Metrarabdotos moniliferum (Milne Edwards, 1836)

Colonies are erect, bifoliate, consisting of fronds varying considerably in width: some are strap-like and bifurcating, others broad and convoluted. The ancestrula is unknown. Zooids in the encrusting colony base are sealed by secondary calcification, as are those of the initial erect stem which is usually subcircular in cross section.

Autozooids are large, averaging about 0.85 mm long by 0.30 mm wide, and elongate rectangular in outline shape with ill-defined boundaries. The frontal shield is cryptocystal, minutely granular, convex in young zooids but flat in older zooids, with about 15-22 large areolar pores along each of its lateral margins; pseudopores are lacking. The primary orifice is about 0.17-0.18 mm long by 0.14 mm wide and hidden inside a short, spout-like peristome. A poorly defined sinus is present in the secondary orifice. 

Small, adventitious avicularia are paired either side of the autozoodal orifice, resting on the lateral or proximolateral sides of the peristome. The rostrum is slightly curved and directed proximally and inwardly such that the distal tips of the two avicularia sometimes meet on the proximal lip of the secondary orifice. Calcified crossbars are present but seldom preserved. Giant avicularia occasionally replace normal avicularia, especially on zooids located laterally of gonozooids. These are about three times longer than normal avicularia, with a calcified crossbar, rounded opesia and pointed rostrum that may be laterally or proximolaterally directed.

Gonozooids, which tend to occur in clusters, are one and a half times longer and twice as wide as autozooids. The orifice is crescent shaped with a straight distal edge usually hidden in frontal view by the projecting proximal edge. They support paired adventitious avicularia which are widely separated on either side of the orifice. Distally of the orifice is a mitre-shaped ovicell with marginal areolae and a surface that is finely and evenly porous. Because of its fragility, the roof of the ovicell is often destroyed, leaving a large hole on the colony surface.