Description of a Pelagic Juvenile of the Poorly Known Anglerfish Sladenia zhui (Lophiidae) from the East China Sea Author Matsunuma, Mizuki Department of Environmental Management, Faculty of Agriculture, Kindai University, 3327 - 204 Nakamachi, Nara 631 - 8505, Japan E-mail: matsunuma @ nara. kindai. ac. jp & Corresponding author matsunuma@nara.kindai.ac.jp Author Muto, Nozomu Department of Marine Biology and Sciences, School of Biological Sciences, Tokai University, 5 - 1 - 1 - 1 Minamisawa, Minami-ku, Sapporo, Hokkaido 005 - 8601, Japan text Species Diversity 2020 2020-05-15 25 2 107 116 http://dx.doi.org/10.12782/specdiv.25.107 journal article 7108 10.12782/specdiv.25.107 577746e0-2596-4518-9616-18524cdf941f 2189-7301 4585252 Sladenia zhui Ni, Wu, and Li, 2012 [New standard Japanese name: Daruma-ankou] ( Figs 1–3 , 5 ; Table 2 ) Sladenia remiger non Smith and Radcliffe in Radcliffe, 1912 : Ni 1988: 317 , fig. 250 (East China Sea; description). Sladenia gardineri non Regan, 1908 : Su 2002: 351 , fig. 163 (South and East China Seas; description). Sladenia zhui Ni, Wu, and Li, 2012: 211 , figs 1–3 ( type locality: East China Sea, 28°09′N , 126°58′E– 28°14′N , 127°01′E ). Sladenia cf. zhui : Ho et al . 2016: 78 , fig. 1 (off Java , Indonesia ; description). Specimen examined. KAUM–I . 70329, 23.1 mm SL, East China Sea , 28°45′39″N , 125°44′53″E– 28°41′08″N, 125°45′07″E, 100–115 m depth , bottom trawl, 13 December 2014 . Description. Morphometrics and selected meristics shown in Table 2 . Pelvic fin with 1 spine (embedded under skin) and 5 soft rays. Vertebrae 12+7=19. Body rounded, moderately compressed anteriorly, more compressed posteriorly. Head and body encased in inflated (balloon-like) smooth transparent skin ( Figs 1 , 2 ). Gill opening small, below pectoral-fin base, not extending in front of base. Dorsal edge of orbit rim slightly expanded dorsolaterally with blunt tip; head surface smooth without other spines or ridges. Mouth relatively large, its width 28.4% of SL; lower jaw slightly extended beyond upper jaw anteriorly; posterior margin of maxilla anterior to vertical through anterior margin of eye. Papilliform nasal sacs above upper jaw. Teeth conical, enlarged and well pointed; premaxilla with single low of 4 teeth; teeth on maxilla slightly smaller, in a single row; teeth on lower jaw forming ca . 2 irregular rows, inner row teeth slightly larger than outer teeth; vomer with 2 discrete, elongate teeth patches laterally; palatine without teeth; tongue without teeth, covered with numerous papillae. Eye moderately large, directed laterally and slightly dorsally. Interorbital space narrow. Table 2. Meristic and morphometric data from specimens of Sladenia zhui (expressed as percentages of SL).

KAUM–I. 70329	HUMZ 191110	HUMZ 191516
Localities
East China Sea	off Java, Indonesia
Dorsal-fin spines	4	4	4
Dorsal-fin soft rays	10	9	9
Anal-fin soft rays	7	6	6
Pectoral-fin rays	19	18	18
Pelvic-fin rays	I, 5	I, 5	I, 5
Caudal-fin rays	8	9	9
SL (mm)	23.1	271.5	278.2
Head length (% SL)	—	33.6	32.5
Head width	—	—	132.5
Head depth	—	31.4	34.4
Pre-dorsal fin length	—	62.7	56.1
Illicial length	86.5 *	36.0	38.3
2nd dorsal-fin spine length	—	20.2	16.6
Pre-preopercle length	—	31.5	29.1
Snout length	12.5	18.3	19.1
Snout width	—	8.8	8.6
Eye diameter	7.5	5.9	5.3
Upper jaw length	21.1	29.2	28.0
Inter-palatine width	—	12.8	13.8
Inter-frontal width	—	10.2	10.0
Inter-sphenotic width	—	16.3	17.8
Inter-pterotic width	—	24.1	25.4
Inter-opercular width	—	32.4	31.6
Length between pterotic and sphenotic spines	—	8.6	8.6
Length between upper palatine and quadrate spines	—	25.6	26.3
Caudal peduncle depth	—	13.2	13.6
Tail length	—	27.1	31.5
Caudal fin length	71.3 *	30.5	32.9

* slightly damaged. Base of illicial bone (tip broken) in interorbital space between anterior margins of eyes. Second dorsal-fin spine thin, very long, its length 86.5% of SL (tip broken); spine base at mid-orbit level, close to illicial base ( Fig. 3A ). Two post-cephalic dorsal-fin spines embedded under skin (determined from X-ray photograph); well separated from each other and dorsal-fin soft-rayed portion. Dorsal-fin softrayed portion relatively large, with semi-truncate profile; all rays unbranched. Anal fin without spines, semi-truncate; all soft rays unbranched; fin base shorter than that of dorsal-fin soft-rayed portion. Caudal fin very long, its length 71.3% of SL (slightly broken); all rays unbranched. Pectoral fin relatively small, fan-shaped, set laterally; all rays unbranched. Pelvic fin relatively small, with elongate filamentous soft rays [3rd ray of right fin only retained (tip broken; other rays broken near base), its length 55.9% of SL; Fig. 3B ]. Coloration . Transparent skin encasing body when fresh ( Fig. 1A ), becoming semi-transparent after preservation ( Figs 1 B–D, 2), entirely covered with numerous minute brown melanophores. Inner surface of head and body brownish, entirely covered with numerous stellate brown melanophores. Eye dark blue. Illicial and 2nd dorsal-fin spine semi-transparent, with scattered minute brown melanophores. Dorsal-fin soft-rayed portion and anal fin semitransparent, with dense melanophores on membranes. Pectoral fin base with scattered minute brown melanophores; rays with few scattered melanophores, membranes semi-transparent without melanophores. Pelvic fin semitransparent, with minute brown melanophores scattered on membranes along rays; filamentous portion of pelvic-fin ray partially brownish. Caudal fin semi-transparent covered with minute brown melanophores on basal portion; minute melanophores densely covered with membranes along rays. Distribution. The species has been collected from the central East China Sea, northern South China Sea (east of Hainan Island) and Indonesia (off Java ) ( Ni et al . 2012 ; Ho et al . 2016 ; this study) ( Fig. 4 ). Two Indonesian specimens, reported by Ho et al . (2016) as S . cf. zhui , were identified herein as S. zhui (see below). Adults of the species were collected in depths of 655–979 m ( Ni et al . 2012 ; Ho et al . 2016 ), whereas the present juvenile specimen was collected on the continental shelf ( 100–115 m depth), suggesting that the pelagic juvenile of the species have a shallower bathymetric distribution before settlement. Identification. The present juvenile specimen was assigned to Lophiidae , differing from currently known larvae and juveniles of other lophiiform families by having 4 dorsal-fin spines ( 3 in Antennariidae ), smooth body skin (covered with spinules in Chaunacidae and Ogcocephalidae ), and developed pelvic fins [absent in ceratioid families, except for Caulophryne Goode and Bean, 1896 (Caulophrynidae) ] (see Pietsch 1984 ; Bertelsen 1984 ; Pietsch 2009 ; Okiyama 2014b). Among lophiid genera, the specimen conformed to Sladenia in both meristic counts, and having a rounded head and body, and undeveloped head spines ( Table 3 ), compared with larvae and juveniles of other lophiid genera, including Lophius Linnaeus, 1758 , Lophiodes Goode and Bean, 1896 and Lophiomus Gill, 1883 , generally characterized as having a moderately depressed head with relatively well developed spines, and laterally compressed body ( Caruso 1983 ; Everly and Caruso 2003 ; Okiyama 2014c ; Okiyama and Minami 2014a , b; this study: Fig. 5 ). The genetic analysis also supported the generic identification of the present specimen (see below). Fig. 2. Preserved juvenile specimen of Sladenia zhui , KAUM–I. 70329, 23.1mm SL, East China Sea, showing melanophores. Right side reversed. Fig. 3. Semi-schematic drawings of illicium ( il ) and 2nd dorsal-fin spine ( sec ) (A), and pelvic fin (B) of juvenile specimen of Sladenia zhui , KAUM–I. 70329, 23.1 mm SL, East China Sea. Right side reversed in both drawings. SR indicates soft ray. Note: 2nd–4th soft rays partially damaged. Bars indicate 1mm. The specimen was further identified as S . zhui , due to having 4 dorsal-fin spines (2 post-cephalic spines), compared with 3 dorsal-fin spines (1 post-cephalic spine) in S . remiger and S . shaefersi ( Table 4 ). Although similar to S . gardineri in meristic counts, Ni et al . (2012) distinguished S . zhui from the former due to the wider snout, sturdy blunt head spines, and uniformly brown body without vermiculations or other contrasting markings in the latter. Although such distinguishing characters were absent in the juvenile specimen, the genetic similarity between it and a published sequence of S . gardineri (see Genetic analysis), and the disjunct distribution of the two species ( S . gardineri , central Indian Ocean; Table 4 ), pointed to the former being S . zhui . Genetic analysis. A Bayesian phylogenetic tree based on a concatenated alignment of 12S, 16S and COI sequences (626, 564 and 648 bp, respectively, including gaps) is shown in Fig. 6A . Among the 39 lophiiform species subjected to the analysis, S. gardineri was most closely related to the present specimen, supporting its generic identification. On the other hand, the overall tree topology was largely consistent with that of Miya et al . (2010) , who analyzed the complete mitogenome sequences ( ca . 16,000 bp) of the same 39 species (each of five suborders being recovered as monophyletic). Such consistency implied that the present analysis had successfully resolved the phylogenetic relationships among lophiiform species to some extent, despite the limited lengths of the sequences analyzed. A second Bayesian phylogenetic tree based on a reduced dataset [a 598 bp (including gaps) alignment of 12S sequences from six lophioid specimens, including both the present juvenile specimen and HUMZ 191110 ( S. cf. zhui sensu Ho et al . 2016 )], is shown in Fig. 6B . Notably, the latter two specimens possessed identical sequences, being clearly separated from other tree branches. On this basis, together with their similarity in meristic counts, the present juvenile and S . cf. zhui ( sensu Ho et al . 2016 ) specimens can be safely considered as conspecific. Remarks. Sladenia zhui was originally described by Ni et al . (2012) on the basis of four specimens collected from the northern South China and central East China Seas, the species having previously been reported as S . remiger or S . gardineri by Ni (1988) and Su (2002) (see synonym list). Ho et al . (2016) subsequently reported two specimens collected off Java , Indonesia as C . cf. zhui ( Fig. 7C, D ), commenting that they differed slightly from the original description of the species, having a narrower snout (mostly due to a different measurement method). Meristic and morphometric data of the Indonesian specimens are given in Table 2 . However, since all congeners are known from only a few specimens of each, intraspecific variations and interspecific differences between them are poorly known ( Caruso and Bullis 1976 ; Ho 2015 ). Fig. 4. Distributional map of Sladenia zhui . Star and open circles indicate present and previous records, respectively. Larval or juvenile Sladenia specimens have not previously been reported ( Richards 1990 ; Everly and Caruso 2003 ). In his comprehensive work, entitled “An atlas of early stage fishes in Japan ”, Okiyama (2014b) provided keys to larval stages of the lophiiform suborders, and stated that Ceratioidei differed from the other suborders by having an inflated, balloon-like skin surrounding the body, and the pelvic fin absent. The juvenile Sladenia specimen also had the former feature. In addition, the latter also possessed the following external adult Sladenia features ( Fig. 7C, D ): rounded head and body [depressed in adults of other lophiid genera ( Fig. 7A, B )], and absence of distinct humeral, articular, quadrate and subopercular spines (present) (see Caruso 1985 ). Table 3. Selected diagnostic characters of lophiid genera.

Sladenia	Lophiodes	Lophiomus	Lophius
1, 2, 3	2, 4	2, 5, 6	2, 5, 7
Head and body	rounded	depressed	depressed	depressed
Third cephalic dorsal-fin spine	absent	present	present	present
Humeral, articular, quadrate and subopercular spines	absent	present	present	present
Dorsal-fin soft rays	9 or 10	8	7–9	9–12
Anal-fin soft rays	6 or 7	6 or 7	5–7	8–10
Pectoral-fin rays	18 or 19	13–22	20–25	19–28
Vertebrae	19	18 or 19	18 or 19	26–31

1, this study; 2, Caruso (1985) ; 3, Ni et al . (2012) ; 4, Caruso (1981) ; 5, Everly and Caruso (2003) ; 6, Okiyama and Minami (2014a) ; 7, Caruso (1983) . Fig. 5. Lateral (A) and dorsal (B) views of preserved juvenile specimen of Lophius litulon , FAKU 109453 (1 of 3 specimens), 26.6mm SL, Japan. Table 4. Distribution and selected diagnostic characters of Sladenia species.

S . zhui	S . gardineri	S . remiger	S . shaefersi
1, 2, 3	4	4, 5	4, 6, 7
Distribution	East and South China Seas and Indonesia	Chagos Archipelago (central Indian Ocean)	Western and Central Pacific	Western Atlantic
Size (mm SL)	23.1–525 ( n =4)	351	92.3	146.2–397 ( n =4)
Dorsal-fin spines	4	4	3	3
Post-cephalic dorsal-fin spines	2	2	1	1
Dorsal-fin soft rays	9 or 10	9	9	8 or 9
Anal-fin rays	6 or 7	6	7	6
Pectoral-fin rays	18 or 19	18	19	17 or 18
Vermiculate body pattern	absent	present	absent?	present

1, this study; 2, Ni et al . (2012) ; 3, Ho et al . (2016) ; 4, Caruso and Bullis (1976) ; 5, Ho (2015) ; 6, Prokofiev and Kukuev (2009) ; 7, Sepúlveda et al . (2013) . The fin rays of the present juvenile are considered to reach the full complement in number ( Table 2 ). A difference of the number of caudal-fin rays between the juvenile specimen (8) and adults (9) is regarded here as an intraspecific variation. A series of larvae and juvenile examples are necessary to reveal the development of the numbers of fin rays in the species. In-situ observations of Sladenia from seamounts around the Ogasawara Islands, Japan , archived in the Japan Agency for Marine-Earth Science and Technology data base [JAMSTEC E-library of Deep-sea Images (J-EDI)], showed several Sladenia individuals characterized by vermiculate markings on the body ( e . g. , J-EDI: HPD0747HDTV0088). Similarly, a Sladenia individual reported by Senou (2012) as “ Chaunacidae gen. et sp. 2” from the Mokuyo Seamount (Ogasawara Islands) also had a vermiculate pattern. Such body markings have been regarded as a diagnostic feature of Sladenia species ( Caruso and Bullis 1976 ; Ni et al . 2012 ; Table 4 ). In-situ images of S . shaefersi in the Gulf of Mexico showed obvious widespread vermiculations on the body ( Pietsch et al . 2013 ), and the drawing of the 500 mm TLholotype of S . gardineri also showed maze-like vermiculations on the body ( Regan 1908 : pl. 32). In contrast, adults of S . zhui have a uniformly brownish body without vermiculations ( Ni et al . 2012 : fig. 1; Ho et al . 2016 : fig. 1; Fig. 7C, D ), suggesting that the in -situ images and footage of Sladenia from the Ogasawara Islands were not consistent with S . zhui . Although Caruso and Bullis (1976) stated that S . remiger lacked vermiculations or other contrasting markings, as originally described by Smith and Radcliffe in Radcliffe (1912) , an underwater photograph of S . remiger , reported by Chave and Mundy (1994) from the Hawaiian Islands, showed dark vermiculations on a whitish body. Ho (2015) reported an underwater photograph of S . cf. remiger from the Kermadec Ridge, with similar vermiculations, suggesting that the specimen may have represented an undescribed species. The new Japanese names “Daruma-ankou-zoku” and “Daruma-ankou” are proposed herein for the genus Sladenia and S . zhui , respectively, such names being derived from a combination of the overall rounded body of the species (= daruma ), plus the Japanese name for lophiid fishes (= ankou ); “ zoku ” refers to “genus”.