Stethopristes eos Gilbert, 1905

Koeda, Keita, Sado, Tetsuya, Hata, Harutaka & Fujiwara, Yoshihiro, 2024, Redescription and first Japanese seamount record of Stethopristes eos (Zeiformes; Parazenidae), Zootaxa 5399 (5), pp. 579-586 : 580-584

Stethopristes eos Gilbert, 1905

[New standard Japanese name: Kagaribi-matodai]

Figures 1–3 ; Table 1

Stethopristes eos Gilbert, 1905: 622 , fig. 241 (original description; type locality: Pailolo Channel, between Molokai Island and Maui Island, Hawaiian Islands); Pequeño 1989:54 ( Chile); Parin 1991: 673; Tyler et al. 2003:15; Mundy 2005: 315 (Hawaiian Islands); Sáez & Lamilla 2017: 97 ( Chile).

Stethopristes sp. : Koeda et al. 2021: 17, fig. 6A (Ritto Seamount, incorrect depth on p. 17).

Material examined. JAMSTEC 106802, 124.2 mm SL, Ritto Seamount (21°37’ N – 21°57’ N, 141°53’ E – 142°13’ E), 519 m depth, 8 Dec. 2020, slurp-gun on KM-ROV, operating from R / V Kaimei ; USNM 51626 , holotype of Stethopristes eos , 104.1 mm SL, Hawaiian Islands , Pailolo Channel, between Molokai and Maui Islands, and northeast approach, Mokuhooniki Islet, 519–530 m depth, 10 Apr. 1902 , R / V Albatross , beam trawl ; USNM 51685 , paratype, 111.9 mm SL, Hawaiian Islands , vicinity of Kauai Island, Hanamaulu Warehouse, 411–593 m depth, 1 Aug. 1902 , R / V Albatross , beam trawl .

Description. Counts and measurements of the Japanese specimen and types are given in Table 1 .

Body oval, strongly compressed laterally. Body depth greatest at dorsal fin origin, least at middle of caudal peduncle. Caudal peduncle depth 1/7.4–7.8 of body depth. Dorsal outline of body generally rounded from snout to dorsal-fin origin, thereafter lowering gradually to middle of caudal peduncle. Ventral outline of head straight, descending obliquely, that of abdomen nearly horizontal, of posterior part of body gradually rising towards middle of caudal peduncle.

Head large, bony, with thin skin. Snout short, rounded. Eyes large, diameter greater than half head length. Orbital margin not protruding above dorsal outline of head. Interorbital space smooth. Anterior nostril round. Posterior nostril slit-like, located on dorsal surface just before eye. Dorsal outline of orbit serrate. Mouth terminal, large, strongly oblique ventrally. Posterior end of upper jaw reaching just below anteriormost point of eye. Gill openings large, with membranes on each side fusing mid-ventrally. Lower end of opercular bone with slight posteriorlydirected taper. Premaxillary with wide band of tiny conical teeth; lower jaw teeth of similar size, forming a narrow band. Tongue slightly flattened, long, rounded at tip. Gill rakers shorter than gill filaments, some of former knoblike.

Body covered with small cycloid scales, except for cheek, top of head, and fins. Ten (nine in USNM 51685) large ridged scutes along midline of abdomen, with continuous sharp ridges centrally. Lateral line elevated from upper end of gill opening, running parallel to dorsal outline of body to just below 3rd dorsal-fin spine, thereafter lowering and becoming parallel to body axis on caudal peduncle. Anus located just before anal-fin origin.

Origin of dorsal fin anterior to middle of body, slightly behind base of pectoral fin; spinous and soft-ray portions of dorsal fin low, with long bases; second spine longest in spinous portion; anterior rays of soft-rayed portion shorter than posterior rays; upper part of fin membrane of spinous portion slightly incised, anterior membrane extended slightly as flap; soft-rayed portion slightly incised. Anal-fin origin just below base of 6th dorsal-fin spine; spines short, weak, lacking fin membranes; soft-rayed portion higher and base longer than dorsal fin; anterior half of fin membrane deeply incised. Pectoral fin small, just behind gill opening, its length less than eye diameter. Pelvic fin very large, lacking spines, all rays divided near base; anteriormost point of base slightly anterior to pectoral-fin base; posterior tip of fin nearly reaching middle of anal-fin base when depressed. Caudal fin doubly truncated. Subcaudal rays small, spine-like, four each in upper and lower lobes.

Color when alive—Body generally bright reddish-pink with golden reflections and scattered whitish patches. Iris silvery-white. Caudal and pelvic fins red.

Color when fresh—Body generally bright red with silvery-white patches. Iris bright red. Dorsal fin red, except membranes of soft-rayed portion white. Anal and caudal fins with pink rays and white membranes. Pectoral fin with reddish translucent rays and translucent membranes. Pelvic fin with red rays and reddish-brown membranes.

Color after long term preservation—Body generally pale brown, without prominent markings; ventral portion whitish. Snout, and dorsal and caudal fins brown.

Distribution. Stethopristes eos has been recorded from the Hawaiian Islands and Salas y Gómez Ridge, Chile ( Gilbert 1905; Sáez and Lamilla 2017). The species is newly recorded here from the Ritto Seamount, West Mariana Ridge (Western Pacific).

Habitat. The Japanese specimen was collected near the ridge of Ritto Seamount. Although another individual was observed near the sampling site, the species was not seen in deeper water (to 700 m depth). Therefore, it is conjectured that S. eos occurs in waters near the top of the seamount and adjacent rocky slopes in ca. 500 m depth.

Remarks. The genetic analysis of the mitochondrial 12S to 16S ribosome RNA region (1,057 bp) confirmed that the Japanese specimen reported herein clearly differed from all other known Japanese zeiform species, and has been assigned correctly to the family Parazenidae ( Fig. 4 ). The specimen was identified as the rare monotypic species Stethopristes eos based on the following combination of morphological characters: six dorsal-fin spines, ten large ridged scales along the midline of the abdomen with continuous sharp central ridges, and small smooth cycloid scales covering the cheek and body lateral surface, which closely matched those of the types of the species. Previously recorded only from the Hawaiian Islands (type locality) and the Salas y Gómez Ridge, Chile ( Gilbert 1905; Sáez & Lamilla 2017), the Japanese specimen represents the first record from the western Pacific Ocean, strongly indicating a much wider distribution of the species across the Pacific region than previously known. The new Japanese names “Kagaribi-matodai-zoku” and “Kagaribi-matodai” are proposed for the genus and species on the basis of the present specimen (JAMSTEC 106802), which exhibited a fiery red color when freshly collected. According to the genetic analysis in this study, the results indicated a monophyletic relationship between the species identified as Parazen pacificus , presently classified under Parazenidae , and instead in Zeniontidae . However, due to the low bootstrap values, indicating low reliability, further taxonomical study within the entire order of Zeniformes is required, encompassing an additional genetic region in future research.

Figures

FIGURE 1. Lateral view of fresh specimen of Stethopristes eos, JAMSTEC 106802, 124.2 mm SL, collected from the Ritto Seamount, West Mariana Ridge.

FIGURE 2. Live specimen of Stethopristes eos, JAMSTEC 106802, 124.2 mm SL, just before collection.

FIGURE 3. Lateral view of preserved type specimens of Stethopristes eos, collected from the Hawaiian Islands. Upper: USNM 51626, holotype, 104.1 mm SL; lower: USNM 51685, paratype, 111.9 mm SL.

FIGURE 4. Unrooted neighbor-joining tree of Stethopristes eos and seventeen specimens representing five zeiform families, based on partial sequences of the mitochondrial 12S to 16S ribosomal RNA gene. Numbers beside internal branches indicate bootstrap values based on 1,000 replications.