Uca uruguayensis (Nobili, 1901)

Armendariz, Laura C., 2005, Redescription of the megalopa of the fiddler crab Uca uruguayensis (Decapoda, Brachyura, Ocypodidae) with special emphasis on its setae, Journal of Natural History 39 (22), pp. 1981-1993 : 1983-1988

Megalopae of Uca uruguayensis

have both cephalothorax and abdomen flattened dorsoventrally ( Figure 1 ). The rostrum is rounded, the cephalothorax is smooth, oval with small simple setae and other sparsely plumose setae longer than the former ones dispersed on the dorsal surface. The carapace has sparsely plumose setae regularly distributed on lateral and posterior margins. The abdomen (as in most brachyurans) comprises six segments and the telson, with small simple setae and some sparsely plumose setae on the dorsal surface. The fifth somite of the abdomen has posterolateral projections. The telson is subquadrate with rounded angles and bears four (rarely five) plumose spines on the posterior margin, and 8– 10 simple setae on its dorsal surface. The cuticle, as in other species of the genus but contrary to that of Ocypode , is not noticeably thick and hard. Sizes of the individuals measured are listed in Table II.

The salinity values were obtained after multiplying the conductivity by 0.9.

Appendages

Antennule ( Figure 2a ). Comprises a basal segment, followed by other three segments, bearing two simple setae in the medial segment and one in the distal segment. Exopodite four-segmented, with 9–11 aesthetascs (three, three, and three to five in each segment, respectively) and two sparsely plumose setae on the outer margin ( Figure 2b ). Endopodite unsegmented with three terminal simple setae and one simple seta subterminally.

Antenna ( Figure 2c ). Peduncle with three segments (basal, medial and distal), bearing one, one, and two simple setae, respectively. Flagellum with seven segments, with two to three short simple setae on the third one, one long sparsely plumose seta on the fourth segment, two long sparsely plumose and one short simple setae on the fifth, two long sparsely plumose setae on the sixth and three to four setae (short simple and long sparsely plumose) on the seventh segment.

Mandible ( Figure 3a ). Molar process with a straight cutting edge, mandibular palp threesegmented, with seven to nine setae on distal segment, two sparsely plumose setae externally and five to seven multidenticulate setae internally ( Figure 3b ).

Maxillule ( Figure 3c ). Endopodite two-segmented, with four setae (simple and sparsely plumose) on distal segment and one sparsely plumose on proximal segment. Basal endite unilobate, with 18–20 setae (10 stout simple setae, surrounded by eight stout cuspidate setae and one sparsely plumose seta). Coxal endite also unilobate, with eight stout multidenticulate setae, and another 4–11 sparsely plumose and simple setae.

Maxilla ( Figure 3e ). Flattened exopodite (scaphognathite) bearing 46–49 plumose fringing setae around outer margin. Endopodite reduced, unsegmented, with one to two plumose setae proximally. Basal endite composed of two lobes, with seven to nine and 9–12 multidenticulate setae, respectively. Coxal endite also bilobate, with two to three and 14– 15 sparsely plumose setae on each lobe, respectively.

First maxilliped ( Figure 3g ). Protopod bilobed, basal endite with 14–16 cuspidate setae and one sparsely plumose seta externally; coxal endite with 10–11 multidenticulate setae. Endopodite three-segmented bearing two simple setae on medial segment and one on distal segment. Exopodite is two-segmented, with three plumose setae on basal segment and five sparsely plumose on distal one. Epipod showing a triangular form, bearing nine long sparsely plumose setae.

Second maxilliped ( Figure 3h ). Protopod unilobate. Endopodite with five segments, showing the following setation from the proximal segment: one, one, one (all of them sparsely plumose setae), five to six setae (sparsely plumose and plumodenticulate) and seven to eight setae (cuspidate, sparsely plumose and plumodenticulate). Exopodite twosegmented, bearing one seta on proximal segment and five sparsely plumose setae on distal one. Epipod bears two sparsely plumose setae terminally.

Third maxilliped ( Figure 3j ). Protopod with 15–21 multidenticulate setae. Endopodite fivesegmented: ischium bearing 11–12 sparsely plumose setae (nine internally and two externally); merus with 10–11 sparsely plumose setae (six internally and four externally); carpus with four to six setae (two short simple setae and the other long plumodenticulate setae); propodus bearing five to eight setae (as the last segment, with two short simple setae and plumodenticulate setae), and dactylus with six to eight plumodenticulate setae. Exopodite two-segmented, bearing one to two simple setae on proximal segment and four to five setae (four sparsely plumose and one simple) on distal segment. Epipod elongate, well developed, with some 17 long setae, very sparsely plumose distally and some 14 sparsely plumose setae proximally. It bears lamellae of a differentiated arthrobranch.

Pereiopods ( Figure 4 ). Chelipeds are equal and well developed, they are large and functional as pincers, and also in crawling. They have a robust chela with the inner margin of the propodus bearing small teeth as shown. When closed, the chelae keep their ends intercrossed. Chelipeds bear simple setae on all of their segments. Pereiopods 2–4 are long and thin, with their ends ‘‘hooked’’, and they also have setae on all of their segments. Pereiopods 3 and 4 bear a cuspidate spine on the propodus. The fifth pereiopod is small, five-segmented and has three long modified hooked serrate setae (‘‘brachyuran feelers’’) on the last segment (dactylus).

Pleopods ( Figure 5 ). Present on abdominal segments 2–6, they are large and well-developed swimming organs. The first four pairs are biramous (bearing exopodite and endopodite), the exopodites are well developed, with flattened lobes, and 15, 16, 15, and 14 plumose setae on each one, respectively. A reduction in size from the first to the fourth pairs of pleopods is noticed. The endopodites are reduced and show three hooked setae on distal end. The fifth pair (uropods) is small, bisegmented and lacking endopodite, with eight plumose setae (a few individuals collected showed seven or nine setae) on exopodite.

Figures

Figure 1a. Dorsal view of the megalopa of Uca uruguayensis. Scale bar: 500 mm.

Figure 2. Uca uruguayensis megalopa: (a) antennule; (b) detail of exopodite showing aesthetascs and sparsely plumose setae; (c) antenna. Scale bar: 300 mm (a, c); 75 mm (b).

Figure 3. Uca uruguayensis megalopa: (a) mandible; (b) detail of palp showing multidenticulate and sparsely plumose setae; (c) maxillule; (d) detail of cuspidate seta; (e) maxilla; (f) detail of marginal setae of scaphognathite; (g) first maxilliped; (h) second maxilliped; (i) detail of plumodenticulate seta; (j) third maxilliped. Scale bar: 300 mm (a, c, e, g, h, j); 75 mm (b, d, f, i).

Figure 4. Uca uruguayensis megalopa: (a) right cheliped; (b) detail of chela teeth; (c) pereiopods 2–4; (d) detail of cuspidate spine of pereiopods 3–4; (e) fifth pereiopod; (f) modified hooked serrate seta of fifth pereiopod. Scale bar: 500 mm (a, c, e); 75 mm (b, d, f).

Figure 5. Uca uruguayensis megalopa: (a) pleopods 1–4; (b) uropods and telson; (c) detail of plumose seta of pleopods; (d) detail of hooked seta of pleopod endopodites; (e) detail of plumose spines of telson. Scale bar: 300 mm (a, b); 75 mm (c, d, e).