Distinguishing ten sympatric species of fiddler crab (Decapoda: Ocypodidae) using a suite of phenotypic characteristics Author Michie, Laura A. Author Barnes, R. S. K. Department of Zoology and Conservation Research Institute, University of Cambridge, CB 2 3 EJ, UK. Author Clark, Paul F. Department of Life Sciences, The Natural History Museum, Cromwell Rad, London, SW 7 5 BD, UK. Author Bennett, Wayne A. University of West Florida, 11000 University Parkway, Pensacola, US. Author Cragg, Simon M. 0000-0003-1082-7653 simon. cragg @ port. ac. uk; https: // orcid. org / 0000 - 0003 - 1082 - 7653 simon.cragg@port.ac.uk text Zootaxa 2021 2021-08-27 5026 4 480 506 journal article 10.11646/zootaxa.5026.4.2 1175-5326 5300736 44594360-3408-4C4C-A4E6-1025F171A49F Austruca perplexa (H. Milne Edwards, 1852) ( Figure 5a–j ) Material examined. 20 ♀ , 20 ♂ , Kaledupa , Indonesia , 5º 29’ 50’’S , 123º 45’ 20’’E , mud flat in front of mangroves, coll. L. Michie , 26.08.2014 . Diagnosis . Carapace: slightly broader than long; smooth; front broad; anterolateral angles moderately acute and slightly produced; anterolateral as well as dorsolateral margins short or nearly absent; anterolateral borders slightly convergent. Major cheliped: long dactyl and pollex; pollex with central tooth. Colouration ( Figure 5a–d ). Similar to A. cryptica . Adult male. Carapace: mainly black with white transverse markings varying in size and number, anterior ventral surface of carapace and third maxilliped white. Major cheliped: dactyl and pollex white with manus and carpus yellow or white, merus, ischium, basis and coxa yellow. Minor cheliped & ambulatory legs: yellow, white, grey, occasionally black. Adult female. Carapace: varies greatly, most often mottled light brown/russet, grey or white, occasionally same as male carapace, anterior ventral surface of carapace and third maxilliped most often white or grey, occasionally black with ischium of third maxilliped white. Ambulatory legs: like males. Juvenile male. Carapace: usually mottled light brown/russet with pattern and dark colours developing with maturity. Major cheliped: usually entirely white and develops colour with maturation. Juvenile female. Same pattern as juvenile males, sometimes difficult to distinguish juveniles of A. cryptica , A. mjoebergi and G. jocelynae . Gonopod morphology ( Figure 5e–h ). G1 with broad termination, directed in dorsolateral direction, mesial border between protuberance and termination with swelling; distal protuberance moderately long, often reaching beyond base of flanges; distal end relatively long mainly due to largely protruding dorsal lobe; pore of sperm channel large, in midline. Gastric mill ( Figure 5i–j ). Urocardiac ossicles moderately complex with 3–4 transverse ridges of median teeth, decreasing in size distally, first one long and strongly arched; stem region has 2 pairs of cusps, first large and rounded, second small and attached to plate dorsally. Lateral tooth plate with 17 comb-shaped teeth. Biology. Austruca perplexa is a small-size species (largest male CL = 10.1 mm , CB = 15.6 mm , largest female CL = 9.1 mm , CB = 14.8 mm ); one of most abundant species on shore, dominates the mid intertidal zone. Distribution . From Nicobar Is. Eastward, Eastern Indian Ocean, Thailand to China , Taiwan , Japan , Philippines , Indonesia , Australia , Pacific Islands. Remarks. The specimens examined concur with the description of Naderloo et al. (2010) , specifically the largely protruding dorsal lobe of the G1 and the moderately complex morphology of the gastric mill, which distinguish A. perplexa from the other Ambeua Austruca species.