Teretia tongaensis, Morassi, Mauro & Bonfitto, Antonio, 2015

Morassi, Mauro & Bonfitto, Antonio, 2015, New Indo-Pacific species of the genus Teretia Norman, 1888 (Gastropoda: Raphitomidae), Zootaxa 3911 (4), pp. 560-570 : 565

Teretia tongaensis sp. nov

Figures 2 .H–N

Type material. Holotype ( MNHN IM- 2000-28379).

Type locality. Tonga Islands, 20°42' S 174°54' W 650–676 m [BORDEAU 2 stn DW 1553]

Material examined. One dd (holotype) from type locality.

Description. Shell fusiform ( Figs. 2 .H–J) (b/l 0.40; a/l 0.44) with high spire, strongly excavated base and relatively short, broad, nearly straight, siphonal canal. Teleoconch of up to 5½ whorls with shallowly impressed, linear suture. Subsutural ramp wide, shallowly concave. Earlier two teleoconch whorls with two weak cords bordering abapical part of subsutural ramp; a relatively prominent peripheral cord and a second main cord at level of abapical suture. On third whorl abapical cord on subsutural ramp becomes bisected, and two additional weak cords appear: one on abapical part of ramp, the other between the two main cords; from this whorl onwards main cords only slightly stronger than weaker cords, with the peripheral cord at about mid- height of the whorl. On penultimate whorl additional weak cords appear: two in the interspace between main cords and two in the abapical part of whorl near suture. Last whorl with one interstitial spiral thread in each interspace between cords; there are about 28 spirals on base and rostrum. Subsutural ramp with two spiral threads bordering adapical suture. Teleoconch whorls sculptured by fine axial growth lines forming relatively strong, widely spaced, arcuate plicules on subsutural ramp, rendering somewhat nodulous the two spiral threads bordering adapical suture. Under SEM ( Fig. 2 .N) surface between spiral cords with a sculpture of microscopic pustules. Aperture oblanceolate, with outer lip simple and fragile, curved in lateral view and forming a very deep, asymmetrical anal sinus, its deepest point on sutural ramp ( Fig. 2 .J). Protoconch damaged of 3+ whorls; tip missing, subsequent whorls with diagonally cancellate sculpture terminating a short distance above suture, abapical part of whorl occupied by fine prosocline riblets ( Figs. 2 . O –P). Maximum diameter about 0.48 mm. Shell yellowish-white with a narrow pale yellowishbrown peripheral band on three earlier whorls. Protoconch yellowish-brown. Dimensions: Holotype 8.2 x 3.4 mm, aperture height 3.4 mm.

Remarks. Although presently known only from a single specimen, this species in our opinion warrants formal description because of its distinctive morphological features. T.tongaensis sp. nov. differs from T. neocaledonica sp. nov. in shape (whorls rounded rather than angulated by the peripheral cord), presence of much more numerous and less prominent spiral cords (the peripheral cord is only barely stronger than other cords in T. tongaensis sp. nov.) and remarkably shorter siphonal canal. Among described fossil species, T. tongaensis sp. nov. resembles Homotoma multicingula Seguenza, 1880 from the “Pliocene” (actually Pleistocene) of Gallina (Reggio Calabria, Italy) in shape and presence of numerous spiral cords, but the latter is much larger (15 mm in length versus 8.7 mm), with longer siphonal canal and, judging from the original description, has even more numerous spiral cords ( Seguenza, 1880: 258). Teretia guersi Schnetler, 2005 from the late Miocene of Denmark lacks angulated earlier whorls but otherwise differs in possessing stronger and more prominent spiral cords.

Etymology. tongaensis = alluding to the fact that the type material was dredged off Tonga Islands.

Figures

FIGURE 2. A – G. Teretia tavianii sp. nov., Gulf of Aden, Cruise RED SED 92, stn RS 1. A – B. Holotype (MZB 60097), 3.2 x 1.5 mm. C. Paratype 1 (MZB 60098), penultimate whorl, scale bar 1 mm. D. Surface microsculpture of penultimate whorl, scale bar 200 µm. E – F. Protoconch, scale bar 200 µm. G. Details of protoconch 1, scale bar 50 µm. H – N. Teretia tongaensis sp. nov. H – N. Holotype (MNHN IM- 2000 - 28379), Tonga, Cruise BORDAU 2, stn DW 1553, 8.2 x 3.4 mm H – J. Frontal and lateral view of holotype, scale bar 2 mm L. Penultimate whorl, scale bar 500 µm. M. Microsculpture of penultimate whorl, scale bar 500 µm. N. Microsculpture of penultimate whorl, scale bar 100 µm. O – P. Protoconch, scale bar 200 µm.