Plotosus papuensis Weber 1910

Plotosus papuensis Weber, 1910

USNM 217104, Fly 75–1, 1: 502 mm.

USNM 217105, Fly 75–13, 1: 30.8 mm.

USNM 217106, Fly 75–14, 9: 31.3–129 mm (1 to AMNH).

Plotosus papuensis, hitherto known only from the type series collected in the Lorentz River, was found in the Upper and Middle Fly. An individual of 1000 mm caught at Fly 75–20 was not preserved. This species is distinguished from its congeners in having a very finely branched (truly dendritic) dendritic organ, usually 9 caudal rays, and a unique color pattern. Specimens from the Fly have length of head 24.1–25.7, eye 26–52 in specimens 30.8–502 mm (negatively allometric), depth of body at origin of dorsal fin 17–20, length of dorsal fin spine 9–13, length of longest dorsal fin ray 11–17, and length of pectoral spine 6–10; dorsal fin typically with four rays; last one or two rays split to base, dorsal procurrent caudal fin 110–120 rays, caudal fin 9(8) or 8(1) rays, anal fin 100–113 rays, total dorsal procurrent caudal + principal caudal + anal fin rays 225–240, pectoral fin 13–14 segmented rays, and pelvic fin 12–13 rays. Gill rakers on first gill arch 18–26. Branchiostegal rays 11–12: 11 + 11(6), 12+12(4). Ribs 7–9. Complete vertebral centra posterior to Weberian apparatus 69–73 (11–12 precaudal+ 58–61 caudal). Color in preservative (similar to that in life in all or almost all respects): dorsum of head, almost entire body, and all fins usually bluish black (brown in very small juveniles; one of the larger specimens from Fly 75–14 has faint light mottling on body and fins); abdomen varying from black to cream colored or pale whitish with scattered melanophores; ventral surface of head dark laterally and light medially in young, pale (almost immaculate) in adults; lips darkly pigmented in young, pale in adults; maxillary and nasal barbels dark except for pale edges, mental barbels entirely pale. Dendritic organ white. Several individuals from Fly 75–14 with a faint, light longitudinal band extending from head along lower half of body and above base of anal fin, tapering posteriorly and disappearing before caudal fin.

The specimens from the Fly agree closely in counts, measurements, and all other respects except coloration with the Lorentz River syntypes of P. papuensis. The smaller and medium-sized syntypes are stunningly marked by two sharply defined white or cream-colored bands on the side of the otherwise darkly pigmented (almost black) body, as illustrated in the original account (Weber, 1913:520, fig. 2). The upper band, which has no counterpart in the Fly specimens, begins below base of dorsal fin and extends almost to caudal fin. The lower band corresponds to the single band present in some of the specimens from Fly 75–14. Lorentz juveniles also differ from Fly juveniles in having head and abdomen almost immaculate ventrally. In the largest specimens from the Lorentz and from the Fly the longitudinal bands on the body are almost or entirely indiscernible, hence they are virtually identical in all respects.

Plotosus papuensis is perhaps most similar to P. canius (Hamilton-Buchanan, 1822) (Figure 24b). Freshly preserved P. canius from Daru, near the mouth of the Fly (USNM 217322, 5: 98–190 mm) and from Panay, Philippines (USNM 217323, 102 mm), differ from P. papuensis in having head and mouth only two-thirds as wide, jaw teeth slightly larger, mental barbels dark, vertical height of dorsal procurrent caudal and anal fins only two-thirds as great; dendritic organ lobose or foliaceous and yellowish, no indication of longitudinal bands on body, and 14 precaudal vertebrae exclusive of Weberian apparatus instead of 11 or 12.

Oloplotosus luteus Gomon and Roberts, new species

USNM 217107, Holotype, Fly 75–9, 122.8 mm.

USNM 217108, Paratypes, Fly 75–11, 2: 123.1–142.0 mm.

The hitherto monotypic genus Oloplotosus Weber, 1913 (type-species Oloplotosus mariae Weber, 1913, by original designation and monotypy), belongs to the group of Plotosidae possessing a dendritic organ and is distinguished from all other members of the family by its dentition: upper jaw toothless, palate and lower jaw with one or two rows of well-developed, opposable teeth. Body moderately elongate, dorsal procurrent caudal fin originating slightly posterior to dorsal fin.

Oloplotosus luteus differs from O. mariae in many respects including head shape, dentition, and almost all meristic characters. Head strongly rounded dorsally and relatively narrow, its length 6.0–6.4 (vs. head relatively flattened and broad, its length 4.8–5.1 in O. mariae). Eye very small, 75–77 (eye slightly larger, 50–63). Snout with a bulbous anterior projection between anterior nostrils (snout broadly rounded, without bulbous projection). Barbels stubby, broad based, almost round to almost flat, nasal barbel reaching to or almost to posterior margin of eye, maxillary barbel to below posterior margin of eye, outer mental barbel to gill opening, inner mental barbel about one-half to three-quarters as long as outer mental barbel (barbels relatively more slender and longer). Lips thick, plicate, and papillose (lips relatively thin and smooth). Snout, lateral and ventral surface of head, branchiostegal membranes and anterior portion of abdomen papillose, papillae especially large and densely distributed on branchiostegal membranes (papillae entirely absent). Branchiostegal membranes broadly united to each other and to isthmus; ventroposterior margin of branchiostegal membranes with only a slight medial indentation (branchiostegal membranes joined to each other and to isthmus but much farther anteriorly; ventroposterior margin of branchiostegal membranes with a deep V-shaped indentation). Oral dentition incisorial, teeth chisel shaped and close set in single rows on palate and on lower jaw (oral dentition not incisorial; teeth elongate and conical, irregularly spaced in two rows on palate and on lower jaw). Gill rakers on anterior face of first gill arch 8–10 (17–18). Branchiostegal rays 8–9 (11–12). Dendritic organ small and foliaceous; relatively prominent in holotype, largely hidden in deep dendritic organ pocket in paratypes. Dorsal spine blunt tipped and entirely smooth, without serrations anteriorly or posteriorly, its length 19.2–20.4; pectoral spine blunt tipped, almost entirely smooth, without serrations posteriorly but minute serrae on base anteriorly, its length 13.0–13.3. Dorsal fin I 5 (I 5), dorsal procurrent caudal fin 103–106 (110–117), caudal fin 5 (6), anal fin 86–92 (101–116), total dorsal procurrent caudal + principal caudal + anal fin rays 195–203 (220–235). Pectoral fin I 10–11 (12–13), pelvic fin 11–12 (13–14). Ribs 9–10 (9–10). Free precaudal vertebrae posterior to Weberian apparatus 12–13 (13–14), free caudal vertebrae 51–52 (60–61), total free vertebrae posterior to Weberian apparatus 63–64 (73–75). Color in life: dorsum of head and body almost uniformly dark brown; side of head and body dark brown, variably mottled; median fins brownish, mottled; pectoral fins mottled or dusky dorsally and pale or slightly mottled ventrally, pelvic fins slightly mottled or pale dorsally and uniformly pale ventrally; distal two-thirds of nasal and maxillary barbels, entire mental barbels, lips, and ventral surface of head bright orange; ventral surface of abdomen pale orangish (color in life of O. mariae unknown; color pattern of preserved specimens similar in most respects to that in O. luteus).

Oloplotosus luteus was obtained at two localities in the highlands of the Upper Fly, where the current was moderate to swift and the bottom consisted of rocks and cobbles of variable size (Figure 3b). Oloplotosus mariae is known only from the type series obtained at Sabang and Alkmaar on the Lorentz River; although the habitat was not specifically indicated, the information about these localities supplied by Weber (1913a: 513) suggests it lives in similar habitat.