Siphonochelus (Siphonochelus) aethomorpha, Roland & Virginie, 2015

Roland, Houart & Virginie, Héros, 2015, New species of Muricidae Rafinesque, 1815 (Mollusca: Gastropoda) from the Western Indian Ocean, Zoosystema 37 (3), pp. 481-503 : 500-502

Siphonochelus (Siphonochelus) aethomorpha n. sp. ( Figs 12 A-H; 13B)

TYPE MATERIAL. — Holotype MNHN-IM-2000-30024, 10 paratypes MNHN-IM-2000-30025, 2 paratypes Coll. RH.

TYPE LOCALITY. — Madagascar, between Majunga and Cap Saint- André, 15°35’S, 45°43’E, 177-199 m [ATIMO VATAE: stn DW3259].

MATERIAL EXAMINED. — South Madagascar. MIRIKY: stn DW3197, West of Cap d’Ambre, 12°07’S, 48°58’E, 362-431 m, 3 dd, juv.— Stn DW3239, in front of Baie de Nazendry, 14°30’S, 47°26’E, 230- 288 m, 1 dd, juv. — Stn CP3241, in front of Baie de Nazendry, 14°30’S, 47°27’E, 274-325 m, 1 dd, juv. — Stn DW3258, between Majunga and Cap Saint-André, 15°34’S, 45°44’E, 200-288 m, 7 dd, juv. — Stn DW3259, between Majunga and Cap Saint-André, 15°35’S, 45°43’E, 177-199 m, 30 dd, ad & juv (holotype MNHN- IM-2000-30024, 10 paratypes MNHN-IM-2000-30025, 2 paratypes Coll. RH). — Stn CP3260, between Majunga and Cap Saint-André, 15°35’S, 45°45’E, 179-193 m, 1 dd, juv. — Stn CP3283, off Baie Mahajamba, 14°52’S, 46°56’E, 228-257 m, 5 dd, juv.

DISTRIBUTION. — North-western Madagascar, 193-362 m (shells only).

ETYMOLOGY. — Greek, morpho, form, shape and aethes, unusual, strange. This species is named for the strange and flattened form of the anal tubes.

DESCRIPTION

Shell medium sized for the subgenus, up to 11.1 mm in height at maturity (holotype). Height/width ratio 1.9-2.1. Slender, lanceolate, narrowly ovate, lightly built. Subsutural ramp narrow, weakly sloping, weakly concave. Shell entirely off white.

Spire high with 1.25-1.5 protoconch whorls and up to 5-5.25 weakly convex, weakly shouldered, smooth whorls. Suture impressed. Protoconch moderately large, narrow, slightly elongate. Whorls rounded, smooth, maximum width 600 µm. Terminal lip delicate, thin, curved.

Axial sculpture consisting of four,low, narrow, rounded, weakly shouldered varices from first to last whorl. Spiral sculpture of very shallow P1 with anal tube, P2 (shoulder) and very weak, narrow striae and lirae, occasionally extending on abapical part of anal tubes. Anal tubes rounded on first or first two teleoconch whorls, flattened from second or third whorl. Last whorl with very broad, very flattened tubes originating from succeeding varix, filling almost entire space between succeeding and preceding varix, forming an angle of approximately 30-40° with axis of shell. Last apertural anal tube strongly outward bent, forming an angle of approximately 70° with axis of shell. Only apertural tube hollow and functional, older tubes broken off and closed. Only small portion of last tube open ( Fig. 12H ).

Aperture moderately small, ovate, weakly erect, forming a continuous peristome. Columellar lip narrow, smooth. Outer lip smooth within. Siphonal canal moderately long, narrow, straight, ventrally sealed, weakly dorsally curved, strongly tapered abapically.

REMARKS

Siphonochelus aethomorpha n. sp. differs from all the other Siphonochelus species in having very broad and flat anal tubes that originate from the succeeding varix and fill almost all the space between the succeeding and the preceding varix. The five other species occurring in Madagascar, Mozambique and/or southern Africa, i.e. S. (S.) arcuatus (Hinds, 1843) , S. (S.) pentaphasios (Barnard, 1959) , S. (S.) rosadoi Houart, 1999 , S. (S.) stillacandidus Houart, 1985 and S. (S.) transcurrens (Martens, 1903) , differ markedly, as do the other Indo- West Pacific species.

Siphonochelus arcuatus ( Fig. 12I, J ) has broader teleoconch whorls with sharper axial varices, more strongly backwardly bent, less flattened anal tubes and an almost three times larger protoconch.

Siphonochelus pentaphasios differs in the same characters and in having teleoconch whorls with five varices per whorl instead of four.

Siphonochelus stillacandidus also differs in having much narrower anal tubes, slightly more distant from the more strongly shouldered axial varices, and in having a shorter siphonal canal.

The two other Indian Ocean species differ in many shell characters and do not need to be compared here.

Figures

FIG. 12.— A-H, Siphonochelus (Siphonochelus) aethomorpha n. sp.; MIRIKY,stn DW3259,177-199 m: A-C, holotype MNHN IM-2000-30024, 11.6 mm; D-F, paratype MNHN IM-2000-30025; 9.0 mm; G, protoconch; H, detail of the anal tube; I, J, Siphonochelus (Siphonochelus) arcuatus (Hinds, 1843); ATIMO VATAE, stn CP3584, 203-210 m, 11.5 mm. Scale bar: 500 µm.