Fredius avilai, Martins & Do Nascimento & Dos Santos & Magalhães & Pinheiro, 2021

Martins, Carlos A. M., Do Nascimento, Whandenson M., Dos Santos, Livanio C., Magalhães, Célio & Pinheiro, Allysson P., 2021, A new species of the genus Fredius Pretzmann, 1967 (Decapoda: Brachyura Pseudothelphusidae) from Brazil, with comments on the southerly distribution of the family, Zootaxa 4903 (2), pp. 285-295 : 286-291

publication ID	https://doi.org/ 10.11646/zootaxa.4903.2.8
publication LSID	lsid:zoobank.org:pub:74443D51-8EC4-4B49-9662-B2F81BC187E3
DOI	https://doi.org/10.5281/zenodo.4423106
persistent identifier	https://treatment.plazi.org/id/390E6F4D-2BCF-4107-9F89-282865FB87D5
taxon LSID	lsid:zoobank.org:act:390E6F4D-2BCF-4107-9F89-282865FB87D5
treatment provided by	Plazi
scientific name	Fredius avilai
status	sp. nov.

Treatment

Fredius avilai View in CoL n. sp.

( Figs 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

urn:lsid:zoobank.org:act:390E6F4D-2BCF-4107-9F89-282865FB87D5

Fredius buritizatilis .—Santos et al. 2020: tab. 1,2, fig. 8.

Type material. Holotype: male (cw 31.5mm, cl 21.1mm), MZUSP 41125 View Materials , Brazil, Rondônia, municipality of Chupinguaia, rio Pimenta Bueno (12°33’21”S 60°54’11”W), 06.iii.2014, R. W. Ávila coll. GoogleMaps

Diagnosis. G1 with mesial lobe elongated, convoluted, proximal portion directed laterally, distal portion sharply recurved in abdominal direction; marginal process rounded, not projected over distal opening of spermatic channel, merging with distal portion of abdominal surface after a shallow depression; lateral suture well demarcated along mesoabdominal surface of stem, distal portion directed inwards.

Description. Carapace ( Fig. 1A View FIGURE 1 ) outline ellipsoid, widest medially (cw/cl = 1.49), dorsal surface smooth, convex, regions poorly defined; pair of gastric pits poorly defined, close to each other, on metagastric region. Cervical grooves shallow and wide, nearly straight, distal ends reaching anterolateral margin; gastric grooves indistinct or incomplete. Post-frontal lobes small, slightly prominent; median groove shallow, clearly distinct between postfrontal lobules. Carapace surface between front, postfrontal lobules smooth, gently deflexed. Front with distinct upper border; upper border slightly convex in dorsal view, marked with row of papillae; lower border carinate, barely visible in dorsal view, sinuous in frontal view, with row of very faint papillae. Upper and lower orbital margins marked with row of faint papillae; exorbital angle obtuse. Anterolateral margins of carapace with distinct notch just behind exorbital angle, followed by row of small tuberculiform teeth; posterolateral margins smooth, rounded, marked by faint suture. Epistome ( Fig. 1C View FIGURE 1 ) narrow, with prominent, triangular epistomal tooth; borders carinate. Sub-orbital, sub-hepatic regions of carapace sidewall smooth; pterygostomial region ( Fig. 1C View FIGURE 1 ) covered with moderately wide patch of pubescent around mouthparts; otherwise smooth.

Eyes ( Fig. 1A, C View FIGURE 1 ) well developed, partially filling orbit; corneas large, approximately twice as wide as long in frontal view; ocular peduncle longer than wide, with distinct median constriction. Mxp3 ( Fig. 1B, C View FIGURE 1 ) endopod with ischium subretangular, slightly longer than broad, outer margin slightly convex, smooth; inner margin straight, setate, bearing few squarish, corneous denticles; merus subtrapezoidal, slightly broader than long, outer margin broadly rounded. Mxp3 exopod short, smooth, approximately 0.40 times length of outer margin of ischium. Orifice of the efferent branchial ( Fig. 1C View FIGURE 1 ) channel wide, subquadrate.

Chelipeds robust, moderately heterochelous, right P1 largest ( Fig. 1A, B, D, E View FIGURE 1 ). Meri subtriangular in cross-section; upper crest rounded, with irregular longitudinal row of tubercles; inner lower crest with irregular row of conical, blunt teeth increasing in size distally; outer lower crest marked with regular row of low tubercles. Carpi with row of small tubercles and prominent spine on mesial crest; outer side rounded, smooth. Chelae ( Fig. 1D, E View FIGURE 1 ) with outer, inner surfaces of palm smooth, glabrous; palms little swollen (major P1: palm length/width 1.26); upper bor- der rounded, smooth, lower border with row of faint papillae. Fingers slightly gaping when closed, tips not crossing; cutting edge of both fingers with large conical, sharp teeth, smaller distally; smaller teeth sometimes interspersed with larger ones; dactylus ornamented with longitudinal rows of granules.

Thoracic sternum ( Fig. 1B View FIGURE 1 ) smooth, glabrous. Sternites I, II completely fused, triangular; sternites II, III fused, suture replaced by shallow transversal furrow; sternites III (mxp3), IV (P1) fused, except for small suture at lateral edges of sternum; sternite VI largest. Sternal sulci s4/5, s5/6 distinct, faint in middle, deeper as approaching midline of thoracic sternum, interrupted, ending just before reaching midline; s6/7, s7/8 distinct, deep, complete, reaching midline. Midline of thoracic sternum marked by deep groove in sternites VII-VIII. Sternoabdominal cavity densely pilose, especially in sternites V-VI. Midline of thoracic sternum marked by deep groove at junction of sternites VII, VIII, indistinct in sternites V, VI. Sternoabdominal cavity moderately deep, densely pilose, especially in sternites V, VI; tubercles of sternoabdominal lock placed anteriorly on sternite V near sulcus with sternite IV. Orifice of the afferent branchial channel slightly pubescent.

All six abdominal somites free. Abdomen+telson arrangement subtriangular ( Fig. 1B View FIGURE 1 ). Telson with lateral margins slightly concave, tip rounded.

G1 ( Figs. 2 View FIGURE 2 , 3 View FIGURE 3 ) robust, nearly straight in mesoabdominal view, wider at base, narrower at approximately 2/3 of its length, apex highly ornamented; subapical bulge well developed around lateral and sternal surfaces ( Fig. 3 View FIGURE 3 A–F). In mesoabdominal view, inner margin of proximal and median portion of stem nearly straight, outer margin gently sinuous, both margins bearing scattered small setae ( Fig. 3A View FIGURE 3 ). Marginal suture situated on mesial side, mostly straight, slightly arched at approximately distal fourth of its length, bearing dense patch of short setae along proximal portion ( Fig. 3A, B, F, G View FIGURE 3 ). Lateral suture well demarcated along mesoabdominal surface of stem, distal portion directed inwards, vanishing very close to marginal process, distinctly crested in relation to marginal suture ( Figs. 3A View FIGURE 3 ). Marginal process (= marginal lobe, according to Magalh„es & Rodríguez 2002; Magalh„es 2009; Magalh„es et al. 2014) rounded in mesoabdominal view, not projected over distal opening of spermatic channel, merging with distal portion of abdominal surface after a shallow depression ( Fig. 3A, B, D, G View FIGURE 3 ). Mesial lobe strongly developed, narrow, sinuous, convoluted, proximal portion directed laterally, distal portion sharply recurved in abdominal direction ( Fig. 3 View FIGURE 3 A–F). Cephalic spine strong, subtriangular, with acuminate tip pointing in abdominal direction ( Fig. 3 View FIGURE 3 A–D, F, G). Cephalic lobe distally rounded, somewhat subtriangular in mesoabdominal view, with irregular rows of spinules along sternal margin; mesosternal surface smooth, clearly concave ( Fig. 3 View FIGURE 3 A–G). Auxiliar lobe shorter than cephalic lobe, proximally inflated, indistinctly merging with cephalic lobe ( Fig. 3 View FIGURE 3 B–D); lateral channel absent. Apex distally compressed in lateral-mesial direction; proximal portion remarkably inflated on mesial, mesoabdominal surfaces, bearing large patch of strong, corneous spines across mesosternal, mesial, abdominal surfaces ( Figs. 3 View FIGURE 3 A–C, E–G); small subapical patch of spinules situated on proximal portion of sternal surface, adjacent to basal portion of field of apical spines ( Fig. 3 View FIGURE 3 D–F). Field of apical spines well developed as longitudinally elongated, dense patch of strong spines of varied sizes along concave lateral surface, enclosed by sternal and abdominal margins of apex ( Fig. 3 View FIGURE 3 C–E). Opening of spermatic channel located subdistally near base of apical field of spines, covered by mesial lobe.

G2 slightly smaller than G1, somewhat sinuous; flagellum slender, and gradually tapering in distal direction, with tiny spinules along abdominal surface.

Type locality and distribution. Brazil, state of Rondônia, outskirts of the municipality of Chupinguaia (12°33’21”S 60°54’11”W). The species is currently only known from the type locality GoogleMaps .

Etymology. This new species is named after the herpetologist Robson W. Ávila, who collected and kindly made the specimen available for our study.

Ecological notes. There is no information available on the habitat of this new species.

Zoogeography. Given that only a single specimen of Fredius avilai is available, a clear picture of the new species’ range of distribution is not yet possible. The municipality of Chupinguaia is drained by a few streams that empty into the rio Anari, a right bank affluent of rio Pimenta Bueno, which is a tributary of rio Machado (or rio Ji- Paraná) that flows into the rio Madeira (IBGE 2011), the largest sub-basin of the Amazon River basin ( Goulding et al. 2003). Taking into account that pseudothelphusid species usually have narrow distributions and that F. avilai n. sp. occurs in the same river system of F. buritizatilis , i.e., the rio Machado watershed, one can expect that the former species could be more restricted to the upper reaches of the rio Pimenta Pueno watershed whereas F. buritizatilis seems to be distributed in the middle course of the rio Machado (Magalh„es et al. 2014). Vertical distribution could also be a factor separating both species: F. avilai n. sp. would occur at slightly higher altitudes than F. buritizatilis , as Chupinguaia is situated at an elevation between 350 and 450 m a.s.l. ( Rempel & Silva 2019) and Ji-Paraná, the type locality of F. buritizatilis , is between 100 and 200 m a.s.l. (IBGE 2011). However, more accurate estimates of the distribution of both species can only be made after carrying out biological surveys across the rio Machado watershed.

In a revision of the Peruvian pseudothelphusids, Rodríguez & Suárez (2004) recorded Hypolobocera gracilignatha (Pretzmann, 1972) from río Camisea, province La Convención, department of Cusco, Peru (11°51’28”S), and commented that the water divides of the río Ucayali forms the southern Amazonian limit for the pseudothelphusids. The occurrence of F. avilai n. sp. in Chupinguaia (12°33’S) is a little further south than the aforecited record of H. gracilignatha as well as that of F. buritizatilis from Ji-Paraná at 10°51’S (Magalh„es et al. 2014), thus establishing the current meridional limit of the distribution for the genus as well as for the family in the Amazon basin ( Tab. 1 View TABLE 1 ). This limit is very similar to the southernmost record so far known of a pseudothelphusid crab given by Pretzmann (1983) for Hypolobocera chilensis (H. Milne Edwards & Lucas, 1842) from the río San Juan, at approximately 13°27’S, in the department of Ica, Pacific slope of Peru.

Rodríguez & Suárez (2004) attributed the absence of Pseudothelphusidae in latitudes higher than 13°S along the Pacific coast of Peru to the climatic conditions, as this is an arid or semiarid area. This is not the case in the Amazon basin and yet the latitudinal limit seems to remain valid as no records of pseudothelphusid species are currently known south of this 12°/ 13°S range ( Tab. 1 View TABLE 1 , Fig. 4 View FIGURE 4 ). Pseudothelphusids are a montane group mainly, with only a few species inhabiting areas lower than 300 m a.s.l. ( Rodríguez 1981; Magalh„es et al. 2016). In the southern portion of the Amazon basin they are mostly found in the piedmont area of the Andean effluents in Peru ( Rodríguez & Suárez 2004) and in the tributaries that originate in the Brazilian Shield; the very few species recorded from lowlands areas have semiterrestrial habits and live in shaded forest streams draining ‘terra firme’ forest, which is never inundated by the periodical floods of the main Amazonian rivers (Magalh„es 1986; 2009; Magalh„es et al. 2005; 2016). Pseudothelphusid species are found in all the southern sub-basins of the Amazon River from the rio Madeira to the mouth. Except for those from the rio Madeira sub-basin, the species occurring in the Tapajós, Xingu, and Tocantins sub-basins are found in their lower portion, usually along the rocky areas that mark the northern boundaries of the Brazilian Shield’s outcrops ( Fig. 4 View FIGURE 4 ). The middle and upper reaches of these sub-basins have not yet been properly surveyed for freshwater crabs and, if that is eventually accomplished, range extensions of those species, or even the discovery of new ones, are likely and the southern boundaries for the distribution of the pseudothelphusids could be extended up to water divides between the Amazon and the Paraguay and upper Paraná River basins between 14° and 15°S. A possible restriction for their occurrence up to this latitude may be the temperature, which can drop to a range of 14̅18°C during the coldest months (INPE 2020).

Remarks. Fredius avilai n. sp. is herein assigned to this genus because its G1 shows a well-developed subapical bulge around lateral and sternal surfaces, a laterally directed ear-shaped field of apical spines, and a simple marginal process ( Figs. 2 View FIGURE 2 , 3 View FIGURE 3 ), a set of characters commonly found in the species of Fredius (see Rodriguez 1982; Rodríguez & Pereira 1992; Rodríguez & Campos 1998).

With respect to G1 morphology, F. avilai n. sp. has the closest resemblance to F. buritizatilis , particularly with regard to the well-developed, narrow mesial lobe; the strong, subtriangular, acuminate cephalic spine; and the apex with the proximal portion distinctly inflated and covered by a large patch of strong, corneous spines across its mesosternal, mesial, abdominal surfaces. However, the apex of the G1 has a more pronounced torsion towards the abdominal side in F. avilai n. sp. ( Figs. 2C View FIGURE 2 , 3A View FIGURE 3 ) than that exhibited by the G1 of F. buritizatilis (see Magalh„es et al. 2014: 106, fig. 1C), which results in some morphological differences that can easily distinguish both species, as follows: (a) in mesoabdominal view, the apex of the G1 looks distally narrower, subtriangular, and compressed in the sternal-abdominal direction in F. avilai n. sp. ( Figs. 2C View FIGURE 2 , 3A View FIGURE 3 ) (versus enlarged, with distal margin broadly rounded in F. buritizatilis , cf. Magalh„es et al. 2014: 106, fig. 1C); (b) the mesial lobe is shorter, with its distal portion truncated and strongly recurved in abdominal direction in F. avilai n. sp. ( Figs. 2A, C View FIGURE 2 , 3 View FIGURE 3 A–E) (versus mesial lobe longer and distal portion gradually tapering and curved upwards in lateral direction in F. buritizatilis , cf. Magalh„es et al. 2014: 106, fig. 1C̅F); (c) cephalic spine points in abdominal direction in F. avilai n. sp. ( Figs. 2C View FIGURE 2 , 3A View FIGURE 3 ̅C) (versus point- ing in mesoabdominal direction in F. buritizatilis , cf. Magalh„es et al. 2014: 106, fig. 1C, D); (d) subapical patch of spinules longitudinally enlarged and subtriangular in sternal view in F. avilai n. sp. ( Figs. 2A View FIGURE 2 , 3E View FIGURE 3 ) (versus short, rounded lobe in F. buritizatilis , cf. Magalh„es et al. 2014: 106, fig. 1F). Moreover, in F. avilai n. sp. the distal fourth of the marginal suture length is slightly arched, the marginal process is narrow and rounded, and the distal portion of the lateral suture is directed inwards ( Fig. 3A View FIGURE 3 ) whereas in F. buritizatilis the marginal suture is straight, the marginal process is large and straight, and the distal portion of the lateral suture is directed outwards (cf. Magalh„es et al. 2014: 106, fig. 1C). The close relationship between these species is also corroborated in the genetic distance analyses based on the mitochondrial loci 16S presented by Santos et al. (2020) using some species of Fredius , in which they clustered together forming a sister species clade.

The affinities of F. avilai n. sp. with the other species of Fredius , even those that have relatively closer geographicaphic distribution ( F. denticulatus , F. reflexifrons , and F. ykaa ), are not so evident after taking into account their gonopodal morphology. These affinities have already been discussed by Magalh„es et al. (2014) for F. buritizatilis and, given the similarities between the G1s of these two species, they can apply to F. avilai n. sp. as well. The very close affinities between these two species, suggested especially by the inflated apex and the long and narrow mesial lobe, their contiguous distribution close to the southern boundaries of the Amazon basin, and the relative differences in the gonopodal morphology in relation to the other species of Fredius may indicate that the relationships within the genus require more detailed study.