Macrolabrum Bacescu 1976, n. sp.

Macrolabrum Bacescu, 1976

Bacescu (1976): 3–4 (diagnosis); Gutu (1997): 299 (key to species); Błażewicz-Paszkowycz & Bamber (2012): 63 (discussion and key to Pagurapseudinae), 87 table 1 (comparison of antennule and uropod characters).

Composition. Macrolabrum abrucei (Bacescu, 1981); M. aenigmaticus Gutu, 1997; M. boeri Bacescu, 1981; M. distonyx Bamber, 2007; M. haikung Błażewicz-Paszkowycz & Bamber, 2012; M. impedimenta Bamber, 2005; M. mansoris Bamber, 2009b; M. maui n. sp. ; M. rugosus Gutu, 1997; M. sarda Błażewicz-Paszkowycz & Bamber, 2012; M. tangaroa Błażewicz-Paszkowycz & Bamber, 2012; M. trichopteroides Bacescu, 1976 (type species); and M. trifidus Gutu, 1997.

Remarks. Moderately species-rich, with thirteen published species (Anderson 2013), Macrolabrum is a predominantly warm-water, Indopacific genus known from Tanzania (Bacescu 1976), through Western Australia (Bamber 2005), Indonesia [Bali and Bunaken Island] (Gutu 1997), Vanuatu (Bamber 2009), New Caledonia (Bamber 2009), the Great Barrier Reef, Queensland (Bacescu 1981), and two recently described from Bass Strait, Victoria (Błażewicz-Paszkowycz & Bamber 2012). Macrolabrum species inhabit a shallow-water to bathyal depth range, 2– 515 m.

A key to the then-known five species of Macrolabrum was given by Gutu (1997) while Błażewicz- Paszkowycz & Bamber (2012) tabulated details of the antennule and uropod for the Australian Pagurapseudinae species. Morphology within the genus is somewhat disparate, particularly with regard to mandible, cheliped, and pereopod setation, as well as meristic characters of the antennule and uropod. Macrolabrum is distinguished from the very similar Pagurapseudes primarily by having an epistome that generally extends beyond the rostrum in dorsal view, but Błażewicz-Paszkowycz & Bamber (2012) also established that the almost round pleopod endopod of Macrolabrum was a valid generic character, and this is a more reliable distinguishing feature.

There are problems in defining sexual dimorphism or discriminating between the sexes of Macrolabrum (and pagurapseudids in general) as cheliped dimorphism occurs within females as well as between females and males (these being usually associated with dimorphic chelipeds); this applies equally to Pagurapseudes and Pagurotanais. There is also variation in the literature concerning the presence or number of antennular aesthetascs and, apart from the assertion, it is not often clear on what characters a sex is identified for a particular species. Extra male antennular aesthetascs are sometimes mentioned, e.g. Pagurapseudes inquilinus Bamber, 2007; P. queirosi Bamber, 2009; Pagurotanais largoensis McSweeny, 1982 (the best account of female-male differences in a Pagurapseudinae species), but in other species there is no difference or it is not mentioned. Males have also been noted with fewer antennule flagellar segments (Macrolabrum abrucei), not more as might be expected. Ultimately, identification of males is only safely done by noting the presence of a penial cone on the ventrum of pereonite-6.