Tubuca coarctata (H. Milne Edwards, 1852)

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 : 496-498

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.

Figures

FIGURE 10. Tubuca coarctata (H. Milne Edwards, 1852): 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 right G1; e, mesial view; f, lateral view; CLSM images of apical part of G1; g, mesial view; h, lateral view; SEM images of male gastric mill; i, median tooth plate, ventral view; j, left lateral tooth plate, mesial view.