Gonaxia tasmanica Watson & Vervoort, 2001

Stems plumose, straight, stiff, erect, fasciculated for about two thirds of length, polysiphonic tubes broad, running almost parallel up stem; stems becoming monosiphonic in distal third, perisarc thick and hyaline.

Hydrocladia alternate, given off above base of stem to apex, up to 27 mm long, monosiphonic, joining stem at an angle of about 65° to cauline axis; hydrocladial apophysis a small indistinct constriction. Three hydrothecae between each hydrocladium, one about halfway between successive hydrocladia, one on opposite side of stem a little below level of hydrocladial apophysis (both these the same as hydrocladial hydrothecae) partially immersed in fascicular tubes; the third hydrotheca partially emergent from fascicular tubes in axil of hydrocladium. Hydrocladial nodes indistinct, oblique to transverse constrictions in perisarc between hydrothecae.

Hydrothecae biseriate, subopposite to alternate, well separated laterally, long and tubular, variable in length, directed upwards at an angle of 55° to internode, adcauline wall smoothly convex, adnate part variable in length from equalling to twice length of free wall, thick, curving down to a hook-shaped floor terminating in thick untidy strands of perisarc. Internode swollen opposite adnate part of adcauline wall; abcauline wall flatly concave to almost straight, a triangular peg of perisarc projecting inward at base just above level of adcauline hook. Margin tilted upwards at an angle of about 30° to hydrocladial axis, with three very low blunt cusps, one abcauline and two lateral, separated by shallow embayments. Operculum of three valves; a few hydrothecae with marginal replications producing rim into a short neck. Axillar hydrotheca differing from others; small, digitate, pointing upwards, adcauline wall slightly convex, abcauline wall straight or concave, narrowing distinctly to margin. Margin variable in shape, ranging from circular with everted rim to incipiently dentate; rim often replicated, extending into a long neck.

Hydranths deeply contracted into hydrothecae, with a ring of about 16 short, stubby tentacles.

Colour: Main stem and fascicular tubes pale brown, hydrocladia pale brown to white.