Ethaliella rhodomphala ( Souverbie, 1875 )

Herbert, David G., 2024, The Umboniinae (Mollusca: Gastropoda: Trochidae) of New Caledonia, with descriptions of two new genera and eight new species, plus an additional new species from the Bismarck Sea, European Journal of Taxonomy 973, pp. 1-143 : 92-98

Ethaliella rhodomphala ( Souverbie, 1875)

Figs 47–51

Trochus (Monilea) rhodomphalus Souverbie in Souverbie & Montrouzier, 1875: 36, pl. 4 fig. 3. Type locality: “ins. Lifou”, Loyalty Islands, New Caledonia (Pierre Lambert).

Trochus rhodomphalus – Fischer 1878: 210; 1879 in 1875–1880: 392. pl. 117 fig. 3.

Monilea (Minolia) rhodomphala – Pilsbry 1889 –1890: 262, pl. 41 figs 22–24.

Minolia rhodomphala – Melvill & Standen 1897: 414.

Ethaliella rhodomphala – Pilsbry 1905: 116. — Héros et al. 2007: 209.

Trochus (Monilea) rhodomphalus – Herbert 1996: 430, figs 41–43, lectotype.

Material examined

Lectotype ( Fig. 47A–C )

NEW CALEDONIA • Lifou, Loyalty Islands; Lambert leg.; MHNBx 2004 .TY.190.1 (designated by Herbert 1996: 430) .

Paralectotypes

NEW CALEDONIA • 1 specimen; Lifou, Loyalty Islands; Lambert leg.; MHNBx 2004 .TY.190.2 • 1 specimen; Lifou, Loyalty Islands; Lambert leg.; specimen located since Herbert (1996); MHNBx 2009.2378 .

Other material

NEW CALEDONIA – Grande Terre, Koumac • 2 specimens, dead; Stn KD563; 20°33.4′ S, 164°6.3′ E; depth 5 m; 15 Nov. 2019; KOUMAC 2.3 leg.; sable blanc; MNHN • 2 specimens, living; Stn KD534; 20°32.4′ S, 164°07.2′ E; depth 16 m; 5 Nov. 2019; KOUMAC 2.3 leg.; sable blanc, éponges, Halophila , algues brunes, Halimeda ; MNHN • 2 specimens, dead; Chenal de l’Infernet, Stn 1305; 20°36.2′ S, 164°11.0′ E; depth 12–15 m; Oct. 1993; Expédition Montrouzier leg.; sable gris; MNHN • 70+ specimens, living; Chenal de l’Infernet, Stn 1306; 20°39.1′ S, 164°12.4′ E; depth 11–13 m; Oct. 1993; Expédition Montrouzier leg.; fonds blancs; MNHN • 6 specimens, living; Stn KD542; 20°38.6′ S, 164°12.7′ E; depth 11 m; 7 Nov. 2019; KOUMAC 2.3 leg.; sable gris; MNHN • 2 specimens, living; Stn KS521; 20°38.4′ S, 164°13.2′ E; depth 16 m; 23 Nov. 2019; KOUMAC 2.3 leg.; sable blanc à Halophila ; DNA voucher, photographed alive (image PM 872); MNHN-IM-2019-10194 • 50+ specimens, living; Chenal de l’Infernet, Stn 1304; 20°38.6′ S, 164°13.2′ E; depth 12–15 m; Oct. 1993; Expédition Montrouzier leg.; sable gris, dalle; MNHN • 3 specimens, living; Stn KD541; 20°39′ S, 164°13.3′ E; depth 11 m; 7 Nov. 2019; KOUMAC 2.3 leg.; sable gris; DNA voucher; MNHN-IM-2019-7703 • 2 specimens, dead; around l’Îlot Kendec, Stn 1309; 20°40.5′ S, 164°13.4′ E; depth 18 m; Oct. 1993; Expédition Montrouzier leg.; sable gris; MNHN • 10 specimens, living; Stn KD516; 20°39.2′ S, 164°13.5′ E; depth 10 m; 1 Nov. 2019; KOUMAC 2.3 leg.; sable gris; DNA vouchers; MNHN-IM-2019-3570 and -3571 • 1 specimen, living; Stn KS522; 20°39.3′ S, 164°13.6′ E; depth 15 m; 23 Nov. 2019; KOUMAC 2.3 leg.; sable blanc à Halophila ; MNHN • 1 specimen, dead; Passe de Koumac, east drop-off, Stn 1311; 20°40.4′ S, 164°14.9′ E; depth 10–60 m; Oct. 1993; Expédition Montrouzier leg.; fonds durs; MNHN • 4 specimens, living; Stn KD560; 20°45.6′ S, 164°15.2′ E; depth 5–9 m; 14 Nov. 2019; KOUMAC 2.3 leg.; sable blanc et quelques algues brunes; MNHN • 6 specimens, living; Stn KD578; 20°43.8′ S, 164°16.4′ E; depth 11–12 m; 19 Nov. 2019; KOUMAC 2.3 leg.; sable fin gris à Halophila ; MNHN • 3 specimens, living; Stn KD574; 20°43.5′ S, 164°16.9′ E; depth 12 m; 19 Nov. 2019; KOUMAC 2.3 leg.; sable gris à Halophila ; DNA voucher; MNHN-IM-2019-8588 • 2 specimens, living; Stn KD583; 20°43.5′ S, 164°17.3′ E; depth 12 m; 21 Nov. 2019; KOUMAC 2.3 leg.; sable fin; MNHN • 20 specimens, living; Stn KD552; 20°49.4′ S, 164°18.5′ E; depth 10–11 m; 13 Nov. 2019; KOUMAC 2.3 leg.; sable blanc; DNA voucher, photographed alive (image PM 652); MNHN-IM-2019-8779. – Grande Terre, Touho • 2 specimens, living; near the Thiem, Stn 1268; 20°45.2′ S, 165°08.0′ E; depth 9–11 m; Sep. 1993; Expédition Montrouzier leg.; sable fin; MNHN • 2 specimens, living; around Baie de Touho, Stn 1251; 20°46.0′ S, 165°13.0′ E; depth 6–15 m; Sep. 1993; Expédition Montrouzier leg.; vase, sable, herbiers; MNHN. – Grande Terre, Bourail • 3 specimens, dead; lagoon of Poé, Stn 1324; 21°36.9′ S, 165°22.7′ E; depth 0–2 m; 1 Sep. 1993; Expédition Montrouzier leg.; fonds mixtes, herbier; MNHN. – Grande Terre, Nouméa • 5 specimens, dead; Récif Senez, Stn 1350; 22°17.9′ S, 166°19.6′ E; depth 3–6 m; 23 Nov. 1992; Bouchet and Marshall leg.; pente interne; MNHN • 7 specimens, dead; Grand Récif Aboré, Stn 1347; 22°23.6′ S, 166°20.1′ E; depth 10 m; 8 Oct. 1992; P. Bouchet leg.; vase sableuse sur dalle; MNHN • 3 specimens, dead; Île aux Goélands, Stn 1503; 22°22.4′ S, 166°22.5′ E; depth 5-7 m; 21 Oct. 2000; Cosel and Trondlé leg.; MNHN • 1 specimen, dead; Anse Vata; 22°18.21′ S, 166°26.30′ E; depth 1–5 m; 6 Jan. 2002; Claude Berthault leg.; MNHN • 4 specimens, dead; Anse Vata; 22°18.1′ S, 166°26.4′ E; depth 1–5 m; 1987–2007; Claude Berthault leg.; MNHN. – Loyalty Islands • 1 specimen, dead; Lifou, Baie du Santal, north of Cap Aimé Martin [= Acadro], Stn 1450; 20°45.8′ S, 167°01.6′ E; depth 27–31 m; 17 Nov. 2000; Atelier LIFOU 2000 leg.; brossages; MNHN • 1 specimen, dead; Lifou, Baie du Santal, Baie de Gaatcha, Stn 1463; 20°55′ S, 167°03.3′ E; depth 20–30 m; 10 Nov. 2000; Atelier LIFOU 2000; dragages sable et débris coralliens; MNHN • 2 specimens, dead; Lifou, Baie du Santal, in front of landing beaches at Drueulu, Stn 1413; 20°55.3′ S, 167°05.0′ E; depth 3–10 m; 26 Nov. 2000; Atelier LIFOU 2000 leg.; fonds meubles; MNHN.

Description ( Fig. 47 )

SHELL. Of small to moderate size (diameter up to 7.6 mm, but most specimens <6.0 mm); low turbiniform to trochoid-turbiniform; periphery rounded or weakly angled, at or below mid-whorl; whorls occasionally weakly shouldered; early whorls with 3–4 distinct spiral cords ( Fig. 48A ); these becoming more numerous and more close-set on subsequent whorls through intercalation of intermediaries; sculpture on last two whorls distinctive, comprising numerous fine, close-set spiral cords, rendered somewhat wavey by indistinct growth-lines; subsutural cord of middle spire whorls often slightly larger and rendered undulant or even weakly beaded by low subsutural pliculae; this evanescing on last adult whorl; axial sculpture comprising only aforementioned growth-lines and microscopic axial threads. Base more glossy, with weaker spiral sculpture, almost smooth in some specimens; umbilicus of moderate width, steep-sided, its margin thickened and radially plicate; interior of umbilicus lacking an obvious funicle, but columella lip substantially thickened.

COLOUR. Pattern variable; ground colour pale, variously mottled with shades of yellowish-brown to greyish-brown, often with darker blotches below suture and at periphery, occasionally more uniformly pale pink; base often more boldly patterned with irregular radiating and anastomosing brown markings separating opaque white blotches; umbilicus and its rim pale to deep pink, but extent of this coloration variable and often absent in immature specimens ( Fig. 47N ); protoconch and apical whorls usually whitish, occasionally yellowish, pink, brown or almost black ( Fig. 47E ).

PROTOCONCH ( Fig. 48B ). Typically umboniine, diameter 170–180 µm; apical beak present and confluent with terminal lip; apical bulb sculptured with an irregular open network of threads, almost hexagonal in places, remainder with fine subspiral threads; terminal lip weakly convex.

OPERCULUM ( Fig. 48C–D ). Corneous, multispiral, but outer whorls relatively broad and with long growing margin; peripheral fringe relatively narrow, radially striate; spiral microsculpture present, but indistinct.

RADULA ( Fig. 49 ). Formula ∞+(1)+ 5+1+ 5+(1) +∞, with 35–40 transverse rows of teeth; teeth of central field reduced, base-plates thin; rachidian base-plate ovate; base-plates of lateral teeth more trigonal, broadly expanded laterally and extensively overlapping, anterior edge slightly raised and with small pointed shaft vestige. Innermost marginal transitional, with truncate vestige of shaft; remaining inner marginals with well-developed shafts and recurved cusps; cusps of marginals 3–8 largest, somewhat palmate; central denticle rounded, not conspicuously larger than others, 3 or more long, pointed denticles on outer margin and further shorter, pointed denticles on inner margin; marginal cusps progressively smaller and more finely denticulate toward radula margin.

EXTERNAL ANATOMY (from photographs and rehydrated specimens) ( Fig. 50 ). Head with distinct forehead between cephalic tentacles; snout cylindrical, with a cluster of subterminal papillae on each side; no cephalic lappets evident; cephalic tentacles slender, that on right perhaps longer; eyestalks well developed, very long, with white internal pigment blotches and large black eye at tip. Left neck-lobe small, comprising only ± 4 slender digits behind eyestalk; right neck-lobe rolled to form well-developed exhalant siphon; four epipodial tentacles posterior to neck-lobes on each side, each evidently with a basal epipodial sense organ. Anterior of foot indented in midline, laterally expanded and pinched in behind this. Head-foot translucent white with frequent blotches of opaque white pigment, sides of snout and foot also with black blotches. Tip of ctenidium free.

Habitat

Mostly associated with white and grey sandy substrata in the outer portions of the lagoon; at depths of 2–27 m, living specimens 9– 16 m.

Distribution ( Fig. 51 )

To date recorded only from the New Caledonian marine ecoregion (Grande Terre and the Loyalty Islands).

Remarks

Fischer (1878 and 1979 in 1875–1880) drew attention to the similarity between this species and Trochus rotellaeformis Philippi, 1850 , but noted that the figure of T. rotellaeformis given by Philippi ( Philippi 1850 in 1846–1855: pl. 44 fig. 2) did not show the pink coloration seen in the umbilical region of T. rhodomphalus . As a result, Fischer was unable to conclude that they were conspecific, preferring to wait to see if further samples would establish whether or not the umbilicus of New Caledonian material was invariably pink. The answer to this question is that the intensity of the pink coloration of the umbilicus of E. rhodomphala is variable, intense in some, very faint in others, and frequently absent in juvenile and subadult specimens ( Fig. 47G, M–N ). This character cannot thus be used to eliminate possible synonymy. However, Philippi also stated that the base of T. rotellaeformis was perfectly smooth. In contrast, the base of E. rhodomphala , although more glossy than the apical surface, almost always retains some spiral sculpture and the peri-umbilical region bears fine radial riblets or even coarser pliculae. Thus, questions remain regarding the synonymy of the two names. No locality was cited for T. rotellaeformis other than that the material reportedly came from Captain Cook’s travels and was in the Sylvanus Hanley collection. The uncertainty regarding the identity of Philippi’s taxon can only be resolved by examination of the type material, but attempts to trace this in the NHMUK and the museums in Cambridge and Leeds have proved unsuccessful. In the absence of type material, I consider Trochus rotellaeformis Philippi, 1850 to be a nomen dubium.

Earlier ( Herbert 1996), I discussed similarities between Ethaliella rhodomphala ( Souverbie, 1875) and Ethalia rhodomphala E.A. Smith, 1903 from the Maldives, Ethalia floccata G.B. Sowerby III, 1903 from Japan, Isanda pulchella A. Adams, 1855 from the Philippines and Ethalia capillata Gould, 1862 from China, all currently referred to Ethaliella (MolluscaBase 2024) . I concluded that E. rhodomphala ( Souverbie, 1875) might be a synonym of and earlier name for E. floccata . Having now examined a good deal more New Caledonian material, I no longer consider this likely. Undoubtedly the two are similar, but the Japanese species has a less elevated spire, weaker spiral sculpture above the periphery, a completely smooth base, a more funnel-shaped umbilicus, a distinct parietal callus lobe and lacks pink colour in the umbilical region ( Sasaki 2000). Furthermore, the New Caledonian material never exhibits the typical colour pattern of E. floccata , including a band of strongly opisthocline red-brown lines below the suture, followed by a spiral row of red-brown blotches at mid-whorl ( Higo et al. 2001: fig. G468, holotype, NHMUK 1903.12.7.15).

The secondary homonymy resulting from the referral of both Trochus (Monilea) rhodomphala Souverbie, 1875 and Ethalia rhodomphala E.A. Smith, 1903 to Ethaliella remains to be resolved. Pilsbry (1905) considered it likely that the Japanese E. floccata was nothing more than a variety of Smith’s Ethalia rhodomphala , in which case a replacement name is already available for Smith’s taxon. I have not seen sufficient material of these taxa to be able to evaluate this and it remains an issue requiring further investigation.

Ethaliella rhodomphala ( Souverbie, 1875) shows considerable variation in size and shape. Specimens from Grande Terre are generally smaller than the lectotype from Lifou and the whorls are less distinctly shouldered. In addition, the peri-umbilical pigmentation of Lifou specimens is generally of a deeper pink colour. However, the material available from Lifou is limited and of poor quality, and these differences are thus difficult to evaluate. Occasional specimens from Grande Terre have a more intensely pigmented umbilical rim ( Fig. 47M ) and some have a lower, less conical profile with somewhat shouldered whorls ( Fig. 47J–K ). Although conical specimens from Grande Terre may ultimately prove to be a distinct and undescribed species, presently I refrain from describing them as such pending the availability of an adequate quantity of fresh Loyalty Islands material and supporting molecular data.

Figures

Fig. 47. Ethaliella rhodomphala (Souverbie, 1875) (A–C: MHNBx 2004.TY.190.1; D–N: MNHN). A–C. Lectotype of Trochus (Monilea) rhodomphalus Souverbie, 1875, Lifou, height 5.0 mm, diameter 7.6 mm (images courtesy of Laurent Charles). D–G. Conical specimen with dark apex, Koumac, Stn KD583, height 3.9 mm, diameter 5.4 mm.H–I. Conical specimen with pale pink colour pattern, Koumac, Stn 1304, height 4.3 mm, diameter 6.0 mm. J–K. Specimens with less elevated spire and somewhat shouldered whorls, Koumac, Stn 1306, diameters 4.9 and 5.1 mm respectively. L–M. Heavily pigmented specimen with bright pink umbilical rim, Koumac, Stn KD516, diameter 4.9 mm. N. Subadult specimen lacking pink colour around umbilicus, Koumac, Stn 1304, diameter 4.6 mm.

Fig. 48. Ethaliella rhodomphala (Souverbie, 1875) (all MNHN).A. Apical whorls, Koumac, Stn KD560. B. Protoconch, Koumac, Stn KD560. C–D. Operculum, Koumac, Stn KD574. Scale bars: A= 100 µm; B=50 µm; C =250 µm; D =200.

Fig. 49. Ethaliella rhodomphala (Souverbie, 1875), radula (all MNHN). A. Entire width of radula, Koumac, Stn 1306.B. Oblique view of latero-marginal transition, Koumac, Stn 1306. C. Marginal series, Koumac, Stn KD574. D. Inner marginal teeth, Koumac, Stn 1306. Scale bars: A=50 µm; B=25 µm; C–D =20 µm.

Fig. 50. Ethaliella rhodomphala (Souverbie, 1875), living animal, Koumac, Stn KD552, shell diameter ± 5.0 mm (MNHN-IM-2019-8779) (image PM652).

Fig. 51. Map of New Caledonia showing the distribution of Ethaliella rhodomphala (Souverbie, 1875). Type locality (approximate) indicated in pink.