Bioacoustics of Macrophthalmus

( Fig. 1A ) Small, carapace breadth < 15 mm ; ocular peduncles short and stout, not projecting beyond lateral carapace margins, subequal in length to breadth of front or shorter; front broad, not constricted between bases of ocular peduncles, where its breadth is 20–30% the distance between external orbital angles; ischium of external maxilliped some 1.25 times length of merus; carapace with breadth <1.3 times length, with lateral margins parallel, with broad-based subrectangular anterolateral teeth, without conspicuous aggregations of granules into rows or clumps on branchial regions; central region of posterior border of epistome straight; males without stridulatory apparatus; fingers of male chela short with index straight or slightly downflexed, and with a differentiated tooth only on dactylus. Intertidal, but unusually for Macrophthalmus , mainly associated with rocky or stony habitats. Two species are included in Chaenostoma (= Mopsocarcinus Barnes, 1967 ): M. boscii Audouin, 1825 ( type species) and M. punctulatus Miers, 1884 . This subgenus was suggested by Barnes (1967) to approximate the form of the ancestral Macrophthalmus , but the molecular sequence analysis of Kitaura, Nishida & Wada (2006) places it as a highly derived form.

( Figs. 3C , 4A ) Large, up to 40 mm carapace breadth; ocular peduncles elongate but not projecting beyond lateral carapace margins, much longer than breadth of front; front narrow, usually constricted between bases of ocular peduncles, where its breadth is 8–15% distance between external orbital angles; ischium of external maxilliped> 1.5 times length of merus (usually 1.7–2.5 times); carapace with breadth 1.3–1.7 times length (and in one species> 1.8 times length), with large, broad-based, subrectangular anterolateral teeth, with lateral margins subparallel or arched (so that greatest carapace breadth not across external orbital angles or even second anterolateral teeth), with longitudinal and/or transverse rows of granules and/or hairs on branchial regions but without clumps of granules; central region of posterior border of epistome straight, with marked concavity or (in some populations of one species) with a central protuberance; males of one species with stridulatory apparatus as described below in Paramareotis ; fingers of male chelae usually elongate with index downflexed and with differentiated teeth on both index and dactylus or on dactylus only. Intertidal, usually in relatively soft muds. Twelve species are included which have been divided between two subgroups on morphological grounds (the groups A and B of Komai et al., 1995 ):

( Fig. 4B ) Small, carapace breadth < 15 mm ; ocular peduncles short and stout, not projecting beyond lateral carapace margins, subequal in length to breadth of front or shorter; front broad, not constricted between bases of ocular peduncles, where its breadth is 20–30% distance between external orbital angles; ischium of external maxilliped ca. 1.25 times length of merus; carapace with breadth 1.3–1.6 times length, with lateral margins subparallel, with broad-based subrectangular or pointed anterolateral teeth, without conspicuous aggregations of granules into rows or clumps on branchial regions (indistinct rows present in some); central region of posterior border of epistome usually straight (with convexity in one species); males with stridulatory apparatus in all species (i.e. with short horny ridge on ventoroflexor margin, or on inner surface near ventoroflexor margin, of cheliped merus, and lower orbital border with 1–2 large triangular protuberances occupying at least one fifth of that margin); fingers of male chela short with index straight or slightly downflexed and with differentiated teeth on both fingers. Intertidal, with one species often occurring in holes in limestone rocks and the others often associated with mangrove pneumatophores. Four species are included: M. boteltobagoe ( Sakai, 1969 ) , M. erato de Man, 1888 , M. holthuisi Serène, 1973 , and M. quadratus A. Milne Edwards, 1873 (the type ), Kosuge & Davie (2001) having demonstrated that M. boteltobagoe and M. holthuisi are distinct species contra the opinion of Barnes (1976) . Molecular sequence data ( Kitaura et al., 2006 ) suggest that M. erato + M. quadratus are only distantly related to M. holthuisi + M. boteltobagoe , but instead are related to the M. brevis group of the subgenus Macrophthalmus .

( Fig. 5A ) Medium-sized, up to 30+ mm carapace breadth; ocular peduncles elongate but not projecting beyond lateral carapace margins, longer than breadth of front; front moderately narrow, not constricted between bases of ocular peduncles, where its breadth is ca. 20% distance between external orbital angles; ischium of external maxilliped ca.1.2 times length of merus; carapace with breadth 1.5–1.6 times length, with lateral margins subparallel, with large, broad-based, subrectangular anterolateral teeth, branchial regions with transverse and longitudinal rows of granules; central region of posterior border of epistome with large convexity; males without stridulatory apparatus; fingers of male chelae elongate with index downflexed and with clearly differentiated tooth on dactylus only. Intertidal in soft sediments. This is a monotypic subgenus for M. latifrons Haswell, 1882 , restricted to south-eastern Australia , the only macrophthalmid in that region. It appears to differ behaviourly from other Macrophthalmus in that allocleaning (foraging on the carapace or walking legs of other conspecific individuals) is not displayed (Kitaura & Wada, 2004).