Bull. Natl. Mus. Nat. Sci., Ser. A, 47(1), pp. 37–42, February 22, 2021
DOI: 10.50826/bnmnszool.47.1_37

First Record of Bathyphylax omen Tyler, 1966 from the Western Paciﬁc(Actinopterygii, Tetraodontiformes, Triacanthodidae)
Keiichi Matsuura1, Hiromitsu Endo2 and Atsushi Ujihara3
1

Department of Zoology, National Museum of Nature and Science,
4–1–1 Amakubo, Tsukuba, Ibaraki 305–0005, Japan
E-mail: matsuura@kahaku.go.jp
2
Laboratory of Marine Biology, Faculty of Science and Technology, Kochi University,
2–5–1 Akebono-cho, Kochi 780–8520, Japan
3
Graduate School of Environmental Studies, Nagoya University,
Furo-cho, Chikusa-ku, Nagoya, Aichi 464–8601, Japan(Received 11 December 2020; accepted 23 December 2020)

Abstract A specimen (51.4 mm standard length) of the triacanthodid ﬁsh Bathyphylax omen
Tyler, 1966 collected oﬀ central Honshu, Japan is reported with detailed description. This species
was previously known only from three specimens collected oﬀ Kenya, western Indian Ocean. The
present specimen represents the ﬁrst record of this species from the western Paciﬁc. The newly
collected specimen reveals fresh color of this species for the ﬁrst time. The specimen from Japanwas identiﬁed as B. omen by its color pattern of the body and the dorsal proﬁle of the snout. Taxonomic comments on distinguishing characters of Bathyphylax bombifrons Myers, 1934 and B.
omen are provided.
Key words : spikeﬁsh, distribution, Japan, taxonomy, color pattern, Bathyphylax bombifrons.

Introduction

Methods

A strange looking deep-sea ﬁsh was captured
oﬀ Kii Peninsula, central Honshu, Japan by abottom trawler, Koei-maru, and brought to thethird author by a local naturalist, Nobuo Aikawa.
The specimen was then transferred to Kochi University for further study by the ﬁrst and second
authors. Our detailed examinations have revealed
that the specimen is the rare triacanthodid Bathyphylax omen Tyler, 1966, previously known only
from the holotype and two additional specimens
collected oﬀ Kenya, East Africa (Tyler, 1966,
1968, 1983). The newly collected specimen represents the ﬁrst record of this species from thewestern Paciﬁc. It also provides fresh color ofthis species for the ﬁrst time.

Counts and measurements follow Tyler (1968,
1983). Body width was measured between the
pectoral-ﬁn bases. Because the gill opening of
spikeﬁshes is very small, the counts of gill rakers
and pseudobranch lamellae can obtained only
when the gill opening is greatly cut downward by
scalpel. We counted these characters only on theright side in order to minimize damage to thespecimen. Abbreviations are as follows: SL, standard length and BSKU, Department of Biological Science, Kochi University. X-ray photographwas used to count the number of vertebrae.
Bathyphylax omen Tyler, 1966
(New Japanese standard name: Yami-kawamuki)(Figs. 1–3)

© 2021 National Museum of Nature and Science

Specimen examined. BSKU 127482, 51.4 mm

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Fig. 1. Bathyphylax omen, BSKU 127482, 51.4 mm SL, Paciﬁc coast of Kii Peninsula, southeast of Daiozaki
Point, Honshu, Japan, photo by Atsushi Ujihara.

Fig. 2. Ventral view of pelvis of Bathyphylax omen, BSKU 127482, 51.4 mm SL, photo by Atsushi Ujihara.

Bathyphylax omen from western PaciﬁcFig. 3.

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X-ray photograph of Bathyphylax omen, BSKU 127482, 51.4 mm SL.

SL, Paciﬁc coast of Kii Peninsula, southeast of
Daiozaki Point, central Honshu, Japan, 360 m
depth, bottom trawl, 13 December 2019.
Description. Dorsal-ﬁn rays VI＋14; anal-ﬁnrays 12; pectoral-ﬁn rays 13 (both sides) pelvicﬁn rays I＋1 (ray very short on right side, absent
on left side); upper jaw teeth 16; lower jaw teeth
19; gill rakers 6＋1＋14＝21 (right side); pseudobranch lamellae 8 (right side); olfactory lamellae 12 (right side); vertebrae 8＋12＝20. Head
length 38.1% SL, snout length 15.2% SL, snout
depth 12.1% SL, eye diameter 15.0% SL, postorbital length 8.4% SL, interorbital width 9.5% SL,
mouth width 6.8% SL, gill opening length 4.9%
SL, snout to spiny dorsal-ﬁn origin 44.6% SL,
body depth 40.3% SL, body width 19.5% SL,
ﬁrst dorsal-ﬁn spine 30.9% SL, second dorsal-ﬁnspine 28.0% SL, third dorsal-ﬁn spine 21.5% SL,
fourth dorsal-ﬁn spine 5.8% SL, ﬁfth dorsal-ﬁnspine 1.8% SL, sixth dorsal-ﬁn spine 2.0% SL,
soft dorsal-ﬁn base 14.0% SL, longest dorsal-ﬁn
ray 18.3% SL, anal-ﬁn base 12.1% SL, longest
anal-ﬁn ray14.2% SL, caudal ﬁn length 24.7%
SL, caudal peduncle depth 9.9% SL, caudal
peduncle length 16.1% SL, pelvic-ﬁn spine
31.3% SL, pelvic-ﬁn ray 2.5% SL, pelvic length
36.4% SL, pelvic width 16.1% SL; pelvic widthin pelvic length 2.3 times.
Anterior three dorsal-ﬁn spines long and welldeveloped, the fourth spine much shorter than thethird but protruding through the dorsal surface ofbody and easily seen, the ﬁfth and sixth spines
shorter than the fourth and not easily discernible;
pelvis thin and basin-like, its ventral surface
externally ﬂat; snout shorter than rest of head,dorsal proﬁle of snout slightly concave; mouthslightly supraterminal; teeth conical, arranged ina single series in each jaw; gill opening moderate, reaching ventrally to level of three-fourths
down pectoral-ﬁn base; pseudobranch short,reaching ventrally to level slightly above dorsal
origin of pectoral-ﬁn base; number of spinules
per upper mid-body scale plate 4–8, arranged ina vertical row with an accessory spinule sometimes in front of or behind the major row.
Color when fresh: dorsal half of body pinkish,with three longitudinal distinct red stripes, theﬁrst originating around nape coursing along baseof spiny dorsal ﬁn to origin of soft dorsal ﬁn, thesecond originating just behind postero-dorsaledge of orbit and running on side of body to endof soft dorsal-ﬁn base, the third starting justbehind posterior edge of orbit, running on mid
body, curving very slightly down below third
dorsal-ﬁn spine, and ending just above posterior
part of anal-ﬁn base with a short disconnection
below anterior part of soft dorsal ﬁn; dorsal sideof caudal peduncle reddish pink; dorsal half ofsnout reddish pink; ventral half of head and bodyanterior to anus white; ventral surface of pelvis

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K. Matsuura et al.

Fig. 4. Relationship of snout depth and standard length of Bathyphylax bombifrons (blue symbols) and B. omen
(red symbols). Triangles: holotypes; square: B. omen, BSKU 127482.

white covered with many dark brown spots (Fig.
2); distal half of pelvic-ﬁn spine white and proximal half light pink; dorsal-ﬁn spines pink; rays ofsoft dorsal and caudal ﬁns light pink; pectoraland anal-ﬁn rays transparent.
Remarks. The spikeﬁsh genus Bathyphylax
Myers, 1934 is diﬀerentiated from other spikeﬁshes by the following combination of characters: the anterior three dorsal-ﬁn spines welldeveloped, much longer than the posterior threespines; mouth slightly supraterminal; pelvis thinand basin-like, its ventral surface externally ﬂatand its width 1.3–2.7 times in its length; snout
shorter than rest of head; teeth conical, arranged
in a single series in each jaw; pseudobranchshort, 12–16 lamellae, reaching ventrally to

between levels of dorsal origin and very slightly
below dorsal origin of pectoral-ﬁn base (Tyler,
1968, 1983; Santini, 2006). Bathyphylax is currently known from three species, B. bombifrons
Myers, 1934 (Indo-West Paciﬁc), B. omen Tyler,
1966 (western Indian Ocean) and B. purvosti
Santini, 2006 (Marquesas Islands).
Santini (2006) showed that Bathyphylax purvosti is easily distinguished from the other two
species by its long snout (17–28% SL vs 14.9–
15.8% SL in B. bombifrons and 13.8–15.5% SL
in B. omen). Bathyphylax bombifrons is similar
to B. omen but the dorsal proﬁle of the snout isconcave in B. bombifrons and slightly concave or
relatively straight in B. omen Tyler (1968, 1983).
Tyler (1983) tried to quantify the degree of con-

Bathyphylax omen from western Paciﬁccavity of the snout by measuring the depth of thesnout midway between the anterior tip of the dorsal lip and the anterior edge of the orbit. He measured the snout depth of ﬁve specimens of B.
bombifrons and three specimens of B. omen. His
measurements resulted in small diﬀerences
between the two species: the snout depth is 10.8–
13.4% (average 12.0%) SL in B. bombifrons and
12.5–15.5% (average 13.9%) SL in B. omen
(Tyler, 1983). Matsuura and Tyler (1997)
reported additional three specimens of B. bombifrons from New Caledonia in which the snout
depth is 11.7–11.9% SL.
The newly collected specimen is identiﬁed as
Bathyphylax omen by the fresh coloration clearly
showing that the third red stripe originates justbehind the posterior edge of orbit, running on the
mid body, curving slightly down below the third
dorsal-ﬁn spine, and ends just above the posterior
part of the anal-ﬁn base with a short disconnection below the anterior part of the soft dorsal ﬁn(Fig. 1A). When it was ﬁxed and transferred to
70% ethanol, the third stripe changed its color
from red to dark brown and ends at a level infront of the anal-ﬁn origin (Fig. 1B): there is nodark marking, neither line nor spot, above theanal-ﬁn base where the very short red line (looks
like a red spot) is found in the fresh specimen.
Although previous authors did not have opportunities to see the fresh color of either B. bombifrons or B. omen, Tyler (1968, 1983) and Matsuura and Tyler (1997) reported the diﬀerence inthe course of the running pattern of the third longitudinal stripe in preserved specimens of these
two species. In B. bombifrons, the third line starts
just behind the eye and courses over the pectoralﬁn base, and curves distinctly downward toward
the anus, whereas that of B. omen does not curve
distinctly downward but, rather, continues along
the body toward the end of the anal-ﬁn base. In
addition to the color, the dorsal proﬁle of thesnout of the specimen from Japan is slightly concave, which is another character of B. omen.
However, the depth of the snout in the specimen from Japan is 12.1% SL, which ﬁgure isincluded in the range of B. bombifrons but very

41

close to the low end of the range of B. omen. In
spite of Tylerʼs (1983) eﬀorts to diﬀerentiate thetwo species by the snout depth, it is diﬃcult toclearly separate them by the relationship of the
proportional measurements of the snout depth
and standard length (Fig. 4). Although we cannot
deny the possibility that B. omen is a junior synonym of B. bombifrons, we identify the specimen
from Japan as B. omen by the color pattern andthe dorsal proﬁle of the snout.
The third dorsal-ﬁn spine of the specimen
from Japan is 21.5% SL, longer than that of thepreviously reported specimens of B. bombifrons(13.4–13.8% SL) and B. omen (14.3–14.6% SL)(Tyler, 1983). The number of spinules per dorsal
mid-body scale plate in the Japanese specimen is
4–8, being arranged in a vertical row, whereas
there are 3–8 spinules in the previous specimensof B. omen (Tyler, 1983).
Hoese et al. (2006) included Bathyphylax
bombifrons in the “Zoological Catalogue of Australia. Volume 35. Fishes”; however, they gave
only distributions of this species in New South
Wales and Queensland, without catalogue numbers of voucher specimens. When considering
the similarity of B. bombifrons and B. omen, it is
impossible to know which species or both they
included in their record. This has led us to
exclude Australian records of B. bombifrons until
Australian specimens are examined.
The new Japanese standard names, “Yamikawamuki zoku” and “Yami-kawamuki”, are proposed for Bathyphylax and B. omen, respectively.
“Yami” means “dark”, implying “dark deep sea”,
the habitat of this species, “kawamuki” refers to
spikeﬁsh, and “zoku” means genus.
Acknowledgments
We thank James C. Tyler of the National
Museum of Natural History, Washington, D.C.,
for providing helpful comments on the manuscript. We are grateful to Nobuo Aikawa forbringing the specimen of B. omen to the third
author. This rare specimen was captured by
Hideaki Kihara, skipper of the bottom trawler,

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K. Matsuura et al.

Koei-maru.
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