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Research Article
A rare and unusual new bittiine genus with two new species from the South Pacific (Cerithiidae, Gastropoda)
expand article infoEllen E. Strong, Philippe Bouchet§
‡ National Museum of Natural History, Smithsonian Institution, Washington, United States of America
§ Muséum National d’Histoire Naturelle, Sorbonne Universités, Paris, France
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Abstract

A new genus, Limatium gen. n., and two new species, L. pagodula sp. n. and L. aureum sp. n. are described, found on outer slopes of barrier reefs and fringing reefs in the South Pacific. They are rare for cerithiids, which typically occur in large populations. The two new species are represented by 108 specimens sampled over a period of 30 years, only 16 of which were collected alive. Three subadults from the Philippines and Vanuatu likely represent a third species. In addition to their rarity, Limatium species are atypical for cerithiids in their smooth, polished, honey to golden brown shells with distinctive white fascioles extending suture to suture. The radula presents a unique morphology that does not readily suggest an affinity to any of the cerithiid subfamilies. Two live-collected specimens, one of each species and designated as holotypes, were preserved in 95% ethanol and sequenced. Bayesian analysis of partial COI and 16S rDNA sequences demonstrates a placement in the Bittiinae, further extending our morphological concept of the subfamily.

Keywords

Bittiinae, new genus, new species, marine, DNA

Introduction

The Cerithiidae is one of 19 families of Cerithioidea currently accepted, and with 219 species considered valid, it is one of the most diverse (Bouchet et al. 2017, MolluscaBase 2018). Members are distributed worldwide from tropical to temperate biotopes, most frequently in shallow waters, with a few species that extend into bathyal depths. As far as is known, most species are microherbivorous grazers and usually occur in large populations (e.g., Houbrick 1992). The family is subdivided into three Recent subfamilies: Cerithiinae, Argyropezinae, and Bittiinae (Bouchet et al. 2017), with the Cerithiinae and Bittiinae containing the majority of the species. As discussed in Strong and Bouchet (2013, and references therein), there is presently no known diagnostic feature of shell morphology or internal anatomy that allows unambiguous placement in Cerithiinae versus Bittiinae. The only possible exception may be internal features of the midgut, but this requires further study to confirm (Strong and Bouchet 2013). The notion that bittiines may be distinguished by small adult size is a frequent misperception.

Unusual polished, golden shells, less than one centimeter in adult length, of an unfamiliar species first became known to us in material collected by the RAPA 2002 expedition to the Austral Islands. Since then, material comprising at least two species has been sorted from residues collected during campaigns led by the MNHN, with particularly rich sources of specimens from the MONTROUZIER expedition to New Caledonia in 1993, and the LIFOU 2000 expedition to the Loyalty Islands. The earliest specimens located thus far were collected during the MUSORSTOM 3 cruise to the Philippines in 1985, from the early years of the Tropical Deep Sea Benthos program (Bouchet et al. 2008). Despite readily identifiable as belonging to the Cerithiidae, their subfamily placement was unclear. Early collections were represented mainly by empty shells, with only a handful of live-collected specimens that had been subsequently dried. This hampered the use of anatomical dissections to explore their systematic placement; the unique radula did not suggest an affinity to any of the cerithiid subfamilies. The ability to assess their affinities more robustly was possible only with the collection of the first live-collected specimen preserved in ethanol during the Moorea Biocode Project in 2008. In 2013 a specimen of a second species was preserved for molecular analysis during the TUHAA PAE 2013 cruise to the Austral Islands. Based on this material, we here describe a new genus, Limatium n. gen., with two new species, L. pagodula sp. n. and L. aureum sp. n.

Methods

The only two live-collected, fluid-preserved specimens were those used for sequencing and are the designated holotypes. The head-foot of each was removed through the aperture after drilling a small hole through the abapertural side of the penultimate whorl of the shell. The radulae of the holotypes were extracted and mounted for examination via scanning electron microscopy. However, the radula of Limatium pagodula sp. n. was teratological with thin, flimsy, poorly formed teeth along its length; no other live-collected material exists for this species and the operculum is unknown. In addition to the holotype of Limatium aureum sp. n., a second specimen live collected in Rapa and subsequently dried was used to extract an operculum and a radula for comparative purposes.

The three radulae and single operculum were tissue digested overnight in 100 µl of ATL lysis buffer (Qiagen, Inc.) containing ~50 µg of Proteinase-K, sonicated and rinsed in de-ionized water. Cleaned radulae were mounted directly on glass coverslips; the operculum was attached to the cover slip using a carbon adhesive tab. The cover slips were then attached to aluminum stubs with carbon adhesive tabs, coated with 25-30 nm gold/palladium (60/40), and photographed using an Apreo scanning electron microscope (FEI Company) at the NMNH. Specimens of subadults and juveniles were selected for examination of protoconchs. These shells were mounted on aluminum stubs with Elmer’s glue© and photographed uncoated in charge reduction mode using a Hitachi TM3000 scanning electron microscope (Hitachi High Technologies America, Inc.) also at the NMNH. Shells were photographed using a Canon EOS 50D camera with a Canon MP-E 65 mm f/2.8 1–5× macro lens and Canon MT-24EX macro twin light flash (Canon USA, Inc.).

The partial COI sequence for the holotype of Limatium pagodula sp. n., was produced under the Moorea Biocode Project (see Geller et al. 2013). For the other newly generated sequences, genomic DNA was extracted from roughly one cubic millimeter of 95% ethanol-preserved foot tissue using an automated phenol:chloroform extraction on the Autogenprep965 (Autogen, Holliston, MA) using the mouse tail tissue protocol with a final elution volume of 50 µl. A 658 base pair (bp) fragment of the cytochrome c oxidase I (COI) gene was amplified using degenerate Folmer primers (dgLCO/dgHCO) (Meyer et al. 2005) with M13 tails, and using JGLCO (Geller et al. 2013) in combination with C1-N-2191R (aka “Nancy”) (Simon et al. 1994). A ~510 bp fragment of the 16S rRNA gene was amplified using the universal primers 16SAR/BR (Palumbi et al. 1991). PCR reactions were performed with 1 μl of undiluted DNA template in 20 μl volumes. Reaction volumes for COI contained 10 µl of Promega Go-Taq® Hotstart Master Mix (1 unit Promega Go-Taq®, 400 μM dNTPs, 4 mM MgCl2), 0.3 µl 10 µM of each primer, 0.25 µg/μl of BSA, and 1.25% DMSO. Amplification consisted of an initial denaturation step at 95 °C for 7 min, followed by 45 cycles of denaturation at 95 °C for 45 s, annealing at 42 °C for 45 s, extension at 72 °C for 1 min and a final extension at 72 °C for 5 min. Reaction volumes for 16S, also in 20 μl volumes, contained 1 μl of undiluted template DNA, 1 unit Biolase DNA Polymerase (Bioline), 2 µl 10X reaction buffer, 500 μM dNTPs, 2 mM MgCl2, 0.25 μg/μl of BSA, and 0.3 µl 10 µM of each primer. Amplification consisted of an initial denaturation step at 95 °C for 5 min, followed by 35 cycles of denaturation at 95 °C for 30 s, annealing at 48 °C for 30 s, extension at 72 °C for 45 s and a final extension at 72 °C for 3 min. PCR products were purified prior to sequencing using the Exo-SAP-IT protocol (Amersham Biosciences, Piscataway, NY). Sequencing reactions were performed with 1 µl of purified PCR product, 1.75 µl BigDye buffer, and 0.5 µl BigDye (ABI, Foster City, CA), and run in the thermal cycler for 30 cycles of 30 s at 95 °C, 30 s at 50 °C, 4 min at 60 °C, and then held at 10 °C. Sequencing reactions were purified using Millipore Sephadex plates (MAHVN-4550, Millipore, Billerica, MA) per manufacturer’s instructions and analyzed on an ABI 3730XL DNA Analyzer Capillary Array.

Chromatograms were trimmed, assembled, and edited as necessary in Geneious 11.0.2. Sequences were aligned separately for each gene with ClustalX (Thompson et al. 1997) using default parameters as implemented in Geneious. COI was translated into amino acids to check for stop codons and frameshift mutations. All newly generated sequences have been deposited in GenBank (Table 1).

Museum registration and GenBank accession numbers for specimens included in the phylogenetic analysis. Representatives of type species (or their subjective synonyms) of genera currently accepted as valid, indicated by ‘*’. Sequences previously published in the analysis of Strong and Bouchet (2013) in regular font, newly sequenced specimens in bold.

Species Voucher COI 16S Locality
Litiopidae
Litiopa melanostoma Rang, 1829 * USNM 1199716 KC699870 KC699903 Marathon Key, Coco Plum Beach, Florida, USA, 24°43.45'N, 81°00.04'W.
Cerithiidae
Bittiinae
Bittiolum varium (Pfeiffer, 1840) USNM 1199719 KC699852 KC699912 Sebastian Inlet, Florida, USA, 27°51.63'N, 80°26.95'W, 1 m.
Bittium glareosum Gould, 1861 MNHN IM-2009-29804 KC699853 KC699905 INHACA 2011, Stn. MS14, Baixo Danae, 25°54.5'S, 33°2.8'E, 23–26 m.
Bittium impendens (Hedley, 1899) USNM 1199720 KC699854 KC699911 Shark’s Cove, Oahu, Hawaii, USA, 21°38.99'N, 158°3.8'W, 1 m.
Bittium latreillei (Payraudeau, 1826) USNM 1199724 KC699855 KC699914 Espigon de Rocas, Benalmádena-Costa, Benalmádena, Spain 36°35.3'N, 04°31.7'W, 1–5 m.
Bittium reticulatum (da Costa, 1778) * USNM 1462732 MH253703 MH253699 Espigon de Rocas, Benalmádena-Costa, Benalmádena, Spain 36°35.3'N, 04°31.7'W, 1–5 m..
Bittium simplex (Jeffreys, 1867) USNM 1199729 KC699856 KC699913 Strait of Gibraltar, Isla de Tarifa, Spain, 36°00.3'N, 05°36.53'W, intertidal.
Cacozeliana granarium (Kiener, 1842) * USNM 1200194 KC699857 KC699904 Long Reef, Sydney, New South Wales, Australia, 33°44.6'S, 151°19.1'E, intertidal.
Ittibittium houbricki (Ponder, 1993) MNHN IM-2013-42433 MH253702 MH253698 Cape Naturaliste, Eagle Bay, Western Australia
Ittibittium parcum (Gould, 1861) * USNM 1199730 KC699869 KC699902 Shark’s Cove, Oahu, Hawaii, USA, 21°39.16'N, 158°3.75'W, intertidal.
Limatium aureum sp. n. (holotype) MNHN IM-2013-42460 MH253701 MH253697 TUHAA PAE 2013. Austral Islands, Maria. Pente externe récif barrière. 24 m. 21°47.8'S, 154°43'W.
Limatium pagodula sp. n. (holotype) * UF 427943 MH253700 Moorea Biocode Project. French Polynesia, Society Islands, Moorea. Haapiti, just NW of Matauvau Pass outer reef slope, brushed from under rubble. 20–22 m. -17.568°, -149.884°.
Pictorium koperbergi (Schepman, 1907) * MNHN IM-2009-26984 KC699871 KC699907 PANGLAO Marine Biodiversity Survey 2004, Stn. B10, Panglao I., Momo Beach, 9°36.5'N, 123°45.6'E, 3–14 m.
Pictorium versicolor Strong & Bouchet, 2013 MNHN IM-2009-26994 KC699874 KC699910 SANTO Marine Biodiversity Survey 2006, Stn. EP36, E Aoré I., Aimbuei Bay, 15°33.1'S-15°33.3'S, 167°12.4/12.7'E, 20–60 m.
Pictorium violaceum Strong & Bouchet, 2013 MNHN IM-2009-26986 KC699875 KC699909 SANTO Marine Biodiversity Survey 2006, Stn. EP36, E Aoré I., Aimbuei Bay, 15°33.1'S-15°33.3'S, 167°12.4/12.7'E, 20–60 m.
Cerithiinae
Cerithium atromarginatum Dautzenberg & Bouge, 1933 USNM 1200200 KC699858 KC699899 Shark’s Cove, Oahu, Hawaii, USA, 21°39.16'N, 158°3.75'W, intertidal.
Cerithium balteatum Philippi, 1848 MNHN IM-2009-29697 KC699859 KC699889 SANTO Marine Biodiversity Survey 2006, Stn. DB53, Palikulo Bay, 15°28.8'S, 167°15.2'E, 5 m.
Cerithium caeruleum GB Sowerby II, 1855 MNHN IM-2009-27010 KC699860 KC699894 Atimo Vatae Madagascar “Deep South” Survey 2010, Stn. TM2, Cap Ranavalona, 25°4.3'S, 46°57.7'E, 0–1 m.
Cerithium egenum Gould, 1849 USNM 1200201 KC699861 KC699900 Shark’s Cove, Oahu, Hawaii, USA, 21°39.16'N, 158°3.75'W, intertidal.
Cerithium lifuense Melvill & Standen, 1895 MNHN IM-2009-29698 KC699862 KC699890 SANTO Marine Biodiversity Survey 2006, Stn. DB53, Palikulo Bay, 15°28.8'S, 167°15.2'E, 5 m.
Cerithium munitum GB Sowerby II, 1855 MNHN IM-2009-29699 KC699863 KC699891 SANTO Marine Biodiversity Survey 2006, Stn. DS4, Segond Channel, Coolidge wreck, 15°31.4'S, 167°14.1'E, 25 m.
Cerithium nodulosum Bruguière, 1792 * MNHN IM-2009-29700 KC699864 KC699893 SANTO Marine Biodiversity Survey 2006, Stn. VM45, N Malo I., Andwélé rivulet, 15°37.7'S, 167°08.6'E, intertidal.
Cerithium rostratum A Adams, 1855 USNM 1200202 KC699865 KC699901 Shark’s Cove, Oahu, Hawaii, USA, 21°39.16'N, 158°3.75'W, intertidal.
Cerithium salebrosum GB Sowerby II, 1855 MNHN IM-2009-29701 KC699866 KC699892 SANTO Marine Biodiversity Survey 2006, Stn. DR64, Palikulo Bay, 15°27.6'S, 167°14.3'E, 6–35 m.
Clypeomorus bifasciata (GB Sowerby II, 1855) * MNHN IM-2009-29702 KC699867 KC699888 SANTO Marine Biodiversity Survey 2006, Stn. ZM15, NW Malo, 15°38.1'S, 167°05.9'E, intertidal.
Clypeomorus petrosa (Wood, 1828) MNHN IM-2009-29703 KC699868 KC699887 SANTO Marine Biodiversity Survey 2006, Stn. LM23, Segond Channel, vicinity of Maritime College, 15°31.5'S, 167°09.6'E, intertidal.
Pseudovertagus aluco (Linnaeus, 1758) * MNHN IM-2009-29704 KC699883 KC699895 SANTO Marine Biodiversity Survey 2006, Stn. VM16, Bruat Channel, N coast of Malo I., 15°37.7'S, 167°11.0'E, intertidal.
Rhinoclavis aspera (Linnaeus, 1758) MNHN IM-2009-29705 KC699884 KC699896 SANTO Marine Biodiversity Survey 2006, Stn. FR29, Palikulo Bay, 15°27.9'S, 167°14.6'E, 5–35 m.
Rhinoclavis fasciata (Bruguière, 1792) MNHN IM-2009-29706 KC699885 KC699897 SANTO Marine Biodiversity Survey 2006, Stn. VM32, W Aésé I., 15°26.6'S, 167°15.2'E, intertidal.
Rhinoclavis vertagus (Linnaeus, 1767) * MNHN IM-2009-29707 KC699886 KC699898 SANTO Marine Biodiversity Survey 2006, Stn. VM40, Surunda Bay, 15°27.7'S, 167°13.2'E, intertidal.

The best fit partitions and models for phylogenetic analyses were determined with PartitionFinder 1.1.1 (Lanfear et al. 2012) which favored the following scheme: COI: SYM+I+G, F81+I, HKY+G, for the first, second and third codon position, respectively; and GTR+I+G for 16S. A subset of the cerithiid dataset of Strong and Bouchet (2013) was used, augmented with newly generated COI and 16S sequences for Ittibittium houbricki (Ponder, 1993) and Bittium reticulatum (da Costa, 1778) (see Table 1). In addition to Limatium, the Bittiinae was represented by five of the 12 Recent genera currently accepted, four by their type species or their subjective synonyms (see Table 1). Bayesian analysis of the concatenated dataset for 29 cerithiids and one outgroup (Litiopidae) was inferred with MrBayes 3.2.6 (Ronquist and Huelsenbeck 2003) on the CIPRES Science Gateway, using the schemes and models indicated by PartitionFinder. Bayesian analyses, consisting of two independent replicates with four heated chains each (0.02), and three swaps per swapping cycle, were run for 50,000,000 Markov chain Monte Carlo (MCMC) generations with a sampling frequency of one tree every 1000 generations. The first 25% were discarded as burn-in. Tracer 1.6 (Rambaut et al. 2014) was used to assess MCMC convergence and to ensure that all ESS values exceeded 200. A majority rule consensus tree was constructed with the sumt command. Nodal support was assessed with posterior probability of each node.

Results

Systematics

Family CERITHIIDAE J. Fleming, 1822

Subfamily BITTIINAE Cossmann, 1906

Limatium gen. n.

Type species

Limatium pagodula sp. n.

Diagnosis

Shells of small size, 6 to 7 mm in adult length on average, with smooth, polished surface, golden honey to dark brown in color. Rachidian with hexagonal to septagonal basal plate, squarish to rectangular, with elevated central portion with rounded, U-shaped lower margin; cutting edge with three, sharply pointed cusps. Operculum paucispiral with large, subcentral nucleus.

Etymology

From the Latin adjective limatus, -a, -um, meaning polished, and the ending -ium of many cerithiid genera. Gender neuter.

Ecology

All known specimens of Limatium come from the outer slope of barrier reefs or, in islands without a coral reef lagoon, from the slope of the fringing reefs in the South Pacific (Fig. 1). Not a single specimen has been collected within a coral reef lagoon. The few live-taken specimens come from a confirmed bathymetric range of 10-100 m, with empty shells, potentially carried downslope, occasionally dredged from deeper water.

Figure 1. 

Distribution map of Limatium pagodula sp. n. («) and Limatium aureum sp. n. (■) in the South Pacific. Symbols with white fill indicate the type localities of the two species, in the Society (L. pagodula) and the Austral islands (L. aureum). The provisional record “■?” is for the unusually tall and narrow specimen from Tonga that was tentatively allocated to L. aureum.

Remarks

Limatium differs from all other bittiine genera in the smooth, shiny, polished surface of the shell and its rich, golden honey to dark brown color. The two species known thus far are further distinguished by the distinctive white fascioles extending suture to suture and which may be a diagnostic feature of the genus, but further comparative material is required. No other bittiine is known to possess a rachidian basal plate that is hexagonal to septagonal in shape, with an elevated central portion; the cutting edge uniquely bears only three, sharply pointed, dagger-like cusps. The paucispiral operculum is also unique among bittiines as understood thus far.

Limatium pagodula sp. n.

Fig. 2

Type material

Holotype UF 427943 (Biocode No. MBIO19550, Specimen No. BMOO-03501,) (Fig. 2A, H); paratypes as listed below.

Figure 2. 

Shell and external morphology of Limatium pagodula sp. n. A Holotype, UF 427943. French Polynesia, Society Islands, Moorea B Paratype, USNM 1462731. Tuamotu Islands, Makemo, Pohue (ex. coll. Letourneux) C Paratype, MNHN IM-2014-6933. Vanuatu, Santo, W. of Tutuba I., SANTO 2006 stn. DS104 D Subadult. Tuamotu Islands, Makemo, Arikitamiro (coll. Letourneux) E Protoconch, USNM 1462729. Tahiti, grotte du chenal d’Arue (ex. coll. Letourneux) F Protoconch. Tuamotu Islands, Makemo, Arikitamiro (coll. Letourneux) (same as in 2D) G Protoconch, Tuamotu Islands, Makemo, Arikitamiro (coll. Letourneux) H Living animal, holotype UF 427943. French Polynesia, Society Islands, Moorea. Scale bars: 5 mm (A–C); 1 mm (D, H); 100 µm (E–G).

Type locality

French Polynesia, Society Islands, Moorea. Haapiti, just NW of Matauvau Pass outer reef slope, brushed from under rubble, 17°34.1'S, 149°53.0'W, 20–22 m (Moorea Biocode; collector’s event ID MIB_087; leg. Chris Meyer & Christian McKeon; 20 October 2008).

Other material examined

FRENCH POLYNESIA. SOCIETY IS: Tahiti, grotte du chenal d’Arue, ca. 17°31'S, 149°31.3'W, 12 m, 1 empty shell (dd), USNM 1462729 ex coll. Letourneux (Fig. 2E); Tahiti, faille d’Arue, 33 m, 1 dd, USNM 1462730 ex coll. Letourneux. TUAMOTU IS: Makemo, secteur de Pohue, 16°40.1'S, 143°22.5'W, 63 m, 1 dd, paratype USNM 1462731 ex coll. Letourneux (Fig. 2B); Makemo, passe Arikitamiro, ca. 16°37.1'S, 143°33.9'W, 45–54 m, 9 dd in coll. Letourneux (Fig. 2D, F; 6 not seen); Rangiroa, passe de Tiputa, ca. 14°58.0'S, 147°37.5'W, 100 m, 2 dd in coll. Letourneux (not seen). VANUATU. SANTO I.: SANTO 2006: stn. ZB9, W. Malo I., 15°40.6'S, 167°05.1'E, 5–7 m, 1 dd, MNHN uncatalogued. – Stn. DS104, W. of Tutuba I., Vunatavoa Bay, 15°34.1'S, 167°16'E, 10–80 m, 1 dd, paratype MNHN IM-2014-6933 (Fig. 2C).

Etymology

From the Latin pagoda, with reference to the strongly angular whorls reminiscent of the upward curving roofs of Asian temples; pagodula is a diminutive, used as a noun in apposition.

Diagnosis

Shell [holotype, unless otherwise noted]. Shell narrow, slender, with high, conical spire, body whorl occupying ~45% of shell height, consisting of 9+ [first three whorls very encrusted] moderately convex but angular teleoconch whorls, suture impressed (Fig. 2A). Protoconch [very worn on holotype; description based on specimens illustrated in Fig. 2E–G] multispiral, of 2.5 whorls, with a sculpture of two strong, pustulose spiral keels at periphery, and a third, much lighter cord on the base, essentially covered by next whorl; strong, prosocline, axial riblets on sutural ramp, fading out abapically towards spiral keel; and irregular, elongated granules that cover the abapical part of the whorl and extend in between the two peripheral keels; protoconch/teleoconch transition sharp, with a lamellar terminal varix and a deeply indented sinusigera notch (Fig. 2E–G). Sculpture of teleoconch consisting of broad, poorly defined axial ribs forming a strong angular projection at adapical two-thirds of the whorl, crossed over by three (on body whorl 4) narrow, sharply defined spiral cords on exposed part of adult whorls, and a 4th, strongly raised, basal cord that is mostly covered by next whorl. Shell base slightly concave, with 7 unevenly spaced spiral cords. Siphonal canal very short, broadly open, constricted. Aperture circular-ovate, ~30% of shell height (in paratype, flaring and subquadrate, forming an angle where basal cord meets the outer lip). Anal canal indistinct. Columella concave with thinly callused columellar lip. Outer lip of aperture forming a terminal varix, subvertical on periphery, regularly convex on base. Shell surface smooth and shiny, as if waxed, color overall deep brown with broad, opaque white fascioles extending from suture to suture at irregular intervals, spiral cords on spire and base white, cord encircling the base brown with white blotches at regular intervals; columellar side of canal and columellar callosity white, parietal callosity transparent. Tip of teleoconch (first 1.5 whorl) white, protoconch dark brown. Dimensions: 6.50 × 2.65 mm. Average 5.98 ± 0.48 mm (n = 3).

External anatomy. Head-foot dark golden brown in color; cephalic tentacles with irregular white blotches and golden tips. Foot sole golden, with thin, transverse white lines, discontinuous across prominent longitudinal groove at midline; condition of pedal glands unknown. Epipodial skirt also with thin, transverse white to golden lines, present from propodium to large, projecting opercular lobe. Epipodial tentacles lacking.

Radula. The radula of the sequenced specimen was teratological, and we do not provide a detailed description or illustration. The gross features that were visible conform to those in L. aureum sp. n. (see below): a rachidian with broad hexagonal basal plate and elevated central portion with rounded base, cutting edge with three pointed cusps, lateral teeth with short lateral extensions roughly 1.5 times length of cutting edge, face of lateral teeth with buttress terminating in prominent, rounded knob midway down face of lateral teeth, outer edges of outer marginal teeth acuspate.

Distribution and ecology

Society Islands and Tuamotus (French Polynesia); Vanuatu. Known only from the material examined. Only one specimen was collected alive, from the outer reef slope, brushed from under rubble, 20–22 m.

Remarks

The sequenced specimen from Moorea is designated as holotype, although its outer lip is not fully mature. In the fully adult paratype from Santo (Fig. 2C), the axial white fascioles are fewer, but are aligned from one whorl to the next, and there is a strong varix one-half whorl before the aperture.

Limatium aureum sp. n.

Fig. 3A–H, K, L, N

Type material

Holotype MNHN IM-2013-42460 (Fig. 3A); paratypes as listed below.

Figure 3. 

Shell and operculum morphology of Limatium aureum sp. n. (A–H, K, L, N) and Limatium sp. (I, J, M). Limatium aureum sp. n.: A Holotype, MNHN IM-2013-42460. Austral Islands, Maria B Austral Islands, Pointe Kauira, RAPA 2002 stn. 36 (MNHN IM-2014-6920) C New Caledonia, CORAIL 2 stn. DW26 (MNHN IM-2014-6921) D Tonga, between Eua and Tongatapu, BORDAU 2, stn. DW1512 (MNHN IM-2014-6922) E Austral Islands, NW of Tauna Islet, RAPA 2002 stn. 44 (MNHN IM-2014-6923) F New Caledonia, Grand Récif Aboré off Nouméa, MONTROUZIER stn. 1352 (MNHN IM-2014-6924). G Loyalty Islands, LIFOU 2000 stn. 1423 (MNHN IM-2014-6925) H Loyalty Islands, LIFOU 2000 stn. 1418 (MNHN IM-2014-6926) K Protoconch, New Caledonia, Grand Récif Aboré off Nouméa, MONTROUZIER stn. 1352 (MNHN IM-2014-6927) L Protoconch, Austral Islands, SE of Tauna Islet, RAPA 2002 stn. 8 (MNHN IM-2014-6928) N Operculum, Austral Islands, Pointe Kauira, RAPA 2002 stn. 36 (MNHN IM-2014-6829) (same as in 3B). Limatium sp.: I Philippines, W of Mindoro, MUSORSTOM 3 stn. DR117 (MNHN IM-2014-6830) J Vanuatu, Santo, W of Tutuba, SANTO 2006 stn. DS103 (MNHN IM-2014-6831) M Protoconch, Vanuatu, Santo, West of Tutuba I., SANTO 2006 stn. DS103 (MNHN IM-2014-6832) (same as in 3J). Scale bars: 5 mm (A–J); 100 µm (K–M); 500 µm (N).

Type locality

Austral Islands, Maria I., outer slope of barrier reef, 21°47.8'S, 154°43'W, 24 m [TUHAA PAE 2013 cruise, stn. AMA02, field number PB16_BC855; leg. A. Fedosov; 5 April 2013].

Other material examined

(all in MNHN uncatalogued, except where noted): FRENCH POLYNESIA. AUSTRAL IS: RAPA Island expedition 2002: Stn. 6, off Baie de Ahurei, 27°36.8'S, 144°16.7'W, 42 m, 1 dd. – Stn. 8, SE of Tauna islet, 27°36.5'S, 144°17.7'W, 52–57 m, 7 dd (MNHN IM-2014-6928, Fig. 3L). – Stn. 28, Pointe Taekateke, 27°38.4'S, 144°20.6'W, 30 m, 1 dd. – Stn. 36, Pointe Kauira, 27°33.5'S, 144°20.8'W, 27 m, 1 live collected (lv), 2 dd (MNHN IM-2014-6920, IM-2014-6929, Fig. 3B, N). – Stn. 44, NW of Tauna islet, 27°36.3'S, 144°18.2'W, 30 m, 2 dd (MNHN IM-2014-6923, Fig. 3E). – BENTHAUS stn. DW1934, Banc Président Thiers, 24°40.6'S, 145°57.4'W, 560-1150 m, 1 dd. TUAMOTU IS: Makemo, secteur Pohue, 16°40.1'S, 143°22.5'W, 63 m, 1 dd, paratype USNM 1462727 ex coll. Letourneux; Makemo, passe Arikitamiro, ca. 16°37.1'S, 143°33.9'W, 45 m, 47 m and 54 m, 3 dd, in coll. Letourneux; Rangiroa, Passe de Tiputa, ca. 14°58.0'S, 147°37.5'W, 81 m and 100 m, 2 dd, USNM 1462728 ex coll. Letourneux. NEW CALEDONIA. Coral Sea. Lansdowne-Fairway Reefs. CORAIL 2 stn. DW26, 20°22'S, 161°05'E, 62 m, 1 lv (MNHN IM-2014-6921, Fig. 3C). – EBISCO stn. DW2622, 20°04'S, 160°21'E, 291–323 m, 1 dd. Mainland New Caledonia. LAGON Stn. 830, off Poindimié, 20°49'S, 165°19'E, 105–110 m, 4 dd. MONTROUZIER Stn. 1269, Récif Doiman off Touho, outer slope, 20°35.1'S, 165°08.1'E, 15–20 m, 4 dd. – Stn. 1331, Grand Récif de Koumac, outer slope, 20°40'-20°40.6'S, 164°11.2'-164°12.1'E, 55-57 m, 4 dd. – Stn. 1352, Grand Récif Aboré off Nouméa, outer slope, 22°22.2'S, 166°16.0/166°16.1'E, 27–35 m, 5 lv, 4 dd (MNHN IM-2014-6924, IM-2014-6927, Fig. 3F, K); – Stn. 1354, Grand Récif Aboré, outer slope, 22°22.3'S, 166°15.9'E, 27–37 m, 2 lv, 2 dd. BATHUS 1 stn. DW692, 20°35'S, 164°59'E, 140–150 m, 2 dd. LOYALTY ISLANDS: LIFOU 2000 Expedition, Baie du Santal: stn. 1418, 20°46.9'S, 167°07.9'E, 1–5 m, 1 dd (MNHN IM-2014-6926, Fig. 3H). – Stn. 1423, 20°54'S, 167°07.3'E, 12 m, 2 dd (MNHN IM-2014-6925, Fig. 3G). – Stn. 1429, 20°47.5'S, 167°07.1'E, 8–18 m, 2 dd. – Stn. 1432, 20°53.5'S, 167°02.7'E, 12–32 m, 2 dd. – Stn. 1434, 20°52.5'S, 167°08.1'E, 5–20 m, 2 dd. – Stn. 1441, 20°46.4'S, 167°02'E, 20 m, 2 dd. – Stn. 1442, 20°46.4'S, 167°02'E, 47 m, 1 dd. – Stn. 1443, 20°53.8'S, 167°07.3'E, 48–52 m, 3 dd. – Stn. 1445, 20°50.8'S, 167°09.7'E, 10–12 m, 1 dd. – Stn. 1448, 20°45.8'S, 167°01.6'E, 20 m, 4 dd. – Stn. 1449, 20°45.8'S, 167°01.6'E, 17 m, 1 dd. – Stn. 1450, 20°45.8'S, 167°01.6'E, 27–31 m, 1 dd. – Stn. 1451, 20°47.3'S, 167°06.8'E, 10–21 m, 3 dd. – Stn. 1453, 20°54.6'S, 167°02.1'E, 21–30 m, 1 dd. – Stn. 1454, 20°56.6'S, 167°02'E, 15–18 m, 2 dd. – Stn. 1455, 20°56.8'S, 167°02.7'E, 15–20 m, 1 lv, 1 dd. – Stn. 1456, 20°49.3'S, 167°10.4'E, 25–30 m, 1 lv, 1 dd. – Stn. 1457, 20°46.8'S, 167°02.8'E, 5–10 m, 2 lv, 1 dd. – Stn. 1461, 20°54'S, 167°02'E, 100–120 m, 1 lv, 1 dd. – Stn. 1469, 20°54.2'S, 167°00.4'E, 70–130 m, 2 dd.

Etymology

Latin adjective aureus, -a, -um, meaning golden, with reference to the background color of the shell.

Diagnosis

Shell [holotype, unless otherwise noted]. Shell short, squat, with regular, conical spire, body whorl occupying ~46% of shell height, consisting of 9+ [tip of teleoconch and protoconch missing] rather flat teleoconch whorls, suture impressed (Fig. 3A). Protoconch [description based on specimens illustrated in Fig. 3K, L] multispiral, of 2.5 whorls, with a complex sculpture of two strongly pustulose, thick and heavy spiral keels at periphery, and a third, much lighter cord on the base, partly covered by next whorl; strong, prosocline, axial riblets on sutural ramp, fading out abapically towards spiral keel; and irregular, short, elongated or rounded granules that cover the abapical part of the whorl and may extend in between the two peripheral keels; protoconch/teleoconch transition sharp, with a lamellar terminal varix and a deeply indented sinusigera notch (Fig. 3K, L). On early teleoconch whorls sculpture consisting of closely-set axial ribs intersected by three spiral cords together forming beaded intersections, abapicalmost cord stronger, forming an angular projection at intersection with ribs; axial and spiral sculpture becoming weaker on exposed parts of subadult and adult whorls, until an almost smooth last whorl; last whorl with weakly defined basal cord encircling convex base bearing six well defined, raised cords. Siphonal canal very short, broadly open, not constricted. Aperture circular-ovate, ~32% of shell height. Anal canal indistinct. Columella concave with very thinly callused columellar lip. Outer lip of aperture slightly thickened, but not forming a terminal varix, subvertical on periphery, regularly convex on base. Shell surface smooth and shiny, as if waxed, color overall rich honey to golden brown with broad, opaque, irregular white fascioles extending from suture to suture at irregular intervals; adapical and basal cords with alternating white and honey blotches at regular intervals; columellar side of anal and columellar callosity white, parietal callosity transparent. Tip of teleoconch (first whorl) white, protoconch dark brown. Dimensions: 7.97 × 3.40 mm. Average 6.83 ± 1.47 mm (n = 12).

Operculum. Subcircular, paucispiral, comprising three whorls. Nucleus large, subcentral, ~72% of operculum length.

Radula. Rachidian (Fig. 4A–C, E, F) with roughly hexagonal to septagonal basal plate, squarish to rectangular, broader than tall, with elevated central portion with rounded, U-shaped lower margin. Cutting edge bearing one strong central and two lateral long, dagger-like pointed cusps; central cusp up to twice as long as lateral cusps. Lateral teeth (Fig. 4A, B, C, E–F) with short lateral extensions, roughly 1.5 times length of cutting edge. Cutting edge with large central, pointed cusp and single, large pointed inner cusp and two to four tapering outer denticles. Thickened buttress extending down face of marginal tooth slightly outside central cusp, terminating in prominent, bluntly rounded peg roughly halfway down face (Fig. 4F). Marginal teeth (Fig. 4A, C–D, E) similar in shape and denticulation. Inner marginal teeth with large pointed central cusp, two to three tapering inner pointed cusps and one to two outer pointed denticles. Outer marginal teeth with large, pointed, central cusp, two to three tapering inner pointed cusps and a smooth, acuspate outer edge.

Figure 4. 

Radula morphology of Limatium aureum sp. n. A–D Holotype, MNHN IM-2013-42460, Austral Islands, Maria E, F Austral Islands, Pointe Kauira, RAPA 2002 stn. 36 A Radular ribbon B Detail of rachidian and lateral teeth C Detail of half row, showing outer edges of lateral and marginal teeth D Detail of marginal teeth, showing inner edges E Radular ribbon of second specimen, showing variation in length of cusps F Detail of rachidian and lateral teeth, showing variation in width of rachidian and in length of cusps. Scale bar: 50 µm (A, C, D, E); 40 µm (B); 30 µm (F).

Distribution and ecology

Austral Islands and Tuamotus (French Polynesia); Loyalty Islands, mainland New Caledonia, and Coral Sea. Known only from the material examined. Collected alive in 10–100 m, empty shells to 560–1150 m were undoubtedly carried downslope.

Remarks

The holotype is “untypical” in the sense that it is an unusually broad specimen that, however, seems to be connected by morphologically intermediate specimens to forms that are more slender and with a strong cord delimiting the basal disc. All these specimens share a color pattern of alternating white and honey blotches on the subsutural and basal cords, in addition to ill-defined axial white fascioles, on an overall rich, golden honey background. Another type of variation comes from the extension/persistence of the spiral cords on subadult/adult whorls – with specimens almost completely smooth on the periphery of the last whorl and others with strong spiral cords persisting onto the last whorl.

An empty shell collected from Tonga (BORDAU 2 stn. DW1512, between Eua and Tongatapu, 21°19'S, 175°01'W, 183–184 m) (MNHN IM-2014-6922, Fig. 3D) is unusually tall and narrow, with spiral and axial sculpture persisting onto the last whorl; its color pattern, however, is very similar to that of L. aureum and we tentatively consider it to belong to that species.

Limatium sp.

Fig. 3I, J, M

Material examined

PHILIPPINES: MUSORSTOM 3 Stn. DR117, W of Mindoro, 12°31'N, 120°39'E, 92–97 m, 1 lv (MNHN IM-2014-6930, Fig. 3I). VANUATU: SANTO 2006 stn. DS103, W of Tutuba I., Vunatavoa Bay, 15°34.1'S, 167°16'E, 10–80 m, 2 dd (MNHN IM-2014-6931, IM-2014-6932, Fig. 3J, M).

Remarks

Three specimens (Fig. 3I, J, M) show an overall resemblance to L. aureum, but differ in a manner that we think they are not conspecific. The three specimens from the Philippines and Vanuatu are subadults; their color pattern does not have the articulated white and golden honey spiral cords. The specimens from Vanuatu have a single cord on the base versus five in the specimen from the Philippines, and these two specimens may not even be conspecific. The protoconch of a Vanuatu specimen (Fig. 3M) is distinctly smaller than in L. aureum, consisting of only two whorls, with fewer and shorter axial riblets on the ramp, and simpler, less ornamented spiral keels. No specimen of this or any other Limatium has been obtained in the Philippines despite extensive sampling by lumun-lumun for the commercial shell trade (G. Poppe and S. Tagaro, pers. comm.).

Phylogenetic analysis

Bayesian analysis of the concatenated COI and 16S dataset recovered the monophyly of the Cerithiinae and Bittiinae, although the latter is not statistically supported. Limatium is monophyletic (PP = 1) and is robustly supported (PP = 0.99) within the Bittiinae as the sister group to Cacozeliana Strand, 1928. Ittibittium and Pictorium are also monophyletic both with robust support (PP = 1). The clade including the type species of Bittium Gray, 1847 [B. reticulatum, B. latreillei (Payraudeau, 1826), B. simplex (Jeffreys, 1867)] also received high support (PP = 1).

Discussion

Houbrick’s (1993) generic review of the Bittiinae published 25 years ago remains the authoritative resource for comparative anatomy and systematics of bittiines. At that time, Houbrick (1993) recognized nine genera in the Bittium-group: Bittium, Argyropeza, Bittiolum, Cacozeliana, Ittibittium, Lirobittium, Neostylidium [then as Stylidium], Varicopeza, and Zebittium; Cassiella was identified as a possible member but its placement uncertain given the paucity of anatomical data. In 2006, Bandel established a separate subfamily for Argyropeza. Since then, the Bittiinae has been expanded (MolluscaBase 2018) to include the Recent genera Cerithidium (provisionally excluded by Houbrick 1993), and Pictorium.

Despite the absence of a diagnostic feature that allows unambiguous placement in the subfamily (Strong and Bouchet 2013), the common perception of bittiines is that they are small in adult size, turreted, with a predominating beaded or spiral sculpture, and cream, gray, tan to dull brown in color. This concept of bittiine teleoconch morphology was expanded by the description of the genus Pictorium, based on a small type species formerly placed in Cerithium, with a pupoid, brilliantly colored reddish-purple shell (Strong and Bouchet 2013). Limatium species differ from all other bittiines in their smooth, glossy, polished shells with a rich honey to golden brown background color. This unique shell morphology is unknown in the Cerithiidae and further expands the conchological concept of the subfamily. The distinctive white fascioles also may be a diagnostic feature of the genus, but further comparative material is required to be certain, particularly of the suspected additional species from Vanuatu and the Philippines. Clearly, more material, and more sequencable material, is needed to understand intraspecific variation within Limatium.

In addition to shell morphology, Limatium differs from known bittiines in several unique features of the radula. Most possess a rachidian with an attached basal portion and a freely projecting face. The face of the tooth has a central to basal constriction that can be quite strongly developed in some species. Thickenings at the lower, outer corners of the tooth extend onto the radular membrane beyond the sides of the tooth. The upper projecting margin of the tooth often forms a prominent crest from below which the teeth project. The cutting edge spans the entire anterior edge of the tooth, or the majority of it, and bears a single, strong central cusp and two to three denticles on each side (e.g., Houbrick 1980b, 1993, Gofas 1987, Ponder 1993, Hasegawa 1998). The rachidian of Limatium has a basal plate that is hexagonal to septagonal in shape, with a central elevated portion that has a U-shaped, rounded lower edge roughly midway down the face of the tooth. The cutting edge is restricted to this elevated portion, and bears only three dagger-like cusps. This configuration is unknown among the Bittiinae, and even more broadly among the Cerithiidae. In terms of operculum morphology, most bittiines are characterized by a multispiral operculum (Houbrick 1980b, 1993, Gofas 1987, Hasegawa 1998); Bittiolum and Cassiella differ in possessing an ovate, paucispiral operculum with a small nucleus (Houbrick 1993, Ponder 1993). In contrast, Limatium possesses a subcircular, paucispiral operculum of only ~3 whorls and a large nucleus. Argyropezinae conform to the bittiine configuration of rachidian morphology and possess a circular, multispiral operculum (Houbrick 1980a).

The phylogenetic analysis supported Limatium and Cacozeliana as sister taxa, although more comprehensive taxon sampling is required to assess the affinities of bittiine genera. The analysis confirmed that Bittium, as presently conceived is polyphyletic (Strong and Bouchet 2013). Inclusion of the type species, Bittium reticulatum, for the first time allows us to tie the genus-group name to a clade including B. latreillei and B. simplex. As in the analysis of Strong and Bouchet (2013), Bittium impendens, only cautiously retained in Bittium by Houbrick (1993), is robustly supported as the sister group to Pictorium; Bittium glareosum is the sister to them but its placement is not supported. Additional sampling is required to resolve the affinities of Indo-Pacific species currently placed in Bittium, with Bittium s.s. possibly retained only for species from the Atlantic.

Limatium is exceptionally rare, represented in museum and personal collections by a scant 108 specimens known to us as enumerated herein, only 16 of them collected alive. As described in Strong and Bouchet (2013), Pictorium also had been rare in museum collections and had never been collected alive prior to the 1980's. Like Limatium, the latter genus is also small and found in steep, hard-bottom habitats that are too deep for diving and too steep for dredging. The use of lumun-lumun and tangle nets in the commercial shell trade in the Philippines, and the adoption of new collecting techniques as brushing baskets and suction sampling in biodiversity surveys (Albano et al. 2011), have revolutionized access to these challenging habitats. While the number of specimens of Pictorium rose dramatically particularly since 2004, the number of Limatium specimens also has increased but not so dramatically, and live collected specimens remain elusive. The unique radular morphology of Limatium suggests a life habit different from that of most other bittiines, which may explain why they remain so tantalizingly rare.

Figure 5. 

Phylogeny of Cerithiidae based on Bayesian analysis of partial COI and 16S sequences. Catalogue numbers for vouchers indicated after species name. Posterior probabilities greater than .50 are shown at the nodes. See Table 1 for details.

Acknowledgments

We thank Jean Tröndlé (La Force, France) who sorted the gastropods of the RAPA 2002 expedition and recognized Limatium aureum as a potentially new species. We are grateful to Jean Letourneux (Tahiti) for his generosity in sharing and donating specimens of the two new species from his personal collections, including several designated paratypes. We thank Alexander Fedosov (Russian Academy of Sciences) for collecting the sequenced holotype of L. aureum during the TUHAA PAE research cruise at the invitation of Cecile Debitus (IRD). We are also indebted to Chris Meyer (NMNH), Gustav Paulay (UF) and the Moorea Biocode Project for making the sequenced holotype of L. pagodula available to us for study and for allowing us to use the image of the live animal and the COI sequence. We thank Serge Gofas (University of Malaga) for the material of Bittium reticulatum from Spain. We are grateful to Freya Goetz and Yolanda Villacampa (both NMNH) for producing the scanning electron micrographs of the protoconchs, operculum and radulae, and to Gilberto Marani (MNHN) for producing the map figure. We also thank Kazunori Hasegawa (National Museum of Nature and Science, Tokyo) for his very thorough and knowledgeable review.

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