Salacia tetracythara
Tangled colonies to 100 mm high and 100 mm wide ranging from groups of simple, stiffly pinnate stems to a large fan-shaped colony of many intergrown stems with one or two orders of branches arising from a thick, ramified hydrorhiza.
Stems up to 2 mm thick at base, stems and major branches fascicled, perisarc thick. Branch internodes visible only on younger, monosiphonic regions, nodes a transverse constriction, each internode with a hydrocladium and three hydrothecae, one axillar, one opposite and one below hydrocladium.
Hydrocladia long, monosiphonic, held out stiffly at an angle of c. 60° to axis of branch from a broad apophysis; apophysis with an indistinct, constricted, distal node; hydrocladial internodes usually absent but when present, with 2-6 pairs of hydrothecae.
Hydrothecae biseriate, immersed in hydrocladium, subopposite, laterally separated, overlapping vertically, long, tubular, narrowing from floor to margin; adcauline wall convex, convexity increasing distally, adcauline wall almost entirely adnate to internode, a very short free part just behind margin, abcauline wall straight to concave, floor of hydrotheca incurved to accommodate a thin circular to ovoid adcauline fenestration. Hydrothecal one median adcauline cusp, in anterior view margin subcircular; operculum a single abcauline flap attached to a small internal submarginal peg, perisarc of operculum delicate.
Gonotheca large, globular, up to six in an upright row along hydrocladium, pedicel short, perisarc very thick, smooth, aperture surmounted by a raised collar with vertical striations and a basal ring of large, internal, inwardly pointing denticles; operculum a thick plug of tissue.
Colour: Pale brown.
Indo-Pacific: Indian Ocean, Japan, Torres Strait and tropical to temperate East and Southeast coasts of Australia.
Subtidal, on invertebrate and rocky substrates.