Sinezona enigmatica, Geiger, Daniel L. & Marshall, Bruce A., 2012

Geiger, Daniel L. & Marshall, Bruce A., 2012, New species of Scissurellidae, Anatomidae, and Larocheidae (Mollusca: Gastropoda: Vetigastropoda) from New Zealand and beyond, Zootaxa 3344, pp. 1-33 : 4-6

Sinezona enigmatica new species

( Figures 2–3 )

Type material. Holotype ( NMNZ M.303302: Fig. 2 ). Paratypes from type locality (AMS C.461493, 13: Fig. 3 ). 1.24 × 0.86 mm.

Type locality. McGregors Bay, Whangarei Harbour, northern New Zealand, 36.750˚S, 175.467˚E, low tide. Etymology. Enigma, Latin for something inexplicable, referring to the surprising finding of a new species in a well-collected area, adjective; see also Remarks.

Description. Shell medium size (to 1.24 mm. Figs 2–3 ), trochiform depressed. Protoconch of 1 whorl, strong axial sculpture with median thickenings, apertural varix not connected to embryonic cap, apertural margin straight. Teleoconch I of 0.9–1.1 whorls, 12–13 strong axial cords, diminishing in strength with growth, hardly perceptible at onset of selenizone, weaker towards suture; interstices with fine irregular growth marks. Teleoconch with moderately impressed suture, 0.25–0.4 whorl. Shoulder slightly convex, weak irregular growth marks, faint spiral threads or low indistinct cords, irregularly spaced, approximately 8 at apertural margin. Base with weak constriction below selenizone, macroscopically smooth, fine indistinct spiral threads, most distinct at apertural margin; threads finest and densest below selenizone, fewer, more prominent cordlets near umbilicus. Umbilicus at angle to base, surrounded by weak cords; walls with finest growth increments, straight. Aperture ovoid, roof overhanging. Selenizone above periphery; keels low, moderately strong; lunules indistinct; foramen with raphe extending anteriorly.

Animal unknown.

Distribution. Northern New Zealand, intertidal.

Remarks. Sinezona brevis (Hedley, 1904) from New Zealand has a proportionally taller shell, its protoconch lacks the strong medial thickenings and has a strong apertural varix, has axial cords also on teleoconch II, and has distinct spiral threads on shoulder and base. Sinezona levigata (Iredale, 1908) from New Zealand has weak or distinct sculpture of spiral and axial cords forming a reticulate pattern, an umbilical callus, and a very short or even no selenizone, at most as long as the foramen. Sinezona finlayi (Laws, 1948) from the Tertiary of New Zealand has stronger spiral sculpture particularly on the base and has axial cords on teleoconch II as well. Sinezona mechanica n. sp. from New Zealand has axial cords on teleoconch I reaching the suture and distinct axial cords on teleoconch II.

The smooth surface of the last whorl and the relatively rapidly expanding whorls are shared with Incisura species, we also compare the new species to similar members of that genus. Incisura lyttletonensis (E.A. Smith, 1894) and I. rosea (Hedley, 1904) from the Recent fauna of New Zealand have an open slit. Incisura auriformis Geiger & Jansen, 2004 , from Australia shares the closed foramen, but has more rapidly expanding whorls, and a very strong bulging cord surrounding the umbilicus.

The finding of the single lot in shallow water from McGregors Bay, Whangarei Harbour raises some questions. This bay has been very thoroughly collected (notably by W.F. Ponder: material NMNZ), yet not a single additional specimen of this species has been obtained from there or anywhere else in the New Zealand region. Whangarei Harbour is an important port for international shipping to and from New Zealand. Various options to account for the specimens were explored. Specimens could have been mislabeled, which is more likely as no further information on collector or date of collection are available, but the adjacent catalog numbers contain typical New Zealand scissurellid taxa, suggesting a single collection event. The specimens could have been brought to New Zealand in commercial ship ballast. If the specimens are indeed adventive, the morphospecies still is new to science and unknown from elsewhere (>10,000 lots and>72,000 specimens examined in the context of a global monograph Geiger, unpubl. data). There are other examples of single lot, shallow water species from other wellcollected areas, such as the western Mediterranean (Geiger, unpubl. data). Reluctantly, we take the collection data at face value, and describe this new species with its associated type locality. Confirmation at the stated type locality, or discovery of its true native location will be desirable.

Figures

FIGURE 2. Sinezona enigmatica new species. Holotype. McGregors Bay, Whangarei Harbour, New Zealand (NMNZ M. 303302). Scale bar shell = 1 mm. Scale bar protoconch = 100 µm.

FIGURE 3. Sinezona enigmatica new species. Paratypes. A – C. McGregors Bay, Whangarei Harbour, New Zealand (AMS C. 461493). Scale bars shell = 1 mm. Scale bars protoconch = 100 µm.