Isotriphora tricingulata Rolán & Fernández-Garcés, 2015

Fernandes, Maurício Romulo & Pimenta, Alexandre Dias, 2020, Unraveling one of the ‘ Big Five’: update of the taxonomy of Triphoridae (Gastropoda, Triphoroidea) from Brazil, European Journal of Taxonomy 665 (665), pp. 1-170 : 12-14

Isotriphora tricingulata Rolán & Fernández-Garcés, 2015

Figs 3 , 23G , 50

Isotriphora tricingulata Rolán & Fernández-Garcés, 2015: 47 , fig. 2.

“ Isotriphora ” sp. – Zhang 2011: 99, fig. 296.

Material examined

Holotype

GUADELOUPE • Port-Louis , Grand Cul-de-Sac Marin; depth 81 m; MNHN IM-2000-30472 .

Other material

BRAZIL – Amapá • 12 specs; 03º58′43″ N, 49º33′24″ W; 2001; MNRJ 32558 * • 2 specs; 03º58′43″ N, 49º33′24″ W; 2001; MNRJ 32556 * • 1 spec.; 03º58′43″ N, 49º33′24″ W; 2001; MNRJ 32563 * • 1 spec.; 03º58′43″ N, 49º33′24″ W; 2001; MNRJ 32569 * • 1 spec.; 03º58′43″ N, 49º33′24″ W 2001; MNRJ 32574 • 1 spec.; 02º45′ N, 48º42′ W; depth 75 m; Nov. 2008; MNRJ 17929 * • 1 spec.; 02º21′12″ N, 48º29′54″ W; depth 72 m; Mar. 1997; MORG 52263 .

Description

Shell sinistral, small, cyrtoconoid, rectilinear profile, up to 4.6 mm long, 1.4 mm wide, length/width ratio 2.8 to 3.1, up to 11 whorls. Protoconch paucispiral with truncated apex, without clear differentiation of the teleoconch; two strongly nodulose spiral cords starting from the slightly pointed and very narrow nucleus, situated at ~37% and ~73% of the last whorl height; median spiral cord usually emerging in the fifth whorl of the shell, sometimes as early as the end of fourth whorl or as late as the end of the sixth whorl, and readily reaching the same size of other cords; on the body whorl, distance between spiral cords is 0.9–1.2 × higher than width of cords; 17–20 orthocline to slightly opisthocline axial ribs at seventh whorl of shell; rounded to slightly elliptical nodules of medium size; distinct and welldeveloped suture, with small sutural cord; wavy subperipheral cord, mainly not developing nodules, two thin and nearly smooth basal cords, abapical one almost indistinct in some cases; no supranumerical cords; ovate aperture, 0.55–0.62 mm long, 0.47–0.50 mm wide, length/width ratio 1.2; anterior canal curved backwards/downwards, short, open or partly closed by projection of outer lip, 0.24–0.30 mm long, 0.14–0.17 mm wide, length/width ratio 1.7–1.8; posterior canal is small sinus, 0.09–0.11 mm long,

not detached from aperture. Two to three initial whorls white, remaining whorls homogeneously cream or light brown; worn shells dirty white.

Remarks

As indicated in the original description, the shell of I. tricingulata superficially resembles that of Isotriphora peetersae ( Moolenbeek & Faber, 1989) , a species widely distributed throughout the Caribbean ( Moolenbeek & Faber 1989; Rolán & Espinosa 1994; Redfern 2013). However, I. peetersae is differentiated by a somewhat bottle-shaped shell, the presence of three spiral cords through most of the protoconch, a late median spiral cord of the teleoconch, the white coloration comprising the five initial whorls of the shell (but only two to three whorls in I. tricingulata , Fig. 3 A–D) and a darker brown coloration in the remaining whorls.

Isotriphora tricingulata is also easily distinguished from Isotriphora onca Fernandes, Pimenta & Leal, 2013 , from the Vitória-Trindade Seamount Chain (southeastern Brazil), by the presence of an evident median spiral cord emerging in the fifth/sixth whorl ( Fig. 3F ), but only with a very reduced size after the 13 th whorl in I. onca ( Fernandes et al. 2013) . The shell of I. onca is more elongated, with a long and almost closed anterior canal, instead of the short and open or partly closed anterior canal of I. tricingulata ( Fig. 3H ).

The single difference between the holotype of I. tricingulata and shells from Brazil is the earlier emergence of the median spiral cord in the holotype (fourth whorl vs usually fifth whorl in shells from Brazil). Despite the supposed intracapsular metamorphosis suggested by protoconch morphology ( Fig. 3I ), different populations of this species may be connected by the stepping stones of the Lesser Antilles and the continental shelf of the Guyana.

One shell of I. tricingulata from Brazil has a late emergence of the adapical spiral cord, only at the end of the third whorl of the shell ( Fig. 3J ). This might be a small abnormality in the development of the initial whorls.

Geographical records

Antigua ( Zhang 2011); Guadeloupe (type locality); Brazil: Amapá (this study).

Bathymetric distribution

Depth: 72 m (this study) to 81 m (type locality).

Figures

Fig. 3. Isotriphora tricingulata Rolán & Fernández-Garcés, 2015. A, C. MNRJ 32558*, 2.75 mm and 3.04 mm, respectively. B. MNRJ 17929*, 4.62 mm. D. MNRJ 32574*, 3.29 mm. E–I, K. Same shell as A. J. Same shell as D. Scale bars: A–E = 1 mm; F–H = 500 µm; I–K = 100 µm.

Fig. 23. Triphoridae from Brazil (2). A. “Inella” sp. 4. B. Iniforis carmelae Rolán & Fernández- Garcés, 1993. C. Iniforis pseudothomae Rolán & Fernández-Garcés, 1993. D. Isotriphora leo sp. nov. E. Isotriphora onca Fernandes, Pimenta & Leal, 2013. F. Isotriphora tigrina Fernandes, Pimenta & Leal, 2013. G. Isotriphora tricingulata Rolán & Fernández-Garcés, 2015. H. Isotriphora uncia sp. nov. I. Isotriphora sp. 1. J. Latitriphora albida (A. Adams, 1854). K. Marshallora sp. L. Marshallora ostenta Rolán & Fernández-Garcés, 2008. M. Marshallora sp. 1. N. Monophorus caracca (Dall, 1927) comb. nov. O. Monophorus olivaceus (Dall, 1889). P. Monophorus verecundus sp. nov. Q. Nanaphora leei Fernandes & Pimenta, 2015. R. Nanaphora verbernei (Moolenbeek & Faber, 1989). S. Nanaphora sp. 1. Scale bars: 1 mm.

Fig. 50. Distribution map of Isotriphora tricingulata Rolán & Fernández-Garcés, 2015 (red circle = type locality; black circles = additional localities) and Isotriphora onca Fernandes, Pimenta & Leal, 2013 (brown circle = type locality; gray circle = additional locality).