Minuca mordax (Smith, 1870)

Masunari, Setuko, Martins, Salise Brandt & Anacleto, Andre Fernando Miyadi, 2020, An illustrated key to the fiddler crabs (Crustacea, Decapoda, Ocypodidae) from the Atlantic coast of Brazil, ZooKeys 943, pp. 1-20 : 1

Minuca mordax (Smith, 1870) Figures 4A , 6A, B

Recognition characters.

Carapace pentagonal moderately arched and with naked dorsal surface, without pile (Fig. 6A ). Dorso-lateral margins well marked and strongly convergent posteriorly; major and minor pairs of postero-lateral striae clearly visible (Fig. 6A ). Front triangular and very wide making up between 34% to 38% of the front-orbital breadth. Male major claw with manus covered by tubercles and with strong groove on dorsal surface; fingers thick and slightly flattened; dactyl ca. 1.5 times the manus length; pollex almost straight with tip curved upwards; dactyl strongly arched ending in a curved downward tip; fingers form a wide gap (Fig. 6B ). Ambulatory legs with narrow merus and dorsal margin almost strait; 1st to 3rdambulatory legs with pile limited to dorsal surface of merus (weakly) and carpus (strongly), but all around the manus (strongly) (Fig. 4A ); last pair with scant pile on merus, carpus and manus. Male abdominal segments never fused. Medium-sized crab: males’ CW up to 26.1 mm in a population from mangrove of Itajaí River, southern Brazil ( Scalco et al. 2016).

Biological notes.

Ovigerous females were collected inside burrows that were ornamented with poorly structured chimney at Guaratuba Bay, southern Brazil, during a warm month (November) ( Martins et al. 2016). The duration of the reproductive period of this species, however, is still unknown. The species dispersal is larval retention type: after larval period in the pelagic environment of the bay, megalopae return to terrestrial areas, by colonizing mats of red algae that grow on humid substrates. Early juveniles seek shelter among entangled thalli of these red algae, and after molting they migrate to soft muddy substrate (S.B. Martins, pers. comm.). Adults live on consolidated sandy banks of rivers flowing into Guaratuba Bay, forming large populations ( Masunari 2006).

Remarks.

The most conspicuous morphological character of M. mordax is the presence of piles covering the entire surface (dorsal, lateral and ventral) of the manus of 1st to 3rd ambulatory legs. This feature allows to easily distinguish M. mordax from two other closely related species, M. burgersi and M. rapax . As no piles are present on carapace of these three species, they hardly will be confused with Leptuca thayeri or Minuca vocator . In the field, these species can also be distinguished by its respective habitat: while M. mordax is mostly found in freshwater or oligohaline areas such as river banks and tidal flats near river mouth, M. rapax and M. burgersi are mainly found in mesohaline tidal flats, often in co-occurrence.

Figures

Figure 4. Third ambulatory leg, posterior view. A Minuca mordax with pile on dorsal surface of merus (seta) and carpus and all around surfaces of manus (seta) B Minuca burgersi with pile limited to dorsal surface of carpus and manus (seta).

Figure 6. Minuca mordax. A carapace without pile and with two pairs of postero-lateral striae, dorsal view B male major claw, frontal view.