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Opistognathus ctenion was discovered from Osumi and Ryukyu islands in southern Japan at depths of 35 - 57 meters and first described in 2023.
The specimen from Ryukyu (NSMT-P 130174) was collected on a sandy gravel bottom.
The species name "ctenion" is an appositional noun derived from the Greek diminutive κτενίον, meaning "small crest."
It refers to the small number of gill ruffles in the new species, one of the lowest recorded for Indo-Pacific Opistognathus species.
The ground color of the head is reddish-brown dorsally, reddish-white ventrally, and the iris is generally reddish-brown, except for a whitish area ventrally, with four faint dark red lines extending from the pupil.
Two faint dark red oblique lines extend from just behind the eye to the middle of the nape or upper part of the cheek .
Five or six whitish spots are visible on the cheek and operculum.
The base of the mouth of the fountain darter is completely white.
The body is reddish-brown, with 3 or 4 longitudinal rows of about 8-10 whitish spots, which are much smaller than the spots on the head; the upper one or two rows and the anterior part of the lower two rows of spots are somewhat indistinct.
There are two whitish spots at the base of the pectoral fins, and the lower spot is distinctly larger.
The base of the mouth of the fountain darter is completely white.
The body is reddish-brown, with 3 or 4 longitudinal rows of about 8-10 whitish spots that are distinctly smaller than the spots on the head; the upper one or two rows and the anterior part of the lower two rows of spots are somewhat indistinct.
There are two whitish spots at the base of the pectoral fins, and the lower spot is distinctly larger.
The dorsal and anal fin bases are fringed with a dark reddish brown, with the anterior edge of the dorsal fin running slightly below the lateral line (sometimes interrupted by the body base color).
The dorsal fin is greenish or yellowish brown, with an ocellus between the 2nd and 5th spines, 4-6 white spots forming a longitudinal row just behind the ocellus. Soft rayed portion of dorsal fin and anal fin hyaline or faint reddish-brown, with two and one reddish-orange stripes, respectively; upper stripe of the former through distal margin, remaining stripes at about 1/3 height of both fins.
Pelvic-fin rays whitish and membrane hyaline with melanophores. Pectoral and caudal fins are uniformly faint orange or reddish yellow.
Fresh coloration of the paratype is generally similar to the other specimens of the type, with the following differences:
The head and body are yellow, and the whitish spots on the body are more prominent.
A whitish spot is visible at the pectoral fin base.
The lateral fins faint yellow (details of pigmentation not visible), an ocellus on the dorsal fin the pelvic fins are white.
Similar species: Opistognathus triops, recently described from Tonga and Vanuatu.
Literature reference
Fujiwara K, Motomura H, Shinohara G (2023)
Opistognathus ctenion (Perciformes, Opistognathidae): a new jawfish from southern Japan.
ZooKeys 1179: 353-364. https://doi.org/10.3897/zookeys.1179.109813
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
The specimen from Ryukyu (NSMT-P 130174) was collected on a sandy gravel bottom.
The species name "ctenion" is an appositional noun derived from the Greek diminutive κτενίον, meaning "small crest."
It refers to the small number of gill ruffles in the new species, one of the lowest recorded for Indo-Pacific Opistognathus species.
The ground color of the head is reddish-brown dorsally, reddish-white ventrally, and the iris is generally reddish-brown, except for a whitish area ventrally, with four faint dark red lines extending from the pupil.
Two faint dark red oblique lines extend from just behind the eye to the middle of the nape or upper part of the cheek .
Five or six whitish spots are visible on the cheek and operculum.
The base of the mouth of the fountain darter is completely white.
The body is reddish-brown, with 3 or 4 longitudinal rows of about 8-10 whitish spots, which are much smaller than the spots on the head; the upper one or two rows and the anterior part of the lower two rows of spots are somewhat indistinct.
There are two whitish spots at the base of the pectoral fins, and the lower spot is distinctly larger.
The base of the mouth of the fountain darter is completely white.
The body is reddish-brown, with 3 or 4 longitudinal rows of about 8-10 whitish spots that are distinctly smaller than the spots on the head; the upper one or two rows and the anterior part of the lower two rows of spots are somewhat indistinct.
There are two whitish spots at the base of the pectoral fins, and the lower spot is distinctly larger.
The dorsal and anal fin bases are fringed with a dark reddish brown, with the anterior edge of the dorsal fin running slightly below the lateral line (sometimes interrupted by the body base color).
The dorsal fin is greenish or yellowish brown, with an ocellus between the 2nd and 5th spines, 4-6 white spots forming a longitudinal row just behind the ocellus. Soft rayed portion of dorsal fin and anal fin hyaline or faint reddish-brown, with two and one reddish-orange stripes, respectively; upper stripe of the former through distal margin, remaining stripes at about 1/3 height of both fins.
Pelvic-fin rays whitish and membrane hyaline with melanophores. Pectoral and caudal fins are uniformly faint orange or reddish yellow.
Fresh coloration of the paratype is generally similar to the other specimens of the type, with the following differences:
The head and body are yellow, and the whitish spots on the body are more prominent.
A whitish spot is visible at the pectoral fin base.
The lateral fins faint yellow (details of pigmentation not visible), an ocellus on the dorsal fin the pelvic fins are white.
Similar species: Opistognathus triops, recently described from Tonga and Vanuatu.
Literature reference
Fujiwara K, Motomura H, Shinohara G (2023)
Opistognathus ctenion (Perciformes, Opistognathidae): a new jawfish from southern Japan.
ZooKeys 1179: 353-364. https://doi.org/10.3897/zookeys.1179.109813
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
