Comprehensive Description

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Acestridium colombiensis ZBK , new species

(Fig. 1)

Holotype . FMNH 115255 , 49.5 mm SL, sex unknown. Colombia : Guainia State : Orinoco Basin: Rio Inirida, lagoon at 1 km up river from Puerto Inirida , 28 March 1974 , Thomerson, Hicks, Baskin, Rofen .

Paratypes . FMNH 105169 , 10 ex., 35.64-44.4 mm SL; same data as holotype. - INHS 99093 , 2 ex., 39.5-45.7 mm SL same data as holotype - USNM 381314 , 2 ex., 38.5-41.4 mm SL same data as holotype .

Diagnosis: Acestridium colombiensis ZBK can be distinguished from its congeners with a unique combination of characters: two unpaired median pre-dorsal plates, body width 10.0 -13.0% of post-dorsal fin length, inter-orbital distance between 10.6-13.0% of post-dorsal fin length, inter-orbital distance between 25.0-29.0% of eye-to-dorsal fin length; low number of jaw teeth (12-15 teeth in upper left jaw, 9-13 teeth in lower left jar), pre-dorsal fin body pigmentation not formed into distinct lines between longitudinal rows of odontodes.

Description: Largest specimen is the holotype, 49.5 mm SL. Meristic and morphometric data given in Tables 1 and 2.

Overall coloration of specimens in alcohol light brown dorsally, less pigmented ventrally but more brownish posterior to anal fin. Top of head brown with sides of head more darkly pigmented anterior to eye, through eye, and fading from side of body anterior to dorsal fin. Predorsally, melanophores mostly scattered, not forming into distinct lines between longitudinal rows of odontodes on plates; melanophores may form faint blotches between plates. Post-dorsal of dorsal fin melanophores mostly scattered but may form faint lines between rows of odontodes.

Small brown melanophores on all fins, dorsal and caudal fins more pigmented than ventral fins. One to three faint bands may be present on caudal fin; melanophores on rays but not on membranes.

Outer portion of the upper lip is lightly pigmented and the inner portion is unpigmented. The lower inner lip is unpigmented and the outer side has a few dark melanophores.

Comparisons: Acestridium colombiensis ZBK is most similar to Acestridium martini but differs in pigmentation and some body proportions. Acestridium colombiensis ZBK has a larger inter-orbital distance in relation to the distance between the eye and dorsal fin (25.0- 29.0% in A. colombiensis ZBK , 17.0-24.0% in A. martini , Fig. 2). The two species also differ in the ratio of the inter-orbital distance to post-dorsal length (10.6-13.0% in A. colombiensis ZBK and 7.0-10.5% in A. martini ). Acestridium colombiensis ZBK has an oral disk width that is 24.0-29.0% of snout to eye length vs. 17.0%-27.0% in A. martini .

Predorsally, the unpigmented rows of odontodes are longitudinally parallel and separated by distinct stripes of melanophores in A. martini . In A. colombiensis ZBK , the melanophores are randomly dispersed under and between the rows of odontodes and no distinct pattern of odontodes and pigment stripes is present.

Acestridium colombiensis ZBK is narrower than A. dichromum (body width equals 10.0- 13.0% of post-dorsal fin length vs. 14.0-18%, Fig. 3) and has fewer jaw teeth than A. dichromum (12-15 teeth in upper left jaw vs. 24-30 and 9-13 teeth in lower left jaw vs. 20-36 teeth).

Acestridium colombiensis ZBK has two median predorsal plates, vs. three for Acestridium discus (Retzer et al., 1999).

Distribution: Acestridium colombiensis ZBK is only known from Río Inirida, (Orinoco Basin), Guainia State of Colombia. This record is the first for a species of Acestridium in Colombia.

Etymology: The species epithet, colombiensis refers to the fact that the species is only known from Colombia.


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