Cyclopecten cincinnatus Dijkstra & Gofas, 2004
DIJKSTRA, H. H. & S. GOFAS. 2004. Pectinoidea (Bivalvia: Propeamussiidae and Pectinidae) from some northeastern Atlantic seamounts. Sarsia, 89: 33-78, figs. 1-22. [p. 47, fig. 11]
2004 Cyclopecten cincinnatus Dijkstra & Gofas, 2004
H. H. Dijkstra & S. Gofas, 2004, figure 11.
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«Type material
Holotype (spm) from Seamount 2, Stn DW263, MNHN, 26 paratypes (v) MNHN, 3 paratypes (v) HD. Type locality
Northeast Atlantic, Atlantis Bank, 34°25.89’N 30°32.49’W, 610–655 m. Material examined
Hyères Bank. Seamount 2: Stn DW203, 31°09.52’N 28°43.52’W, 845 m, 2 spm, 1 v. Irving and Cruiser Banks. Seamount 2: Stn DW237, 32°15.86’N 27°31.85’W, 670–715 m, 2 spm, 3 v. Atlantis Bank. Seamount 2: Stn DW263, the type material. (Cyclopecten cf. cincinnatus). Tyro Bank. Seamount 2: Stn DW279, 33°55.61’N 28°23.75’W, 760–805 m, 5 spm, 1 v. Atlantis Bank. Seamount 2: Stn DW263, 34°25.89’N 30°32.49’W, 610–655 m, 1 spm. – Stn DW265, 34°28.60’N 30°337.70’W, 545 m, 1 v. Azores. Biacores: Stn DR197, 37°49’N 25°01’W. 815 m, 1 spm. Distribution
Present material from 31°09.52’N 34°25.89’N and 27°31.85’W 30°32.49’W, alive at 655–845 m. Description
Shell up to Ca 5 mm high, very fragile, semitransparent, somewhat higher than anteroposterior length, slightly inequivalve, equilateral, auricles unequal, diameter of prodissoconch 192 μm (Fig. 11F, I), colour whitish. Left valve with narrow but distinct commarginal lamellae, first very widely spaced, then becoming less separated on the later part of the disc, and with a radial sculpture of very fine, wavy radial lines, more definite where they abut on the commarginal lamellae but not overriding them. The lamellae are continued on the anterior and posterior auricles. Early dissoconch of right valve quite smooth, then with a gradual onset of closely spaced, regularly arranged commarginal striae; auricles weakly sculptured with commarginal striae, the posterior one also with distinct radial folds. Hinge line straight, dorsal margin weakly denticulated. Internal surface smooth. Byssal notch well developed, no ctenolium. Dimensions of holotype
Height 4.5 mm (ventral margin incomplete), anteroposterior length 4.5 mm, thickness of appressed valves 1.15 mm. Etymology
The Latin adjective for a curled hair, alluding to the aspect of curled commarginal lamellae on the left valve. Remarks
We found several specimens on Tyro Bank, one on Atlantis and one in the Azores, which we tentatively refer to as Cyclopecten cf. cincinnatus. These specimens (Fig. 12) differ in being slightly larger (up to 7.6 mm), in their outline with nearly equal height and length, and the commarginal lamellae becoming more crowded near the ventral margin. These may possibly represent a distinct species, but could also be geographical variants along a north/south gradient. Despite the sympatric occurrence of the two forms in DW263 of Atlantis Bank, we consider that more material is needed before a decision is taken on whether to recognize one more species. A somewhat similar looking and sized congeneric species is Cyclopecten ambiannulatus Schein, 1989, known from the bathyal–abyssal zone of the temperate northeastern Atlantic (Bay of Biscay and southwest–northwest Ireland). This species (see Table 2) differs from C. cincinnatus in having crowded commarginal lirae, which are more delicate and not curled; on the early part of the dissoconch, these are Ca 10 per mm instead of about two in C. cincinnatus. Moreover, C. ambiannulatus lacks radial microsculpture between commarginal lamellae on the left valve, which is present in C. cincinnatus. The byssal notch of C. ambiannulatus is somewhat deeper than in the present species. Cyclopecten imbrifer var. lamellosa (Posselt, 1898), known from the boreal Atlantic and Arctic Sea, also has commarginal curled lamellae on the left valve (Ca three per mm on the central part of the disc), but these are more prominent and more irregularly developed, sometimes to vesicles. This species is much larger (up to Ca 15 mm in height) and also lacks radial microsculpture between commarginal lamellae on the left valve.»
HENK H. DIJKSTRA & SERGE GOFAS, 2004
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