Bull. Natl. Mus. Nat. Sci., Ser. A, 49(2), pp. 47–56, May 22, 2023
DOI: 10.50826/bnmnszool.49.2_47

A New Species of Cryptoplax (Mollusca, Polyplacophora,
Cryptoplacidae) Described from Southern Japan
Hiroshi Saito
Department of Zoology, National Museum of Nature and Science,
4–1–1 Amakubo, Tsukuba, Ibaraki 305–0005, Japan
E-mail: h-saito@kahaku.go.jp(Received 19 December 2022; accepted 21 December 2022)

http://zoobank.org/urn:lsid:zoobank.org:pub:581CC45D-9E79-45B3-B24D-48DD71F8EEC9Abstract A new chiton species Cryptoplax brunoi is described from the Ryukyu Islands, southern Japan. The new species has long been confused with a widespread Indo-West Pacific species,
Cryptoplax burrowi (E. A. Smith, 1884), because of its close resemblance. It is distinguishable
from the latter by having more fleshy, brownish girdle that is lacking greenish maculation, narrower tegmentum of the intermediate valves, wider, and flared articulamentum of the tail valve,and finely grooved, club-shaped dorsal spicules. Among five syntypes for C. burrowi, four syntypes in one of two lots were emphasized in Smith’s original description while the single syntype
in a second lot is here identified as belonging to the new species. One of the four syntypes corresponding to the more familiar widespread species is here designated as the lectotype of C. burrowi.
Key words: chiton, Acanthochitonina, Cryptoplax, new species, taxonomy, West Pacific.

Introduction
The species of Cryptoplax de Blainville, 1818are medium to large chitons that have elongated,
worm-like bodies. They have relatively small
shell valves that for many species do not even incontact with each other for the posterior four of
their eight valves. A typical Cryptoplax species
lives in a very narrow space for its body, which
requires flexibility of the body such as intersticesof dead coral blocks, holes in rocks, among theholdfasts of kelps whereas other chitons are more
likely to be found on the underside of rocks. Currently, 18 extant species are currently accepted(Molluscabase, plus see Park et al., 2022); theseare mostly restricted to the shallow waters of thetropical Indo-West Pacific except for some species found in warm temperate regions of eastern
Asia or southern Australia.
© 2023 National Museum of Nature and Science

The present author obtained 22 specimens of a
distinctive Cryptoplax species from the Ryukyu
Islands in southern Japan, with a peculiar wide,
flared articulamentum in the tail valve, which
expands laterally and even posteriorly beyond
the tegmentum. This feature resembles the similar condition of a specimen illustrated in Haddon(1886: plate 3, fig 11k) as C. burrowi (E. A.
Smith, 1884). This figure was drawn by E. A.
Smith based on the specimen kept in the Natural
History Museum, London, and provided to
Haddon. However, taxonomic examination of the
syntypes of C. burrowi kept in Natural History
Museum revealed that the syntypes consist of
two species: one is supposed to be the species
figured in Haddon (1886), and the other isconsidered to be C. burrowi. They have been
confused for long time, and there are somesynonymous names, but no species with such awide articulamentum of the tail valve has yet
been described with other scientific names than

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H. Saito“C. burrowi” to date. Here the species collectedfrom the Ryukyu Islands is described as a new
species.
Material and Methods
All examined specimens are deposited in themolluscan collection of the Department of Zoology, National Museum of Nature and Science,
Tsukuba (NSMT). The valves, girdle scales andspicules, and the radula were imaged by thescanning electron microscope (SEM) JEOLLV6380, Jeol Co., Tokyo. Preparation for theexamination by SEM followed Sirenko (2012)
with modification: The boiling time in maceration was shorter, about 1–3 minute; girdle elements and radula were dried with a critical pointdryer JCPD-5, Jeol Co. The girdle scales andspicules and a part of the radula were observed
also with light microscope, AxioImager® M1light microscope with AxioCam® HRC image
capture equipment controlled by AxioVision®
ver. 4.8, Carl Zeiss, Jena. Those hard parts were
mounted on glass slides with Entellan neu®
Merck, Darmstadt.
Underwater photograph (Fig. 1C) was taken witha digital camera TG-2 housed in the underwater
housing PT-053, and a flash UFL-3, Olympus
Imaging Corp., Tokyo.
TaxonomyClass Polyplacophora Gray, 1821
Order Chitonida Thiele, 1909
Suborder Acanthochitonina Bergenhayn, 1955
Superfamily Cryptoplacoidea H.
and A. Adams, 1858
Family Cryptoplacidae H. and A. Adams, 1858
Genus Cryptoplax de Blainville, 1818
Type species: Chiton larvaeformis (deBlainville MS) Burrow, 1815, subsequent designation by Gray, 1821.
Distribution: Indo-West Pacific and southern
Australia; Miocene–Recent

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 deadcoral 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 Natureand Science, Tsukuba.
Etymology: Named after Dr. Bruno
DellʼAngelo 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 remain-A New Species of Cryptoplax from Southern Japan

49

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 60.0 mm, dorsal and ventral views;
B, paratype (NSMT-Mo 82404), Iriomotejima Island, BL 52.5 mm, dorsal view; C, same specimen with B,
underwater photograph; D, paratype (NSMT-Mo 82411), Kuroshima Island, BL 43.0 mm, dorsal view; E, paratype (NSMT-Mo 82413), Ishigakijima Island, BL 22.5 mm, dorsal view. Scales: 10 mm for A, B, D; 5 mm for E.

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H. SaitoFig. 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, lateralview; K, paratype (NSMT-Mo 82413, same specimen with Fig. 1E), valve VIII, dorsal view. Scale: 1 mm for A–K.

A New Species of Cryptoplax from Southern Japan

51

Fig. 3. Cryptoplax brunoi n. sp. SEM images of the valves and girdle spicules. A, C, E, F, H, holotype (NSMTMo 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: 100 µm for A–F;
50 µm for G, H.

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H. SaitoFig. 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: 100 µm for A, 50 µm for B.

ing 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 spiculesand minute obtusely pointed spicules. Hyponotum beige with obsolete light brownish maculation.
Description of the holotype: Animal large,
60.0 mm×14 mm, 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. Colorof tegmentum pinkish in head valve, brick red invalves 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 inhead 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 inshape 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 insize and fused into riblets anteriorly, andarranged in slightly divergent 5–6 rows in valves
II and VIII, 3–4 rows in the valves III–VII. Eachpustule 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.

A New Species of Cryptoplax from Southern Japan

53

Comparisons of valve shape and girdle spicules in Cryptoplax brunoi n. sp. andC. 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.
40 mm). 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: 100 μm.

Fig. 5.

54

H. Saito

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 to550 (length)×115 (width) µm; smaller one
nearly straight, up to 260×40 µm. Needles ofsutural 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 eachside. Gonopore located between posterior 8th
and 9th gills, nephridiopore situated between
posteriormost two gills.
Radula 10.4 mm in length with 54 rows ofmature 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 ofcentral tooth short, propped basally. Centro-lateral (first lateral) tooth with shallow groove at
inner surface of antero-dorsal corner. Head ofmajor 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 ofperinotum 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 onwhole 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 theholotype.
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 tropicaland 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 tailvalve 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 “Chitonellus larvaeformis” 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 thefirst 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 isclub-shaped, the latter of which is identical withthose 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 withanother species with a flared articulamentum of
its tail valve, as illustrated in Haddon (1886).
Subsequently, Leloup (1940) showed that thevalves of C. burrowi are identical with thoseshown by Nierstrasz (1905), that is, the articulamentum of the tail valve is narrow, diﬀerent fromthat 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, scoopshaped. DellʼAngelo et al. (2010) also pointed
out the taxonomic confusion of C. burrowi.
Revisiting the original description of C. burrowi,

A New Species of Cryptoplax from Southern Japan

Smith described the body to have “a buﬀ colour,
copiously mottled with green”. Also, Reeve(1847) described the species 3, as “Chitonellus
larvaeformis”, 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, scoopshaped 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 lotsof the syntypes of C. burrowi deposited in the
Natural History Museum, London: NHMUK1881.11.10.100 from Port Molle, Queensland,and NHMUK 1992.053 from Port Adelaide (inerror ﬁde Iredale and Hull, 1925). The former lot
consists of one soft body kept in ethanol, and 7
disarticulated dried valves, among which the tailvalve is missing. This specimen has club-shaped
dorsal girdle spicules, and the features of thevalves 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 basedon this specimen. The latter lot 1992.053 consistsof 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 “figʼd in Reeve,
1847. Conch. Icon., 4 Chitonellus, sp. 3, pl. 1,
fig.3 as larvaeformis”. Thus, the syntype of thefirst lot is a diﬀerent species from the four syntypes in the second lot. E. A. Smith originallydescribed C. burrowi as a new name for C.
“larvaeformis” that was erroneously identified byReeve (1847), but later he provided the drawingof the valves of the specimen from the first lot to
Haddon (1886: Fig. 11). However, C. burrowi isconsidered to be the species with its name-baring
syntype 1992.053 because, as Iredale and Hull
(1925) remarked, “E. A. Smith regarded thefigure given by Reeve for his ʻChitonellus
larvaeformisʼ as suﬃciently exact to represent his
species,” and he described the color of the species as “a buﬀ colour, copiously mottled withgreen.” In order to avoid further confusion and to
fix the identity of Cryptoplax burrowi, the largest

55

specimen, BL 58 mm among four syntypes
NHMUK 1992.053 is herein designated as thelectotype (NHMUK 1992.053/1), and all theremaining 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 tailvalve. 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 thanthe 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 thanC. burrowi, lacking greenish maculation; and thedorsal 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.
Acknowledgements
I would like to thank Masayuki Osawa, Shimane University, Takeharu Kosuge, Kamakura
City, and Isamu Soyama, Takayama City, whokindly provided the specimens, and Toshihiko
Fujita, NSMT who provided the underwater photograph of the new species, as well as the specimen. Thanks are also due to Kathie Way, Natural

56

H. Saito

History Museum, London who allowed me to
examine the type material, and Tom White in thesame museum, for providing the images of thetype material. I am grateful to Douglas Eernisse,
University of California, Fullerton, and Enrico
Schwabe, Zoologische Staatssammlung Muenchen,
Boris Sirenko, Zoological Instiute, Russian
Academy of Science, for their valuable comments and suggestions. Douglas Eernisse kindly
helped strengthen the English writing as well.
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