Cyclochlamys delli 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. 26, figs. 23A-23F]
2008 Cyclochlamys delli Dijkstra & Marshall, 2008
H. H. Dijkstra & B. A. Marshall, 2008, figure 23.
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«Cyclopecten aupouria.— Dell, 1956: 22, 165 (in part not Powell, 1937); Powell, 1979: 380 (in part not Powell, 1937).
Type material
Holotype NMNZ M.155920 and paratypes (many pr, M.51155; 2 pr, ZMA Moll. 4.07.002); head of Karitane Canyon, off Otago Peninsula, south-eastern South Island, New Zealand, 45°38.5’S, 171°05.0’E, alive, 585–530 m, 19 Mar. 1976, RV Acheron. Material examined
The type material (see above). Chatham Rise: NE of Mernoo Bank, 42°50.8’S, 175°43.8’E, 683–703 m (3 v, M.60315); 43°14’S, 176°11’E, 366 m (3 v, M.10723); off Mernoo Bank, 43°31.17’S, 175°37.62’E, alive, 320–419 m (2 pr, M.155389); 43°32’S, 178°38’E, 549 m (2 v, M.10722). Pegasus Canyon wall, NE of Banks Peninsula, 43°14’S, 173°39’E, 1006–512 m (4 v, M.52812). Chatham Islands: NE of Kaingaroa, 43°35’S, 176°03.5’W, 220–229 m (2 v, M.10725); E of Forty Fours, 44°04’S, 175°23.5’W, 238 m (7 v, M.10727); SE of Pitt Island, 44°32’S, 176°05’W, 302 m (38 v, M.10724); SE of Pitt Island, 44°35.5’S, 176°04’W, 604 m (2 v, M.10721). Head of Waitaki Canyon, off Oamaru, 45°10’S, 171°30’E, 293–256 m (27 v, M.51336). Off Oamaru: 439 m (4 v, M.111760); 366 m (3 v, M.111720). Doubtful Sound: entrance, 45°16’S, 166°48’E, 117–128 m (1 v, M.58646); SW of Hare’s Ears, 45°17.2’S, 166°49.3’E, alive, 146 m (1 pr, 2 v, M.58804). Karitane Canyon, off Otago Peninsula: 45º37.5’S, 171º03’E, 420 m (42 v, M.45529); 45°37.5’S, 171°06.0’E, 476–640 m (29 v, M.9157). Taiaroa Canyon, NE of Otago Peninsula: 45°45.4’S, 171°05’E, 549 m (40 v, M.9091); 45°45.6’S, 171°05’E, 549 m (3 v, M.12860); 45°46’S, 171°03’E, 660 m (many v, M.58533). Papanui Canyon, off Taiaroa Head: 45º51.65'S, 171º00.86'E, alive, 620–340 m (many pr, M.173009). Off Otago Peninsula, 45°50.85’S, 171°01.71’E, alive, 555–604 m (1 pr, 5 v, M.155388). Saunders Canyon, off Otago Peninsula: 45º55’S, 170º56’E, 421 m (3 v, M.26305); 45º55.2’S, 170º56.4’E, 457 m (1 v, M.9415); 45º56’S, 170º54’E, 360 m (3 v, M.48842). Description
Shell up to 5 mm wide, subcircular, juveniles circular, adults broader than high and slightly oblique posteriorly, equivalve (broad, thin ventral margin of right valve disintegrating post mortem: thickened inner part 76–80% height of left valve), left valve somewhat more convex than right valve, umbonal angle c. 110º; typically opaque white in umbonal area, elsewhere colourless and translucent. Prodissoconch 310–370 μm long (brooded), D-shaped (i.e. valve margins), sharply bounded by commarginal lamella; PI c.120 μm long, D-shaped, flattened, smooth, bounded by rounded rim; PII convex, sculptured with crowded, crisp punctae, outer surface glossy, surface within pits matt. Dissoconch left valve sculpture commencing immediately, crisp; comprising widely and somewhat irregularly spaced, thin commarginal lamellae, and much finer, more closely spaced radial threads (16–20 per mm on central disc). Commarginal sculpture progressively weakening ventrally, typically becoming obsolete after shell attains 1–2 mm in height, rarely persisting to maturity, or obsolete when as small as 0.6 mm. Radial sculpture typically persisting throughout, becoming obsolete in few specimens. Posterior auricle slightly larger than anterior; anterior auricle with closely spaced, commarginal lamellae and delicate radial lirae; posterior auricle with fine radial or reticulated sculpture. Right valve disc and all but dorsal border of posterior auricle with outer layer of commarginally elongate, hexagonal prisms that form broad, flexible ventral apron. Posterior auricle typically with up to 5 radial threads on dorsal third. Anterior auricle reticulately sculptured throughout with crowded commarginal lamellae and finer radial threads. Byssal notch of moderate depth, byssal fasciole rather broad. Distribution
Eastern South Island and Chatham Rise, New Zealand, 117–1006 m; taken alive at 146–585 m from muddy substrata (Fig. 24). Remarks
Cyclochlamys delli resembles Cc. favus and Cc. aupouria in gross dissoconch morphology, differing from Cc. favus in being less oblique, in having weaker commarginal lamellae on the left valve that tend to obsolescence in late ontogeny, and in having stronger radial threads, and from Cc. aupouria in being more finely sculptured. Cyclochlamys delli differs most markedly from both these species, however, in size, shape and sculpture of the prodissoconch (Figs 20F, 23C). One of the adult paratypes was opened to reveal a number of shelled young, all about 270 μm wide. These larvae had pitted sculpture throughout and none had a thickened rim. Since prodissoconchs on metamorphosed specimens are up to 370 μm wide, it would seem that there is some incremental growth prior to hatching, presumably of the narrow zone outside the pitted area, up to and including the commarginal varix (evidently the prodissoconch/dissoconch boundary). Etymology
In honour of the late Richard Kenneth (Dick) Dell, former malacologist of the Dominion Museum (now Museum of New Zealand Te Papa Tongarewa), Wellington.» HENK H. DIJKSTRA & BRUCE A. MARSHALL, 2008
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