(Figs 1 C, 2 D, 6, 18B)
Material examined. One specimen in one sample. Holotype: AM W. 44115, MI QLD 2364.
Diagnosis. Parapodia biramous, with prechaetal lobe and ventral lobe; prechaetal lobe asymmetrical, with short ventrally displaced tip; ventral lobe wide, becoming longer than prechaetal lobe in posterior chaetigers. Branchiae present from chaetiger 2 to last body chaetiger, thin, much longer than chaetae, conspicuously twisted after fixation and not decreasing in length in posterior chaetigers. Anal tube funnel-like; narrow at base, increasing in width at distal end and opening directed posterio-dorsally, appearing obliquely truncate in lateral view. Posterior border with numerous (~ 25) pairs of small paired anal cirri; paired basal cirri and internal unpaired cirrus not observed.
Description. Based on holotype. Specimen complete, 8.0 mm long and 0.8 mm wide, with 29 chaetigers. Body slender, slightly tapering towards anterior end; posterior end wide and truncated. Prostomium conical provided with a pair of small red eyes (Figs 2 D, 6 A); palpode well developed but short and narrow, weakly clavate (Fig. 6 A). One pair of ring-shaped nuchal organs (Fig. 6 A); pharynx eversible, provided with about 10 oral tentacles (only observed when alive; Fig. 2 D), hidden after fixation. Branchiae present from CH 2 to last body chaetiger (CH 29), thin, much longer than chaetae (Fig. 2 D), conspicuously twisted after fixation (Fig. 6 A), not decreasing in length in posterior chaetigers (Fig. 6 B). Parapodia biramous, with prechaetal lobe and ventral lobe on each parapodium; dorsal cirrus not seen (Fig. 6 C–F). Prechaetal lobe asymmetrical, with short ventrally displaced tip; ventral lobe wide, becoming longer than prechaetal lobe in posterior chaetigers. Lateral eyespots anterior to parapodia on chaetigers CH 7 – CH 17, orange, horizontally oval; those of CH 7 and CH 15 – CH 17 smaller than others. Simple capillary chaetae in two bundles; notochaetae generally longer than neurochaetae in posterior chaetigers (Fig. 6 B). Anal tube funnel-like; narrow at base, increasing in width at distal end (Figs 2 D, 6 B). Anal tube opening directed posterio-dorsally, appearing obliquely truncate in lateral view. Ventral side as long as about 7 chaetigers, and about twice as long as dorsal side, with V-shaped ventral incision (Fig. 6 B). Posterior border with numerous (~ 25) pairs of small paired anal cirri (Fig. 6 B); paired basal cirri and internal unpaired cirrus not observed.
Remarks. This new species is unique within the genus Armandia because of the thin and extremely long branchiae, which become conspicuously twisted after fixation. The anal tube is particularly fragile and apparently deciduous because it is lacking in the holotype after fixation; the truncate shape of the posterior end in this only preserved specimen resembles that of Ophelina, namely that of Ophelina abranchiata Støp-Bowitz, 1948 (see Parapar et al. 2011, Fig. 9 a). Furthermore, the ecological distribution of A. filibranchia n. sp. differs from the other species described herein because its has only been collected on the outer barrier of the GBR.
Etymology. The epithet filibranchia (L.) refers to the long and thin parapodial branchiae.
Habitat / Distribution. Only one specimen was collected in sublittoral sand at 9 m depth at North Direction Island (outer reef SE Lizard Island) (Fig. 1 C).