Boonea scymnocelata, Pimenta, Alexandre Dias, Absalão, Ricardo Silva & Miyaji, Cintia, 2009

Pimenta, Alexandre Dias, Absalão, Ricardo Silva & Miyaji, Cintia, 2009, A taxonomic review of the genera Boonea, Chrysallida, Parthenina, Ivara, Fargoa, Mumiola, Odostomella and Trabecula (Gastropoda, Pyramidellidae, Odostomiinae) from Brazil, Zootaxa 2049, pp. 39-66 : 48-49

Boonea scymnocelata new species

( Figs. 15−20 )

Description: Shell small, moderately conical; color white. Teleoconch with 3.5 whorls, somewhat convex in profile. Suture deep, straight. Protoconch heterostrophic, with about one whorl, immersed into first teleoconch whorl, with no visible nucleus; diameter about 210 Μm. Axial ribs, straight and prosocline; 17 on last whorl of holotype; interspaces about as wide as the ribs, bearing microscopic axial lines. Spiral sculpture formed by four spiral cords per whorl, of same width as axial ribs, forming rounded nodules when crossing them; below the abapical spiral cord, there is a deeper channel, with no traces of axial ribs, but entirely crossed by axial lines; an additional smooth spiral cord is sometimes visible just above the suture, especially on the periphery of the last whorl. Base elongate and bearing five smooth, low spiral cords with axial lines in their interspaces. Aperture ovoid. Columella obliquely straight, with small fold. Outer lip thin. Small chink-like umbilicus.

Dimensions: Holotype with three teleoconch whorls; height 2.0 mm; width 0.5 mm.

Type material: Holotype: MZSP 89107. Paratypes: MNRJ 10957, type locality [8]; MZSP 89108, PADCT sta 6595 [2]; MZSP 89109, PADCT sta 6571 [6]; MZSP 89110, PADCT sta 6541 [1]; MZSP 89111, PADCT sta 6631 [1]; MZSP 89112, PADCT sta 6606 [1]; MZSP 89113, PADCT sta 6642 [1]; MZSP 89114, PADCT sta 6635 [4]; MZSP 90115, REVIZEE sta 6664 [1]; MZSP 89116, REVIZEE sta 6666 [1].

Type locality: off Paraná State, PADCT sta 6595 (26°23.55'S, 46°39.49'W, 175m).

Etymology: This species is named after its partially concealed protoconch, in which the nucleus is hidden in the first teleoconch whorl (scymnus, L. = a young animal; cello, - atus, L. = conceal).

Remarks: Boonea scymnocelata ( Figs. 15−20 ) resembles B. seminuda ( Figs. 9–14 ), both in the shape of aperture and sculpture, with small nodules where the axial and spiral cords cross and a small chink-like umbilicus.

However, all shells of B. scymnocelata only have up to four teleoconch whorls, whereas shells of B. seminuda may reach six teleoconch whorls. In spite of this, general proportions of both species are very similar, with similar width of the third teleoconch whorl: 0.67mm to 0.87mm (mean = 0.76mm, n=25) in B. seminuda ; 0.67mm to 0.80mm (mean = 0.73mm, n= 12), in B. scymnocelata . In this last species, the width on fifth whorl ranges from 0.9mm to 1.2mm (mean= 1.03mm, n=8).

The main difference between the two species is the protoconch, which, in B. scymnocelata has about only one whorl; besides that, its apex is immersed in the first teleoconch whorl ( Figs. 17−19 ), without a visible nucleus; whereas in B. seminuda , two protoconch whorls are well visible beyond the first whorl of the teleoconch ( Figs. 13–14 ). This difference in protoconch whorls can also be seen when comparing B. scymnocelata with young specimens of B. seminuda (up to four whorls) ( Fig. 11 ). Robertson (1978) diagnosed the protoconch as greatly tilted, which is in accordance to the protoconch of B. scymnocelata .

Also, both species have a smooth suprasutural spiral cord from the third teleoconch whorl, however, this cord become more conspicuous in newer whorls, and so it is much more visible in larger shells of B. seminuda . The columelar fold in B. seminuda is also a more developed that in B. scymnocelata .

The illustrations of Odostomia ornatissima (Hass) in Abbott (1974: 294, fig. 3507), a species from California in the Pacific Ocean, is very similar to B. scymnocelata , but lacks the deep channel below the suture that is present in B. scymnocelata .

The small protoconch of B. scymnocelata , with about one whorl, would suggest a non-pelagic development for this species. However, such assumption should be confirmed after reproductive and development studies, since, as discussed by Robertson (1996), who found that the protoconch of Fargoa bartschi ( Winkley, 1909) , with 0.9 whorls is indeed planktotrophic, larval ecology of pyramidellids cannot be determined from shell characters alone.

In some cases, this kind of pyramidellid protoconch may not be detectably heterstrophic, as stated by Robertson (1996), when redescribing the genus Fargoa . This is due to its immersed nucleous into first teleoconch whorl. It was defined as “ type C” by Schander (1994), diagnosed as “angle in almost 180o, here the protoconch has almost disappeared into the first teleoconch whorl”, and by Peñas et al. (1996), diagnosed as “the coiling axis of protoconch and teleoconch are the same, but in opposite directions (angle of 180o)”. Such protoconch kind is common in Odostomiinae species, for instance: Chrysallida interstincta (J. Adams) , illustrated in Peñas and Rolán (1998: fig. 125–126); Chrysallida impercepta Schander, 1994 : fig. 10a; Odostomia boermani Aartsen, Gittenberger and Gould, 1998 : fig. 61; Boonea cincta (Carpenter) illustrated in Wise (1996: fig. 9d).

Figures

FIGURES 9 − 20. 9 − 14. Boonea seminuda. 9. holotype (MCZ 186052); 10 − 14 (MNRJ 10956); 9 − 11. whole shells (lengths: 9: 3.81 mm; 10: 4.0 mm; 11: 1.8 mm); 12. last whorl; 13 − 14: protoconchs. Scale bars: 200 Μm. 15 − 20. Boonea scymnocelata: 15, 17, 19 − 20. holotype (MZSP 89107); 16, 18. paratype (MZSP 89108); 15 − 16: whole shells (lengths: 15: 2.0 mm; 16: 2.0 mm); 17 − 19: protoconchs; 20: last whorl. Scale bars: 200 Μm.