(Bleeker)
1. Distinctive characters of early developmental stages
(a) Eggs
Adult males with eggs in the brood pouch have not yet been collected from the mangrove waterways.
(b) Larva (Based on 20 mm specimen)
Halicampus koilomatodon 1
Caudal fin present; cristae yet to develop fully; dorsal and caudal fins have 17 and 9 countable rays respectively. The shape of opercular keel intermediate between rectilinear and convex. Base of dorsal well elevated. Edges of shields spinous but dorsal profile of snout and head yet to become spinous at this stage.
2. Distinguishing characters of early developmental stages in similar species occurring in the mangrove estuaries
(a) Larvae of Syngnathus argyrostictus
Syngnathus argyrostictus 1 (Courtesy: Dr. M. Thangaraja, India)
Base of dorsal fin not elevated. Larvae measuring around 10 mm have 22 rays in dorsal fin and 10 rays in caudal fin. Seven patches of brownish black pigments are present in the posterior part of the body between dorsal and caudal fin (which transform as seven longitudinal series of pearly ocelli spread over the trunk in adults.
3. Salient biological characteristics
Adults exhibit sexual dimorphism. Male parents show parental care by incubating the fertilized eggs in the brood pouch.
4. Salient ecological information
Both larval and adult forms occur rarely in the lower reaches of the mangroves of Thailand, where neritic conditions prevail.