Catillopecten brandtae 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. 656, figs. 7, 8]
2017 Catillopecten brandtae Kamenev, 2017
G. M. Kamenev, 2018, figures 7, 8.
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«Cyclopecten sp. 2: Kamenev 2015, p. 191.
Type material and locality: Holotype (MIMB 34147), abyssal plain adjacent to Kuril-Kamchatka Trench, Pacific Ocean (43°58,26′N, 157°19,68′E – 43°58,33′N, 157°17,98′E), 5,417-5,423 m, epibenthic sledge, Coll. A. Brandt, 30-VII-2012 (RV Sonne, cruise no. 223, stn. 1-10); paratypes (2) (ZMH 119350), from holotype locality; paratype (MIMB 34152), abyssal plain adjacent to Kuril-Kamchatka Trench, Pacific Ocean (46°13,60′N, 155°33,42′E – 46°14,93′N, 155°32,57′E), 4,860-4,866 m, epibenthic sledge, Coll. A. Brandt, 2–3-VIII-2012 (RV Sonne, cruise no. 223, stn. 2-9).
Other material examined: One young specimen (MIMB 34169) from holotype locality; 1 young, heavily damaged specimen (MIMB 34170), abyssal plain adjacent to Kuril-Kamchatka Trench, Pacific Ocean (43°35,50′N,153°57,89′E – 43°34,30′N, 153°58,18′E), 5,378-5,376 m, epibenthic sledge, 11-VIII-2012 (RV Sonne, cruise no. 223, stn. 5-9); 1 young, heavily damaged specimen (MIMB 34171), 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); 2 young, heavily damaged specimen (MIMB 34172), 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); 1 young specimen (MIMB 34173), abyssal plain adjacent to Kuril-Kamchatka Trench, Pacific Ocean (43°02,78′N, 152°59,30′E – 43°01,65′N, 152°58,45′E), 5,217-5,223 m, epibenthic sledge, 17–18-VIII-2012 (RV Sonne, cruise no. 223, stn. 7-10); 1 young specimen (MIMB 34174), 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, 20-VIII-2012 (RV Sonne, cruise no. 223, stn. 8-9); 1 specimen (MIMB 34175), abyssal plain adjacent to Kuril-Kamchatka Trench, Pacific Ocean (40°35,49′N, 150°59,92′E – 40°34,25′N, 150°59,91′E), 5,399-5,398 m, epibenthic sledge, 23–24-VIII-2012 (RV Sonne, cruise no. 223, stn. 9-9); 1 young specimen (MIMB 34176), abyssal plain adjacent to Kuril-Kamchatka Trench, Pacific Ocean (40°35,40′N, 150°59,84′E – 40°34,27′N, 150°59,00′E), 5,398-5,389 m, epibenthic sledge, 25-VIII-2012 (RV Sonne, cruise no. 223, stn. 9-12). Total of 9 specimens.
Description: Shell small (to 7.0 mm in length), extremely thin and fragile, translucent, very compressed, film-like, Dshaped, slightly longer than higher (H/L = 0.679-0.933), strongly inequilateral (beaks much anterior to midline, A/L = 0.393-0.492), inequivalve, concave upward (left valve convex and right valve concave to left valve). Anterodorsal and posterodorsal shell margins slightly concave; anterior, posterior and ventral shell margin smoothly rounded. Auricles very large (auricle length almost equal to shell length, AL/L = 0.721-1.056), strongly unequal in length (anterior auricles much shorter than posterior, AAL/AL = 0.329-0.400). Umbonal angle very large, approximately 140°.
Right valve disc concave; surface with very weak, irregular, commarginal undulations and very fine, radial, dark, thread-like, curved lines, more noticeable in central part of shell disc (Figs. 7g and 8g). Anterior auricle concave, narrow, with rounded anterior end, sharply demarcated from shell disc by a well expressed byssal fasciole. Surface of auricle with very fine, commarginal growth lines. Byssal notch moderately deep, rounded. Byssal fasciole narrow, ray-like, opaque, somewhat folded. Posterior auricle continuous with shell disc; surface with very weak, irregular, commarginal undulations and very thin, radial, dark, thread-like lines.
Left valve disc convex; surface crumpled due to intersection of irregular, wide, commarginal undulations and indistinct, weak, very wide, radial undulations, broadening toward ventral margin in form of rays. Anterior and posterior auricles continuous with shell disc; surface with very weak, irregular, commarginal undulations. Prodissoconch large (length 280 μm), smooth, D-shaped, convex, distinct, sharply separated from shell disc. Variability: Individual and age-related variability of the shell of this species is difficult to assess based on the material at my disposal. Almost all specimens have shell margins damaged to varying degree, not allowing an evaluation of shell shape and exact measurements of morphological features. It can only be noted that the dorsal margin in smaller specimens (shell length less than 4 mm) is straight (Fig. 7j, k), but not concave, as in the larger ones.
Distribution and habitat (Fig. 6): This species was recorded at the abyssal plain adjacent to the Kuril-Kamchatka Trench (northwestern Pacific) at the latitudes from southern Hokkaido (Japan) (40°35,40′N, 150°59,84′E – 40°34,27′N, 150°59,00′ E) to the middle Kuril Islands (46°13,60′N, 155°33,42′E – 46°14,93′N, 155°32,57′E) at 4,860-5,423 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: The new species is easily distinguished from almost all species of the genus Catillopecten, except Catillopecten micaceus (Dautzenberg and Bavay, 1912), by having a D-shaped, very compressed shell, with strongly anterior beaks and very long auricles almost equal to shell length, auricles of the left valve continuous with the shell disc, and by lacking noticeable sculpture and periostracal spines on the surface of the shell (Table 4). Catillopecten brandtae sp. nov. is most close in shell shape and proportions and in the absence of shell sculpture and periostracal spines to C. micaceus, but differs from it by having a inequivalve shell, the anterior auricle of the left valve continuous with the shell disc, and a much shorter anterior end of the shell (Dautzenberg and Bavay 1912).
Derivatio nominnis: The species name honors Professor, Dr. A. Brandt, an organizer and leader of the KuramBio expedition (2012), as well аs leader of epibenthic sledge research team, which collected the entire material of this species.
Remarks
All species of this genus were recorded in the bathyal and abyssal zones at depths from 341 to 4,829 m (Dautzenberg and Bavay 1912; Knudsen 1970; Bernard 1978; Schein-Fatton 1985; Schein 1989; Coan et al. 2000; Dijkstra and Maestrati 2008; Dijkstra and Marshall 2008; Coan and Valentich-Scott 2012). However, most of them are bathyal species. Only three species (C. eucymatus, Catillopecten graui (Knudsen, 1970), and Catillopecten squamiformis (Bernard, 1978)) were found in the abyssal zone (depths greater than 3,000 m). Catillopecten brandtae sp. nov. found only in the lower abyssal zone at a depth greater than 4,500 m is most likely an exclusively abyssal species. It is fairly widely distributed in the northwestern Pacific, not forming dense populations at the abyssal plain. This species cannot be categorized as "rare" (Kamenev 2015), because 1 to 4 specimens
in a sample were found at 7 out of 12 stations of the KuramBio expedition covering an extensive region of the Pacific from the northern Kuril Islands to Japan. Catillopecten brandtae sp. nov. may possibly form denser populations in the abyssal northwestern Pacific. This species has a very thin and fragile shell, and it cannot therefore be ruled out that a large number of specimens are destroyed when collecting and washing samples.» GENNADY M. KAMENEV, 2017
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