Gymnangium japonicum
Stems plumose, monosiphonic, lower region ahydrocladiate, cauline internodes short, nodes transverse, distinct, not constricted.
Hydrocladia closely alternate, one per internode, long, gracefully recurved, inserted on a long apophysis on front of stem, apophysis with a strong transverse distal node. Cauline internode with three nematothecae; one above, the other at base of apophysis on front of stem, and one behind. Hydrocladial nodes transverse, indistinct, marked by a notch in perisarc along base of internode; no intranodal septa.
Hydrothecae boot-shaped, without intrathecal septa; adnate adcauline wall flatly convex, free part almost straight, at an angle of 105-110° to hydrocladial axis; abcauline wall deeply sinuated, posteriorly convex, adnate to mesial nematotheca, free wall deeply recurved to margin. Margin circular, strongly everted, parallel to or slightly inclined to hydrocladial axis, anterior wall thickened, produced into a minute cusp (lateral view), rim with a pair of asymmetrical ear-shaped cusps shifted posteriorly (viewed from above). Perisarc thickest at hydrothecal floor and at margin, thinner in middle.
Mesial nematotheca very long, tubular, thin, narrowing apically, arching forward over succeeding hydrotheca; base narrow. Terminal orifice very small, circular, a larger secondary orifice just above, but not connecting with hydrotheca. Lateral nematothecae small, saccate, directed obliquely upwards, with a large, deeply excavated orifice facing inwards to hydrotheca and a small orifice connecting with internode. Cauline nematothecae saccate, of similar size to laterals. Frontal nematothecae set closely above one another; orifice of proximal nematotheca extended into a long, upwardly directed tube, similar to but shorter than mesial nematotheca. Distal nematotheca with a much shorter tube, also pointing distally; orifice of posterior axillar nematotheca the same as that of laterals.
Colour: Lower stems glistening golden brown, distal part of colony possibly pale yellow in life.
Pacific ocean: Japan, Tasmania, Macquarie Island.
Subtidal, 250m to >900m