Arxellia, Vilvens, Claude, Williams, Suzanne T. & Herbert, David G., 2014

Vilvens, Claude, Williams, Suzanne T. & Herbert, David G., 2014, New genus Arxellia with new species of Solariellidae (Gastropoda: Trochoidea) from New Caledonia, Papua New Guinea, Philippines, Western Australia, Vanuatu and Tonga, Zootaxa 3826 (1), pp. 255-281 : 258-260

publication ID

https://doi.org/ 10.11646/zootaxa.3826.1.8

publication LSID

lsid:zoobank.org:pub:57A3F7A4-A395-4D41-8C18-8EF64B98F414

DOI

https://doi.org/10.5281/zenodo.6140270

persistent identifier

https://treatment.plazi.org/id/E518B10E-DA09-C449-FF11-FEC7FA029E2E

treatment provided by

Plazi

scientific name

Arxellia
status

gen. nov.

Genus: Arxellia new genus

Clade A, Williams et al., 2013

Type species: Arxellia trochos n. sp. —Recent, New Caledonia.

Diagnosis. Shell small to moderate (height up to 11.8 mm, width up to 13.0 mm), more or less conical in shape, spire moderate to high. Protoconch diameter 300–350 µm, with up to 6 thin spiral threads (in one species only abapical threads visible) and a thin, straight terminal lip without varix. Early teleoconch whorls usually with 5 or 6 beaded spiral cords of equal strength; adapical cord P1 rapidly strengthening and becoming beaded; one abapical primary cord (P5 or P4 according to species) forming a low suprasutural carina starting from third whorl; carina may weaken or disappear on last whorl. Peristome incomplete; columella thickened in some species, with callus lobes at base and mid-point; granular deposition of calcium carbonate occurs where columella is thickened. Base convex to almost flat, with beaded cords on whole surface or with an intermediate smooth area, but always with at least one strong beaded spiral cord bordering umbilicus. Umbilicus open, narrow to moderately wide. The pink, green and opalescent shell colour of most species is larely due to a nacreous shell layer, rather than pigment. However, in some species shells do appear to be pigmented (e.g. the brown colour in A. boucheti , A. herosae , A. helicoides , A. maestrati and A. erythrea ).

Radula of type species with well-developed latero-marginal plates; formula (5–6)+1+4+1+4+1+(5–6).

External anatomy typical of family; eyes pigmented (where known; see Williams et al. 2013); left neck lobe in the form of two short, non-papillate tentacles, the right one a trigonal lobe just behind eye-stalk; three papillate epipodial tentacles of more or less equal size present on each side, and additional smaller tentacle-like projection between the anterior pair on both sides. Operculum corneous, straw-brown, shallowly concave, multispiral with central nucleus; growing margin short.

Remarks. Diagnosis of the new genus is based on the nine species discussed herein. Live specimens collected at 242– 650 m.

Discussion. The new genus Arxellia corresponds to "Clade A" in the recent molecular phylogeny of the Solariellidae published by Williams et al. (2013). Seven of the new species and many of the specimens photographed were included in that study. The type species was not included, but unpublished molecular data confirm that it belongs in this clade (Williams, unpub. data). Genetic studies place Arxellia as the sister taxon to Archiminolia Iredale, 1929 with strong support. The two genera can be separated by shell shape ( Archiminolia species have turban-shaped shells whereas Arxellia species have conical shells) and by the ontogeny of teleoconch spiral cords. In Arxellia there are numerous beaded spiral cords and a suprasutural carina on the intermediate whorls, whereas in Archiminolia there are at most a few subsutural cords on these whorls.

Arxellia and Archiminolia View in CoL form a well supported clade with Spectamen Iredale, 1924 View in CoL , Solariella Wood, 1842 View in CoL , Bathymophila Dall, 1881 View in CoL , Minolia A. Adams, 1860 View in CoL , Hazuregyra Shikama, 1962 , Zetela Finlay, 1926 View in CoL and an as yet undescribed genus (Clade B) in the molecular tree ( Williams et al. 2013). Although relationships between genera within this larger clade are not well resolved, the first five genera comprise a poorly-supported clade in the MrBayes tree. The presence of well-developed latero-marginal plates in the radula of Arxellia is consistent with the radula morphology of other members of this latter clade, such plates having been reported in Bathymophila View in CoL , Spectamen View in CoL , Archiminolia View in CoL and at least some species of Solariella View in CoL ( Herbert 1987; Warén 1993; Marshall 1999). In other solariellid genera outside this clade, namely Ilanga Herbert, 1967 , Clade C (new genus, Vilvens & Williams 2014) and Minolia View in CoL but also Zetela View in CoL , this plate is either not present or only weakly developed, retaining a flimsy shaft and cusp. The presence of strong, elongate-rectangular latero-marginal plates may thus be an apomorphic character state shared by most genera comprising this broader clade.

Etymology. Stronghold, citadel (Latin: arx)—referring to the strong columella of some species of the new genus (feminine).

FIGURE 10: Approximate locations of MNHN and WAM expeditions discussed in this paper: ★: PANGLAO 2005; DZ: BIOPAPUA; D MUSORSTOM 8, VOLSMAR; ⊙: BORDAU 1; r: BORDAU 2; ♠: BIOCAL, MUSORSTOM 6, VOLSMAR, SMIB 8, BATHUS 1, BATHUS 2, LITHIST, NORFOLK 1, NORFOLK 2, EXBODI; DZ: CHALCAL 2, SMIB 8; ®: MUSORSTOM 7; + 'Southern Surveyor'.

Key to Arxellia species (based on conchological features).

1. Later whorls with at least 3 beaded or subgranular spiral cords................................................. 2

- Later whorls smooth......................................................................... A. thaumasta

2. Later whorls mostly covered with beaded or subgranular spiral cords............................................ 3

- Later whorl with only 3, widely spaced, beaded or subgranular spiral cords................................ A. tenorioi View in CoL

3. Shell much higher than wide................................................................... A. helicoides

- Shell height and width more or less equal.................................................................. 4

4. Shell height attaining 12 mm, periphery more or less rounded.......................................... A. boucheti

- Shell height less than 9 mm ............................................................................. 5

5. Columella callus with two lobes extensively covering umbilicus........................................ A. herosae

- No columella callus or expansion slightly covering umbilicus.................................................. 6

6. Peripheral carina on P5................................................................................ 7

- Peripheral carina on P4................................................................................ 8

7. Intervals between spiral cords narrower than cords, carina relatively weak................................. A. trochos

- Intervals between spiral cords wider than cords, carina stronger....................................... A. maestratii

8. Intervals between spiral cords wider than cords..................................................... A. tracheia

- Intervals between spiral cords narrower than cords.................................................. A. erythrea

Kingdom

Animalia

Phylum

Mollusca

Class

Gastropoda

Order

Vetigastropoda

Family

Solariellidae

Loc

Arxellia

Vilvens, Claude, Williams, Suzanne T. & Herbert, David G. 2014
2014
Loc

Ilanga

Herbert 1967
1967
Loc

Hazuregyra

Shikama 1962
1962
Loc

Zetela

Finlay 1926
1926
Loc

Spectamen

Iredale 1924
1924
Loc

Bathymophila

Dall 1881
1881
Loc

Minolia

A. Adams 1860
1860
Loc

Solariella

Wood 1842
1842
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