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Austruca triangularis (A. Milne-Edwards, 1873) (Figure 6a–j) Material examined. 10 ♀, 10 ♂, Kaledupa, Indonesia, 5º 29’ 51’’S, 123º 45’ 21’’E, mud flat in front of mangroves, under houses to the east, coll. L. Michie, 26.08.2014. 10 ♀, 10 ♂, Kaledupa, Indonesia, 5º 29’ 49’’S, 123º 45’ 20’’E, mud flat in front of mangroves, under houses to the west, coll. L. Michie, 28.08.2014. Diagnosis. Carapace: broader than long; smooth; front broad; anterolateral angles strongly acute and produced; anterolateral margins absent; dorsolateral margins proceeding directly from anterolateral angle strongly converging. Major cheliped: dactyl and pollex relatively wide; pollex arched, dactyl also arched, but less so than pollex; pollex and manus have teeth in proximal and distal portion. Colouration (Figure 6a–b). Adult male. Carapace: mainly black, with white transverse markings varying in size and number, anterior ventral surface of carapace and merus of third maxilliped, black. Major cheliped: dactyl and pollex white/off-white with darker hue extending to manus and carpus, manus, carpus, merus and ischium with dark brown speckled pattern. Minor cheliped and ambulatory legs: black or grey. Adult female. Carapace: similar to males, black with white transverse markings, with greater degree of variability than males, sometimes white and occasionally posteriorly black, frequently with turquoise transverse markings across posterior region. Ambulatory legs: black or grey. Juvenile male and female. Carapace: usually white, sometimes light brown/russet with pattern and darker colours developing with maturity. Major cheliped: normally light brown at juvenile stage but becomes darker and develops patterning with maturation. Minor cheliped & ambulatory legs: black or grey. Gonopod morphology (Figure 6e–h). G1 curved in dorso-lateral direction; distal end long and narrow with flanges extend throughout length of distal part of shaft; distal edge of flanges rounded; pore of sperm channel large, extending beyond overlapping flanges; protuberance well developed, elongated, ending above base of flanges; distal end curved in lateral direction. Gastric mill (Figure 6i, j). Urocardiac ossicles complex, with 5 transverse ridges of median teeth, different in shape, 1–4 decreasing in size distally, 5 much larger being twice as broad as other ridges; stem region has 5 pairs of cusps, decreasing in size distally, fifth is much shorter and attached to the plate dorsally; lateral tooth plate with 20 comb-shaped teeth. Biology. Austruca triangularis is a small-size species (largest male CL = 8.2 mm, CB = 12.1 mm, largest female CL = 8.2 mm, CB = 12.8 mm); one of least abundant species on shore, present in high intertidal zone under stilted houses. Distribution. Australia, Indonesia, Malaysia, Philippines, Taiwan, China, Papua New Guinea. Remarks. The specimens examined comply with the description of Shih et al. (2019) specifically with the elongated protuberance of the G1 and the complex morphology of the gastric mill, with the highest number of transverse ridges and cusps of all Austruca species at Ambeua. Austruca triangularis can be distinguished from the other Austruca species by the strongly acute anterolateral angles, the elongated protuberance of the G1, the distinct speckled pattern of the major cheliped and the small size., Published as part of Michie, Laura A., Barnes, R. S. K., Clark, Paul F., Bennett, Wayne A. & Cragg, Simon M., 2021, Distinguishing ten sympatric species of fiddler crab (Decapoda: Ocypodidae) using a suite of phenotypic characteristics, pp. 480-506 in Zootaxa 5026 (4) on pages 488-491, DOI: 10.11646/zootaxa.5026.4.2, http://zenodo.org/record/5300736, {"references":["Shih, H. T., Ng, P. K. L., Ravichandran, S. & Prema, M. (2019) Resurrection of Gelasimus variegatus Heller, 1862, A Fiddler Crab Closely Related to Austruca bengali (Crane, 1975) and A. triangularis (A. Milne-Edwards, 1873) (Decapoda, Brachyura, Ocypodidae), from the Bay of Bengal, Indian Ocean. Zoological Studies, 58, e 12. https: // doi. org / 10.6620 / ZS. 2019.58 - 12"]}

Paraleptuca crassipes (White, 1847) (Figure 9a–j) Material examined. 10 ♀, 10 ♂, Kaledupa, Indonesia, 5º 29’ 50’’S, 123º 45’ 20’’E, mud flat in front of mangroves, coll. L. Michie, 26.08.2014. 10 ♀, 10 ♂, Kaledupa, Indonesia, 5º 29’ 51’’S, 123º 45’ 20’’E, on the mangrove perimeter, coll. L. Michie, 29.08.2014. Diagnosis. Carapace: broader than long; smooth; front broad; anterolateral angles marginally acute; anterolateral margins short; dorsolateral margins distinct. Major cheliped: manus similar length to dactyl and pollex; outer manus with small round, almost triangular, depression near pollex base. Colouration (Figure 9a–d). Colour variation is one of highest at this site, but that of major cheliped remains constant. Adult male. Carapace: generally red, sometimes with black or blue markings and occasionally all black with blue and red markings, anterior ventral surface often black, sometimes red. Third maxilliped: normally blue. Major cheliped: dactyl and pollex pale pink/red, manus pink/red and remainder red. Minor cheliped & ambulatory legs: generally black or red. Adult female. Carapace: varies greatly, sometimes entirely red, often red with blue and white markings, can be black with white/blue transverse markings. Ambulatory legs: similar to those of males. Juvenile male. Carapace: similar to adults, usually red or black, often has white and blue markings. Major cheliped: light brown or pink and, becoming darker with maturation. Juvenile female. Similar colour patterns to juvenile males. Gonopod morphology (Figure 9e–h). G1 strongly curved in dorso-lateral direction; distal end long, strongly curved in lateral direction, tapers before bulging slightly at tip, termination rounded; margins folded causing a twisting longitudinal groove visible on posterior surface; pore of sperm channel in midline; distal protuberance short. Gastric mill (Figure 9i, j). Urocardiac ossicles moderately complex, with 6 transverse ridges of median teeth, different in shape, 1 and 2 strongly arched, 1–4 decreasing in size distally, 5 and 6 are sometimes fused and appear almost as one; stem region has just 1 pair of cusps. Lateral tooth plate with 22 comb-shaped teeth. Biology. Paraleptuca crassipes is a relatively small-size species (largest male CL = 10.5 mm, CB = 16.2 mm, largest female CL = 11.3 mm, CB = 17.1 mm); one of most abundant species on shore, present in mid and high intertidal zones, often in mangroves and under stilted houses. Distribution. China, Japan, Philippines, Thailand, Indonesia, Papua New Guinea, Melanesia, Micronesia. Remarks. Paraleptuca crassipes can be distinguished by the strong curve of the G1, the depression on the manus of the major cheliped and the striking red colouration. The specimens examined compare well with the original description, but this is the first description of the gastric mill for P. crassipes and the moderately complex morphology is similar to that of A. perplexa., Published as part of Michie, Laura A., Barnes, R. S. K., Clark, Paul F., Bennett, Wayne A. & Cragg, Simon M., 2021, Distinguishing ten sympatric species of fiddler crab (Decapoda: Ocypodidae) using a suite of phenotypic characteristics, pp. 480-506 in Zootaxa 5026 (4) on pages 493-496, DOI: 10.11646/zootaxa.5026.4.2, http://zenodo.org/record/5300736

Gelasimus tetragonon (Herbst, 1790) (Figure 8a–j) Material examined. 10 ♀, 10 ♂, Kaledupa, Indonesia, 5º 29’ 49’’S, 123º 45’ 21’’E, mud flat southwest of boat jetty, coll. L. Michie, 27.08.2014. 10 ♀, 10 ♂, Kaledupa, Indonesia, 5º 29’ 50’’S, 123º 45’ 21’’E, mud flat between houses and boat jetty, coll. L. Michie, 28.08.2014. Diagnosis. Carapace: broader than long; smooth; front narrow; anterolateral angles acute, slightly produced; anterolateral margins short, converging from angles; dorsolateral margins short, sometimes absent; carapace lateral margins slightly converging, practically straight posteriorly. Major cheliped: long, slender dactyl and pollex; pollex almost straight; dactyl moderately arched; dactyl and pollex with one or more sub-distal teeth. Colouration (Figure 8a–d). Adult male. Carapace: blue with black mottled pattern varying in size and shape, anterior ventral surface of carapace generally black, dark brown or navy blue and ventral surface of third maxillipeds normally same blue as carapace, anterolateral angles can be pale straw coloured, occasionally pale anterolateral areas can be extensive. Major cheliped: orange, with dactyl often possessing a lighter tip, proximally pollex with darker hue of orange which extends onto part of manus, proximally manus with dark brown mottled pattern extending to carpus and merus. Minor cheliped & ambulatory legs: black or dark brown, 4 th pair of legs often with black and blue mottled pattern. Adult female. Carapace: similar to male, often with a darker hue of blue. Chelae & ambulatory legs: orange, often have blue dactyl and pollex. Juvenile male. Carapace: mottled black and white pattern with colours developing with maturity. Major cheliped: similar to adults but with white distal end to dactyl and pollex. Minor cheliped: blue dactyl, pollex and manus. Ambulatory legs: black. Juvenile female: same colour pattern as juvenile males. Gonopod morphology (Figure 8e–h). G1 strongly curved in dorso-lateral direction; distal end slightly curved laterally; anterior flange slightly narrower than posterior; pore of sperm channel large; distal protuberance moderately large, not reaching base of flanges. Gastric mill (Figure 8i, j). Urocardiac ossicles moderately complex, with 4 transverse ridges of median teeth, decreasing in size distally, different in shape, first two arched, 3 and 4 straighter, fourth large and attached to plate dorsally; stem with setae present on lateral margins of posterior stem region. Lateral tooth plate with 19 combshaped teeth. Biology. Gelasimus tetragonon is a medium-size species (largest male CL = 16.8 mm, CB = 23.1 mm, largest female CL = 9.4 mm, CB = 14.3 mm); present in mid and low intertidal zones, often associated with presence of coral rock where crabs were seen feeding on small patches of algae on rock surfaces. Distribution. South Africa to Iran, Madagascar, Thailand, Malaysia, Australia, Indonesia, Philippines, Papua New Guinea, Taiwan, Micronesia, Melanesia. Remarks. Gelasimus tetragonon is distinguished by the strong curve of the G1, the long, slender dactyl and pollex and the distinct blue carapace and orange major cheliped. The specimens examined fit the original description and the moderately complex gastric mill conforms to the description by Shih (2015) and is similar to that of G. jocelynae., Published as part of Michie, Laura A., Barnes, R. S. K., Clark, Paul F., Bennett, Wayne A. & Cragg, Simon M., 2021, Distinguishing ten sympatric species of fiddler crab (Decapoda: Ocypodidae) using a suite of phenotypic characteristics, pp. 480-506 in Zootaxa 5026 (4) on page 493, DOI: 10.11646/zootaxa.5026.4.2, http://zenodo.org/record/5300736, {"references":["Shih, H. - T. (2015) Uca (Xeruca), a new subgenus for the Taiwanese fiddler crab Uca formosensis Rathbun, 1921 (Crustacea: Decapoda: Ocypodidae), based on morphological and molecular evidence. Zootaxa, 3974 (2), 151 - 169. https: // doi. org / 10.11646 / zootaxa. 3974.2.1"]}

Tubuca dussumieri (H. Milne Edwards, 1852) (Figure 12a–j) Material examined. 9 ♂, 13 ♀, Kaledupa, Indonesia, 5º 29’ 50’’S, 123º 45’ 20’’E, mud flat in front of mangroves, under houses, L. Michie, 26.08.2014. 11 ♂, 7 ♂, Kaledupa, Indonesia, 5º 29’ 50’’S, 123º 45’ 21’’E, mud flat in front of mangroves, coll. L. Michie, 28.08.2014. Diagnosis. Carapace: broader than long, smooth; front narrow and practically straight; anterolateral angles acute, not produced; anterolateral margins short; dorsolateral margins distinct and converging. Major cheliped: elongated dactyl and pollex; pollex with medial tooth; gape between dactyl and pollex is triangular in shape due to distinct angle of dactyl; breadth of dactyl consistent along its entire length and only tapers at tip. Colouration (Figure 12a–d). Adult male. Carapace: black, sometimes with two or three central white markings, anterior ventral surface of carapace and third maxillipeds normally black. Major cheliped: dactyl generally white extending dorsally onto manus, pollex with a white tip and remainder orange which extends ventrally onto manus, usually becoming darker, carpus is a mixture of white, orange and brown, remainder of cheliped usually orange. Minor cheliped & ambulatory legs: generally black, sometimes with last pair blue/white. Adult female. Carapace: similar to male. Ambulatory legs: similar to males, except sometimes all legs are blue/white. Juvenile male. Carapace: most often black with two or three central white markings. Major cheliped: dactyl and pollex normally white, remainder is orange. Juvenile female. Similar to adult females. Ambulatory legs: blue/white. Gonopod morphology (Figure 12e–h). G1 curved in dorso-lateral direction; large anterior flange, with dark spine at tip of anterior edge; distal protuberance short; pore of sperm channel in midline. Gastric mill (Figure 12i, j). Urocardiac ossicles simple, with 5 transverse ridges of median teeth, 1–4 decreasing in size distally, fifth one larger and attached to plate dorsally; stem region has 1 pair of cusps. Lateral tooth plate with 18 comb-shaped teeth. Biology. Tubuca dussumieri is a medium-size species (largest male CL = 14.6 mm, CB = 29.4 mm, largest female CL = 15.9 mm, CB = 24.9 mm); one of the least abundant species on shore, present in mid and high intertidal zones, predominantly associated with shade under buildings or mangrove trees. Distribution. China, Taiwan, Thailand, Indonesia, Northern Australia, Papua New Guinea. Remarks. Tubuca dussumieri is the largest species at Ambeua which, along with the large anterior flange of the G1, distinguishes it from the other Tubuca species. The specimens examined agree with the original description. This is however, the first description of the gastric mill for T. dussumieri and the simple morphology which distinguishes it from other Ambeua genera and is similar to the other Tubuca species., Published as part of Michie, Laura A., Barnes, R. S. K., Clark, Paul F., Bennett, Wayne A. & Cragg, Simon M., 2021, Distinguishing ten sympatric species of fiddler crab (Decapoda: Ocypodidae) using a suite of phenotypic characteristics, pp. 480-506 in Zootaxa 5026 (4) on page 501, DOI: 10.11646/zootaxa.5026.4.2, http://zenodo.org/record/5300736

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., Published as part of Michie, Laura A., Barnes, R. S. K., Clark, Paul F., Bennett, Wayne A. & Cragg, Simon M., 2021, Distinguishing ten sympatric species of fiddler crab (Decapoda: Ocypodidae) using a suite of phenotypic characteristics, pp. 480-506 in Zootaxa 5026 (4) on page 488, DOI: 10.11646/zootaxa.5026.4.2, http://zenodo.org/record/5300736, {"references":["Naderloo, R., Turkay, M. & Chen, H. - L. (2010) Taxonomic revision of the wide-front fiddler crabs of the Uca lactea group (Crustacea: Decapoda: Brachyura: Ocypodidae) in the Indo-West Pacific. Zootaxa, 2500 (1), 1 - 38. https: // doi. org / 10.11646 / zootaxa. 2500.1.1"]}

Tubuca coarctata (H. Milne Edwards, 1852) (Figure 10a–j) Material examined. 20 ♀, 20 ♂, Kaledupa, Indonesia, 5º 29’ 50’’S, 123º 45’ 20’’E, mud flat in front of mangroves, under houses, coll. L. Michie, 26.08.2014. Diagnosis. Carapace: broader than long, smooth; front narrow; anterolateral angles acute; anterolateral margins practically absent with dorsolateral margins produced almost immediately after anterolateral angle. Major cheliped: hook like projection at distal end of dactyl. Colouration (Figure 10a–d). Adult male. Carapace: varies greatly, mostly black, with either a small white/ yellow square (~ 2 mm) or three blue markings across central carapace, during mating some adult males have largely blue carapace with black markings (often associated with juveniles); some have a half black and half white carapace, anterior ventral surface of carapace and third maxilliped generally black. Major cheliped: dactyl and pollex distally white and proximally orange, extending across manus with ventral half darker, sometimes red/maroon, ventrally manus can be white, carpus usually same colour as adjacent manus, merus, ischium, basis and coxa generally orange or light brown. Minor cheliped & ambulatory legs: tend to be black. Adult female. Carapace: varies greatly, similar to males being largely black with either a small white/yellow square (~ 2 mm) or three blue markings across the central carapace, sometimes blue with black markings or with ventral carapace dark orange; anterior carapace light orange. Ambulatory legs: like those of males. Juvenile male. Carapace: normally blue, with black markings across the anterior and centre. Major cheliped: dactyl and pollex normally white, remainder of cheliped orange. Minor cheliped & ambulatory legs: black, occasionally all blue. Juvenile female. Normally same pattern as juvenile males, some have orange carapace instead of blue. Gonopod morphology (Figure 10e–f). G1 curved in dorso-lateral direction; distal end relatively short and tapering; distal end curved in slightly lateral direction; pore of sperm channel in midline. Gastric mill (Figure 10i, j). Urocardiac ossicles simple, 6 transverse ridges of median teeth, different in shape, first two arched, 1–5 decreasing in size distally, last one broader and longer; stem region has 1 or 0 pairs of cusps. Lateral tooth plate with 19 comb-shaped teeth. Biology. Tubuca coarctata is a medium-size species (largest male CL = 13.3 mm, CB = 21.4 mm, largest female CL = 10.2 mm, CB = 16.8 mm); one of least abundant species on shore, present in mid and high intertidal zones, predominantly associated with shade under buildings or mangrove trees. Distribution. Australia, Indonesia, Philippines, New Guinea, Taiwan. Remarks. Tubuca coarctata can be distinguished from other Tubuca species by the curved tip of the G1 and the hook like projection at the tip of the dactyl. The specimens examined fit the original description but this is the first description of the gastric mill for T. coarctata and the simple morphology distinguishes it from other Ambeua genera and is similar to the other Tubuca species described here., Published as part of Michie, Laura A., Barnes, R. S. K., Clark, Paul F., Bennett, Wayne A. & Cragg, Simon M., 2021, Distinguishing ten sympatric species of fiddler crab (Decapoda: Ocypodidae) using a suite of phenotypic characteristics, pp. 480-506 in Zootaxa 5026 (4) on pages 496-498, DOI: 10.11646/zootaxa.5026.4.2, http://zenodo.org/record/5300736

Gelasimus jocelynae (H.-T. Shih, Naruse and P.K.L. Ng, 2010) (Figure 7a–j) Material examined. 10 ♀, 10 ♂, Kaledupa, Indonesia, 5º 29’ 49’’S, 123º 45’ 21’’E, mud flat southwest of boat jetty, coll. L. Michie, 27.08.2014. 10 ♀, 10 ♂, Kaledupa, Indonesia, 5º 29’ 51’’S, 123º 45’ 20’’E, mud flat in front of mangroves, coll. L. Michie, 27.08.2014. Diagnosis. Carapace: slightly broader than long; smooth; front narrow, practically straight; anterolateral angles acute, slightly produced; anterolateral margins short; dorsolateral margins short or nearly absent. Major cheliped: elongated dactyl and pollex; pollex with distinct wave pattern occurring near middle of the gape, hook like tooth distally. Colouration (Figure 7a–d).Adult male. Carapace: variable, nearly always light/dark brown or grey with varying degrees of markings in colours including blue, aqua, orange and white, anterior ventral surface and third maxillipeds normally light brown or grey. Major cheliped: dactyl generally white extending dorsally to manus, pollex often with white tip, remainder of pollex orange extending to manus, carpus is grey or white dorsally and orange ventrally, remainder of cheliped either white or orange, in young adult males manus or pollex has a small brown mark. Minor cheliped & ambulatory legs: generally brown or grey. Adult female. Similar to males. Chelipeds: often orange. Juvenile male. Carapace: most often light brown. Major cheliped normally white at juvenile stage, often with brown mark, similar to adults. Juvenile female. Normally like juvenile male. Gonopod morphology (Figure 7e–h). G1 curved in dorso-lateral direction; simple flanges; pore of sperm channel small; distal protuberance relatively short, wide, can vary, often reaching beyond base of flange. Gastric mill (Figure 7i, j). Urocardiac ossicles moderately complex, with 4 pairs of ridges on median tooth plate, 1–3 decreasing in size distally, larger gap between third and fourth, fourth large and attached to plate dorsally; stem with setae present on lateral margins of posterior stem region. Lateral tooth plate with 18 comb-shaped. Biology. Gelasimus jocelynae is a relatively small-size species (largest male CL = 10.6 mm, CB = 16.4 mm, largest female CL = 9.4 mm, CB = 14.3 mm); one of most abundant species on shore, present in mid and low intertidal zones. Distribution. Pacific islands west of Fiji, including Japan, Taiwan, the Philippines, Indonesia, Papua New Guinea, and Vanuatu. Remarks. Gelasimus jocelynae is distinguished by the distinct wave pattern occurring near the middle of the pollex, the hook like distal tooth and the colouration, specifically the white dactyl and orange pollex. The specimens examined fit the original description, but this is the first description of the gastric mill for G. jocelynae which is similar to that of G. tetragonon described here and Gelasimus vocans described by Shih (2015)., Published as part of Michie, Laura A., Barnes, R. S. K., Clark, Paul F., Bennett, Wayne A. & Cragg, Simon M., 2021, Distinguishing ten sympatric species of fiddler crab (Decapoda: Ocypodidae) using a suite of phenotypic characteristics, pp. 480-506 in Zootaxa 5026 (4) on pages 491-493, DOI: 10.11646/zootaxa.5026.4.2, http://zenodo.org/record/5300736, {"references":["Shih, H. - T. (2015) Uca (Xeruca), a new subgenus for the Taiwanese fiddler crab Uca formosensis Rathbun, 1921 (Crustacea: Decapoda: Ocypodidae), based on morphological and molecular evidence. Zootaxa, 3974 (2), 151 - 169. https: // doi. org / 10.11646 / zootaxa. 3974.2.1"]}

Austruca mjoebergi (Rathbun, 1924) (Figure 4a–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 margins slightly convergent; anterolateral and dorsolateral margins short or nearly absent. Major cheliped: dactyl and pollex twice as long as manus; pollex almost straight; dactyl slightly wider than fixed finger, with sub-proximal tooth. Colouration (Figure 4a–d). Adult male. Carapace: light brown with yellow/brown mottled pattern, ventral surface of carapace and merus of third maxilliped generally similar to carapace. Major cheliped: dactyl and pollex yellow with white tips, remainder of cheliped yellow. Minor cheliped & ambulatory legs: black or grey with mottled pattern, occasionally grey/white/yellow striped. Adult female. Similar to male. Juvenile male. Carapace: usually light brown with pattern and colour developing with maturity. Major cheliped: normally light brown or yellow. Juvenile female. Similar to male. Gonopod morphology (Figure 4e–h). G1 curved in dorso-lateral direction; border between protuberance and terminal end swollen; protuberance moderately short, sometimes reaching base of termination, longer than broad; distal end has largely protruding dorsal lobe; pore of sperm channel marked by distinct indentation. Gastric mill (Figure 4i–j). Urocardiac ossicles complex, with 2 transverse ridges of median teeth, both large, different in shape with first being strongly arched; second much broader; stem region has 5 pairs of cusps, 1–3 of similar size and shape, 4 and 5 decreasing in size distally. Lateral tooth plate with 17 comb-shaped teeth. Biology. Austruca mjoebergi is a small-size species (largest male CL = 7.3 mm, CB = 13.3 mm, largest female CL = 6.8 mm, CB = 10.8 mm); one of least abundant species on site, present on margin of mangroves in mid intertidal zone. Distribution. Northwest Territory and Western Australia, New Guinea and central Indonesia. Remarks. The specimens examined fit that of Naderloo et al. (2010), differing slightly in the form of the gastric mill with the stem region described here having a higher number of cusps, but the urocardiac ossicles are still complex. The largely protruding dorsal lobe of the G1 and the distinct yellow colour of the major cheliped distinguish A. mjoebergi from the other Ambeua Austruca species., Published as part of Michie, Laura A., Barnes, R. S. K., Clark, Paul F., Bennett, Wayne A. & Cragg, Simon M., 2021, Distinguishing ten sympatric species of fiddler crab (Decapoda: Ocypodidae) using a suite of phenotypic characteristics, pp. 480-506 in Zootaxa 5026 (4) on page 486, DOI: 10.11646/zootaxa.5026.4.2, http://zenodo.org/record/5300736, {"references":["Naderloo, R., Turkay, M. & Chen, H. - L. (2010) Taxonomic revision of the wide-front fiddler crabs of the Uca lactea group (Crustacea: Decapoda: Brachyura: Ocypodidae) in the Indo-West Pacific. Zootaxa, 2500 (1), 1 - 38. https: // doi. org / 10.11646 / zootaxa. 2500.1.1"]}