the only species, besides the type species Cheirodonta pallescens ( Jeffreys, 1867) , that undoubtedly belongs to this genus, as the Pacific species Cheirodonta labiata ( A. Adams, 1854) was tentatively referred to this genus ( Marshall 1983) and the assignments of Cheirodonta for the western Atlantic are incorrect. The few differences between C. mizifio and C. pallescens involve the whorl of emergence of the median spiral cord [sixth to eighth whorl in C. mizifio ; ninth whorl in C. pallescens ( Bouchet 1985) ], and the more curvilinear profile and paler shell coloration in C. pallescens ( Rolán 2005: fig. 447).

Although Marshall (1983) created the genus Cheirodonta based solely on its exclusive radular morphology, some conchological features can also be used to distinguish it from similar genera, such as Marshallora Bouchet, 1985 . Cheirodonta possesses supranumerical cords before the peristome ( Fig. 2 G), hemispherical and arrowheadshaped granules in the embryonic shell ( Fig. 2 J) and an almost detached posterior canal. Species of Marshallora apparently do not develop such cords or arrowhead-shaped granules, and possess a less developed posterior canal; in addition, the suture of Cheirodonta ( Fig. 2 F) is less distinct than in Marshallora .

Geographic distribution. Brazil: Rio Grande do Norte, Bahia to Rio de Janeiro.

Bathymetric distribution. 22 to 100 m. The depth of 607–620 m from Expedition MD55 is probably incidental, derived from turbidity currents.

Figures

FIGURE 2. Cheirodonta mizifio sp. nov. A. MNRJ 18696, holotype, 6.28 mm long. B. MNRJ 32555, paratype, 5.07 mm long. C. MNRJ 33082, paratype, 7.76 mm long. D. MNRJ 31622, paratype, 3.36 mm long. E – F, I, holotype, coated for SEM. G – H, MNRJ 31620. J, MNRJ 31614. K, MNRJ 32901. Scale bars: A – E, 1 mm; F – H, 500 µm; I, K, 100 µm; J, 50 µm.