Sinezona macleani, Geiger, Daniel L., 2006

Geiger, Daniel L., 2006, Eight new species of Scissurellidae and Anatomidae (Mollusca: Gastropoda: Vetigastropoda) from around the world, with discussion of two new senior synonyms, Zootaxa 1128, pp. 1-33 : 16-19

Sinezona macleani new species: Figures 12–13

Type material. Holotype: USNM 289748. Paratypes ( USNM 276829, 2), from type locality. Paratype 820–863 m, Fiji, 17.300°S, 179.550°W ( MNHN, 1: Fig. 13 A). Paratypes 675–680 m, New Caledonia, 23.167°S, 167.167°E ( MNHN, 2: Figs. 13 B–C). Paratype 1000 m, off Curtis Island, Kermadec Islands, New Zealand, 30.467°S, 178.622°W ( NMNZ M257059, 1).

Type locality. 534 m, Station 5584, Sibuko Bay, off Si Amil Island, Borneo, Indonesia [3.773°N, 118.364°E].

Etymology. Named for James H. McLean, my graduate co–advisor, mentor, and friend.

Description. Shell medium size (holotype 2.3 mm wide), depressed trochiform, inflated. Protoconch of 0.75 whorls, flocculant sculpture (eroded in holotype), no apertural varix, apertural margin straight. Teleoconch I of 1.75 whorls, 27 distinct axial cords on first whorl, spiral threads equispaced, increasing in number with growth, approximately 10 on shoulder at onset of selenizone. Teleoconch II of 0.66 whorls. Shoulder irregularly convex, axials of similar density as on teleoconch I, slightly increasing in strength with growth, spirals increasing somewhat in strength, always weaker than axials, forming minute tubercles at intersection with axials, most prominent near apertural margin. Base inflated, axials of similar strength and density as on shoulder, axials becoming weaker towards umbilicus, some terminating before reaching umbilicus. Umbilicus open, wide, bordered by sharp lamella, walls smooth. Selenizone above periphery, keels of moderate height and strength, foramen elongate­teardrop­shaped. Aperture subquadratic, with indentation in lower corner of parietal wall, roof overhanging; past indentations visible inside umbilicus.

Differential diagnosis. Surprisingly, there are very few described Sinezona species from the Indo­Malayan Archipelago. Sinezona globosa from the Western Pacific is more globular in general outline, lacks the periumbilical lamella and the adumbilical indentation of the aperture, and has a protoconch with spiral lines and a well­formed apertural varix. Sinezona plicata (Hedley, 1899) , widely distributed in the Indo­Pacific, has strong axial folds and a well­developed apertural varix on the protoconch. Sinezona ferriezi (Crosse, 1867) , described from New Caledonia, of similar size (to 2.1 mm) and widely distributed in the Indo­Malayan Archipelago has an almost flat shoulder, more raised axial cords, a rounded aperture in the basal­adumbilical portion, a protoconch with an apertural varix, and a teleoconch I of slightly more than one whorl. Sinezona modesta ( A. Adams, 1862) , described from Japan, has never been illustrated, and there are no type specimens in the BMNH ( Thiele, 1912; Geiger, pers. obs. II. 2003). It is described as being very depressed and similar in shape to a Stomatella . The only very depressed form in Scissurellidae is Depressizona exorum Geiger, 2003 from Easter Island, which is rather calyptraeiform than stomatelliform.

Sinezona concinna (Sowerby I, 1831) [not Anatomus concinnus A. Adams, 1862 ], of unknown provenance, has markedly decreasing strength of the axials towards the aperture, whereas in Sin. macleani the axials are rather increasing in strength towards the aperture. The identity of Sin. concinna is uncertain. The species was introduced as a nomen et figura and has not been mentioned in the literature since. Given that the first scissurellid was described only in 1824 by d’Orbigny ( Scissurella costata ), it is very likely that Sin. concinna was also an European species. The rather well executed drawing agrees well with the European Sin. cingulata (O. G. Costa, 1861). Particularly the number, strength, and spacing of the axials, decreasing in strength close to the aperture, and the very fine spirals are clearly shown in Sowerbys illustration. Given the rather uncertain status of this synonymy, I prefer to treat Sin. concinna as a nomen dubium; a case for a nomen oblitum/ protectum cannot be made as the synonymy with Sin. cingulata is at best circumstantial, though Sin. cingulata has been used as a valid species at least 25 times by 10 different authors in the preceeding 10–50 years.

Distribution. Indo­Malayan archipelago to western Pacific, 25–1600 m.

Specimen records. 25–30 m, Santal Bay, Lifou, New Caledonia, 20.820°S, 167.173°E (MNHN, 1). 425–430 m, Southern, New Caledonia, 22.283°S, 167.233°E (MNHN, 1). 775 m, New Caledonia, 23.000°S, 167.483°E (MNHN, 1; MNHN, 1). 770– 830 m, Loyality Ridge, New Caledonia, 24.733°S, 170.133°E (MNHN, 2). 440 m, New Caledonia, 22.783°S, 167.233°E (MNHN, 14). 825–830 m, New Caledonia, 23.050°S, 167.533°E (MNHN, 1). 675–680 m, New Caledonia, 23.167°S, 167.167°E (MNHN, 1). 1575–1600 m, New Caledonia, 20.783°S, 55.633°E (MNHN, 1: complete). 441–443 m, S. of Viti Levu, Fiji, 18.320°S, 177.862°E (MNHN, 1).

Remarks. The holotype was chosen as the specimen showing a fully mature shell, with well formed umbilical and apertural features, while the protoconch is eroded. The MNHN and NMNZ paratypes ( Fig. 13 ) have the flocculant protoconch sculpture, while also showing the periumbilical lamella as well as a hint of the adumbilical indentation, both unique features in Scissurellidae .

Figures

FIGURE 12. Holotype of Sinezona macleani new species. USNM 289748. 534 m, Station 5584, Sibuko Bay, off Si Amil Island, Borneo, Indonesia, 3.773 ° N, 118.364 ° E, (USNM 289748, 1). Scale bar shell = 1 mm. Scale bar protoconch = 100 µm.

FIGURE 13. Paratypes of Sinezona macleani new species. A. 820 ­ 863 m, Fiji, 17.300 ° S, 179.550 ° W (MNHN). B­C. 675 ­ 680 m, New Caledonia, 23.167 ° S, 167.167 ° E (MNHN). Scale bar shell = 1 mm. Scale bar protoconch = 100 µm.