Monocle Coralblenny

Ecsenius monoculus

Ecsenius (Ecsenius) oculus Springer.—Springer, 1971:35 [paratypes, in part: Ilot du Sud, South China Sea].

Ecsenius oculus.—McKinney and Springer, 1976:12 [Type D; Ilot du Sud and Indonesia: Bawean, Ambon, Saparua, and Haruku, Molucca Islands].

DESCRIPTION.—Dorsal fin XI-XII (rarely XI), 12–14 (rarely 12) deeply notched between spinous and segmented-ray portions. Anal fin II,14–16 (rarely 14). Pectoral fin 13 to 14 (rarely 14, and only unilaterally). Segmented caudal-fin rays 13 or 14 (rarely 14). Vertebrae 9–10 (rarely 9) + 21–23 = 31–33. Dentary incisor teeth 42–59 (includes anterior canine teeth, which differ little, if at all, in appearance from incisors); posterior canines 1 on each side. Lateral line without vertical pairs of pores, terminating posteriorly at point between verticals from interspace between dorsal-fin spines 10 and 11 and vertical from first segmented ray (usually between spines 11 and 12). Cirrus present on posterior rim of anterior nostril; none on anterior rim.

Preserved Color: Important features include: No pair of dark spots present dorsally on nape; nape usually with 2–4 dark stripes separated by pale interspaces. Dark stripe extending from postorbital margin across opercle often indistinct or absent; stripe, when present, continuing onto body anteriorly; no deep, short, dark stripe present just ventral to dorsal opercular portion of postorbital stripe. Conspicuous blackish pigment present ventroanteriorly to corners of mouth. Body sides usually darkly dusky with 4 or 5 rows of pale spots; single, conspicuous, pale-margined, large, dark, saddle-like spot on dorsal body contour at posterior end of dorsal fin; occasionally 1–3 irregular, large, dark, pale-margined spots at ventroposterior end of body (not including ventral dark spot that extends onto caudal fin), but these spots not as intensely dark as dark saddle-like spot at posterior end of dorsal fin. Venter of large or sexually mature males sprinkled with fine melanophores; venter of females and immature males unpigmented. Spinous dorsal fin of males only occasionally with faint, fine, dusky suprabasal stripe.

Live Color: An underwater photograph (Plate 7: figure 4), taken in the Philippines, of a living specimen, shows the dark areas on the body to be various shades of olive brown, except for the dark saddle-like spot, which is black, on the dorsal body contour at the posterior base of the dorsal fin. A vertical pair of spots at the caudal-fin base is dark brown. A brilliant white spot is present immediately anterior to the saddle-like spot, and another is present between the vertical pair of dark spots. Most of the pale markings on the head and body are pale gray or cream colored, but on the fleshy pectoral-fin base there is a vertical pair of yellow spots, followed in line posteriorly on the body by two rows of pale yellow spots or dashes, which gradually become fainter posteriorly. There is a narrow, faint–yellow ring around the pupil; the remainder of the iris is olive brown interrupted by yellow vermiculations.

DISTRIBUTION.—Known only from the Philippine Islands, Ilot du Sud (10°29′15″N, 108°57′30″E, off South Viet Nam), and the Molucca Islands. The distribution of E. monoculus is bounded by that of E. oculus to the north, E. paroculus to the west, and E. sellifer to the east. There are gaps, from which no species of the Oculus Group are known, between the distributions of E. monoculus and the other Oculus–group species. It would be important to know what species of the Oculus Group occur on the coasts of Borneo, Sulawesi, Halmahera, western New Guinea, southeastern China, and North Viet Nam, before hypothesizing vicariance scenarios to explain the distributions of the species.

COMPARISONS.—The presence of a single, large, saddle–like dark spot on the dorsal body contour (on the caudal peduncle) distinguishes E. monoculus from all other members of the Oculus Group. I am unable to hypothesize its closest relative unequivocally, but I believe that it is E. sellifer, as these two species uniquely share in having dark saddles together with a lack of ocelli on the body. Within the Oculus Group, however, Ecsenius sellifer shares a character (transverse pair of dark spots on the nape) only with E. paroculus and E. oculatus, which two species appear otherwise to form a monophyletic group. I believe that the nape spots are either a synapomorphy of the Oculus Group or homplastic in E. sellifer, especially as I believe that E. oculus, which lacks the spots, is the sister group of E. paroculus and E. oculatus.

ETYMOLOGY.—The specific name is from the Greek “monos,” meaning “one,” plus “oculus,” Latin for “eye,” in reference to the characteristic single, dark, saddle–like spot on each side of the body.

HOLOTYPE.—USNM 261243, male, 36 mm SL, NW side Putic Island, Cuyo Islands, Philippine Islands (10°55′05″N, 121°02′03″E), 0–4.6 m, V.G. Springer et al., 22 May 1978.

PARATYPES.—Philippine Islands: USNM 219309 (18 specimens: 16–42 mm SL) and USNM 226575 (6:13–38), both collected with holotype; USNM 226581 (7:23–49), Cocoro Island, Cuyo Islands, 0–3 m, V.G. Springer et al., 26 May 1978; USNM 219308 (1:43), Tagauayan Island, Cuyo Islands, 0–2.4 m, V.G. Springer et al, 25 May 1978; USNM 226577 (5:15–30), Maloh, Negros Oriental, 0–3.1 m, H.A. Fehlmann et al., 18 May 1979; USNM 226579 (31:22–38), near Maloh, Negros Oriental, L. Knapp et al., 24 April 1979; USNM 227537 (1:24) and 226578 (15:14–35), near Giligaon, north of Maloh, Negros Oriental, 0–1.8 m, L. Knapp et al., 26 April 1979; USNM 228928 (1:30), USNM 228926 (2:27, 41), and USNM 225049 (5:27–43), all Sombrero Island, Batangas, 0–5 m, C.J. Ferraris, 23 April 1980; USNM 226580 (1:28), Sombrero Island, Batangas, C.J. Ferraris and E.O. Murdy, 30–31 January 1980; AMS I.21909–001 (2:43 each), Sombrero Island, Batangas, 0–1 m, C.J. Ferraris, 25 April 1980; USNM 225050 (7:16–33), Bolinao, Pangasinan, 0–2 m, C.J. Ferraris and E.O. Murdy, 17 April 1980. Indonesia, Molucca Islands: BPBM 18046 (1:27), 18048 (1:20), 18049 (1:28), 18052 (4:19–32), all from Ambon; USNM 211925 (7:13–17), SE tip of Haria Bay, Saparua, 1.5–4.6 m, V.G. Springer and M.F. Gomon, 5 March 1974; USNM 209577 (7:13–49), point E of Tandjung Naira, Haruku, 4.6 m, V.G. Springer and M.F. Gomon, 15 January 1973.

OTHER MATERIAL.—South China Sea: CAS 13464 (1:41; previously CAS GVF–2113, paratype of Ecsenius oculus), W shore Ilot du Sud (off S tip of Poulo Cecir de Mer), 0–7 m, R. Bolin et al., 10 March 1960.