Macrorhynchia quadriarmata Watson, 2000

Hydrorhiza of a few fragmentary stolons. Colony 30 mm high, stem lightly fascicled, polysiphonic tubes running almost to broken tip of stem; prosegment long, lowest two branches broken off, a hinge joint overgrown by fasciculations above stump of proximal branch; six remaining branches regularly alternate, distant, directed upwards, perisarc firm; frontal tube of caulus hydrocladiate. Branches monosiphonic, borne on a long apophysis, distal node of apophysis transverse, followed by an athecate internode with a long blade-shaped distal joint, the two sections joined by a thin membrane, branch nodes thereafter transverse, narrow, obscure proximally, becoming more pronounced distally.

Hydrocladia alternate, frontal on stem and branches, one, sometimes two on branch internode, inserted on a short apophysis with slender, acute distal node, hydrocladia bearing up to six hydrothecae, internodes rather long, nodes transverse, deeply constricted, base of internode curving from node below hydrotheca; two distinct, complete, almost vertical intranodal septa, one at proximal third of hydro theca and one below lateral nematotheca.

Hydrotheca slipper-shaped, adcauline wall flat, bisected by an inclined, almost complete intrathecal septum connecting with intranodal septum, a small proximal foramen in base of wall usually obscured by tissue, abcauline wall convex to base of mesial nematotheca then recurving to margin, a deep pocket of perisarc behind margin. Margin almost parallel with internodal axis with a pair of broad, sometimes proximally displaced lateral lobes; lobes everted, a small, blunt cusp between lateral nematothecae. Perisarc of hydrocladia and hydrothecae thin.

Mesial nematotheca erect, increasing in length distally along hydrocladium, proximal nematotheca on hydrocladium not reaching hydrothecal margin, distalmost nematotheca very long, thin, tubular, considerably overtopping hydrothecal margin, distal end swollen, terminal orifice of both forms small, circular, a large secondary orifice on a short neck above junction with hydrotheca. Lateral nematothecae bifid, superior nematotheca long, thin, tubular, sinuous, extending beyond hydrothecal margin, terminal orifice circular, inferior nematotheca tubular, much shorter and wider than superior, pointing obliquely downwards from internode; openings of both nematothecae to internode confluent through a small foramen.

Branch apophysis with one large cowl- shaped adcauline nematotheca, a similar nematotheca on succeeding athecate internode; orifice small, circular, facing downwards to internode, both nematothecae with a large foramen connecting with branch. A cauline nematotheca on branch at base of hydrocladium, large, like inferior lateral, pointing away from hydrocladium; nematothecae also present on axillar tube of stem above proximal hinge joint.

Pseudophylactocarps replacing first hydrocladium on lowest branches, rachis unbranched, first two or three internodes with normal hydrothecae followed by up to six internodes with long, tubular nematothecae similar to superior laterals, pointing obliquely forwards and outwards, terminal orifice circular, a secondary orifice just above base.

Colour: Honey brown.