Bull. Natl. Mus. Nat. Sci., Ser. A, 41(1), pp. 69–75, February 20, 2015

An Additional Record of Bassozetus levistomatus Machida, 1989 fromthe Western North Paciﬁc (Teleostei, Ophidiiformes, Ophidiidae)
Shinpei Ohashi and Gento Shinohara
Department of Zoology, National Museum of Nature and Science,
4–1–1 Amakubo, Tsukuba, Ibaraki 305–0005, Japan
E-mails: s-ohashi@kahaku.go.jp (SO)/s-gento@kahaku.go.jp (GS)(Received 16 November 2014; accepted 24 December 2014)

Abstract An ophidiid ﬁsh specimen (592 mm in standard length) was collected from 5,531–
5,606 m depth off Fukushima Prefecture, Japan in 2013 and identiﬁed as the rare Bassozetus levistomatus Machida, 1989 by its unique absence of basibranchial tooth patches and vomerine teeth,and combination of following counts: dorsal-ﬁn rays 122; anal-ﬁn rays 99; pectoral-ﬁn rays 28–29;
long gill rakers 11. The specimen is the second record from the Western North Paciﬁc and only thethird from the Paciﬁc Ocean. We document its morphology in detail and discuss the morphologicalcharacteristic of the species with reexamination of the holotype.
Key words : Additional specimen, deepest record, holotype, Japan, Neobythitinae.

Introduction
The deep-sea genus Bassozetus Gill, 1883 is amember of the ophidiid subfamily Neobythitinae
that is characterized by its possession of 21–29
pectoral-ﬁn rays not reaching to anus, pelvic ﬁnwith one ray, 9–22 long gill rakers on the anteriorarch, large head, its length about a half the preanal length, elongate body tapering caudally, eyediameter much smaller than snout length, opercular spine weak or absent (Nielsen and Merrett,2000). According to Nakabo and Kai (2013),
there were 4 species, Bassozetus glutinosus(Alcock, 1890), Bassozetus levistomatus Machida,
1989, Bassozetus robustus Smith and Radcliffein Radcliffe, 1913 and Bassozetus zenkevitchi
Rass, 1955, in Japanese waters. Two species ofthem, B. glutinosus and B. robustus, wererecently reported by Tomiyama et al. (2011) andTakami et al. (2011), respectively.
Bassozetus levistomatus was originallydescribed from a single specimen collected in the
Izu-Bonin Trench, southern Japan (Machida,1989). Subsequently, Nielsen and Merrett (2000)
reviewed the genus and reported nine additional

specimens (180＋–805 mm SL) of this species
from the Paciﬁc (one specimen from off California, USA), Indian and Atlantic Oceans.
A large specimen of B. levistomatus was collected by the R/V Soyo-maru of the Fisheries
Research Agency (FRA) from abyssal waters off
Fukushima Prefecture, northern Honshu Island,
Japan in the summer of 2013. The specimen represents the second record from the Western North
Paciﬁc, the third from the Paciﬁc Ocean and the
deepest record for the species. We here describe
morphological characters of the present specimen and discuss several taxonomic characters of
the species.
Materials and Methods
Counts and measurements mainly follow
Nielsen and Merrett (2000), except for snout
length, eye diameter, postorbital length and pectoral-ﬁn length that follow Hubbs and Lagler(1958). Vertebrae and median-ﬁn rays were
examined from radiographs. Scales on head andbody, and sagittal otolith were observed by SEM(scanning electron microscopy) with Digital

70

Shinpei Ohashi and Gento ShinoharaFig. 1. Bassozetus levistomatus from Japan. — A, NSMT-P 114823, 592 mm SL, male; B, NSMT-P 29533, holotype, 471 mm SL, female. Photograph of NSMT-P 114823 taken by S. Chiba. Bars indicate 5 cm.

Microscope VHX-D500/D510 (Keyence, Tokyo)
without metallic coat. Standard length was
abbreviated as SL. All specimens examined here
are deposited in Department of Zoology,
National Museum of Nature and Science, Tsukuba (NSMT).
Bassozetus levistomatus Machida, 1989
[Japanese name: Soko-fukumen-itachiuo](Figs. 1–5, Table 1)
Bassozetus levistomatus Machida, 1989: 187 (originaldescription, type locality: Izu-Bonin Trench, Japan);
Nakabo, 1993: 376 (keys, Izu-Ogasawara Trench,
Japan); Nielsen and Cohen, 1999: 57 (keys and list, alloceans); Nakabo, 2000: 442 (keys: Izu-Ogasawara
Trench, Japan); Nielsen and Merrett, 2000: 34(description, Paciﬁc, Indian and Atlantic Oceans);
Nakabo, 2002: 442 (keys, Izu-Ogasawara Trench,
Japan); Nielsen and Robins, 2003: 968 (list, circumtropical); Garrido-Linares and Acero P., 2006: 294(list, Atlantic); Nakabo and Kai, 2013: 521 (keys, IzuOgasawara Trench, off California, Arabian sea, northof Madagascar, Caribbean sea and 20°N–55°N in theeastern Atlantic).

Material examined. NSMT-P 114823, 592 mm
SL, male, off Fukushima Prefecture, northern
Japan, Paciﬁc Ocean (37°30.90′N, 145°56.27′E–
37°28.84′N, 145°03.34′E), 5,531–5,606 m depth,
R/V Soyo-maru, crab trap “Kanikago” (＝crab
basket), 3–4 Aug. 2013, collected by K. Fujimotoand J. Inoue.
Diagnosis. Dorsal-ﬁn rays 115–126; anal-ﬁnrays 93–105; pectoral-ﬁn rays 27–29; long rakers
on anterior gill arch 9–11; single pelvic-ﬁn ray
relatively short, 8.1–13.5% SL; scales on headsmaller than on body; basibranchial tooth patchesabsent; vomer usually edentate except for single
large specimen (735 mm SL) with 5 mm circular
tooth patch.
Description. Selected counts and measurements are shown in Table 1. Head large, swollen
with internal mucus: its length about half preanallength. Body elongate, slender posteriorly andcompressed. Head and body covered by smallA Rare Ophidiid Fish from Japan71

Fig. 2. Photographs showing present specimen of Bassozetus levistomatus (NSMT-P 114823) on shipboard(upper), right side of head and anterior body (middle), and ventral aspect (lower). Photographs taken by J.
Inoue and S. Chiba.

cycloid scales: scales on head much smaller thanon body (Fig. 3) 28 in oblique row. Lateral line
indistinct. Snout blunt. Two nostrils between
snout tip and eye: anterior nostril small without
ﬂeshy raised rim; posterior nostril at midpoint
between snout tip and eye, its diameter larger
than anterior nostril. Eye circular and extremely
small, smaller than posterior nostril. Mouth large
and subterminal: upper jaw longer than half headlength; posterodorsal portion of upper jaw
sheathed by cheek skin. Upper jaw and dorsal
portion of lower jaw without scales. Granular
tooth bands on both jaws and palatine. Vomer

edentate, completely covered with oral epithelium. Basibranchial tooth patches absent. Preopercle soft: its posterior margin with weak serration. Opercular spines absent. Gill opening
wide, upper end above pectoral-ﬁn base. No
tubular pore above gill opening (Fig. 4). Anterior
gill arch with long and rudimentary rakers: longrakers comb-like on epibranchial and ceratobranchial; rudimentary rakers knob-like on epibranchial and hypobranchial. Pseudobranchial ﬁlaments 2: anterior rudimentary; posterior longer
and distinct. Pectoral ﬁn relatively long, but its
posterior tip not reaching to above anus: all rays

72

Shinpei Ohashi and Gento ShinoharaFig. 3. SEM images of scales on head (A) and body (B) of Bassozetus levistomatus NSMT-P 114823, 592 mm
SL. Under illustration shows areas removed scales on head (a) and body (b). Bar indicates 1 mm.

unbranched. Dorsal and anal ﬁns with longbases, continuous with caudal ﬁn posteriorly:
both ﬁn rays unbranched. Dorsal-ﬁn origin anterior to pectoral-ﬁn base. Anal ﬁn originating
below about 25th dorsal-ﬁn ray. Pelvic ﬁn relatively long, its length about half distance
between pelvic-ﬁn base and anal-ﬁn origin: pelvic-ﬁn origin inserted below hind margin of preopercle. Caudal ﬁn slender, its rays branched.
Anus adjacent to anal-ﬁn origin.
Sagittal otolith (Fig. 5). Thick and rounded.

Dorsal and ventral margins rounded. Posterodorsal portion slightly protruding posteriorly. Shallow sulcus centrally. Ostial channel absent.
Color when fresh (Figs. 1A, 2). Groundcolor of head and body pale brown. Areas withskin damaged such as cheek region and posterior
portion of body, whitish. Posteroventral portionof opercular region black. Abdomen and pectoral
ﬁn dark brown. When captured, head and abdomen somewhat blue.
Color in alcohol. Ground color of head andA Rare Ophidiid Fish from Japan
Table 1.

73

Selected counts and measurements of Bassozetus levistomatus.
Holotype
NSMT-P 29533

Nontypes*(9 specimens)

592

471

185–80512299
8
28 (left)/29 (right)
1
14
51
65
0
11
5
2
8
27
3
17

115
93
10
29/28
1
13
51
64
0
11
7
2
8
—
—
—

118–126
93–105
8–9
27–29
1
14–16
—
64–68
0
9–11
6–7
—
—
25–36
3–4
17–23

21.0
5.4
11.5
1.8
15.0
21.0
13.5
13.5
16.0
27.0
40.5
15.5

23.5
5.5
13.0
2.5
15.5
21.5
14.0
9.6
17.5
19.5
38.0
11.5

21.0–23.5—
11.5–13.0——
18.5–22.5—
8.1–12.0
15.0–18.0
19.0–32.0
33.5–45.5
10.5–19.0

Present specimen
NSMT-P 114823
SL (mm)Counts
Dorsal-ﬁn rays
Anal-ﬁn rays
Caudal-ﬁn rays
Pectoral-ﬁn rays
Pelvic-ﬁn rays
Precaudal vertebrae
Caudal vertebrae
Total vertebrae
Basibranchial tooth patchesLong rakers on anterior gill arch
Rudimentary rakers on anterior gill arch
Pseudobranchial ﬁlaments
Branchiostegal rays
Number of dorsal ﬁn ray above anal-ﬁn origin
Number of vertebra below dorsal-ﬁn origin
Number of vertebra above anal-ﬁn origin
Measurements
As % of SL
Head length
Snout length
Upper jaw length
Horizontal eye length
Postorbital length
Predorsal-ﬁn length
Pectoral-ﬁn length
Pelvic-ﬁn length
Prepelvic-ﬁn length
Length from base of pelvic ﬁn to anal-ﬁn origin
Preanal-ﬁn length
Body depth at anal-ﬁn origin*Data from Nielsen and Merrett (2000).

body dark brown, but damaged skinless areas
creamy white. Posteroventral portion of opercular region black. Abdomen and pectoral ﬁn darkbrown.
Distribution. Known from the Caribbean Sea
and off Spain in the Atlantic, off Kenya andOman in the Western Indian Ocean, and off
Japan and California in the Paciﬁc at depths
between 3,965 and 5,606 m (Nielsen and Merrett,2000; present study).
Remarks. The 13 species of the genus Bassozetus may be separated into two groups by thepresence or absence of basibranchial tooth
patches (present in 10 and absent in three species) (Nielsen and Merrett, 2000). The present
specimen matches the three species, B. levistomatus, Bassozetus werneri Nielsen and Merrett,2000 and Bassozetus zenkevitchi Rass, 1955, inlacking basibranchial tooth patches. Of the three,
it agrees only with B. levistomatus in lacking
vomerine teeth (vomerine tooth patch present in
the remaining two species). In addition, the present specimen clearly differs from the latter two
by the following characters: dorsal-ﬁn rays (122in present specimen and 115–126 in other specimens of B. levistomatus vs. 131 in B. werneri),anal-ﬁn rays (99 and 93–105 vs. 108) and totalvertebrae (65 and 64–68 vs. 71); pectoral-ﬁn rays
(28–29 in present specimen and 27–29 in otherB. levistomatus vs. 23–25 in B. zenkevitchi), longgill rakers (11 and 9–11 vs. 15–18) and body
depth at anal-ﬁn origin (15.5% and 10.5–19.0%
vs. 8.1–11.0% SL) (Nielsen and Merrett, 2000).
Only the pelvic-ﬁn length does not agree with

74

Shinpei Ohashi and Gento ShinoharaFig. 4. Posterodorsal portion of head in Bassozetus levistomatus, arrows indicate damaged areas on operculum. — A, NSMT-P 114823; B, NSMT-P 29533, holotype. Bars indicate 10 mm.

Fig. 5. SEM image and illustration showing mesial side of left sagittal otolith of Bassozetus levistomatus(NSMT-P 114823, 592 mm SL). Bars indicate 1 mm.

any of these three species, but the value is mostsimilar to that of B. levistomatus (13.5% and8.1–12.0% in other B. levistomatus vs. 17.5% in
B. werneri, and 5.7–8.8% SL in B. zenkevitchi).
In comparison with the holotype of B. levistomatus, most characters of the present specimen
agree with those of the holotype (e.g., 2 pseudobranchial ﬁlaments, snout length and scales onbody larger than on head). We therefore feel justiﬁed in identifying the present specimen as B.
levistomatus and consider the differences
observed in pelvic-ﬁn lengths as representing
intraspeciﬁc variation.
Nakabo (1993, 2000, 2002) and Nakabo andKai (2013) noted a single pore above the upper
end of gill opening in B. levistomatus, that they
considered to be a character that separates the
species from B. zenkevitchi. We examined boththe holotype and the present specimen in detail,but could only ﬁnd damaged areas that may havebeen mistaken for a pore in the former (Fig. 4).
Hence, the presence or absence of the pore is nota suitable character for separates the two species.
Because Nielsen and Merrett (2000) reported a
specimen from off the Paciﬁc coast of California,
the present specimen represents the second
record from the western North Paciﬁc and thethird record from the Paciﬁc Ocean. The habitat
depth of B. levistomatus was previously reported
as 3,965–5,200 m (Nielsen and Merrett, 2000).
The present specimen expands its vertical distribution slightly to 3,965–5,606 m.
Comparative material. Bassozetus levistomatus. Holotype: NSMT-P 29533, 471 mm SL,
Izu-Bonin Trench, southern Japan, Paciﬁc Ocean(31°10.4′N, 141°44.0′E), 5,160 m depth, R/V
Soyo-maru, 20 June 1973.

A Rare Ophidiid Fish from Japan

Acknowledgments
We express our sincere thanks to Ken Fujimoto (FRA) and Junko Inoue (University ofTokyo) for supplying the specimen and photograph on shipboard. Satoru Chiba (NSMT)
kindly provided clear photographs of the specimen. Special thanks go to Martin Gomon(Museum of Victoria) for his English corrections
and critical comments. This study was partly
supported by MEXT KAKENHI Grant number
2412001.
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