Cyclochlamys pileolus Dijkstra & Marshall, 2008
DIJKSTRA, H. H. & B. A. MARSHALL. 2008. The recent Pectinoidea of the New Zealand region (Mollusca: Bivalvia: Propeamusiidae,Pectinidae and Spondylidae). Molluscan Research, 28 (1): 1-88, figs. 1-70 [p. 33, fig. 28]
2008 Cyclochlamys pileolus Dijkstra & Marshall, 2008
H. H. Dijkstra & B. A. Marshall, 2008, figure 28.
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«Type material
Holotype (pr, height 1.5 mm, width 1.4 mm, thickness 0.5 mm) NMNZ M.155879, Halfmoon Bay, Stewart Island, New Zealand, alive, 27 m, E.C. Smith, Dec. 1955. Paratypes: off Taieri, S of Dunedin, 46º15.0’S, 170º29.0’E, alive, 91 m (1 pr, M.66281); off Flat Rock, Foveaux Strait, alive, 18 m (2 pr, M.63969); off Poutama Island, Big South Cape Island, Stewart Island, 47°16’S, 167°23’E, 55 m (2 v, M.155880). Material examined
The type material (see above). Seamount 130 km S of Esperance Rock, Kermadec Ridge, NE New Zealand, 32°28.3’S, 179°15.9’W, 538 m, 15 Apr. 1997, FV Santa Maria, coll. N. Mitchell, from foraminiferal ooze in cavities in longlined block bryozoan/shell limestone hardground (1 v, M.137540). Proclamation Island, Bounty Islands, 47º42’S, 179º05’E, 39 m (1 pr, 3 v, M.155460). Off Rose Island, Auckland Islands, 50°31.45'S, 166°15.1'E, 20 m (2 v, M.173800). Description
Shell up to 1.50 mm high, suborbicular, weakly posteriorly oblique, equivalve (relatively narrow, thin ventral margin of right valve disintegrating post mortem: thickened inner part 70–77% height of left valve), inequilateral, left valve rather strongly convex, right valve weakly convex, auricles slightly equal in shape and size (anterior slightly larger), translucent white. Prodissoconch very prominent, acutely conical, 370 μm long; PI 150 μm long, finely malleated, surmounted by prominent, rounded, median dorsal ridge; PII finely malleated, with obscure radial threads and commarginal lines, and with prominent, rounded ridge that extends posteriorly and obliquely from centre. Dissoconch left valve disc and auricles sculptured with very strong, ventrally sloping commarginal lamellae, and weak radial riblets (6–8, including 1 on posterior auricle) that commence 0.5 mm below tip of prodissoconch and multiply by intercalation, with strong, rounded, fingernail-like scales at intersections; interspaces of commarginal ribs almost linear grooves before appearance of radials, about as wide as each rib thereafter. Right valve disc and ventral half of posterior auricle with outer layer of commarginally elongate, hexagonal prisms that form broad, flexible ventral apron. Anterior auricle with weak commarginal near margin. Byssal notch moderately deep. Distribution
SE South Island, Foveaux Strait, and Stewart, Auckland and Bounty islands, S New Zealand, taken alive at 18–91 m from clean, bryozoan/shell substrata (Fig. 27). Remarks
Cyclochlamys pileolus is distinctive in the combination of small size (height up to 1.50 mm), very strong commarginal lamellae and scales, and prominent, acutely conical prodissoconch. Cyclochlamys bacata has a similar prodissoconch though entirely different dissoconch sculpture. The largest of the four specimens known from the Bounty Islands (heights 0.80 mm and 0.81 mm) have no trace of radial sculpture or scales, yet are identical to Stewart Island specimens in all other respects. The single valve from the Kermadec Ridge was among loosely consolidated calcareous material washed from cavities in a block of bryozoan/shell limestone (hardground), the cemented part of which includes shells of some molluscs that clearly lived at considerably shallower depths, notably Barbatia novaezelandiae (E.A. Smith, 1915), Mesopeplum convexum (Quoy & Gaimard, 1835), Modelia granosa (Martyn, 1784), and Maoricolpus roseus (Quoy & Gaimard, 1834), probably dating from a late glacial maximum. We presume that the specimen of C. pileolus is approximately contemporaneous, and ranged further north than at present during glacial maxima. Etymology
From the Latin pileus (cap), alluding to the acutely conical prodissoconch.» HENK H. DIJKSTRA & BRUCE A. MARSHALL, 2008
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