Gemixystus calcareus, Houart & Héros, 2012

Houart, Roland & Héros, Virginie, 2012, New species of Muricidae (Gastropoda) and additional or noteworthy records from the western Pacific, Zoosystema 34 (1), pp. 21-37 : 30-31

Gemixystus calcareus n. sp.

( Fig. 2C, D, N)

TYPE MATERIAL. — Holotype (dd) MNHN 24180 .

MATERIAL EXAMINED. — Only known from the holotype.

TYPE LOCALITY. — Coral Sea, Chesterfield Reefs, 19°36’S, 158°43’E, 568-570 m [ EBISCO: stn DW2603, Bouchet, Lozouet, Warén, Richer-IRD coll., 18/X/2005].

DISTRIBUTION. — Known only from the Chesterfield Reefs at the type locality.

ETYMOLOGY. — From Latin “calcareus”: chalk-white.

DESCRIPTION

Shell medium-sized for the genus, height 5.4 mm, height/width ratio 1.7. Broadly-ovate, lightly built, lamellate. Subsutural ramp narrow, weakly sloping, weakly convex. Shell entirely chalk-white.

Spire high with 1.6 protoconch whorls ( Fig. 2N) and 4.2 broad, weakly shouldered teleoconch whorls. Suture of teleoconch whorls impressed, partially obscured by small axial lamellae of following whorl. Protoconch comparatively large, broad, weakly acuminate with broad keel adapically, otherwise smooth. Diameter 500 µm. Terminal lip delicate, thin, weakly curved.

Axial sculpture of teleoconch whorls consisting of low, narrow, frilled lamellae, each with short, broad, open spinelets occurring at crossings of axial lamellae with spiral cords. Spines more conspicuous on P1. First whorl with 8 lamellae, 2nd with 13, 3rd with 16 and 4th with 20. Apertural lamella strongly erect, broad. Spiral sculpture of low, broad, rounded primary cords: P1-P3 visible on 1st to 3rd whorl with slightly visible, very narrow P2. P3 partially covered by following whorl. Last teleoconch whorl with P1-P5, ADP, MP. P1- P5 equidistant, P1 slightly larger, P2 narrow. ADP and MP narrower, MP low.

Aperture broad, rounded. Columellar lip narrow, smooth. Lip adherent at adapical extremity. Anal notch obsolete. Outer lip strongly erect with five weak, elongate denticles within: D1-D5. D4 and D5 narrower, more strongly elongate within. Siphonal canal short, narrow, straight, open, with ADP and MP and low axial lamellae over whole length.

REMARKS

The genus Gemixystus was revised by Houart (2004) and contains six fossil and eight Recent species.

None of the fossil species is closely related to the new species and of the eight Recent species, only three need to be compared here: Gemixystus leptos (Houart, 1995) from southern Queensland, Australia, to the Chesterfield Reefs, Gemixystus rippingalei (Houart, 1998) from Queensland, Australia, and Gemixystus stimuleus (Hedley, 1907) , from southern Queensland and Sydney, New South Wales, Australia, type species of Apixystus .

Gemixystus calcareus n. sp. differs from the quite similar G. stimuleus ( Fig. 2E) in having a comparatively larger shell with twice as large a protoconch, more numerous axial lamellae, 20 vs 11 or 12 on last whorl and 16 vs 13-15 on penultimate whorl. The spiral sculpture also differs, G. calcareus n. sp. having P1-P5, ADP and MP on last teleoconch whorl vs P1-P 3 in G. stimuleus ,which has no spiral sculpture on the siphonal canal.

Gemixystus calcareus n. sp. also differs from G. rippingalei ( Fig. 2F) in having a comparatively larger shell, G. rippingalei reaching only 4.4 mm in height and having a longer siphonal canal, a less spiny shell and a different spiral sculpture morphology, that is, a last whorl with closely spaced P1-P4 and a smooth siphonal canal.

Finally, G. calcareus n. sp. differs from G. leptos ( Fig. 2G) in having a comparatively broader, but otherwise similar protoconch, a less shouldered and less spiny shell with more numerous axial lamellae, 20 vs 10 or 11 on 4th whorl and 16 vs 11 on penultimate whorl, while having fewer lamellae on first whorl, 8 vs 10 or 11 in G. leptos . The spiral sculpture morphology also differs, G. leptos having two broad, broadly spaced P1 and P2 and two small, narrow, closely spaced P3 and P4. The siphonal canal is smooth in G. leptos or with a very shallow and narrow MP only.