Austruca mjoebergi (Rathbun, 1924)

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, Zootaxa 5026 (4), pp. 480-506 : 486

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.

Figures

FIGURE 4. Austruca mjoebergi (Rathbun, 1924): a–d Sulawesi Tenggara, Indonesia. Adult male colouration; a, large chela; b, carapace dorsal view. Adult female colouration; c, frontal view; d, carapace dorsal view. Photos credit L. Michie. Line drawing of left G1; e, lateral view; f, mesial view; CLSM images of apical part of G1; g, lateral view; h, mesial view; SEM images of male gastric mill; i, median tooth plate, ventral view; j, left lateral tooth plate, mesial view.