Diagnosis: 23+1 up to 27+1 (median 25+1) dorsal spines; distance from anterior border of snout to last externally visible dorsal spine relatively short, 46.2-52.5% SL (m=49.6), increasing with size; distance from posterior edge of pectoral fin to anterior origin of 1st dorsal spine between (-8.1) and 10.4% HL (m=1.0); no pre-orbital or pre-opercular spines; snout with a more blunted appearance; distance from anterior border of snout to last externally visible dorsal spine smaller than distance from anterior border of snout to last externally visible anal spine, which is 51.8-59.3% SL (m=56.3), both decreasing with size; post-anal length 44.3-51.6% SL (m=47.7), smaller than pre-anal length, becoming equal to latter with increasing size, 47.0-53.6% SL (m=51.1); 9-11 caudal fin rays; 5-7 predorsal vertebrae; 34-38 abdominal vertebrae; 3-8 in-between vertebrae; 52-60 caudal vertebrae (Ref. 57415).

Coloration: uniformly light brown overall background colour; dorsal midline with a series of small, dark brown spots; not well contrasted dark brown band originating at base of rostral appendage, passing through eye, above pectoral fin and continuing along lateral side of body and tail; indeed, a battlement pattern delimiting upper edge is still discernable at some places; lower sides of body and tail lighter brown, yellowish, with small, irregularly shaped yellowish white spots; ventral side of head, belly and abdomen uniformly yellowish-white; dorsal, caudal and anal fins white of overall background colour; dorsal and anal fin base with a series of dark brown spots; dorsal fin base brown, diminishing contrast between dorsal-fin base series of dark brown spots with remaining part of dorsal-fin base; dorsal fin with some small, irregularly disposed, dark brown, spots; caudal fin with a vertical, dark brown, bar towards outer margin of fin; nevertheless, caudal fin with a white outermost margin; in addition, unpaired fins quite white of overall general appearance; pectoral fins white of overall background colour with a few dark brown spots; colour pattern changes with size, notably a general darkening of unpaired fins; nevertheless, outermost margin of unpaired fins remains white; in addition, small dark brown spots situated towards distal part of unpaired fins form a more or less continuous band; sometimes, brown spots at base of anal fin may contact dark brown, black band resulting in a series of yellowish, white or light brown spots at base of anal; colour pattern of M. praensis shows close affinity with that of M. nigromarginatus (Ref. 57415).