Macrophthalmus depressus, Ruppell, 1830

Bom, Roeland A. & Ebbinge, Maaike, 2022, Simple and complex burrow morphology in two Macrophthalmus species on the intertidal mudflats of Barr Al Hikman, Sultanate of Oman, Journal of Natural History 56 (5 - 8), pp. 475-485 : 479

Macrophthalmus depressus

The casted burrows of M. depressus were complex, with multiple entrances and branches ( Figures 2 and 3 ). In fact, we never managed to make a complete cast of an entire burrow as the tunnels always continued after where the plaster stopped. One burrow appeared to have five entrances and another had two entrances (the 10 burrow entrances into which plaster was poured ultimately proved to belong to five burrows). Branches were observed leading in every direction and tunnels had various slopes and angles. The maximum depth of a cast was 35 cm, at which the water level was reached. In two casted burrows a single crab was found. In the three other burrows the crabs were probably able to escape, as the burrows were more extensive than our casts. The 16 excavated burrows were similarly complex as the casted burrows. In six of the 16 excavated burrows more than one crab per burrow was encountered (up to four crabs per burrow; Figure 4 ). In total 27 crabs were captured, of which we identified seven as males and eight as females. Sex could not be convincingly determined in 12 smaller individuals. There was no relationship between burrow size at entrance and crab size (t = 1.109, P = 0.28, R2 = 0.01; Figure 4 ).

Figures

Figure 2. Cast of a burrow of Macrophthalmus depressus. Note that the two casts were originally connected but broke during excavation.

Figure 3. Drawing of a typical cast of the burrow of the two crabs studied. The ends of the burrow of Macrophthalmus depressus are open as the burrows were more extensive than our casts.

Figure 4. Relationship between crab carapace width and burrow size at entrance for the two studied crab species. The dashed red line gives the significant linear model relating Macrophthalmus sulcatus carapace width to burrow size at entrance. Symbols within the points refer to burrows in which more than one crab was encountered; similar symbols refer to the same burrow.