Based on the number of vertebrae and its plain colour Pangio longimanus can be assigned to the oblonga-group, as defined by Kottelat and Lim (1993).
1 male (holotype) and 2 females (paratypes) studied.
Ventral view of male Pangio longimanus pectoral fin, showing the hypertrophied and extremely elongated 2nd fin ray. (Image: Ralf Britz, Natural History Museum)
- Elongate body, only slightly compressed laterally
- Mid-body cross section almost circular to slightly oval
- Body depth 1.4-1.6 times its body width
- Standard length 9.6-12.6 times its body depth
- Caudal peduncle moderately laterally compressed, its depth 1.3-2 times its width, its length 1.8-2.5 times its depth, with distinct, but low, dorsal and ventral adipose keels.
- Mouth: 6 barbels (2 pairs of maxillary and 1 pair of mandibular barbells). Median lobe of lower lip extended into short barbel.
- Posterior margin of anterior naris developed into a long pointed flap, often referred to as nasal barbel.
- Bifid spine below eye
- Eye covered by thick skin
- Opercular opening restricted to small orifice above pectoral-fin base
- Caudal fin truncate to slightly emarginated
A male Pangio longimanus eel-loach from Laos. This holotype specimen (ZRC 51933) measures 20.2mm standard length. Top = lateral view, bottom = dorsal view. (Images: Ralf Britz, Natural History Museum)
Vertebrae and ray characteristics:
- Total vertebrae: 46 or 47
- Pectoral-fin rays: 7
- 2nd pectoral ray of male hypertrophied with segments of hemitrichs up to 6 times as wide as those of adjacent rays and extremely elongated, longer than head, with posterior tip folded back, reaching 9th myoseptum (to 6th in female).
- Posterior end of pelvic girdle at level of 22nd vertebra
- Anterior base of anal fin only slightly behind vertical through posterior base of dorsal fin
- Pelvic-fin rays: 6
- Dorsal-fin rays: 9 or 10, with 2 or 3 unbranched followed by 6 branched rays and last unbranched ray
- Anal-fin rays: 9, with 3 unbranched followed by 5 branched rays and last unbranched ray
- Caudal-fin rays: 8+8 or 8+7
- Dorsal procurrent rays: 3 to 6
- Ventral procurrent rays: 4 to 6
A female Pangio longimanus eel-loach from Laos. This paratype specimen (CMK 19692) measures 22.9mm standard length. Top = lateral view, bottom = dorsal view. (Images: Ralf Britz, Natural History Museum)
Colour of specimens in alcohol:
- Background colour yellowish-light brown, with numerous brown chromatophores giving fish a freckled appearance.
- Chromatophores dense on top and side of head.
- In area of body between head and a vertical through base of pelvic fin, brown chromatophores extend from dorsal midline, where more densely set, to dorsal half of body.
- In abdominal area, chromatophores extend further ventrally, covering upper three quarters of side of body.
- At level of anus chromatophores reach down to base of anal fin. Further posteriorly chromatophores cover entire caudal peduncle including adipose keels.
- Brown chromatophores also present along modified pectoral ray of male, at base of pelvic fin in 1 female and male, and lining dorsal, anal and caudal-fin rays in both sexes.