Short Tail Thryssa

Thryssa brevicauda

USNM 217043, Holotype, Fly 75–32, 49.4 mm.

USNM 217044, Paratypes, Fly 75–32, 30: 30.3–56.5 mm (5 to BMNH).

Thryssa brevicauda is known only from a single series of (juvenile?) specimens from a mangrove creek in the Lower Fly, the largest of which is 56.5 mm. Feeding habits unknown. Lower jaw relatively short, extending anteriorly to a point considerably short of snout tip. Maxillary bone not extending posteriorly to beyond opercle. Diameter of eye 14.6–17.5. Gill rakers on anterior face of first gill arch 22–25 + 27–29; 5–7 gill rakers on posterior face of third gill arch. Total anal fin rays 32–36. Scales in lateral series 34–36. Abdominal scutes 14–16 + 9. Tips of pelvic fins extending posteriorly beyond a vertical line through origin of dorsal fin. Free vertebral centra 38–40 (usually 39). Length of caudal peduncle 8.8–9.2 No humeral pigment blotch. A diffuse nuchal pigment blotch well developed in all specimens.

Thryssa brevicauda agrees with T. scratchleyi and T. rastrosa, and differs from all or almost all other Thryssa, in having maxillary bone not extending posteriorly beyond opercle, tips of pelvic fins extending posteriorly to a vertical line through origin of dorsal fin, and no humeral pigment blotch. It differs from T. scratchleyi and T. rastrosa in having a diffuse nuchal pigment blotch, fewer scales, fewer abdominal scutes, fewer vertebrae, and a relatively short, deep caudal peduncle.

Thryssa spinidens (Jordan and Seale, 1925), new combination

USNM 217045, Fly 75–32, 1: 118 mm.

This species was kindly identified by T. Wongratana.