MACROPHTHALMIDAE, Dana, 1851

Barnes, R. S. K., 2010, A Review Of The Sentinel And Allied Crabs (Crustacea: Brachyura: Macrophthalmidae), With Particular Reference To The Genus Macrophthalmus, Raffles Bulletin of Zoology 58 (1), pp. 31-49 : 31-32

THE FAMILY MACROPHTHALMIDAE

For many years, the genus Macrophthalmus and others believed at the time to be related to it were unquestionably regarded as representing a component subfamily of the Ocypodidae Rafinesque, 1815 , and were thus thought to be relatively far removed systematically from members of the various genera then considered to form the Grapsidae MacLeay, 1838 . Indeed, these two families were placed in different superfamilies (Ocypodoidea and Grapsoidea). This, for example, is the system adopted in the recent classifications of Martin & Davis (2001) and Sakai (2004). Molecular sequence data produced and analysed by Kitaura, Wada & Nishida (2002), however, strongly suggested that Macrophthalmus is more closely related to grapsids of the subfamily Varuninae H. Milne Edwards, 1853 , and to some genera traditionally regarded as being members of the grapsid subfamily Sesarminae Dana, 1851 (i.e. Metaplax H. Milne Edwards, 1852 , Cyclograpsus H. Milne Edwards, 1837 , and Helice de Haan, 1833 ) than it is to any other crab within the Ocypodidae . This includes to the camptandriids that historically (following Tesch, 1918) had also been included within the Macrophthalminae Dana, 1851 , until they were removed to form a separate subfamily within the Ocypodidae by Serène (1974) and later in several classifications (following Ng, 1988) to comprise a separate family within the Ocypodoidea. Kitaura et al.’s (2002) conclusions were confirmed by the sequence data of Schubart, Cannicci, Vannini & Fratini (2006) that indicated that Macrophthalmus is indeed more closely related to all grapsids, mictyrids and gecarcinids than it is to the typical ocypodid genera Uca Leach, 1814 , and Ocypode Weber, 1795 , or to Heloecius Dana, 1851 . These sequence data also showed that the erstwhile other ocypodid subfamilies Camptandriinae Stimpson, 1858, and Dotillinae Stimpson, 1858 (= Scopimerinae Alcock, 1900) also nestled within a group of grapsid and gecarcinid lines within the traditional Grapsoidea.

The families Ocypodidae and Grapsidae , let alone the superfamilies Ocypodoidea and Grapsoidea, may therefore have little real systematic or phylogenetic validity as currently constituted (see also Brösing, Richter & Scholtz, 2007). It must be said, however, that although these analyses of sequence data may seem completely to overthrow the systematic and phylogenetic status quo, those systematists actually concerned with the day-to-day business of macrophthalmine, varunine and sesarmine species had long realised how difficult it was in fact to decide wherein some of these species should be placed because of the considerable ‘overlap in the familial definitions’ (see, e.g., Davie, 1993).

Nevertheless, Ng et al. (2008) have recently strongly defended the traditional morphological basis of the higher systematic units within the thoracotrematan Brachyura and they defiantly retained the superfamilies Ocypodoidea and Grapsoidea, and included Macrophthalmus as a component genus of the Ocypodoidea whilst maintaining within the Grapsoidea the grapsid genera associated with Macrophthalmus by Kitaura et al. (2002) and Schubart et al. (2006). Their view that a concensus of both molecular and morphological approaches to the question is both possible and will ultimately emerge ( Ng et al., 2008: 214), however, is perhaps over-optimistic in the light of controversies that have run for more than 10 years over the relationships on molecular versus morphological grounds of some arthropod groups (see, e.g., Giribet & Ribera, 2000; Cook, Yue & Akam, 2005). Pending further phylogenetic analysis of the entire ‘Ocypodoidea’ and ‘Grapsoidea’, the Macrophthalmidae seems best regarded as a separate family within the ocypodoid+grapsoid complex of the Thoracotremata Guinot, 1977 or within the Grapsoidea sensu Rathbun (1918) (see Kitaura et al., 2002), and likewise the Varunidae (see Schubart, Cuesta & Diesel, 2000; Schubart, Neigel & Felder, 2000; Schubart, Cuesta & Felder, 2002).

On this basis, the Macrophthalmidae comprises the four genera Macrophthalmus , Australoplax Barnes, 1966 , Enigmaplax Davie, 1993 , and Lutogemma Davie, 2009 , together it has been argued (see Ng et al., 2008 for details) with two other genera that have long been regarded as belonging to other taxa entirely: Ilyograpsus Barnard, 1955 (hitherto usually placed in the Grapsidae : Grapsinae ) and Tritodynamia Ortmann, 1894 (of the pinnotherid subfamily Asthenognathinae Stimpson, 1858 ). In the scheme put forward by Ng et al. (2008), each of the two latter genera is placed in its own subfamily within the Macrophthalmidae , the Ilyograpsinae Stevcic, 2005 , and Tritodynamiinae Stevcic, 2005 , respectively, whilst the more traditionally recognised macrophthalmid genera then constitute the Macrophthalminae Dana, 1851 . Komai & Wada (2008), however, have recently argued strongly that Ilyograpsus , together with a related new genus, Apograpsus Komai & Wada, 2008 , that they erect for a species originally described in Ilyograpsus , are even closer to the Macrophthalminae than proposed by Ng et al. (2008) and do not warrant separation from them in a distinct subfamily. Interestingly in the light of the suggested affinity between Macrophthalmus and the varunids on molecular grounds, the DNA sequence data of Cuesta, Schubart & Felder (2005) also suggest close relationships between some asthenognathines and the Varunidae ; and Ng et al. (2008) transferred the genus Asthenognathus Stimpson, 1858 to that family. Further, Ng et al. (2008) considered that although seven species of Tritodynamia showed affinity with the Macrophthalmidae , two other species currently included in the genus are more likely to be related to the Varunidae .

The Macrophthalmidae is today restricted to the Indo-West Pacific, although fossil material of Macrophthalmus is known from former brackish-water deposits in Europe (Provence, France, and the Austrian Vienna Basin). Remy (1952) thought that Macrophthalmus originated in what is now the Mediterranean, although apart from a recent Lessepsian migrant into the eastern part of that sea, the family appears to have become extinct in the region of the Mediterranean basins in the late Miocene or early Pliocene. An Eocene-Oligocene origin considerably further east in the former Tethys Sea was argued by Barnes (1968). Nevertheless, it is curious that within the main subfamily, the Macrophthalminae , three of the four component genera are restricted to Australia, and so is one of the subgenera of Macrophthalmus whilst another is known only from New Zealand. Perhaps, as Davie (2009) suggests, the broad-fronted members of the subfamily comprise a separate lineage, that might then have evolved around Australia (although note below that the molecular sequence analysis of Kitaura, Nishida & Wada (2006) places the broad-fronted subgenus Chaenostoma as a highly derived form descended from narrow-fronted ancestors within Macrophthalmus ).