Cryptoplax brunoi n. sp., 2023

Alamri, Nasser & Alotaiby, Faraj, 2023, A New Species of Cryptoplax (Mollusca, Polyplacophora, Cryptoplacidae) Described from Southern Japan, Bulletin of the National Museum of Nature and Science. Series A, Zoology 49 (2), pp. 47-56 : 48-55

Cryptoplax brunoi n. sp.

( Figs. 1–5 ) urn:lsid:zoobank.org:act:215F28D5-9F7A-4F83-8D7BD5B0B7197108

Cryptoplax burrowi : Haddon, 1886: 42 (in part), pl. 3 fig. 11; Pilsbry, 1893: 54 (in part), pl. 9 fig. 7–10; Bednall, 1897; 158 (in part, as doubtful record from South Australia);?Nierstrasz,, 1905: 71 (in part), fig. 143;? Thiele, 1909: 56; Iredale and Hull, 1925: pl. 12, fig. 32;? Slieker, 2000: 54 (in part), pl. 15, fig. 11;? Schwabe, 2005: 54 (in part), pl. 2, fig. 12. [all not of Chiton (Chitonellus) burrowi E. A. Smith, 1884 ]

Type material: Holotype. NSMT-Mo 82405, BL 60.0 mm, Kuroshima Island , 24°14′16″N, 123°59′25″E, on reef, in dead coral block, 25 Aug. 1992, leg. M. Osawa. Paratypes. NSMTMo 82406–82416, 17 specimens, BL 35.7– 67.5 mm, same locality of the holotype, Aug– Sept 1992 and Aug. 1993, leg. M. Osawa ; NSMT-Mo 82417, 1 specimen, BL 38.7 mm, Yarabuzaki , Ishigakijima Island, Yaeyama Islands, 24°25′53″N, 124°04′06″E, under rock at low tide level, 16 May 2007, leg. T. Kosuge ; NSMT-Mo 82418, 1 specimen, BL 20.9 mm, Inoda, Ishigakijima Island, 24°27′N, 124°15′– 16′E, on dead coral block at 2 m, 27 July 2007, leg. T. Kosuge ; NSMT-Mo 82404, 1 specimen, BL 52.5 mm, Off Iriomotejima Island between Uehara and Hatomajima Island, Yaeyama Islands, 24°27′14″N, 123°48′30″E, under dead coral block at 7.4 m, 20 July 2019, leg. T. Fujita ; NSMT-Mo 76700, 1 specimen, BL. ca. 50 mm, Sukomo beach, Kakeromajima Island, Amami Islands, 3 m, 26 May 1989, leg. I. Soyama.

Type locality: Kuroshima Island , Yaeyama Islands, southwestern Japan .

Type depository: National Museum of Nature and Science, Tsukuba .

Etymology: Named after Dr. Bruno Dell`Angelo who is a specialist of both extant and fossil chitons of the world.

Diagnosis: Large sized chiton with very narrow tegmentum, especially in valve IV. Tegmentum pinkish or brick red in head valve, brick red or yellow with fine orange maculation in remaining valves. Tail valve with widely flared insertion plate that expands laterally and even posteriorly beyond the tegmentum. Perinotum light grayish brown with finely grooved club-shaped spicules and minute obtusely pointed spicules. Hyponotum beige with obsolete light brownish maculation.

Description of the holotype: Animal large, 60.0mm× 14mm, vermicular. Tegmentum reduced to small and narrow, especially in valves IV, which is almost linear in appearance. Size of tegmentum widest and shortest at head valve, narrowest at valve IV, longest at tail valve. Valve VI shortest among intermediate valves. Valves I–III in contact with each other, valve IV shortly separated, and valves V –VIII widely separated. Color of tegmentum pinkish in head valve, brick red in valves II and III, yellow with fine orange maculation in valves IV–VIII. Perinotum light grayish brown, beige in sutural tufts and girdle margin. Hyponotum beige with obsolete brownish maculation ( Fig. 1A ).

Outline of tegmentum horseshoe-shaped in head valve, wide, oval in valve II, narrow, spindle-shaped in valves III–VIII. Mucro of tail valve not raised, located near posterior end ( Fig. 2A–J ). Jugum wide wedge-shaped in valve II, narrow wedge-shaped in valves III and IV, parallel sided in remaining valves, nearly smooth on both surface and side margins. Jugal macraesthetes roughly quincuncially distributed; no micraesthete on jugum ( Fig. 3A ). Head valve sculptured with rather fine pustules which are irregular in shape and often merged with neighboring pustules. Pleurolateral areas of valves II–VIII sculptured with longitudinal series of round to rectangular pustules, which are gradually increasing in size and fused into riblets anteriorly, and arranged in slightly divergent 5–6 rows in valves II and VIII, 3–4 rows in the valves III–VII. Each pustule with 1–3 macraesthetes on top. Micraesthetes sparsely distributed along inner basal portion of riblets and prepustular area of pustules; no micraesthete on top of pustules ( Fig. 3A ).

Articulamentum rather thick, white in color. Insertion plate of head valve rather long, which is approximately 1/3 of the length of the tegmentum. Sutural laminae moderately projected anteriorly with round anterior tip in valve II–VII, whereas less projected in tail valve. Insertion plate of tail valve wide, flared postero-ventrally, with weak radial grooves on posterior surface. Slit formula 3/0/0 ( Fig. 2A–J ).

Perinotum densely covered with thick, slightly curved, finely grooved, cylindrical, obtusely pointed spicules of two distinct sizes ( Fig. 3C ). Larger one club-shaped, weakly curved, up to 550 (length)×115 (width) µm; smaller one nearly straight, up to 260×40 µm. Needles of sutural tufts long, slender, slightly curved, smooth, bluntly pointed, up to 800×43 µm ( Fig. 3E ). Marginal spicules long, slender, slightly curved, finely grooved, pointed at tip, up to 860×50 µm ( Fig. 3F ). Spicules on hyponotum small, lanceolate in outline, deeply grooved, pointed at tip, up to 115×15 µm ( Fig. 3H ).

Arrangement of gills merobranchial, abanal type. Holotype specimen with 18 gills on each side. Gonopore located between posterior 8th and 9th gills, nephridiopore situated between posteriormost two gills.

Radula 10.4 mm in length with 54 rows of mature teeth. Central tooth small, narrow, roughly spatula-shaped in outline of posterior surface which is concaved in the distal half, keeled in the basal portion and rounded, weakly angulate at the dorsal edge; anterior process of central tooth short, propped basally. Centro-lateral (first lateral) tooth with shallow groove at inner surface of antero-dorsal corner. Head of major lateral tooth with three denticles of nearly equal length, which have weak transverse ridgeline, and obtusely pointed tip. Major uncinal tooth narrow with obtuse tip ( Fig. 4 ).

Additional description on paratypes: Color of perinotum darker, and with reddish tint on sutural tufts and girdle margin in living animal ( Fig. 1C ), which became similar color with the holotype by preservation in ethanol ( Fig. 1B ). Perinotum occasionally with brownish dots on whole dorsal surface ( Fig. 1D ), and/or lighter cream color portion in anterior end ( Fig. 1D, E ).

Fig. 3B, D, G , and Fig. 5A, B showing features of paratypes NSMT-Mo 82404 and 76700, respectively, which match well with those of the holotype.

Articulamentum of tail valve considerably wide even in specimen of BL 22.5 mm ( Fig. 2K ). Distribution: Only known from the Ryukyu Islands, Japan, and Port Molle, North Queensland, Australia so far, but may widespread in tropical and subtropical West Pacific.

Remarks: The present species has perhaps long been confused with Cryptoplax burrowi (E. A. Smith, 1884) . Two years after the publication of the original description of C. burrowi, Haddon (1886) included drawings of the valves identified as of C. burrowi . Those drawing were made by E. A. Smith reported to be based on a specimen kept in the Natural History Museum, London. The valves of those drawings, especially the tail valve with its flared articulamentum closely resembles that of the present new species. The drawings were also reproduced in Pilsbry (1893) together with the color figure of the animal in Reeve (1847, species 3). That figure was presented as l Chitonellus larvaeformis z by Reeve was distinguished from what is presently known as Cryptoplax larvaeformis (de Blainville MS, Burrow, 1815) by E. A. Smith (1884) as a new species, C. burrowi . Nierstrasz (1905) was the first to illustrate the girdle spicules of C. burrowi . However, Nierstrasz showed (1905, pl. 5, figs 141–143) two distinct types of larger dorsal spicules, one is flat, scoop-shaped, and another is club-shaped, the latter of which is identical with those of the present new species. Then, Thiele (1909) examined other specimens from Makassar, Indonesia, and noted that the spicules of C. burrowi were club-shaped. Iredale and Hull (1925) were first to notice the confusion, concluding that Smith had confused C. burrowi with another species with a flared articulamentum of its tail valve, as illustrated in Haddon (1886). Subsequently, Leloup (1940) showed that the valves of C. burrowi are identical with those shown by Nierstrasz (1905), that is, the articulamentum of the tail valve is narrow, different from that of the figure in Haddon (1886, 11k) here regarded as C. brunoi n. sp., and the larger dorsal girdle spicules of C. burrowi are flat, scoop-shaped. Dell`Angelo et al. (2010) also pointed out the taxonomic confusion of C. burrowi . Revisiting the original description of C. burrowi, Smith described the body to have la buff colour, copiously mottled with greenz. Also, Reeve (1847) described the species 3, as l Chitonellus larvaeformis z, has a red and green marble pattern. The present new species never has green or greenish maculation on the girdle. Specimens with such greenish pattern have flat, scoop-shaped dorsal girdle spicules and narrow articulamentum in the tail valve (personal observations). For this study, I was fortunately provided with an opportunity to examine two lots of the syntypes of C. burrowi deposited in the Natural History Museum, London: NHMUK 1881.11.10.100 from Port Molle, Queensland, and NHMUK 1992.053 from Port Adelaide (in error fide Iredale and Hull, 1925). The former lot consists of one soft body kept in ethanol, and 7 disarticulated dried valves, among which the tail valve is missing. This specimen has club-shaped dorsal girdle spicules, and the features of the valves also match with those of C. brunoi n. sp. The drawings in Haddon (1886, Fig. 11) provided by E. A. Smith are presumed to be based on this specimen. The latter lot 1992.053 consists of four dried specimens, and five valves are disarticulated. All the four specimens were of a single species and have scoop-shaped flat dorsal girdle spicules. The label indicates lfig`d in Reeve, 1847. Conch. Icon., 4 Chitonellus , sp. 3, pl. 1, fig.3 as larvaeformis z. Thus, the syntype of the first lot is a different species from the four syntypes in the second lot. E. A. Smith originally described C. burrowi as a new name for C. l larvaeformis z that was erroneously identified by Reeve (1847), but later he provided the drawing of the valves of the specimen from the first lot to Haddon (1886: Fig. 11). However, C. burrowi is considered to be the species with its name-baring syntype 1992.053 because, as Iredale and Hull (1925) remarked, lE. A. Smith regarded the figure given by Reeve for his b Chitonellus larvaeformis` as sufficiently exact to represent his species,z and he described the color of the species as la buff colour, copiously mottled with green.z In order to avoid further confusion and to fix the identity of Cryptoplax burrowi , the largest specimen, BL 58 mm among four syntypes NHMUK 1992.053 is herein designated as the lectotype ( NHMUK 1992.053/1), and all the remaining syntype specimens (including the one in a different lot identified as C. brunoi n.sp.) are regarded as paralectotypes.

Of the synonymous names for C. burrowi , none is based on one or more type specimen(s) with such a wide articulamentum of the tail valve. This leaves the specimen in the first lot described above without an available name, justifying its description as C. brunoi n. sp. It differs from C. burrowi by the following: the tegmentum of the head valve is the shortest of all valves (that of valves V –VII are clearly shorther than the head valve in C. burrowi ); the valves are narrower, which is most obvious for valves II and IV ( Fig. 5 ); the tail valve has a flared articulamentum; the girdle is more fleshy brownish than C. burrowi , lacking greenish maculation; and the dorsal girdle spicules are large and club-shaped, among longer finely grooved marginal spicules ( Fig. 5 ).

Cryptoplax hartmeyeri Thiele, 1911 , Cryptoplax mjoebergi Bergenhayn, 1933 , and Cryptoplax vittata Ang, 1967 resemble the present new species by having small intermediate valves V –VII. The first two species were synonymized with C. burrowi by Leloup (1940). They have flat, striated spicules. The identity of C. vittata is unclear, but the articulamentum of the tail valve is not wide as the present new species.

E. A. Smith (1903) reported Cryptoplax burrowi from Hulule Island, Maldives. However, due to the taxonomic confusion mentioned above, the specimen needs to be re-identified.

Figures

Fig. 1. Cryptoplax brunoi n. sp. Habitus. A, B, D, E, preserved specimens; C, specimen in situ, underwater photograph (by T. Fujita).A, holotype (NSMT-Mo 82405), Kuroshima Island, BL 60.0mm, dorsal and ventral views; B, paratype (NSMT-Mo 82404), Iriomotejima Island, BL 52.5mm, dorsal view; C, same specimen with B, underwater photograph; D, paratype (NSMT-Mo 82411), Kuroshima Island, BL 43.0mm, dorsal view; E, paratype (NSMT-Mo 82413), Ishigakijima Island, BL 22.5mm, dorsal view.Scales:10mm for A, B, D; 5mm for E.

Fig. 2. Cryptoplax brunoi n. sp. SEM images of the valves.A–J, holotype (NSMT-Mo 82405):A, valve I, dorsal view; B, valve II, dorsal view; C, valve III, dorsal view; D, valve IV, dorsal view; E, valve V, dorsal view; F, valve. V, frontal view; G. valve VI, dorsal view; H, valve VII, dorsal view; I. valve VIII, dorsal view; J, valve VIII, lateral view; K, paratype (NSMT-Mo 82413, same specimen with Fig.1E), valve VIII, dorsal view.Scale:1mm forA–K.

Fig. 3. Cryptoplax brunoi n. sp. SEM images of the valves and girdle spicules. A, C, E, F, H, holotype (NSMT- Mo 82405); B, D, G, paratype (NSMT-Mo 82404).A, B, detail of tegmentum in jugal and pleurolateral areas; C, D, dorsal spicules; E, tuft needles; F, G, marginal needles; H, ventral spicules. Scales: 100µm for A–F; 50µm for G, H.

Fig. 4. Cryptoplax brunoi n. sp. SEM images of the radula. A, B, holotype (NSMT-Mo 82405). A. radula, dorsal view; B. central part of radula, dorsal view. Scales: 100µm for A, 50µm for B.

Fig. 5. Comparisons of valve shape and girdle spicules in Cryptoplax brunoi n. sp. and C. burrowi (E. A. Smith, 1884). A, B, C. brunoi, n. sp., paratype (NSMT-Mo 76700). C, D, C. burrowi (NSMT-Mo 76701, from Kakeromajima Island, Amami Islands, Japan, BL. ca. 40mm). A, C, outline of the valves. B, D, girdle spicules: 1, small dorsal spicule; 2, large dorsal spicule; 3, spicule of the tuft; 4, marginal spicule; 5, ventral spicule. Scale for A, C: 1 mm; B, D: 100μm.