A taxonomic survey of
Marphysa species (Polychaeta: Eunicida: Eunicidae) from coastal regions of northern Australia including recently collected specimens from a fish farm near Darwin, yielded three species:
M. mullawa Hutchings & Karageorgopolous, 2003, a first record from northern Australia;
M. mossambica (Peters, 1854; was
Nauphanta mossambica), first confirmed record from Australia; and a new species,
M. fauchaldi. The new species was recorded from intertidal muddy shores as well as in the sediments of fish farm ponds, where it was extremely abundant. It is characterised by a unique combination of chaetal features. A newly proposed informal subgroup of
Marphysa, the Teretiuscula-group, is erected to contain the new species and other
Marphysa species that share the possession of compound spinigerous chaetae in anterior parapodia only and the peculiar behaviour of encapsulating embryos in jelly cocoons. Morphologically, the new species falls between a group of
Marphysa species having only compound spinigers and the recently resurrected genus
Nauphanta, which completely lacks compound chaetae. The discovery of this new species necessitated a re-evaluation of the morphological features of
Nauphanta and
Marphysa species lacking falcigers, in particular homology of fan chaetae, the only apparent synapomorphy of
Nauphanta. Fan chaetae appear to be a specialised type of pectinate chaetae, which are found also in species of
Marphysa including the new species. Based on this finding, and an evaluation of other characters,
Nauphanta is returned to synonymy with
Marphysa. Further, an analysis of size-related variation of key morphological characters in
M. mossambica and comparison with those in the types of
M. novaehollandiae (Kinberg, 1865; formerly
Nauphanta) and
M. simplex Treadwell, 1922, indicated that both species should be synonymised with
M. mossambica. A key is provided to identify
Marphysa species of the Indo-west Pacific.
