The Pygmy Leatherjacket is one of the smallest of 100 species in the Monacanthidae family, growing to a maximum size of 9 centimetres. They have a rounded body shape, with tiny pectoral fins and a relatively large tail fin. The tail fin rays are able to be fanned out for propulsion or flattened and used as a rudder. This aids in maneuverability through the seagrass meadows, but results in a fairly slow swimming fish. The base colour of the Pygmy Leatherjacket is highly variable, ranging in shades of green or brown, to yellow, red and orange with small dark spots, or ocelli, covering the body. Their colouration can change depending on their surroundings enabling the pygmy leatherjacket to remain well hidden from predators. This change in body colour is also important during courtship. An inflatable abdomen can be used to increase their small size to defend their territory and warn off any potential predators.
As with most leatherjackets, the Pygmy Leatherjacket is active during the day and feeds on a variety of small invertebrates. While sleeping at night they will anchor themselves to a blade of seagrass with their teeth to avoid being swept away by the currents. Male and female Pygmy Leatherjackets pair during the spawning season and will produce a small number of relatively large eggs physically attached to blades of seagrass or other suitable substrate. The eggs then hatch into the plankton and are distributed by the currents.
The Pygmy Leatherjacket is a temperate marine species found in a range of habitats, from seagrass meadows to kelp gardens. Distribution of this species ranges from Lancelin, WA. south to Moreton Bay, QLD. They are a species which is endemic to Australia.
Occurrence at the Busselton Jetty
Pygmy leatherjackets are rarely observed from the Underwater Observatory. Their small size and cryptic lifestyle hidden amongst weed makes them difficult to be seen. When they have been spotted it’s often been as a pair, floating amongst the build up of algae on the concrete ledge of the observatory. Beachcombers may well discover a Pygmy Leatherjacket washed up on the beach amongst the seagrass wrack after a storm.