B i ogeogra phy 14.
81–85．Sep. 20, 2012

77-81

New Records of the Noline Scorpionfish, Phenacoscorpius megalops(Actinopterygii: Scorpaeniformes: Scorpaenidae), from the Emperor
Seamounts, Central North Pacific
Makoto Okamoto1*, Hiroyuki Motomura2, Koichi Hoshino1,
Takashi Yanagimoto3 and Takeshi Hayashibara4
1

Seikai National Fisheries Research Institute, 1551-8 Taira-machi, Nagasaki 851-2213, Japan
2
The Kagoshima University Museum, 1-21-30 Korimoto, Kagoshima 890-0065, Japan
3
National Research Institute of Fisheries Science, 2-12-4 Fukuura, Kanazawa-ku,
Yokohama 236-8648, Japan4National Research Institute of Far Seas Fisheries, Fisheries Research Agency,
2-12-4 Fukuura, Kanazawa-ku, Yokohama 236-8648, Japan

Abstract. Eight specimens (36.7–70.0 mm standard length) of a scorpionfish, Phenacoscorpius megalops
Fowler, 1938, were collected from the Koko Seamount, Emperor Seamounts, in the central North Pacific. Thisspecies can be distinguished from other congeners by its lack of palatine teeth, branched pectoral fin rays inadults, small or no second preopercular spine, shorter snout, longer and deeper caudal peduncle and largereyes. Taiwan was previously regarded as the northernmost locality for this species; thus the present specimens
are the northernmost records for the species.
Key words: Scorpaenidae, Phenacoscorpius, distribution, Koko Seamount, northernmost record.

Introduction
The genus Phenacoscorpius is a scorpaenid
genus, containing five valid species: P. adenensis
Norman, 1939; P. eschmeyeri Parin and Mandrytsa
in Mandrytsa, 1992; P. longirostris Motomura andLast, 2009; P. megalops Fowler, 1938; and P. nebris
Eschmeyer, 1965. The type species, P. megalops,
was described by Fowler (1938) as a new genus andspecies of scorpionfish from the Philippines. Taxonomic problems remained with the species until Motomura (2008) concluded that Scorpaenopsis stigma
Fowler, 1938 is a junior synonym of P. megalops*Corresponding author : jitabagu@yahoo.co.jp

and described the morphological characters of thespecies based on a reexamination of the type series.
In an on-going study of the fauna of the Emperor Seamounts in the central North Pacific (e.g.,Okamoto et al. 2012), we obtained eight specimensof P. megalops from the Koko Seamount in October
2009 and June 2011. Phenacoscorpius megalops
has been reported from the Taiwan, Philippines, Indonesia, Vietnam, and the Hawaiian Islands (Poss1999; Motomura 2008; Motomura and Last 2009).
Our specimens represent the first confirmed recordsof the species from the Emperor Seamounts and arealso the northernmost record for the species.
Counts and measurements follow Motomura(2008). The last two soft rays of the dorsal and anal
fins are counted as single rays, each pair being asso-− 81 −77

Phenacoscorpius megalops from the Emperor Seamounts

ciated with a single pterygiophore. Counts of vertebrae were taken from radiographs. Standard length isexpressed as SL. Morphometric values are expressedas percentage of SL. Sex was confirmed by dissection of the right side of the abdomen. The specimens
are deposited at the Seikai National Fisheries Research Institute (SNFR).
Phenacoscorpius megalops Fowler, 1938
[English name: Noline scorpionfish](Fig 1)
Phenacoscorpius megalops Fowler, 1938: 70 (typelocality: 27 miles southeast of Bagatao Island
Light between Burias and Luzon, Philippines);Eschmeyer and Randall 1975: 293 (Oahu, Hawaiian Islands); Chen 1981: 51 (Taiwan); Poss 1999:
2328 (in part, Taiwan, Philippines, Indonesia, andHawaiian Islands); Poss 2000: 605 (list, SouthChina Sea); Motomura 2008: 776 (Indonesia andPhilippines); Shao et al. 2008: 246 (list, SouthChina Sea); Motomura and Last 2009: 28 (Taiwan,Vietnam, and Philippines).
Scorpaenopsis stigma Fowler, 1938: 66 (type locality: 8.7 miles southwest of Point Tagolo Light,northern Mindanao, Philippines).
Material examined. 8 specimens, 36.7–70.0 mm
SL: SNFR 16430, 50.1 mm SL, female, 34˚58.92´N, 171˚56.31´ E–34˚59.03´ N, 171˚56.39´ E,
Koko Seamount, Emperor Seamounts, 350–351 mdepth, 1.5 m width beam trawl, 5 October 2009;
SNFR 16431, 51.8 mm SL, female, data sameas SNFR 16430; SNFR 16506, 55.9 mm SL, female, 34˚58.98´ N, 171˚56.40´ E–34˚59.10´N, 171˚56.51´ E, Koko Seamount, Emperor
Seamounts, 350 m depth, 1.5 m width beam trawl,
5 October 2009; SNFR 17790, 70.0 mm SL,male, 35˚38.17´ N, 171˚03.10´ E–35˚37.79´N, 171˚03.21´ E, Koko Seamount, Emperor
Seamounts, 435–500 m depth, 1.5 m width beam
trawl, 14 June 2011, SNFR 17791, 36.7–64.9 mm
SL, 4 specimens, 3 males (36.7, 60.6, 64.9 mm SL),
1 female (47.0 mm SL), 35˚38.90´ N, 171˚00.71´
E–35˚38.84´ N, 171˚00.94´ E, Koko Seamount,Emperor Seamounts, 400–425 m depth, 1.5 m widthbeam trawl, 15 June 2011.
Counts and measurements. Dorsal-fin rays XII,9; anal-fin rays III, 5 or 6 (1 of 8, SNFR 16431);
pelvic-fin rays I, 5; pectoral-fin rays 16–17 (mode16), 1 or 2 uppermost rays and 6–10 lower rays
unbranched, other rays branched; pored lateral-line
scales 2–5; gill rakers 4–6 + 13–15 = 18–20; branchiostegal rays 7; vertebrae 25.
Body depth 34.4–37.8 (mean 36.0); head length
41.4–48.2 (43.5); head width 14.5–15.9 (15.2); snout

Fig. 1. Phenacoscorpius megalops, 64.9 mm SL, SNFR 17791, Koko Seamount, central North Pacific.

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Makoto Okamoto, Hiroyuki Motomura, Koichi Hoshino, Takashi Yanagimoto and Takeshi Hayashibara

length 8.9–10.9 (9.9); orbital diameter 12.5–16.9(14.1); interorbital width between preocular spine
bases 5.0–6.3 (5.7); interorbital width at mid-line ofeye 4.2–5.3 (4.8); upper-jaw length 20.5–22.6 (21.3);
maxillary depth 5.2–6.8 (6.2); postorbital length
18.7–21.7 (20.1); predorsal-fin length 38.4–43.1(40.5); preanal-fin length 69.2–74.7 (71.2); prepelvic-fin length 37.8–42.6 (39.8); first dorsal-fin spine
length 5.2–6.4 (5.8); second dorsal-fin spine length
10.1–13.1 (11.6); third dorsal-fin spine length 15.0–18.5 (17.0); fourth dorsal-fin spine length 15.7–18.5(16.6); fifth dorsal-fin spine length 14.1–17.2 (15.2);
sixth dorsal-fin spine length 11.4–14.3 (13.3);
seventh dorsal-fin spine length 11.4–13.7 (12.6);
eighth dorsal-fin spine length 8.2–12.0 (10.4); ninth
dorsal-fin spine length 6.4–8.5 (7.5); tenth dorsal-fin
spine length 4.7–6.8 (5.5); eleventh dorsal-fin spine
length 4.6–6.4 (5.3); twelfth dorsal-fin spine length
11.3–12.4 (11.5); longest dorsal-fin soft ray length
17.7–19.7 (18.8); first anal-fin spine length 5.9–9.9(8.2); second anal-fin spine length 17.9–19.9 (18.9);
third anal-fin spine length 13.1–15.8 (14.2); longest
anal-fin soft ray length 16.5–20.6 (18.5); pectoralfin length 32.0–37.1 (34.8); pelvic-fin spine length
14.7–17.2 (16.3); longest pelvic-fin soft ray length
21.8–24.1 (23.2); caudal-fin length 21.9–24.4 (22.9);
caudal-peduncle length 18.6–23.2 (21.1); caudalpeduncle depth 8.3–9.2 (8.8).
Remarks. The present specimens from the Emperor Seamounts are identified as Phenacoscorpius
megalops on the basis of the following combinationof characters: palatine teeth absent; branched pectoral fin rays present; second opercular spine small;snout length 8.9–10.9% SL; orbital diameter 12.5–
16.9% SL; caudal-peduncle length 18.6–23.2% SL;
and caudal-peduncle depth 8.3–9.2% SL. According
to Motomura and Last (2009), although P. megalopsand P. longirostris lack palatine teeth (vs. palatine
teeth present in P. adenensis, P. eschmeyeri, and P.
nebris), P. megalops can be distinguished from P.
longirostris in lacking or having only a small second
preopercular spine and in having branched pectoral fin rays in adults (vs. having a well-developed
second preopercular spine and all pectoral fin rays

unbranched in P. longirostris), a greater orbital diameter, longer and deeper caudal peduncle, wider
head, and shorter snout (Motomura and Last 2009).
However, Motomura and Last (2009) mistakenlydescribed the head widths of P. megalops and P.
longirostris as 34.0–36.5% of SL and 24.4–28.3%of SL respectively. These values were in fact of % ofHL, instead of % of SL. Characters of our specimensfrom the Emperor Seamounts agree with the data forthe type and other specimens of P. megalops given
by previous literature reports, with the exception of
the anal-fin soft rays for which one of our specimens
had 6 rays (vs. 5 in Eschmeyer and Randall 1975;
Chen 1981; Motomura 2008; Motomura and Last2009). Intraspecific variation of the anal-fin soft ray
counts in other congeners has not been reported (5 inP. longirostris and 6 in P. adenensis, P. eschmeyer,and P. nebris; Eschmeyer 1969; Mandrytsa 1992,1993; Motomura 2008; Motomura and Last 2009).
Because the anal-fin soft ray counts of species ofPhenacoscorpius, except for P. megalops, are basedon a small number of specimens (e.g., P. eschmeyer,n=1; P. logirostris, n=2) and many scorpaenids haveintraspecific variation in anal-fin soft rays (Chen,1981; table 4), we regard that our specimen with 6
anal-fin soft rays to be P. megalops.
Distribution records of Phenacoscorpius megalops, including present specimens, are shown in Fig.
2. This species has been reported from temperate totropical waters in the western North Pacific (Taiwan,Vietnam, Philippines, and Indonesia) and in theHawaiian Islands. Our specimens represent the firstrecord of P. megalops from the Emperor Seamounts
and the northernmost record of the species. Several
studies have reported P. megalops in New Zealand(Paulin 1982; Paulin et al. 1989; Fricke et al. 2011)
and New Caledonia (Rivaton et al. 1990; Fricke etal. 2011), but these are based on misidentifications,and the species appears to be restricted to the North
Pacific (Motomura 2008; unpublished data). Four ofour specimens (47.0–55.9 mm SL) are females withmature gonads filled with relatively large eggs ofseveral developmental stages. The most developed
eggs are ca. 0.4 mm in diameter.

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Phenacoscorpius megalops from the Emperor Seamounts

Fig. 2. Distributional records of Phenacoscorpius megalops. Circles and stars indicate localities of previously recorded specimens and specimens examined in this study, respectively.

Acknowledgements
We are grateful to T. Jintoku and Y. Matsunaga(SNFR) and M. Miyamoto (NRIFSF) for their curatorial assistance. Thanks also go to M. F. Gomon(Museum Victoria, Australia) for his critical readingof the initial manuscript with helpful comments, andR. Fricke (Staatliches Museum für Naturkunde, Germany) for providing literature. We thank the captain,officers, and crews of the R/V Kaiyo-maru for theirassistance with sampling. The present study wasfunded by International Fishery Resource Measure
Promotion Project conducted by Ministry of Agriculture, Forestry and Fisheries, Japan.

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(Received April 27, 2012; Accepted June 20, 2012)− 85 −81