Neritopsis richeri, Lozouet, 2009

Lozouet, Pierre, 2009, A new Neritopsidae (Mollusca, Gastropoda, Neritopsina) from French Polynesia, Zoosystema 31 (1), pp. 189-198 : 191-196

Neritopsis richeri n. sp.

( Figs 2 ; 3 A-D; 4)

? Neritopsis radula – Salvat & Rives 1975: 262, fig. 36. Not N. radula (Linnaeus, 1758) .

TYPE MATERIAL. — Holotype ( MNHN 21374 ) and 6 paratypes ( MNHN 21375 ) from BENTHAUS stn DW 1996.

TYPE LOCALITY. — French Polynesia, Austral Islands, Rurutu (Avera).

ETYMOLOGY. — Dedicated to Bertrand Richer de Forges who has carried out French Pacific explorations for more than a quarter of a century.

MATERIAL EXAMINED. — A total of 128 specimens (23 lots): 103 specimens, from Austral Islands ; 20 specimens from Marquesas ; 1 specimen from Moorea ; 4 specimens from Tuamotu ( Takapoto ) .

Austral Islands. BENTHAUS, Tubuai, 23°21’S, 149°34’W, stn CP 1965, 500- 1200 m, 19.XI.2002, 1 spm. — Banc “Président Thiers”, 24°41’S, 146°01’W, stn DW 1932, 500- 800 m, 14.XI.2002, 4 spm. — Banc “Président Thiers”, 24°40’S, 146°01’W, stn DW 1933, 500- 850 m, 14.XI.2002, 3 spm. — Nord de Raivavae, 23°48’S, 147°39’W, stn DW 1943, 950 m, 15.XI.2002, 2 spm. — Tubuai, 23°19’S, 149°25’W, stn DW 1953, 280- 390 m, 18.XI.2002, 1 spm. — Tubuai, 23°19’S, 149°29’W, stn DW 1957, 558- 1000 m, 18.XI.2002, 3 spm. — Tubuai, 23°25’S, 149°33’W, stn DW 1961, 470- 800 m, 19.XI.2002, 1 spm. — Banc Arago, 23°22’S, 150°43’W, stn DW 1972, 500- 1020 m, 20.XI.2002, 1 spm. — Banc Arago, 23°26’S, 150°44’W, stn DW 1985, 100 m, 21.XI.2002, 2 spm. — Rurutu, Avera, 22°29’S, 151°22’W, stn DW 1995, 212- 450 m, 23.XI.2002, 2 spm. — Rurutu, Avera, 22°29’S, 151°21.9’W, stn DW 1996, 489- 1050 m, 23.XI.2002, 7 spm. — East coast of Rurutu, 22°27’S, 151°19’W, stn DW 2003, 250- 330 m, 24.XI.2002, 2 spm. — East coast of Rurutu, 22°28’S, 151°19’W, stn DW 2004, 430- 850 m, 24.XI.2002, 4 spm. — East coast of Rurutu, 22°28’S, 151°18’W, stn DW 2005, 690- 1800 m, 24.XI.2002, 3 spm. — Rimatara, 22°28’S, 152°49’W, stn DW 2012, 270- 320 m, 25.XI.2002, 2 spm. — Rimatara, 22°39’S, 152°50W, stn DW 2013, 80- 93 m, 25.XI.2002, 6 spm. — Rimatara, 22°38’S, 152°49’W, stn DW 2015, 250- 280 m, 25.XI.2002, 6 spm. — Rimatara, 22°37’S, 152°49’W, stn DW 2018, 770 m, 25.XI.2002, 21 spm. — Rimatara, 22°37’S, 152°49’W, stn DW 2020, 920 m, 25.XI.2002, 19 spm. — Rimatara, 22°36.6’S, 152°49’W, stn DW 2021, 1200 m, 25.XI.2002, 13 spm.

Marquesas Islands. MUSORSTOM 9, Hiva Oa, 9°48’S, 139°09’W, stn DW 1208, 117 m, 28.VIII.1997, 20 spm.

Moorea. Tiahura, pente externe, 33 m, 1 spm.

Tuamotu. Takapoto, 1 spm, Hereheretue, 4 spm.

MEASUREMENTS (holotype). — Height 21.5 mm; maximum width 23.2 mm.

DESCRIPTION

Shell of relatively large size, heavy, globose, consisting of 3.25 convex teleoconch whorls, rapidly expanding, last whorl shouldered. Protoconch (abraded on the holotype), smooth, of at least 2 whorls delimited from teleoconch by obvious line; embryonic shell is partially eroded. Spire protruding weakly, occupying about 22% of the total shell height. Penultimate whorl with 4 strong nodulose spiral cords with 1 or 2 subordinate cords in the interspaces. Last whorl, a little wider than high, occupying 78% of the total height; sculpture consisting of 8 prominent, nodulose, unevenly spaced, primary cords, with 1 to 4 fine secondary spiral cords in each interspaces. Surface between spiral cords bearing numerous scabrous axial costae. Irregular growth lines cover entire surface, more rugose near aperture than elsewhere. Aperture subcircular; outer lip strongly prosocline, sharp, thickened within, bearing numerous coarse lirae, with a long semilunar ridge representing inner limit of the operculum retraction. Inner lip is strongly concave, thick, bearing elongate rightangled notch at centre. Umbilicus represented by shallow depression.

ONTOGENY OF SPIRAL CORDS ( Fig. 2 )

Relatively prominent, oblique axial costae commence at the beginning of the teleoconch and cross primary cords, forming regular square meshwork on the first 0.75 whorl. After 1 whorl, axial costae broader, scabrous, restricted to the interspaces between spiral cords. Four primary spiral cords detectable after 0.25 whorl (P1, P2, P3, P4), then P5, P6 detectable after 1.5 whorl. Secondary cords (S1-S3) detectable only after the first whorl: S1 between P3 and P4, S2 between P4 and P5, S3 between P2 and P3. After 1.5 whorl: S4 added between P1 and P2, S6 and S5 added between suture and P1. After 1.7 whorl, additional secondary cords (S1’, S2’, S3’) detectable, forming double row of spiral cords between primary cords.

COMPARISON

The calcareous operculum of Neritopsi s were described since long time from fossil deposits. For instance Eudes-Deslongchamps & Eudes-Deslongchamps (1858) described some opercula of Neritopsis from Jurassic deposits as new genus Peltarion Deslongchamps & Deslongchamps, 1858 . Living specimens of Neritopsis radula were collected in abundance only recently. The operculum of N. moniliformis has not been described previously, it is illustrated here for the first time ( Fig. 5 ). Batten (1984) considered that Neritopsis radula occurred since Eocene time in the Paris Basin and was present in Miocene rocks of the Paratethys but, in fact, the Paris Basin species is N. parisiensis Deshayes, 1864 and the Paratethys species is closer to N. moniliformis , a species that ranges from lower Oligocene to lower Miocene in the Aquitaine Basin ( Lozouet & Maestrati 1982). However, it is clear that these three species are

B

closely related and can be included in the Neritopsis radula species group.

All specimens were collected dead, and hence lacked the unusual trapezoidal calcareous operculum ( Fig. 5 ). Neritopsis specimens collected in the Marquesas ( Fig. 4 E-H), Tuamotu and Moorea have a multispiral protoconch, but have only one secondary spiral cord in the interspaces between the primary cords; the primary cords are also beaded. Compared with the Austral Islands population, they are also smaller and have a narrower sutural ramp. These specimens are only tentatively included in N. richeri n. sp.

Neritopsis richeri n. sp. from the Austral Islands is highly distinctive in having one to four secondary spiral cords in each interspaces between the primary cords and so is readily distinguished from all other Neritopsis species known since Oligocene time (35 Ma): the recent species Neritopsis radula , N. aqabaensi and N. atlantica , the European fossils N. moniliformis (lower Oligocene to lower Miocene), N. vokesorum Hoerle, 1972 (lower Miocene of Florida, Hoerle 1972) and N. cf. moniliformis (middle Miocene of Europe). Moreover, the New World Neritopsis are umbilicate (a slight umbilicus in the Florida species, a deep, narrow umbilicus in N. atlantica ) whereas the others are not. Superficially, N. richeri n. sp. resembles some Cretaceous species of the genus Hayamia Kase, 1980 (see Kase & Maeda 1980: pl. 35 fig. 9a, b). Among others differential characters, Neritopsis richeri n. sp. has a sutural ramp defined by a shoulder angle and a multispiral protoconch. The Indo-Pacific species N. radula has a paucispiral protoconch ( Kano & Kase 2000: fig. 13) and a non-planktotrophic development can be inferred from its protoconch morphology ( Kano 2006). Despite this, N. radula has a wide distribution in the Indo-West Pacific realm (from Japan, Okinawa to New Caledonia and Red Sea). In contrast, Neritopsis richeri n. sp. with a multipiral protoconch indicating planktotrophic development, with a high dispersal ability, apparently has a geographical distribution restricted to French Polynesia. I suspect that this is probably an artefact resulting from confusion in the literature between N. richeri n. sp. and N. radula . Indeed, Bandel & Frýda (1999) figured from Mauritius (Indian Ocean), under the name Neritopsis radula , a species that has a multispiral protoconch which may be close to N. richeri n. sp. Careful examination of all material identified as N. radula is required before we can exclude the possibility that N. richeri n. sp. extends from Polynesia to the Indian Ocean.

The relationship with Neritopsis aqabaensis from the Gulf of Aqaba (northern Red Sea) is more questionable. The protoconch of N. aqabaensis has two whorls ( Bandel 2007) similar to that of N. richeri n. sp., but the embryonic shell is sculptured with growth lines. Despite partially eroded embryonic and larval shells, the protoconch of N. richeri n. sp. appears clearly to be smooth and is regarded as a multispiral protoconch of the planktotrophic type ( Kano 2006: figs A, D). Moreover, N. aqabaensis was described from a juvenile specimen with only a half whorl of teleoconch, and the adult shells collected in the same locality were indicated by Bandel (2007) as identical to Neritopsis radula . It is unclear whether they belong to one or the other species. Bandel (2007) did not mention the very characteristic secondary cords present in N. richeri n. sp.

Figures

FIG. 2. — Neritopsis richeri n. sp., paratype MNHN 21375, BENTHAUS stn DW 1993, maximum width 8.8 mm: A, protoconch; B, ontogeny of sculpture on teleoconch whorls. Scale bars: A, 200 μm; B, 2 mm.

FIG. 3. — A-D, Neritopsis richeri n. sp., holotype MNHN 21374, BENTHAUS stn DW 1993, maximum width 23.2 mm; E-H, N. radula (Linnaeus, 1758), specimen from New Caledonia, Touho, Montrouzier expedition stn 1272 (10 m), maximum width 29 mm.

FIG. 5. — Operculum of Neritopsis moniliformis Grateloup, 1832, type species of the genus, from the upper Oligocene of France (Aquitaine Basin), Peyrehorade, showing the outer (A) and the inner (B) surfaces; width 7.7 mm.

FIG. 4. — Neritopsis richeri n. sp.: A-D, paratype MNHN 21375, BENTHAUS stn DW 1993, maximum width 12 mm; E-H, specimen from Marquesas Islands, Hiva Ova, MUSORSTOM 9, stn DW 1208, maximum width 13.8 mm.