Idiastion paci cum Ishida and Amaoka, 1992

Okamoto, Makoto, Motomura, Hiroyuki, Hoshino, Koichi, Yanagimoto, Takashi & Saruwatari, Toshiro, 2012, Occurrence and Additional Specimens of a Scorpionfish, Idiastion pacificum (Actinopterygii: Scorpaeniformes: Scorpaenidae), from the Central North Pacific, Species Diversity 17 (1), pp. 1-5 : 2-5

Idiastion paci cum Ishida and Amaoka, 1992

[Japanese name: Kakure-kasago]

[New English name: Flame humpback scorpion sh]

(Figs 1, 2A)

Scorpaeninae sp.: Kanayama 1982: 275 (Kyushu-Palau Ridge).

Idiastion paci cum Ishida and Amaoka, 1992: 357 (type locality: Kyushu-Palau Ridge, western North Paci c); Poss 1999: 2305 (listed, following Ishida and Amaoka (1992)); Nakabo 2002: 571 (key and gure, based on holotype).

Material examined. 2 specimens: SNFR 13482, 124. 0 mm SL, female, Koko Seamount, central North Paci c, 35°34 .00′N, 171°34 .50′E– 35°34.90′N, 171°38.60′E, 360 m depth, trawl, 5 Nov. 2007; SNFR 13522, 148. 6 mm SL, male, Koko Seamount, central North Paci c, 35°39 .00′N , 171°03.00′E – 35°38.70′N, 171°03.00′E, 430 m depth, trawl, 28 Sep . 2007 .

Comparative materials. I diastion paci cum, BSKU 31153, holoype, 128. 4 mm SL, Kyushu-Palau Ridge, western North Paci c, 26°11 .5′N , 135°45.4′E – 26°04.7′N, 135°50.4′E, 355–375 m depth, trawl, 16 Dec . 1979 .

Idiastion kyphos, CAS 24401, 86. 5 mm SL, o Angola, eastern South Atlantic , 19°18′S, 11°24′E, 229 m depth, trawl, 24 Mar . 1968 ; CAS 31886, 83. 0 mm SL, Caribbean Sea , 12°11′N, 72°52′W, 550 m depth, trawl, 19 Nov . 1970; GMBL 2332, 66.2–79. 0 mm SL (2 specimens), o Florida , western North Atlantic, 30°28′N, 79°51′W, 494 m depth, shrimp trawl, 19 Jan . 1972 .

Diagnosis. A species of Idiastion with the following combination of characters: dorsal- n so rays 9; pectoral-

n rays 17–19; ctenoid scales in interorbital space; cycloid scales on belly; origin of rst dorsal- n spine slightly posterior to a vertical drawn through supracleithral spine base; posterior tip of pectoral n not reaching anal- n origin; head length 44.4–46.0% SL.

Description. C ounts and proportional measurement given as percentages of SL in Table 1. Body relatively deep, slightly hump-backed in appearance, compressed posteriorly. Nape steep; anterior body pro le strongly arched. Head large, its length greater than body depth. Eye large and oval. One or 2 rows of small papillae along outer margin of pupil. Slender tentacle present on posterodorsal edge of low membranous tube associated with anterior nostril; length of tentacle slightly greater than diameter of anterior nostril opening; no other distinct tentacles on head. Pectoral axil without skin aps.

Scales covering dorsal and lateral surfaces of head and upper part of lateral surface of maxilla. Exposed ctenoid scales on lateral surface of trunk, scales becoming cycloid on abdomen. Small ctenoid scales present on maxilla and in interorbital space. Exposed cycloid scales on anteroventral surface of body. Body scales extending onto basal n rays or membranes of bases of dorsal, anal, pectoral, and caudal

ns. Lateral line gently sloping downward from posterodorsal corner of opercle. Series of pored lateral-line scales complete (but incomplete in SNFR 13482 owing to loss of scales from body during capture). Pair of small pores just behind symphysial knob of lower jaw in ventral view. Underside of dentary with 3 large sensory pores on each side.

Posterior margin of maxilla extending slightly beyond a vertical drawn through posterior margin of pupil. No distinct longitudinal ridge on lateral surface of maxilla. Jaws with villiform tooth bands. Width of symphysial gap separating premaxillary teeth bands subequal to width of each band. Vomerine and palatine teeth villiform, forming Vshaped and elliptical tooth patches respectively.

Dorsal pro le of snout steep, forming angle of about 40 degrees with respect to horizontal axis of head and body. Nasal spine simple, directed dorsally, base embedded in skin. Ascending process of premaxilla not intruding into interorbital space, with its posterior tip of process extending beyond level of anterior margin of posterior nostril in dorsal view. Median interorbital ridge absent. Interorbital ridges weakly developed and unbranched, separated by shallow channel. Interorbital space moderately shallow, with about one- h of orbit extending above dorsal pro le of head. Preocular, supraocular, postocular, and tympanic spines simple (tips of preocular, supraocular, and postocular spines bifurcate in SNFR 13482). Minute, simple coronal spine present in SNFR 13522, absent in SNFR 13482. Interorbital and pretympanic spines absent. Occipital region nearly

at, with low ridges between tympanic and parietal spines. Parietal and nuchal spines simple, joined at base. Upper posttemporal spine absent. Lower posttemporal and supracleithral spines simple. Cleithral spine large, broad at base.

Lateral lachrymal spine present in SNFR 13522, absent in SNFR 13482. Anterior lachrymal spine broad, not pointed. Posterior lachrymal spine simple, triangular, directed ventroposteriorly. Five to 9 suborbital spines; an additional spine present below suborbital ridge, located along a vertical drawn through posterior margin of pupil. Space between ventral margin of eye and suborbital ridge narrow. Suborbital pit indistinct. Preopercle with 4 or 5 spines (on le and right sides, respectively in SNFR 13482 and SNFR 13552), former specimen lacking second preopercular spine; second opercular spine minute if present; uppermost spine largest with supplemental preopercular spine its base. Preopercle smooth above uppermost preopercular spine, lacking serrae or spine in that region. Upper opercular spine simple without median ridge. Lower opercular spine simple with low median ridge. Space between upper and lower opercular spines without ridges. Posterior tips of upper and lower opercular spines respectively short of and just reaching (or just short of in SNFR 13522) opercular margin.

Origin of rst dorsal- n spine slightly posterior to a vertical drawn through supracleithral spine base. Posterior margin of opercular membrane reaching vertical drawn through base of third dorsal- n spine. Posterior tip of pectoral n extending beyond anus but not reaching to origin of anal n. Origin of pelvic n just below origin of pectoral n. Posterior tip of depressed pelvic n not reaching origin of anal n. Origin of rst anal- n spine slightly posterior to a vertical drawn through last dorsal- n spine.

Gill rakers relatively short and spinous, length of longest gill raker on lower limb of rst gill arch approximately equal to or shorter than length of gill lament; slit present behind fourth gill arch. Formula for con guration of anterior neural spines and anterior dorsal pterygiophores 0//2+1/1/1/1/1/1/1/1/1/1/1+1/. Dorsal series of caudalprocurrent rays 6, ventral series 4 or 5. Swimbladder present.

Color when fresh (based on photograph of SNFR 13482: Fig. 1). Body reddish dorsally, becoming whitish ventrally, without any distinct black markings (except for black of eye). Two broad, dark red bands from eye to lower preopercular margin and middle of opercular margin. Four obscure saddle-like bands on dorsal body: rst band above pectoral- n base, second below middle of spinous portion of dorsal n, third below so -rayed portion of dorsal n, and fourth on caudal- n base. Membranes of spinous portion of dorsal n uniformly red. Membranes of so -rayed portion of dorsal and anal ns and caudal n transparent, their so rays reddish. Pectoral n reddish centrally, whitish marginally. Pelvic n pinkish.

Color in ethanol (Fig. 2A). Head and body entirely pale yellow, with large number of scattered small melanophores on cheek, pectoral- n base, lateral side of posterior body, and caudal-peduncle region.

Distribution. C urrently known from the western North Paci c [Kyushu-Palau Ridge, at a depth of 355–375 m ( Kanayama 1982; Ishida and Amaoka 1992)] and the Emperor Seamounts, central North Paci c (at depths between 350–430 m, present study).

Remarks. ffl e present specimens from the central North Paci c agree with all diagnostic characters of Idiastion paci cum given by Ishida and Amaoka (1992) except for the presence of ctenoid scales on the maxilla. One of cum.

the present specimens (SNFR 13522) and the holotype of I. paci cum have small ctenoid scales on the maxilla, whereas the other present specimen (SNFR 13482) lacks such scales. ffle scales on this area are deciduous, though, and SNFR 13522 and the holotype have only a few scales on the le and right sides of the maxilla. fflerefore, we conclude that the lack of the scales on the maxilla in SNFR 13482 is due to loss during capture.

According to Ishida and Amaoka (1992), the longest dorsal- n spine of the holotype of I. paci cum was the fourth. When, we reexamined the holotype, we noticed that the tip of the third spine was broken but that its length was the same as the data given in the original description. fflis indicates that the tip of the spine was broken before the type specimen was described. In the present two specimens, the

ns are complete and the longest dorsal- n spine in both instances is the third.

ffle fresh coloration of our specimens agrees with the color photograph of " Scorpaenidae sp". in Kanayama (1982), identi ed as I. paci cum in Ishida and Amaoka (1992). Unfortunately, that specimen [its catalog number was not shown by Kanayama (1982)] has not been rediscovered since Ishida and Amaoka (1992) noted that it was missing.

Dissection of the abdomen on the right side of the small- er present specimen of I. paci cum (124.0 mm SL, SNFR 13482) showed it to have mature ovaries full of relatively large eggs (ca. 0.4 mm diameter) at several developmental stages. Information on sexual maturity in the genus Idiastion is limited to the holotype with mature ova of I. hageyi (95 mm SL; McCosker 2008). In our examination of specimens of I. kyphos , both GMBL 2332 (66.2 and 79.0 mm SL) and CAS 31886 (83.0 mm SL) proved to have expanded ovaries full of relatively large eggs (ca. 0.4 mm diameter), and these observations represent the rst con rmed information about sexual maturity in that species.

ffle present study revealed that I. paci cum, previously known only from Kyushu-Palau Ridge , is also distributed in the central North Paci c, approximately 3,500 km northeast of the type locality (Fig. 3). As for its congeners, I. kyphos is known from the Caribbean Sea and o Florida in the western North Atlantic , and also o Angola in the eastern South Atlantic, in depths of ca. 229–622 m ( Eschmeyer 1969; An- derson et al. 1975), and I. hageyi is known only from the Galápagos Islands at a depth of 522 m. fflus, the genus Idiastion is distributed in deep waters in temperate and tropical regions, with a reddish body color similar to that of many other deep-water species of scorpion sh ( Eschmeyer 1965b; McCosker 2008: g. 2).

Comparison. I shida and Amaoka (1992) noted that I. paci cum could be distinguished from I. kyphos in having "ctenoid scales on nape and maxilla, and cycloid scales on isthmus, breast, anterior part of belly and membrane of anal, lower part of pectoral and pelvic ns", although they did not make a direct comparison of these species (Fig. 2). In this study, we compared the two species and con rmed that I. kyphos (Fig. 2B) also possesses ctenoid scales on the nape and maxilla and mixed cycloid and ctenoid scales on the isthmus, breast, and n membranes. However, I. paci-

cum di ers from I. kyphos in having cycloid scales on the ventral surface of the abdomen (vs ctenoid scales in I. kyphos ) and in the origin of the rst dorsal- n spine, which is located slightly posterior to a vertical drawn through the supracleithral spine base (vs just above the supracleithral spine base in I. kyphos ). Also, I. paci cum (124. 0–148.6 mm SL) attains a larger size than I. kyphos does (105.4 mm maximum recorded SL: Anderson et al. 1975).

Idiastion paci cum is clearly distinguished from I. hageyi in having scales in the interorbital region (vs no scales there in I. hageyi ), and in that the posterior tip of the pectoral n does not reach the anal- n origin (it exceeds the anal- n origin in I. hageyi: McCosker 2008 ). Moreover, the relative length of the head of I. paci cum is remarkably shorter than that of I. hageyi (44.4–46.0% SL vs. 50.7% SL in I. hageyi: McCosker 2008 ).