Synodus macrocephalus Cressey 1981

Synodus macrocephalus

Synodus macrops.—Cressey and Cressey, 1979:12 [in part].

MATERIAL EXAMINED.—Holotype: USNM 217776, SL 158.1 mm, SOMALIA, R/V Anton Bruun, Cruise 9, Sta 463, 75–175 m (trawl), 17 Dec 1964. Paratypes (6): USNM 217739, SL 97.0–165.0 mm, ARABIAN SEA (off Bombay), R/V Anton Bruun, Cruise 4B, Sta 202A, 52.5 fms (trawl), 13 Nov 1963. Other Material: ANDAMAN ISLANDS (1): USNM 217616.

DIAGNOSIS AND COMPARISONS.—A species of Synodus with the following combination of characters: dorsal-fin rays (branched and unbranched) 11–13 (usually 13); anal-fin rays 9–11 (usually 10); pored lateral-line scales 55–56 (usually 56); transverse scale rows 3.5/5; vertebrae 55 (usually 55); combined dorsal and anal procurrent rays 26–27; anterior palatine teeth not longest and not in a discrete group; peritoneal spots 7; posterior pelvic process narrow.

The narrow posterior pelvic process separates this species from all known Indo-West Pacific Synodus except S. gibbsi, S. kaianus, S. macrops, and S. oculeus. The vertebral counts of S. macrocephalus are lower (55) than those of S. gibbsi (58–61) and S. kaianus (58–63). The pectoral fin of S. macrocephalus extends beyond a line from the origin of the pelvic fin to the origin of the dorsal fin—that of S. macrops does not. Also, the peritoneal spot counts of S. macrocephalus are higher than those of S. macrops (7 vs. 5–6). Synodus macrocephalus has a pointed snout, whereas that of S. oculeus is rounded. The bony interorbital space is greater in S. oculeus than in S. macrocephalus (5.6 vs. 4.2 percent SL). Synodus macrocephalus shares the parasitic copepod Metataeniacanthus aquilonius Cressey and Cressey with macrops. This in addition to other shared morphological features (narrow posterior pelvic process, vertebral counts, lateral external markings) seems to indicate that they may be closely related. Synodus oculeus also appears to be closely related, sharing the same morphological similarities cited for S. macrops and also a similar dermal flap on the anterior nares (S. oculeus does not share the same parasitic copepod species).

DESCRIPTION (holotype plus range).—Dorsal-fin rays 13(11–13); anal-fin rays 9(9–11); pectoral-fin rays 12; pelvic-fin rays 8; procurrent rays 26 (26–27), dorsal 14, and anal 12(12–13); lateral line continuous, 55(55–56) pored scales; scale rows above lateral line from dorsal origin 3.5; scale rows below lateral line to anal origin 5; predorsal scales 15; rows of cheek scales 3(3–4); vertebrae 55; peritoneal spots 7.

Percentages of Standard Length: Mean (range) : head length 31.6 (30.4–32.1); snout length 7.4(7.0–8.0); upper jaw length 19.1(18.3–19.8); diameter of bony orbit 7.3(7.0–7.7); least width of bony interorbital 4.2 (4.1–4.3); snout to dorsal origin 44.8(42.2–46.2); snout to adipose origin 87.3(84.6–88.3); snout to anal origin 78.2(76.5–78.4); snout to pelvic insertion 40.0(37.8–41.8); snout to pectoral insertion 31.5(30.1–33.1); first-dorsal-ray length 9.5(7.9–11.2); longest-dorsal-ray length 13.4(11.7–14.1); pectoral-fin length 15.2(14.9–15.4); pelvic-fin length 23.5(22.8–24.8); dorsal-fin base 11.8(9.5–13.3); anal-fin base 9.7(8.7–10.7); based on 7 specimens 97.0 to 158.1 mm SL.

Body fusiform, head somewhat depressed, caudal region a little compressed. Large cycloid scales on body, cheeks, and operculum, postoral portion of cheeks scaly. Snout sharply pointed, broader than long; the anterior nostril on each side bearing a broad triangular flap extending beyond margin when depressed anteriorly. Interorbital space concave, occipital region bony. Palatine teeth in an elongate V-shaped pad, teeth pointing backwardly, those in front not largest and not in a discrete group. Lingual teeth well developed, those on free end of tongue largest and about 30 in number. Teeth caniniform, larger teeth with arrow-shaped tips. Pectoral fins reaching beyond a line from base of pelvic fins to origin of dorsal fin. Outer pelvic ray unbranched and short, fifth branched ray (sixty ray) longest. Posterior bony process of pelvic girdle narrow. Peritoneum pale.

COLOR PATTERN.—Preserved specimens are darker above lateral line with a series of darker blotches along lateral line. The blotches are not well defined and not present in all specimens. Dorsal fin with 2 to 3 bars. Other fins unmarked.

DISTRIBUTION AND HABITAT.—This species is known only from the western Indian Ocean. The specimens were collected in shrimp trawls at depths of 75 to 175 m.

Synodus macrocephalus is a species of lizardfish that lives mainly in the Indo-West Pacific. A common English name largehead lizardfish.