Catillopecten malyutinae Kamenev, 2017
KAMENEV, G. M. 2018. Four new species of the family Propeamussiidae (Mollusca: Bivalvia) from the abyssal zone of the northwestern Pacific, with notes on Catillopecten squamiformis (Bernard, 1978). Marine Biodiversity, 48: 647-676, figs. 1-16 (published online: 21 November 2017). [p. 659, figs. 9-11]
2017 Catillopecten malyutinae Kamenev, 2017
G. M. Kamenev, 2018, figures 9-11.
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«Cyclopecten sp. 1: Kamenev 2015, p. 191.
Type material and locality: Holotype (MIMB 34148), abyssal plain adjacent to Kuril-Kamchatka Trench, Pacific Ocean (42°14,69′N, 151°44,05′E – 42°14,26′N, 151°42,49′E), 5,127 m, epibenthic sledge, Coll. A. Brandt, 20-VIII-2012 (RV Sonne, cruise no. 223, stn. 8-9); paratype (ZMH 119351), from holotype locality; paratype (MIMB 34149), abyssal plain adjacent to Kuril-Kamchatka Trench, Pacific Ocean (42°14,57′N, 151°43,51′E), 5,130 m, boxcorer, Coll. G. M. Kamenev, 19-VIII-2012 (RV Sonne, cruise no. 223, stn. 8-5); paratype (MIMB 34153), abyssal plain adjacent to Kuril-Kamchatka Trench, Pacific Ocean (43°02,87′N, 152°59,45′E – 43°01,50′N, 152°58,35′E), 5,216-5,221 m, epibenthic sledge, Coll. A. Brandt, 17-VIII-2012 (RV Sonne, cruise no. 223, stn. 7-9).
Other material examined: One young, heavily damaged specimen (MIMB 34177) from holotype locality; one young, heavily damaged specimen (MIMB 34178), abyssal plain adjacent to Kuril-Kamchatka Trench, Pacific Ocean (43°58,35′ N, 157°19,74′E – 43°58,62′N, 157°18,15′E), 5,407-5,418 m, epibenthic sledge, 30-VII-2012 (RV Sonne, cruise no. 223, stn. 1-11); 2 young specimens (MIMB 34179), abyssal plain adjacent to Kuril-Kamchatka Trench, Pacific Ocean (47°13,83′N, 154°41,88′E – 47°14,87′N, 154°43,18′E), 4,988-4,989 m, epibenthic sledge, 5-VIII-2012 (RV Sonne, cruise no. 223, stn. 3-9); one young specimen (MIMB 34180), abyssal plain adjacent to Kuril-Kamchatka Trench, Pacific Ocean (42°29,58′N, 154°00,04′E – 42°28,47′N, 153°59,67′E), 5,290-5,305 m, epibenthic sledge, 15-VIII-2012 (RV Sonne, cruise no. 223, stn. 6-11); 3 young specimens (MIMB 34181), abyssal plain adjacent to Kuril-Kamchatka Trench, Pacific Ocean (43°02,87′N, 152°59,45′E – 43°01,50′N, 152°58,35′E), 5,216-5,221 m, epibenthic sledge, 17-VIII-2012 (RV Sonne, cruise no. 223, stn. 7-9); one young specimen (MIMB 34182), abyssal plain adjacent to Kuril-Kamchatka Trench, Pacific Ocean (42°14,73′N, 151°44,38′E – 42°14,34′N, 151°42,95′E), 5,112-5,126 m, epibenthic sledge, 21-VIII-2012 (RV Sonne, cruise no. 223, stn. 8-12); one young specimen (MIMB 34183), abyssal plain adjacent to Kuril-Kamchatka Trench, Pacific Ocean (41°12,47′N, 150°05,64′E – 41°11,18′N, 150°05,61′E), 5,252-5,249 m, epibenthic sledge, 26-VIII-2012 (RV Sonne, cruise no. 223, stn. 10-9). Total of 10 specimens.
Description: Shell small (to 8.2 mm in length), very thin and fragile, translucent, weakly inflated, rounded-triangular, slightly drawn out anteriorly, slightly longer than higher (H/L = 0.866-0.966), inequilateral (beaks slightly posterior to midline, A/L = 0.513-0.552), inequivalve (left valve more convex than right). Dorsal shell margin straight. Anterior shell margin rounded. Posterior shell margin straight. Ventral shell margin rounded. Auricles moderate length (AL/L = 0.500-0.571), unequal in length (anterior auricles longer than posterior, AAL/AL = 0.556-0.588) and dissimilar in shape; anterior auricles slightly twisted to the right. Umbonal angle 110°.
Right valve disc with numerous, weak, regular, low, narrow, commarginal undulations with closely spaced, antimarginal rows of stubs of broken periostracal setae (Fig. 9h, l). Elongate, tetragonal prisms of outer prismatic layer forming commarginal rows corresponding to commarginal undulations; height of elongate, tetragonal prisms equal of width of undulations (Fig. 11b, c). Anterior
auricle with rounded anterior end, sharply demarcated from shell disc by a byssal fasciole and a sharp suture. Surface of auricle with closely spaced, prominent, commarginal, coarse, lamellate ribs. Byssal notch moderately deep, rounded. Byssal fasciole narrow, somewhat folded. Posterior auricle smaller and narrower than anterior, slightly pointed, poorly demarcated from shell disc. Surface of auricle with weak, narrow, regular, commarginal undulations and growths lines and closely set stubs of broken periostracal setae; setae stubs higher than in central part of disc (Fig. 11g, h). Left valve disc with regular, low, wide, broadly rounded, commarginal undulations and closely spaced, overlying, antimarginal rows of stubs of periostracal setae broken off at different height (Fig. 10e, f); stubs higher at anterior and posterior margins of disc. In flexures between disc and auricles are undamaged periostracal setae of varying height (to 20 μm), triangular-rounded or oval-elongate in cross section, with beaks branching into 3 long pointed processes rounded in cross section (Fig. 10i, l). Anterior and posterior auricles poorly demarcated from shell disc; anterior auricle separated from disc by a shallow sulcus, anterior auricle margin extending vertically down. Anterior and posterior auricles with weak, narrow, commarginal undulations; surface with growths lines and closely set stubs of periostracal setae broken at different height (Fig. 10h, k). Prodissoconch large (length 240-260 μm), smooth, Dshaped, convex, distinct, sharply separated from shell disc. Variability: Shell shape and proportions of adults (shell length more than 5mm) vary insignificantly (Table 4). In adult specimens, the angle between the posterior and dorsal margins of posterior auricles varies from acute to right. In juvenile specimens (shell length less than 4 mm), compared to adults, the shell is relatively higher (shell height is equal to shell length), the relative length of auricles is greater, posterior auricles almost continuous with shell disc.
Distribution and habitat: This species was recorded at the abyssal plain adjacent to the Kuril-Kamchatka Trench (northwestern Pacific) at the latitudes from the middle of Hokkaido (Japan) (41°12,47′N, 150°05,64′E – 41°11,18′N, 150°05,61′E) to the northern Kuril Islands (47°13,83′N, 154°41,88′E – 47°14,87′N, 154°43,18′E) at 4,988-5,418 m depth (bottom temperature (6-8 m above bottom) 1.5-1.6 °C, salinity 34.7‰, oxygen 7.71-7.72 ml/l).
Comparisons: Catillopecten malyutinae sp. nov. well differs from all species of the genus Catillopecten in the presence of periostracal setae and their stubs on the shell, which are more expressed and better preserved on the left valve and form closely spaced, antimarginal rows overlying commarginal undulations on both valves (Table 3). Catillopecten malyutinae sp. nov. is closest in shell shape and proportions to C. eucymatus but differs from it in having setae on the shell and relatively smaller length of auricles with respect to total shell length, posterior auricles more separated from shell disc and longer than anterior auricles, and in its straight posterior shell margin (versus curved in C. eucymatus) (Schein-Fatton 1988; Schein 1989; Dijkstra and Gofas 2004; Dijkstra et al. 2009; Oliver et al. 2016).
Derivatio nominnis: The species name honors Dr. M. V. Malyutina, head of the Russian research team and one of organizers of the KuramBio expedition, as well as an active participant of the epibenthic sledge research team that collected almost the entire material of this species.
Remarks
Catillopecten malyutinae sp. nov. as well as C. brandtae sp. nov. is relatively widely distributed in the northwestern Pacific. It was found in the Pacific Ocean from Hokkaido to the northern Kuril Islands at 6 out of the 12 stations of the KuramBio expedition. It is not excluded that С. malyutinae sp. nov. is more widely distributed and forms denser populations at the abyssal plain of the northwestern Pacific. This species also has a very thin and fragile shell, which is easily
destroyed by sampling.» GENNADY M. KAMENEV, 2017
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