Flatface Seahorse, Hippocampus planifrons Peters 1877

Endemic to Western Australia, from Dirk Hartog Island to Broome. Inhabits tidepools, macroalgal and rubble reefs in shallow bays from the intertidal to a depth of about 20 m.

Dorsal fin 23-24 (usually 23); Anal fin 4; Pectoral fin 18-19; trunk rings 11; tail rings 37-38; subdorsal rings 3-4 + 1.

Head relatively small, snout short, about equal to postorbital length; nasal profile convex, rising upwards to angle of about 45° from snout; trunk slender, more than twice as long as its depth in adults.

Spines and tubercles: Body ridges with small tubercles becoming smooth with age. Subdorsal spines 4/0,0,1,1 or 5/0,0,0,1,1; small outwards curving spine above eye; nape spine small, directed anterodorsally; shoulder ring spines small, uppermost spine low and directed outward next to gill-opening, central spine at level just below level of centre of pectoral-fin base, lowermost spine directed outward; small lateral head spine; small spine behind eye; body spines of small to moderate size along dorsal and lateral ridges, few enlarged, most prominently along dorsal-fin base.

Coronet: Coronet slightly raised, 2 small anterior spines, 3 posterior spines of moderate size, central spine enlarged and recurved.
Lateral line: Lateral line pores small, distinct, situated just above lateral ridge at each ring on trunk, reaching about 18^th tail ring.

Fins: Dorsal-fin origin variable in position, ranging from before, in front of, on, or behind 8^th trunk ring.

In life - females overall greenish brown with dark blotching over dorsal region of trunk and tail; snout with dark lateral spots. In preservative - body mainly brown, snout with dark spots.

Like most other seahorses, this species presumably feeds by sucking small crustaceans and other small prey items, including planktonic zooplankton, into its mouth.

The female transfer her eggs into an elaborate enclosed pouch under the abdomen of the male. The male not only fertilizes the eggs inside the pouch and provides physical protection for the developing embryos, he also osmoregulates and aerates the embryos and may provide some nourishment until the offfspring are born.

Of no interest to fisheries, and not traded in the Asian Traditional Medicine market.

Listed under Appendix II of the Convention on the International Trade in Endangered Species of Wild Flora and Fauna (CITES). As a result, the species is subject to the Convention, http://www.cites.org/.
Listed as Least Concern on the IUCN Red List of Threatened species.
Marine Listed under the Federal Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act 1999). http://www.environment.gov.au/epbc/species/marine.html

H. planifrons has been regarded by some authors as a synonym of H. trimaculatus. Specimens from the Northern Territory and Queensland which were previously misidentified as H. planifrons are the Lowcrown Seahorse, H. dahli.

Some authors regard H. biocellatus to be a junior synonym of H. planifrons.

The specific name planifrons is from the Latin plan (= flat or level), and frons (= brow, forehead or forepart), in reference to the flat face of this species.

Hippocampus planifrons Peters 1877, Mber. K. Preuss. Akad. Wiss. Berl. 1876: 851 Type locality: "Naturalists Channel", NW. Australia, 10 fathoms.

Bray, D.J. 2020

Atlas of Living Australia