Deep-sea Fauna and Pollutants off Pacific Coast of Northern Japan, edited by T. Fujita, National Museum of Nature andScience Monographs, No. 39, pp. 467-481, 2009

Deep-sea Cymothoid Isopods (Crustacea: Isopoda: Cymothoidae) of Pacific
Coast of Northern Honshu, Japan
Takeo Yamauchi
Toyama Institute of Health, 17 1 Nakataikoyama, Imizu, Toyama, 939 0363 Japan
E-mail: takeo.yamauchi@pref.toyama.lg.jp

Abstract: During the project “Research on Deep-sea Fauna and Pollutants off Pacific Coast of Northern Japan”, a small collection of cymothoid isopods was obtained at depths ranging from 150 to 908 m. Four speciesof cymothoid isopods including a new species are reported. Mothocya komatsui sp. nov. is distinguished fromits congeners by the elongate body shape and the heavily twisting of the body. Three species, Ceratothoa
oxyrrhynchaena Koelbel, 1878, Elthusa sacciger (Richardson, 1909), and Pleopodias diaphus Avdeev, 1975
were fully redescribed. Ceratothoa oxyrrhynchaena and E. sacciger were firstly collected from blackthroat
seaperchs Doederleinia berycoides (Hilgendorf) and Kaup’s arrowtooth eels Synaphobranchus kaupii Johnson, respectively.
Key words: Ceratothoa oxyrrhynchaena, Elthusa sacciger, Mothocya, new host record, new species, Pleopodias diaphus, redescription.

Introduction
Cymothoid isopods are ectoparasites of marine, fresh, and brackish water fish. In Japan, about
45 species of cymothoid isopods are known (Saito et al., 2000), but deep-sea species have not been
well studied. This paper deals with a collection of cymothoid isopods from the project “Researchon Deep-sea Fauna and Pollutants off Pacific Coast of Northern Japan” conducted by the National
Museum of Nature and Science, Tokyo. The collection obtained at depths ranging from 150 to 908
m includes a total of 36 specimens (apart from those not identifiable to species level) representing
four species. On the basis of this material, I herein describe a new species, Mothocya komatsui sp.
nov. and fully redescribe three poorly known species in Japanese waters, Ceratothoa oxyrrhynchaena Koelbel, 1878, Elthusa sacciger (Richardson, 1909), and Pleopodias diaphus Avdeev, 1975.
Materials and Methods
The collection was made by using R/V Wakataka-maru of the Fisheries Research Agency(FRA). Collecting sites of the expeditions were located at depths ranging from 146 to 1521 m off
the Pacific coast of northern Honshu, Japan. Stations where cymothoid isopods were recovered areshown in Table 1. Samples were fixed in 80% ethanol or 10% neutralized Formalin/sea water solution, and later preserved in 70% ethanol. Terminology follows Bruce (1986b). The common andscientific names of fishes follow those recommended by Froese and Pauly (2008). The material
examined in this study is deposited in the National Museum of Nature and Science, Tokyo(NSMT).

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Table 1. List of sampling data.
Station

Date

Gear Position in

Position out

Depth (m) Temp. (˚C)

WA05-F550
WA05-G350
WA05-H310
WA05-H380
WA05-H480
WA06-B450
WA06-E510
WA06-E900
WA06-F150
WA06-F380
WA06-F480
WA06-G550
WA06-G650
WA06-H550
WA07-B510
WA07-B550
WA07-C410
WA07-C450
WA07-C550
WA07-D510
WA07-D650
WA07-E480
WA07-F510
WA07-G150

27 October 2005
3 November 2005
30 October 2005
1 November 2005
1 November 2005
13 October 2006
3 November 2006
2 November 2006
29 October 2006
30 October 2006
31 October 2006
28 October 2006
28 October 2006
14 November 2006
12 October 2007
12 October 2007
14 October 200717 October 200716 October 200717 October 2007
5 October 2007
27 October 2007
4 November 2007
2 November 2007

OT
OT
OT
OT
OT
OT
OT
OT
OT
OT
OT
OT
OT
OT
OT
OT
OT
OT
OT
OT
OT
OT
OT
OT

37˚ 42.0′ N, 142˚ 04.0′ E
36˚ 58.0′ N, 141˚ 31.5′ E
36˚ 30.5′ N, 141˚ 00.4′ E
36˚ 30.0′ N, 141˚ 01.7′ E
36˚ 33.1′ N, 141˚ 07.3′ E
40˚ 13.3′ N, 142˚ 16.1′ E
38˚ 23.9′ N, 142˚ 05.7′ E
38˚ 29.1′ N, 142˚ 21.5′ E
37˚ 36.7′ N, 141˚ 33.9′ E
37˚ 40.1′ N, 141˚ 50.6′ E
37˚ 39.9′ N, 141˚ 59.0′ E
36˚ 59.2′ N, 141˚ 38.8′ E
36˚ 50.9′ N, 141˚ 35.2′ E
36˚ 32.6′ N, 141˚ 09.8′ E
40˚ 17.3′ N, 142˚ 15.6′ E
40˚ 18.0′ N, 142˚ 16.5′ E
39˚ 48.5′ N, 142˚ 17.9′ E
39˚ 40.6′ N, 142˚ 17.7′ E
39˚ 34.2′ N, 142˚ 18.5′ E
39˚ 05.3′ N, 142˚ 12.0′ E
39˚ 03.3′ N, 142˚ 14.9′ E
38˚ 22.9′ N, 142˚ 05.2′ E
37˚ 39.4′ N, 142˚ 01.2′ E
37˚ 00.5′ N, 141˚ 17.7′ E

551–546
373–356
311–306
380–384
481–476
461–475
514–506
905–908
150–165
386–379
483–478
558–554
648–648561–557
510–509544–555
409–415467–458
552–559505–513
640–661475–478506–508
151–151

37˚ 41.0′ N, 142˚ 04.7′ E
36˚ 56.3′ N, 141˚ 30.9′ E
36˚ 29.0′ N, 140˚ 59.5′ E
36˚ 29.1′ N, 141˚ 00.8′ E
36˚ 32.3′ N, 141˚ 06.2′ E
40˚ 14.9′ N, 142˚ 15.3′ E
38˚ 22.6′ N, 142˚ 06.3′ E
38˚ 29.8′ N, 142˚ 21.6′ E
37˚ 35.3′ N, 141˚ 33.2′ E
37˚ 38.5′ N, 141˚ 50.5′ E
37˚ 41.7′ N, 141˚ 59.0′ E
36˚ 58.1′ N, 141˚ 38.0′ E
36˚ 50.2′ N, 141˚ 34.3′ E
36˚ 31.8′ N, 141˚ 08.7′ E
40˚ 16.0′ N, 142˚ 16.0′ E
40˚ 16.9′ N, 142˚ 16.6′ E
39˚ 50.3′ N, 142˚ 17.9′ E
39˚ 42.3′ N, 142˚ 18.0′ E
39˚ 35.5′ N, 142˚ 18.6′ E
39˚ 04.2′ N, 142˚ 11.8′ E
39˚ 02.3′ N, 142˚ 14.7′ E
38˚ 23.5′ N, 142˚ 04.9′ E
37˚ 38.3′ N, 142˚ 01.1′ E
36˚ 59.6′ N, 141˚ 17.4′ E

4.2
4.0
4.5
4.0
4.1
2.8
3.4
2.8
13.7
3.8
3.6
4.2
3.8
4.1
3.4
3.4
3.7
3.7
3.6
3.6
3.6
―
4.0
12.9

Taxonomy
Family Cymothoidae Leach, 1818
Genus Ceratothoa Dana, 1852
［New Japanese name: Higebuto-uo-no-e-zoku］
Ceratothoa oxyrrhynchaena Koelbel, 1878
［Japanese name: Soko-uo-no-e］(Figs. 1 2)
Ceratothoa oxyrrhynchaena Koelbel, 1878: 401 403, Tafel I fig. 1 (type locality: “Mare Japonicum”); Schioedte and Meinert,
1883: 368 371, table XVI (Cym. XXIII) figs. 10 14; Avdeev, 1982: 72; Rokicki, 1985: 97 (table 1), 99, 103 104 (tables
2 3), 106, 110, 112 113, 122, fig. 6; Trilles, 1986: 624, 631 (table); Trilles et al., 1989: 292, fig. 10; Trilles, [1994]: 34(list), 124; Horton, 2000: 1046 (key), 1048, fig. 7; Bariche and Trilles, 2005: 57 58; Ramdane et al., 2007: 69 (table 1),
71, 73 (list); Ramdane and Trilles, 2008: 175 177 (table 1).
Meinertia oxyrrhynchaena; Thielemann, 1910: 36 38, 98 99 (Table), figs. 35 36, Tafel. I figs. 10 15; Nierstrasz, 1915: 89(list); Gurjanova, 1936a: 84 86, fig. 41; 1936b: 258 (list); Trilles, 1972a: 1208 1212, figs. 137 155, plate I III; 1972b:
1250 1251; Yamaguchi and Baba, 1993: 193, fig. 20.
Meinertia oxyrhynchaena (sic); Komai, 1927: 1148, fig. 2215; Iwasa, 1947: 816 (?part).
Codonophilus oxyrhynchaenus (sic); Nierstrasz, 1931: 132 (list); Shiino, 1965b: 544 (?part); Saito et al., 2000: 65 (list);
Tatsu, 2002: 41 (list).
Ceratothoa oxyrhanchaenus (sic); Nunomura, 2006: 36.
Not Meinertia oxyrhynchaena (sic); Yamaguti, 1938: 27; Iwasa, 1947: 816 (?part), no. 2351. (See Remarks.)
Not Codonophilus oxyrhynchaenus (sic); Shiino, 1965b: 544 (?part), no. 728. (See Remarks.)
Not Ceratothoa oxyrrhynchaena; Bruce, 1980: 320, figs. 3 4; Yu and Li, 2003: 224 227, fig. 2. (See Remarks.)

Material examined. 2 males (19.5 mm, 18.0 mm), 2 ovig. females (40.0 mm, 35.0 mm),
WA07-G150, ex blackthroat seaperchs Doederleinia berycoides (Hilgendorf, 1879) (Acropomati-

Deep-sea Cymothoid Isopods from Northern Japan469dae), coll. T. Kuramochi, NSMT-Cr 19588.
Description of ovigerous female. Body (Fig. 1A) stout, bilaterally symmetrical, about 2.1
times as long as maximum width, widest at pereonites 4 5; dorsal surface (Fig. 1B) smoothly
vaulted. Cephalon (Fig. 1C) triangular; anterior margin acute, visible ventrally (Fig. 1D). Eyes
distinct, occupying 0.43 0.57 width of cephalon. Pereonite 1 (Fig. 1C) sharply produced on anterolateral sides; anterolateral angles reaching level of eyes; pereonite 1 longest; pereonites 5 7
distinctly shorter, progressively concave posteriorly; posterolateral margins of pleonites (Fig. 1B)rounded. Pleon (Fig. 1A) strongly immersed in pereonite 7; pleonites becoming wider towards
posterior side; pleonite 1 distinctly less wide than others; pleonite 5 (Fig. 1E) wider than precedingpleonites with sinuate posterior margin. Pleotelson (Fig. 1E) 0.53 0.54 times as long as maximum
width; lateral margins evenly rounded; posterior margin almost straight or shallowly convex.
Antennule (Fig. 2A) with 7 articles, extending to anterior of pereonite 1; first 3 articles wider
than others. Antenna (Fig. 2B) with 7 articles, extending to anterior of pereonite 1; outer marginsmooth. Mandible palp (Fig. 2C) without setae; article 3 smaller than others. Maxillule (Fig. 2D)with 4 spines. Maxilla lateral lobe (Fig. 2E) with about 15 spines; medial lobe with 8 spines. Maxilliped (Fig. 2F) article 3 with 9 spines.
Pereopod 1 (Fig. 2G) basis with weakly developed carina; merus with anterior expansions.
Pereopods 2 3 (Fig. 2H) bases with triangular carina; meri with anterior expansions. Pereopods
4 6 (Fig. 2I) bases with developed carina; meri with weak anterior expansion. Pereopod 7 (Fig. 2J)
basis with well developed carina; merus with anterior expansion.
Pleopods 1 5 (Figs. 2K L) approximately equal in size. Pleopod 1 (Fig. 2K) lamellar. Pleopods 2 5 (Fig. 2L) with weekly folded endopods. Uropod endopod (Fig. 2M) longer than exopod,
curve medially, narrowing gradually to round apexes.
Coloration. Pale tan in alcohol.
Remarks. The present specimens closely agree with the previous descriptions of Ceratothoa
oxyrrhynchaena collected from Japanese water (Koelbel, 1878; Schioedte and Meinert, 1883;
Thielemann, 1910; Horton, 2000). Ceratothoa oxyrrhynchaena is very similar to C. collaris
Schioedte and Meinert, 1883, redescribed in detail by Bariche and Trilles (2008) based on theholotype and many specimens obtained mainly from Lebanese coast. However, C. collaris can be
distinguished from C. oxyrrhynchaena by the indented outer margin of antenna.
Although identical illustrations of the species were used in Iwasa (1947) and Shiino (1965b),
the illustrations are considerably different from the true C. oxyrrhynchaena. For example, the cephalon is elliptical, and its anterior margin weekly produced; the anterolateral sides of pereonite 1
are bluntly produced; the pleon is weekly immersed in pereonite 7; and the uropod rami are subequal in length and very short. There is no doubt that the illustrations in Iwasa (1947) and Shiino(1965b) were based on other cymothoid species. Furthermore, descriptions of the species in Iwasa(1947) and Shiino (1965b) are scanty and lacking information of diagnostic features. Therefore, it
is impossible to be certain of the identity of the species shown by Iwasa (1947) and Shiino(1965b).
A specimen collected from Scolopsis sp. (Nemipteridae) in Hong Kong was identified as “C.
oxyrrhynchaena (?)” by Bruce (1980), and specimens collected on the body surface of shrimp
scads Alepes djedaba (Forsskål, 1775) (as Carnax kalla [sic], Carangidae) in Chinese water wereidentified as C. oxyrrhynchaena by Yu and Li (2003). The specimens recorded by Bruce (1980)
and Yu and Li (2003) might actually represent other cymothoid species because of following characters in these specimens: cephalon anterior margin not produced, pereopod 7 basis without welldeveloped carina, and pereopod 7 merus without anterior expansion.
Yamaguti (1938) recorded Meinertia oxyrhynchaena (sic) collected from the mouth cavity of
the red seabream Pagrus major (Temminck and Schlegel, 1843) (as Pagrosomus unicolor Quoy

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Takeo Yamauchi

Fig. 1. Ceratothoa oxyrrhynchaena Koelbel, 1878. A‒E, female (35.0 mm; NSMT-Cr 19588); F, male (19.5 mm;
NSMT-Cr 19588). A, habitus, dorsal; B, same, lateral; C,
head, dorsal; D, frons, ventral; E, pleotelson, dorsal; F,
habitus, dorsal. Scale in mm.

and Gaimard, Sparidae) in the Inland Sea, Japan. This record might be attributable to misidentification because only another cymothoid species inhabits in the mouth cavity of P. major in Japanesewater (Yamauchi, unpublished data).
The blackthroat seaperch Doederleinia berycoides is commercially caught in Japanese waters. The species is highly appreciated as food, being expensive fish in the country. More study isneeded on C. oxyrrhynchaena in Japan because little is known about the pathology of fishes due toC. oxyrrhynchaena.
Distribution. Previous records were summarized by Horton (2000): Japan, China, Mediterranean (France, Italy, Tunisia, Algeria, Montenegro, Yugoslavia), and north-east Atlantic coasts(Mauritania). In Japanese water, C. oxyrrhynchaena was recorded from Sea of Japan coast of Honshu, Uchiura, Ishikawa Prefecture (Tatsu, 2002), Pacific coast of northern Honshu eastward to
Onahama, Fukushima Prefecture (present study), and Sagami bay (Thielemann, 1910; Nunomura,2006), at the depths of 110 151 m (Thielemann, 1910; present study).

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471

Fig. 2. Ceratothoa oxyrrhynchaena Koelbel, 1878. A‒B, G‒H, K‒L, female (35.0 mm; NSMT-Cr 19588); C‒F, I‒J,
M, female (40.0 mm; NSMT-Cr 19588). A, left antennule, dorsal; B, left antenna, dorsal; C, left mandible,
ventral; D, left maxillule, ventral; E, left maxilla, ventral; F, left maxilliped, ventral; G, left pereopod 1, ventral; H, left pereopod 2, ventral; I, left pereopod 6, medial; J, left pereopod 7, medial; K, left pleopod 1, ventral;L, left pleopod 5, dorsal; M, left uropod, dorsal. Scales: 2 mm.

Host. Previous records were summarized by Bariche and Trilles (2005) and Ramdane et al.
(2007): the bogue Boops boops (Linnaeus, 1758), the striped seabream Lithognathus mormyrus(Linnaeus, 1758) (Sparidae), the blotched picarel Spicara maena (Linnaeus, 1758), the picarel
Spicara smaris Linnaeus, 1758 (Centracanthidae), the John dory Zeus faber Linnaeus, 1758 (Zeidae), the nursehound Scyliorhinus stellaris (Linnaeus, 1758) (Scyliorhinidae), the spotted torpedo
Torpedo marmorata Risso, 1810 (Torpedinidae), the starry ray Raja asterias Delaroche, 1809, and472

Takeo Yamauchi

the thornback ray Raja clavata Linnaeus, 1758 (Rajidae). In the present study, D. berycoides is
newly recorded as a host.
Genus Elthusa Schioedte and Meinert, 1884
［New Japanese name: Eru-uo-no-e-zoku］
Elthusa sacciger (Richardson, 1909)［Japanese name: Hora-anago-no-e］(Figs. 3 4)
Livoneca sacciger Richardson, 1909: 87 88, fig. 12 (type locality: station 4957, by way of Bungo Channel and Inland Sea at
Mizimoko Shima Light N. 22˚ W., 29 miles, lat. 32˚36′N, long. 132˚23′E, at a depth of 437 fathoms, Japan); Gurjanova, 1936a: 90 91, fig. 45; 1936b: 258 (list); Shiino, 1951: 86, fig. 2A; 1965a: 544, no.727; Saito et al., 2000: 66 67(list).
Lironeca saccigera; Nierstrasz, 1931: 144 (list).
Lironeca sacciger; Kussakin, 1979: 300 301, fig. 168; Brusca, 1981: 124; Avdeev, 1982: 70 71, fig. 2; Trilles, [1994]: 37(list), 189 190.
Elthusa sacciger; Bruce, 1990: 254, 255 (key), 268 270, figs. 13 15; Yamauchi et al., 2004: 2 3.

Material examined. 1 ovig. female (45.5 mm), WA05-F550, NSMT-Cr 19589; 1 male (16.5mm), WA05-H480, NSMT-Cr 19590; 1 male (12.0 mm), WA05-H380, NSMT-Cr 19591; 1 female(26.5 mm), WA06-F480, NSMT-Cr 19592; 1 male (19.5 mm), WA06-E510, NSMT-Cr 19593; 1
male (14.5 mm), WA06-F150, NSMT-Cr 19594; 1 male (16.0 mm), WA06-G550, NSMT-Cr
19595; 1 male (15.0 mm), WA06-G650, on the body surface of a broadbanded thornyhead Sebastolobus macrochir (Günther, 1877) (Sebastidae), NSMT-Cr 19596; 1 ovig. female (39.0 mm),
WA06-H550, NSMT-Cr 19597; 1 ovig. female (42.5 mm), WA06-B450, NSMT-Cr 19598; 1 ovig.
female (46.5 mm), WA07-C550, NSMT-Cr 19599; 1 ovig. female (49.0 mm), WA07-C450, NSMT-Cr 19600; 4 ovig. females (34.0, 34.5, 40.0, 41.0 mm), WA07-B510, ex Kaup's arrowtootheels Synaphobranchus kaupii Johnson, 1862 (Synaphobranchidae), NSMT-Cr 19601; 1 ovig. female (40.0 mm), 1 male (19.5 mm), WA07-F510, in gill chamber of S. kaupii, NSMT-Cr 19602; 1
ovig. female (52.0 mm), WA07-B550, NSMT-Cr 19603; 1 ovig. female (39.0 mm), 1 male (23.0mm), WA07-E480, in gill chamber of S. kaupii, NSMT-Cr 19604; 1 ovig. female (42.0 mm),
WA07-D510, NSMT-Cr 19605; 4 males (20.5, 21.0, 21.0, 21.5 mm), WA07-B510, NSMT-Cr
19606; 1 male (19.5 mm), WA07-D650, NSMT-Cr 19607; 1 male (17.0 mm), WA07-C410, NSMT-Cr 19608.
Description of ovigerous female. Body (Fig. 3A) bilaterally symmetrical, 1.6 1.8 times aslong as maximum width, widest at pereonites 4 5; dorsal surface (Fig. 3B) smoothly vaulted. Cephalon (Fig. 3C) chestnut-shaped; anterior margin acute, not ventrally folded (Fig. 3D); with
notches in proximal sides. Eyes distinct or indistinct, occupying about 0.2 width of cephalon. Pereonites 5 6 longest; pereonite 7 shorter than 5 6, concave posteriorly. Coxae of pereonites 6 7 (Fig.
3A) project laterally, bulbous. Pleon (Fig. 3A) strongly immersed in pereonite 7; pleonite 1 laterally overlapped by pereonite 7. Pleotelson (Fig. 3E) semicircular, 0.7 0.8 times as long as maximum width; posterior margin evenly rounded.
Antennule (Fig. 4A) with 8 articles, extending to pereonite 1; basal articles in contact (Fig.
3D). Antenna (Fig. 4B) extending about halfway along pereonite 1, with 12 articles; bases set wide
apart (Fig. 3D); articles 4 and 5 distinctly longer than 1 3; articles 6 12 short, becoming progressively shorter. Mandible palp (Fig. 4C) with abundant short setae on distolateral margin of articles
2. Maxillule (Fig. 4D) with 1 large and 4 small spines. Maxilla (Fig. 4E) with 2 spines each on
medial and lateral lobes. Maxilliped (Fig. 4F) article 3 with 7 curved spines.

Deep-sea Cymothoid Isopods from Northern Japan

473

Fig. 3. Elthusa sacciger (Richardson, 1909). A‒E, female (52.0mm; NSMT-Cr 19603); F, male (21.0 mm; NSMT-Cr
19606). A, habitus, dorsal; B, same, lateral; C, head, dorsal; D, frons (left mouth parts removed), ventral; E, pleotelson and uropods, dorsal; F, habitus, dorsal. Scale inmm.

Pereopods 1 4 (Figs. 4G H) slender, without carina on bases. Pereopods 5 7 (Figs. 4I J) very
slender, with weakly developed carina on bases.
Pleopods (Figs. 4K L) all lamellar; pleopods 3 5 (Fig. 4L) with weakly developed endopod
proximomedial lobes; pleopod 2 with appendix masculina. Uropod (Fig. 3E) rami not extending
beyond posterior of pleotelson; exopod longer than endopod, with subparallel margin and abruptly
rounded to subtruncate apices.
Coloration. Pale tan in alcohol.
Remarks. Elthusa sacciger was redescribed in detail by Bruce (1990) based on Australianmaterials. The preset specimens agree closely with previous descriptions (Richardson, 1909; Shiino, 1951, 1965a; Bruce, 1990). This species is readily distinguished from others of the genus by
the bulbous coxae of pereonites 6 and 7.
Distribution. Elthusa sacciger was collected from Japan (Richardson, 1909; Shiino, 1951;

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Takeo Yamauchi

Fig. 4. Elthusa sacciger (Richardson, 1909). Female (52.0 mm; NSMT-Cr 19603). A, left antennule, dorsal; B, left
antenna, dorsal; C, left mandible, ventral; D, left maxillule apex, ventral; E, left maxilla, ventral; F, left maxilliped, ventral; G, left pereopod 1, ventral; H, left pereopod 2, ventral; I, left pereopod 6, medial; J, left pereopod 7, medial; K, left pleopod 1, ventral; L, left pleopod 5, medial. Scales: A‒C, E‒L, 2 mm; D, 0.5 mm.

present study) and off the central coast of New South Wales at the depths of 823 995 m (Bruce,1990). In Japanese water, E. sacciger was recorded from Pacific coast of Hokkaido, off Akkeshi
and off Muroran (Shiino, 1951), Pacific coast of Hokkaido, lat. 42˚10′40″N, long. 142˚14′E (Richardson, 1909), Pacific coast of northern Honshu (present study), and Bungo Channel, lat. 32˚36′N,
long. 132˚23′E (Richardson, 1909), at the depths of 150 786 m (Richardson, 1909; present
study).
Host. Previous records were only from mouth cavity of cutthroat eels (Synaphobranchidae):Synaphobranchus sp. collected from Japan (Richardson, 1909) and grey cutthroats S. affinis
Günther, 1877 (as S. pinnats (Gronow)) (Shiino, 1951). Hence, the present specimens from gillchamber of S. kaupii are new host and infection site records for E. sacciger. In the present study, amale of E. sacciger was collected on the body surface of Sebastolobus macrochir among theDeep-sea Cymothoid Isopods from Northern Japan

475

captured fishes consisting of various species. However, it is uncertain that S. macrochir is the hostof E. sacciger because the male of cymothoids often abandoned their dying or stressed host (Brusca, 1981).
Genus Mothocya Costa, in Hope, 1851
［New Japanese name: Era-nushi-zoku］
Mothocya komatsui sp. nov.
［New Japanese name: Shinkai-era-nushi］(Figs. 5 6)Material examined. Holotype, ovig. female (19.5 mm), WA06-E900, off Kinkazan, Miyagi
Prefecture, 38˚ 29.8′ N, 142˚ 21.6′ E 38˚ 29.1′ N, 142˚ 21.5′ E, 905 908 m, 2 November 2006,
NSMT-Cr 19609.
Description of holotypic female. Body (Fig. 5A) bilaterally asymmetrical, about 2.5 times aslong as maximum width; widest at pereonite 3; Dorsal surface (Fig. 5B) smoothly vaulted. Cephalon (Fig. 5C) deeply immersed in pereonite 1; anterior margin evenly rounded, turned down, but
not posteriorly (Fig. 6A). Eyes distinct, occupying about 0.38 width of cephalon. Pleonites 1 4
subequal in length; pereonite 7 shortest. Coxae (Fig. 5B) not produced beyond posterior of respective segments; posterior margins rounded. Pleon (Fig. 5D) immersed in pereonite 7; pleonite 1
largely concealed by pereonite 7. Pleotelson (Fig. 5D) semicircular, about 0.66 times as long as
maximum width; lateral margins evenly rounded.
Antennule (Fig. 6B) with 8 articles; antennules set wide apart (Fig. 6A). Antenna (Fig. 6C)with 8 articles. Mandible palp (Fig. 6D) articles without setae. Maxillule (Fig. 6E) with 1 large and3 small spines. Maxilla (Fig. 6F) with 2 spines each on medial and lateral lobes. Maxilliped (Fig.
6G) article 3 with 3 curved spines.
Pereopods 6 7 (Figs. 6J K) significantly larger than pereopods 1 5 (Figs. 6H I).
Pleopods (Figs. 6L M) approximately equal in size. Pleopod 1 (Fig. 6L) with weakly developed peduncle lateral lobe, those of pleopods 2 5 (Fig. 6M) moderately developed. Pleopods 3 5(Fig. 6M) with developed endopod proximomedial lobe. Uropod rami (Fig. 6N) not extending

Fig. 5. Mothocya komatsui sp. nov. Holotype female (19.5 mm; NSMT-Cr 19609). A, habitus, dorsal; B, same,
lateral; C, head, dorsal; D, pleon and pleotelson, dorsal. Scale in mm.

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Fig. 6. Mothocya komatsui sp. nov. Holotype female (19.5 mm; NSMT-Cr 19609). A, frons, ventral; B, left antennule, dorsal; C, left antenna, dorsal; D, left mandible, ventral; E, left maxillule apex, ventral; F, left maxilla,
ventral; G: left maxilliped, medial; H, right pereopod 1, ventral; I, left pereopod 2, ventral; J, left pereopod 6,
medial; K, left pereopod 7, medial; L, left pleopod 1, ventral; M, left pleopod 5, medial; N, left uropod, dorsal.
Scales: A, H‒N, 2 mm; B‒G, 0.1 mm.

beyond posterior of pleotelson; exopod longer than endopod, with subparallel margin and roundedapices.
Coloration. Pale brown in alcohol, densely covered by chromatophores.
Remarks. The present new species is assigned to Mothocya, having a set of the diagnostic
features described by Bruce (1986b).

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Mothocya komatsui can be distinguished from its congeners by the elongate body shape, theheavily twisting of the body, and the wide apart antennules set. The new species is similar to
Mothocya panamica Bruce, 1986, known from the Pacific coast of Panama, and Mothocya ihi
Bruce, 1986, known from New Zealand, in having the elongate body shape and the wide apartantennules set (Bruce, 1986b). However, the present new species differs from M. panamica in thefollowing features (those of M. panamica in parentheses): the body heavily twisted (straight); thecoxa of pereonite 7 not produced beyond posterior of segment (extending beyond posterior of segment); the pleon immersed in pereonite 7 (pleon not immersed in pereonite 7); the pleotelson about
0.66 times as long as maximum width (about 1.3 times as long as maximum width); the maxilla
with 2 spines each on medial and lateral lobes (with 2 spines on medial lobe, 5 spines on laterallobe); the pereopod 1 posterior margins of ischium to carpus not distinctly convex (distinctly convex); the pleopod peduncle lateral lobes large (extremely large); the uropod rami not slender (slender). Mothocya komatsui differs from M. ihi in the following features (those of M. ihi in parentheses): the body heavily twisted (straight); the cephalon anterior margin evenly rounded (with distinct
rostral process); the maxilliped article 3 with 3 spines (with 4 spines); the uropod rami not extending beyond posterior of pleotelson (extending slightly beyond posterior of pleotelson).
Etymology. This species is named after Dr. Hironori Komatsu, who collected the holotype of
this species.
Distribution. This species was collected only from Pacific coast of northern Honshu, eastward to Kinkazan, Miyagi Prefecture, Japan, at depth of 905 908 m (present study).
Host. Unknown. It seems that the new species is a gill parasite because of its heavily twistingof the body.
Genus Pleopodias Richardson, 1910
［New Japanese name: Kaitei-ginka-zoku］
Pleopodias diaphus Avdeev, 1975
［New Japanese name: Kaitei-ginka］(Figs. 7 8)
Pleopodias diaphus Avdeev, 1975: 254 256, figs. 1 11 (type locality: East China Sea); Bruce and Harrison-Nelson, 1988:
600; Trilles, [1994]: 33 (list), 109.
Pleopodias superatus Williams and Williams, 1986: 656, figs. 62 68 (type locality: Yui, Shizuoka Prefecture, Honshu, Japan,
50˚06.1′N, 138˚33.7′E).

Material examined. 1 ovig. female (23.5 mm), WA05-G350, NSMT-Cr 19610; 1 ovig. female(27.0 mm), WA05-H310, NSMT-Cr 19611; 1 female (12.0 mm), WA06-F380, NSMT-Cr 19612.
Description of ovigerous female. Body (Fig. 7A) 3.4 3.9 times as long as maximum width,
bilaterally symmetrical; pereon dorsum strongly vaulted (Fig. 7B). Rostrum (Fig. 7C) broad; its
anterior margin truncate in dorsal view; its folding area triangular in ventral view, produced between bases of antennae 1 (Fig. 8A). Eyes occupying 0.56 0.57 width of cephalon. Shortest pereonite 2, longest 6. Posterolateral margins of pleonites (Fig. 7D) rounded. Pleotelson (Fig. 8B)
about 2.2 times as long as maximum width; lateral margins bent dorsally; posterior margin deeply
emarginated; medial longitudinal ridge weakly developed.
Antennule (Fig. 8C) with 8 articles, extending to anterior of pereonite 2; anterodistal marginof article 3 produced; antennule bases contiguous. Antenna (Fig. 8D) with 12 articles, extending toposterior of pereonite 3. Mandibular palp (Fig. 8E) article 2 with numerous setae along lateral
margin. Maxillule (Fig. 8F) with 3 spines. Maxilla (Fig. 8G) with 1 large spine and 1 small spine,each on medial and lateral lobes respectively. Maxilliped (Fig. 8H) article 3 with 3 spines.

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Takeo Yamauchi

Pereopods 4 7 (Figs. 8K L) significantly larger than pereopods 1 3 (Figs. 8I J). Pereopod 6(Fig. 8K) carpus and propodus with spines on posterior margin. Pereopod 7 (Fig. 8L) very long,with abundant small spines on inner surface from distal carpus to propodus.
Pleopod 1 peduncle (Fig. 8M) slightly more than 4 times as long as wide; peduncles of pleopods 2 5 (Fig. 8N) becoming progressively narrower towards posterior. Pleopod 1 rami (Fig. 8M)
distal margins rounded; pleopods 2 5 (Fig. 8N) with rami becoming progressively narrow; endopod of pleopod 5 (Fig. 8N) with 2 folds in medial surface and a fold in ventral surface. Uropod(Fig. 8O) extending beyond posterior end of pleotelson; rami subequal in length; both rami narrowing gradually to round apexes.
Coloration. Dorsal surface with dense chromatophores appearing dark reddish brown in alcohol.
Remarks. Pleopodias superatus was regarded as a junior synonym of P. diaphus by Bruce
and Harrison-Nelson (1988). The preset specimens agree very well with the original description of
P. diaphus by Avdeev (1975) and P. superatus by Williams and Williams (1986).
Only two nominal species of the genus Pleopodias were recorded from the Pacific: Pleopodias elongatus Richardson, 1910, recorded from the Philippines, and P. diaphus. Pleopodias diaphus can be distinguished from P. elongatus redescribed by Bruce (1986a), in the following features (those of P. elongatus in parentheses): the slender body shape, 3.4 3.9 times as long as
maximum width (about 2.5 times), the deeply emarginated posterior margin of pleotelson (rounded posterior margin of pleotelson), and contiguous antennule bases (not contiguous).
Distribution. Pleopodias diaphus was collected from East China Sea (= Sea of Japan)(Avdeev, 1975) and Pacific coast of Honshu, Japan (Williams and Williams, 1986; present study),
at depths of 310 380 m (present study).
Host. Avdeev (1975) recorded P. diaphus attached above to the dorsal fin of the blue lanternfish Diaphus caeruleus (Klunzinger, 1871) (Myctophidae). In Japanese deepsea, P. diaphus is the
only cymothoid species attached to the body surface of fishes.

Fig. 7. Pleopodias diaphus Avdeev, 1975. Female (27.0 mm; NSMT-Cr 19611). A, habitus, dorsal; B, same, lateral;C, head, dorsal; D, pleon, lateral (all left pleopods removed). Scale in mm.

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479

Fig. 8. Pleopodias diaphus Avdeev, 1975. Female (27.0 mm; NSMT-Cr 19611). A, frons, ventral; B, pleotelson,
dorsal; C, left antennule, dorsal; D, left antenna, dorsal; E, left mandible, ventral; F, left maxillule, ventral; G,
left maxilla, ventral; H, left maxilliped, ventral; I, left pereopod 1, ventral; J, left pereopod 2, ventral; K, left
pereopod 6, ventral; L, left pereopod 7, medial; M, left pleopod 1, ventral; N, left pleopod 5, medial; O, left
uropod, dorsal. Scales: A‒E, I‒O, 2 mm; F‒H, 0.1 mm.

Acknowledgements
I am especially grateful to Dr. Hironori Komatsu and Dr. Toshiaki Kuramochi (National Museum of Nature and Science, Tokyo) for allowing me to use the material described here. I thank Dr.
Michitaka Shimomura (Kitakyushu Museum of Natural History and Human History) and Dr.

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Susumu Ohtsuka (Hiroshima University) for reviewing the manuscript. Thanks are also due toMrs. Noriko Orita (Toyama Institute of Health) for fine illustrations and Mrs. Rika Konda (Toyama
Institute of Health) for her support with laboratory work. Part of the present study was supported
by a Grant-in-Aid for Scientific Research (B) (No. 20380110) from the Japan Society for the Promotion of Science.
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