Onigocia grandisquama ( Regan, 1908 )

Imamura, Hisashi, 2016, Rediagnosis of Onigocia grandisquama (Actinopterygii: Perciformes: Platycephalidae) and Comparison with Congeners, Species Diversity 21, pp. 151-159 : 153-158

Onigocia grandisquama ( Regan, 1908)

( Figs 1 , 4 ; Tables 1–3)

Platycephalus grandisquamis Regan, 1908: 239 (original description; type locality: Amirante Islands , Seychelles, western Indian Ocean).

Platycephalus macrocephalus Weber, 1913: 508 , fig. 107 (original description; type locality: Sapeh Strait , Indonesia) (in part); de Beaufort and Briggs 1962: 146, fig . 36 (description; Sapeh Strait, Indonesia) (in part).

Platycephalus grandisquamis Weber, 1913: 509 , fig. 108 [original description; type locality: northwest of New Guinea (1°42.5′S, 130°47.5′E)] (in part) .

Onigocia grandisquamis: Matsubara and Ochiai 1955: 71 (discussion of generic assignment).

Onigocia grandisquama: Imamura 1996: 214 (discussion of generic assignment); Imamura and Sakashita 1997: 119, figs 1–4 (redescription; Amirante Islands, Seychelles, western Indian Ocean and Gulf of Thailand, western Pacific Ocean); Knapp et al. 2000: 8 (list of comparative material; Amirante Islands, Mauritius, and Somalia, western Indian Ocean); Manilo and Bogorodsky 2003: S103

(list, Arabian Sea); Imamura and McGrouther 2008: 239,

figs 1–2 (redescription, Queensland, eastern Australia);

Imamura 2011: 59 (list of comparative material; Ceram

Sea, Mauritius, and Somalia); Imamura 2012: 30 (list of comparative material; Sapeh Strait, Indonesia).

Diagnosis. A species of the genus Onigocia Jordan and Thompson, 1913 with the following characters: first dorsalfin rays I+VII–VIII (usually I+VIII); second dorsal-fin rays 10–11 (usually 11); anal-fin rays 11–12 (usually 11); pectoral-fin rays 19–22; branched caudal-fin rays 9–10; pored lateral-line scales 32–39, anterior 2–8 scales each with a spine; gill rakers 1+4–5=5–6; lachrymal spines 2–5 (usually 2), tending to increase in number with growth; inner, middle, and outer ridges on lachrymal lacking spines; preocular spines 1–6, tending to increase in number with growth; suborbital spines 14–30, tending to increase in number with growth; pterotic spines 2–11, tending to increase in number with growth; HL 41.6–45.6% SL, single ocular flap present on posterior part of eye, not extending to its posterior margin; small, short papillae absent on posteromedial part of eye; upper iris lappet short and branched; notch absent on suborbital ridge below eye; interopercular flap absent; pelvic fin brownish to blackish, lacking distinct spots.

Distribution. Onigocia grandisquama has been record- ed widely in the Indo-West Pacific, including the Amirante Islands, Seychelles (type locality; Regan 1908), Mauritius and Somalia ( Knapp et al. 2000; this study), the Arabian Sea ( Manilo and Bogorodsky 2003), Pandjang Island, Indonesia (new record), Sapeh Strait ( Imamura 2012), North West Shelf, Australia (new record), Timor Sea (new record), Coral Sea, eastern Australia ( Imamura and McGrouther 2008; this study), Chesterfield Islands (new record), Ceram Sea ( Imamura 2011), and Gulf of Thailand ( Imamura and Sakashita 1997) (see also Fig. 2 ).

Remarks. Table 1 shows counts and proportional measurements of this species from five geographical areas. See Imamura and Sakashita (1997) and Imamura and McGrouther (2008) for descriptions of characters (including coloration) not mentioned in the Diagnosis above.

A difference in the number of pectoral-fin rays was recognized between specimens from the Indian and western Pacific oceans in this study ( Table 2). In addition, wider variations in the numbers of lachrymal, preocular, suborbital, and pterotic spines were found among these 52 specimens than had previously been known ( Fig. 3 ). However, the difference between pectoral-fin ray numbers in the two oceans was rather minor and the ranges mostly overlapped, and the greater variation in spine numbers appeared to be sizerelated, with larger specimens tending to have more spines. I conclude that the difference in numbers of pectoral-fin rays represents geographic variation, and the wide intraspecific variation in spine numbers represents change with growth in O. grandisquama . A detailed account of these characters is given below.

Pectoral-fin rays ( Table 2).—The number of pectoral-fin rays ranged from 20 to 22 in specimens from the Indian Ocean and from 19 to 21 in those from the western Pacific Ocean. Because the modes of the two ranges also differed from each other (21 in the Indian Ocean vs 20 in the western Pacific Ocean), it can be assumed that the difference has a genetic basis, although specimens with 22 pectoral-fin rays may be found in the western Pacific Ocean in the future. However, as no other remarkable differences between specimens from the two oceans were recognized, I regard this difference as an expression of geographic variation within the species. This is the first record of geographic variation in fin ray counts reported for any platycephalid species.

Lachrymal spines ( Figs 3A , 4 ).—The number of lachrymal spines has been reported as two or three (usually two) in previous studies ( Imamura and Sakashita 1997; Imamura and McGrouther 2008). The present study revealed the variation to be from two to five (including small spines), with a tendency for spine number to increase with growth as follows: only two spines were observed in specimens of 33.8–57.3 mm SL; the third, fourth, and fifth spines were first seen in specimens of 58.1 mm SL (WAM P. 28754-009, right side only), 66.6 mm SL (QM I. 40097, right side only), and 72.0 mm SL (QM I. 37839, right side only), respectively. Still, specimens with only two spines were present at most body sizes.

Preocular spines ( Figs 3B , 4 ).—Although one or two (usually two) preocular spines have been known in this species ( Imamura and Sakashita 1997; Imamura and McGrouther 2008), this study found that the number of spines varied from one to six. Change with growth was also observed, with larger specimens tending to have more spines, although the smallest specimen examined (QM I. 37297, 33.8 mm SL) has just three (left) and four (right) spines. In addition, as with the lachrymal spines, specimens with only one preocular spine were found at most body sizes.

Suborbital spines ( Figs 3C , 4 ).—Although species of Onigocia have been known to have a serrated suborbital ridge (e.g., Imamura 1996), most authors have not paid attention to the number of small spines on it. This study found the number of suborbital spines to be greatly variable in O. grandisquama , ranging from 14 to 30 and tending to increase with growth.

Some specimens of moderate to large size have fewer suborbital spines than other, similarly sized fish of Onigocia , and with wider interruptions of the serration that differ from the typical condition for O. grandisquama of mostly continuous serration. However, the suborbital spine number serially varied among the 52 examined specimens and could not be clearly separated into any distinct groups. I conclude that the variation in spine number represents intraspecific variability.

Pterotic spines ( Figs 3D , 4 ).—Although the number of pterotic spines has not been used previously to separate species of Onigocia , this study revealed that this feature distinguishes O. grandisquama from several congeners to some degree (see discussion under Comparison below for details). Pterotic spine numbers varied from two to 11 in the specimens examined, with usually four or more present and with the number tending to increase with growth.

Comparison. Data used for the following comparison are from Knapp (1999), Imamura and McGrouther (2008), Imamura and Knapp (2009), Imamura (2011, 2012), and this study.

In addition to O. grandisquama , the genus Onigocia includes the following eight valid species at present: Onigocia bimaculata Knapp, Imamura, and Sakashita, 2000 , Onigocia lacrimalis Imamura and Knapp, 2009 , Onigocia macrocephala (Weber, 1913) , Onigocia macrolepis (Bleeker, 1854) , Onigocia oligolepis ( Regan, 1908) , Onigocia pedimacula ( Regan, 1908) , Onigocia sibogae Imamura, 2011 , and O. spinosa (see Imamura 2012). Onigocia grandisquama is easily separable from O. bimaculata , O. lacrimalis , O. oligolepis , O. pedimacula , and O. sibogae in having 9–10 branched caudal-fin rays, an ocular flap on the posterior part of the eye, and a short and branched upper iris lappet (vs. eight branched caudal-fin rays, no ocular flap, and an upper iris lappet that is variously bilobed, trilobed, scalloped, crenate, or absent in the others. The holotype of O. oligolepis , the sole specimen of that species examined here, has a broken caudal fin, which makes its ray number uncountable.

Among O. macrocephala , O. macrolepis , and O. spinosa , which share the three above-mentioned characters with O. grandisquama , O. spinosa most closely resembles O. grandisquama in lacking a notch on the suborbital ridge below the eye (vs. notch present in O. macrocephala and O. macrolepis ). Knapp (1999) described O. spinosa as having XI total first dorsal-fin spines, 11 or 12 (usually 12) second dorsal-fin rays, 11 or 12 (usually 12) anal-fin rays, 34–42 pored lateral-line scales, the anterior 7–27 scales each with a spine or ridge, five or six total gill rakers, three lachrymal spines, and three to five preocular spines, all values that mostly or partly overlap those of O. grandisquama . In addition, two specimens of O. spinosa examined in the present study have two lachrymal spines, and one of them (NTM S. 15848-001, 48.8 mm SL) also has 11 second dorsal- and anal-fin rays, a spine on each of the anterior seven lateral-line scales, and three or four preocular spines, all of which overlap with the counts of O. grandisquama . Accordingly, this specimen cannot be separated from O. grandisquama using the characters, which were previously considered useful for separating the two species.

The present study, however, revealed a valuable feature that does separate O. grandisquama and O. spinosa , the presence or absence of spines on the inner, middle, and/or outer ridges on the lachrymal. In O. grandisquama , spines are absent on these ridges even in larger specimens ( Fig. 4 ), while spine(s) are present at least on the inner ridge in O. spinosa at lengths of 48.8 mm SL or more [an even smaller specimen (NSMT-P 53253, 40.7 mm SL) from Nagasaki, Japan, also has a spine on the inner ridge], and tend to increase in number with growth and to develop from the inner to outer ridges [for example, CSIRO CA 1876 (64.0 mm SL) has three, two, and no spines on the inner, middle, and outer ridges, respectively, on the left side, and CAS 15237 (98.3 mm SL) has five, five, and two spines on the right side]. Accordingly, the presence or absence of the spines is useful for separating specimens of these two species above a certain size. In addition, this difference also distinguishes O. grandisquama from O. macrocephala and O. macrolepis , which usually have the spines (although they are absent in smaller specimens of the latter two species and in a few larger specimens of O. macrocephala ), supplementing the above-mentioned presence or absence of a notch on the suborbital ridge below the eye. Head length is also valuable for separating O. grandisquama from O. spinosa , O. macrocephala , and O. macrolepis (41.6–45.6% SL in O. grandisquama vs. 37.7–42.5% SL in O. spinosa , 38. 8–42.3% SL in O. macrocephala and 35.6–38.4% SL in O. macrolepis ), although there is some overlap between O. grandisquama , and O. spinosa and O. macrocephala ( Fig. 5A ). As was mentioned above, the number of pterotic spines in O. grandisquama varies from two to 11, and is usually four or more. Although these numbers do not clearly distinguish O. grandisquama from the three species with an ocular flap, they help to separate them, as there are generally fewer pterotic spines in the latter species, especially in O. macrolepis : two to six (tending to increase with growth) in O. spinosa , two to five (usually two) in O. macrocephala , and two to three (usually two) in O. macrolepis ( Fig. 5B ).

Characters capable of separating O. grandisquama from other congeners, including some not discussed here, are summarized in Table 3.

Figures

Fig. 1. Onigocia grandisquama. A–B, BMNH 1860.3.19.270, collected from the Amirante Islands, Seychelles, western Indian Ocean; C–D, QM I. 37419, 69.5mm SL, collected from northeast of Hadge Reef, Queensland. A and C, dorsal views; B and D, lateral views.

Fig. 4. Dorsal view of left side of head of Onigocia grandisquama, QM I. 37414, 71.2mm SL. IR (inner), MR (middle), and OR (outer) ridges on lachrymal; LS, lachrymal spines; POS, preocular spines; PTS, pterotic spines; SS, serration on suborbital ridge. Arrows indicate interruptions of serration on suborbital ridge.

Fig. 2. Map showing collection localities of 52 examined specimens of Onigocia grandisquama. Blue, western Indian Ocean; red, eastern Indian Ocean; yellow, Coral Sea; pink, Ceram Sea; green, Gulf of Thailand.The arrow indicates the holotype.

Fig. 3. Comparison of numbers of head spines from five areas and standard length in Onigocia grandisquama. A, lachrymal spines; B, preocular spines; C, suborbital spines; D, pterotic spines. Squares, left side of head; circles, right side of head. Arrows indicate holotype values. Colors of symbols represent specimens from the color-coded localities in Figure 2.

Fig. 5. Comparison of head length (A) and number of pterotic spines (B: square, left side; circle, right side), with standard length in four species of Onigocia with an ocular flap. Red, O. grandisquama; yellow, O. macrocephala; green, O. macrolepis; blue, O. spinosa. Arrows indicate holotype or lectotype specimens.