Dilocarcinus montinavis, Felix Caetano França & Magalhães & Mantelatto, 2024

Felix Caetano França, Nielson, Magalhães, Célio & Mantelatto, Fernando Luis, 2024, Integrative approach revealing a species complex in the Neotropical freshwater crab Dilocarcinus septemdentatus (Herbst, 1783) (Decapoda: Trichodactylidae) with a description of a new species, Arthropod Systematics & amp; Phylogeny 82, pp. 385-405 : 385-405

3.3. 3. Dilocarcinus montinavis sp. n.

Figures 1 C , 2 (L 3), 7

Dilocarcinus septemdentatus — Magalhães and Türkay 2008: 187 [part, only USU 510, 514, INPA 584].

Diagnosis.

G 1 with distal portion distinctly sinuous, strongly curved laterally; subdistal lobe (“ sl ” in Figs 1 , 7 ) well developed, rounded, bearing dense field of short spines; apex (form a in Figs 1 , 7 ) directed apically, very short, less than 1 / 3 length of subdistal lobe.

Description of the holotype.

Carapace (Fig. 7 A ) smooth, distinctly convex longitudinally, slightly curved transversally; post-frontal lobes as very low protuberances, barely distinguishable; carapacial regions ill discernible; H-shaped central groove (delimited by the posterior and lateral borders of the gastric and lateral borders of the cardiac regions) very shallow; meso, urogastric and branchial regions not elevated compared to other regions; post-gastric pits present, very faint. Frontal margin (Fig. 7 A, C, D ) smooth, unarmed, distinctly bilobed, slightly directed downwards, fringed by minute papillae only seen under magnification. Exorbital tooth with sharp tooth; anterolateral borders bearing 6 regularly spaced acute teeth, posterolateral borders unarmed, marked by conspicuous ridge. Suborbital borders (Fig. 7 C, D ) with 8 slender spines increasing size towards inner corner, one at inner corner distinctly curved, largest and strongest. Eyes (Fig. 7 C ) well developed. Anterolateral corner of the buccal cavity (Fig. 7 C, D ) bearing 4 strong sharp spines. Suborbital region (Fig. 7 C, D ) somewhat pilose, pilosity denser towards inner side. Epistome (Fig. 7 C ) barely visible in dorsal view, its median portion smooth, glabrous; opening of efferent channels wide, upper arch distinctly curved, mid-gutter with 2 distinct points separated by narrow concavity. Grooves dividing subhepatic and pterygostomial regions (Fig. 7 D ) somewhat deep, distinctly pilose. Pterygostomial regions with scattered hairs, smooth and glabrous towards buccal frame.

Third maxilliped (Fig. 7 D ) with subtrapezoidal merus, its outer margin slightly convex, about 2.3 × longer than inner one, bearing distinct blunt tooth-like projection at distal corner; ischium outer margin slightly concave. Exopodite about 0.8 times as long as endopodite, bearing well-developed flagellum recurved inwards and downwards.

Chelipeds (Fig. 7 A, B ) slender, slightly heterochelous, right chela a little stronger than left one. Merus outer border with subdistal acute spine, inner corner of distal lower border blunt, outer corner of distal lower border with small spine; distal upper border distinctly arched, with row of minute hairs. Carpus upper border with strong acute spine, outer surface smooth, glabrous. Palm smooth, mostly glabrous, with minute hairs scattered along inner, outer surfaces, with small distal, blunt spine on upper border; lower border rounded, smooth. Fingers slender, no distinct gap between them, bearing triangular blunt teeth usually slightly larger in middle section of cutting edge; tips not crossing. P 2 –4 (Fig. 7 A, B ) smooth, lower margin of dactylus and half distal portion of propodus with longitudinal row of hairs; P 5 lower margin of both dactylus and propodus bering longitudinal row of hairs [P 3 left detached from body of holotype].

Median line of sternum as deep sulcus extending from somites V – VIII, interrupted by transversal link at somites VI / VII; furrow corresponding to endosternite IV / V reaching midline, following ones ending about halfway between beginning of sternopleonal cavity and midline.

Pleon (Fig. 7 B ) broader proximally at somites III, IV; somites III – VI fused; lateral borders somewhat concave; lateral borders of somite VI roughly continuous with those of telson. Telson (Fig. 7 B ) about 2.3 × broader than long; lateral borders bearing slight concavity subterminally; tip rounded.

G 1 (Figs 1 C , 7 E, F ) slender, straight for about 4 / 5 of its length; broader proximally, with several short, long setae along proximal portion of mesial, lateral surfaces; irregular row of short setae extending distally along median portion of lateral border. Lateral border slightly sinuous proximal- and medially, with strong concavity subdistally and well-developed, rounded subdistal lobe. Distal portion narrower, distinctly sinuous, strongly curved laterally (slightly curved in subadult specimen). Marginal suture (“ ms ” in Fig. 7 ) running along mesial surface, twisted towards lateral side very close to apex (“ a ” in Figs 1 , 7 ); its proximal portion with narrow, rounded protrusion bearing few long setae. Field of short spines continuous, located subterminally on lateroventral side, denser along subdistal lobe (“ sl ” in Figs 1 , 7 ), extending distally to dorsal surface. Subapical bristles, when present, in small number. Apex flat, narrow, very short, less than 1 / 3 length of subdistal lobe; distal aperture very narrow, slit-like, directed apically.

G 2 (Fig. 7 G ) as very slender flagellum, slightly sinuous, just 1.1 × longer than G 1, with slight median constriction; tip flat, rounded.

Type material.

Holotype: 1 ♂ (cw 39.5, cl 32.7), MZUSP 17440 , Brazil, Amapá, Serra do Navio region, rio Amapari, município de Porto Grande, vila de Cupixi [≈ 00 ° 38 ′ N 51 ° 45 ′ W], comunidade do Vila Nova , 5. v. 1994, M. D. S. Tavares coll. (Projeto Diversitas Neotropica n ° 335) . — Paratypes: 1 ♂ (cw 36.6, cl 31.2) 2 ♀♀ (cw 35.1, cl 30.4; 21.0: 18.8), MZUSP 42728 , same data as holotype • 1 ♂ (cw 38.9, cl 30.7), INPA 584 , same data as holotype • 1 ♂ (cw 35.5, cl 29.5), MZUSP 44033 , Brazil, Amapá, Serra do Navio region, rio Amapari , 6. v. 1994, M. D. S. Tavares coll. (Projeto Diversitas Neotropica n ° 405) .

Additional material examined.

1 ♂ 1 ♀, MPEG 1045, Brazil, Amapá, Floresta Nacional ( FLONA) do Amapá [≈ 00 ° 55 ′ N 51 ° 35 ′ W], 27. x. 2009, C. R. Santos and J. E. M. Wanzeler.

Type locality.

Serra do Navio region, rio Amapari, Cupixi , state of Amapá, Brazil.

Etymology.

The specific epithet refers to the region where the type locality of the species is situated, Serra do Navio (Serra = mountain range; Navio = ship). It is composed by the root (mont) of the Latin word montes (nominative plural, meaning “ mountains ”), the connecting vowel i, and the word navis (genitive singular, meaning “ of the ship ”).

Distribution.

The currently known distribution is limited to the state of Amapá, rio Araguari basin, Brazil (Fig. 6 A ).

Remarks.

Magalhães and Türkay (2008) considered that the peculiar morphology of the distal portion of the gonopod exhibited by the few male specimens from Amapá examined in their study would be within the variation range they observed in the G 1 of D. septemdentatus (C. M., pers. observation). This characteristic was also verified in a subadult male from the FLONA of Amapá ( MPEG 1054), although the lateral curvature of the G 1 distal portion is much less pronounced than that observed in fully adult specimens. This peculiar morphology of the distal portion of the G 1 of these specimens and the results of the molecular analyzes (Fig. 2 ), which showed a significant genetic divergence (Table 3), support the decision of considering them a new species for the genus Dilocarcinus . The geographical distribution of this new species, based on currently available data, seems to be restricted to the state of Amapá, Brazil.

The type series of the present species was listed by Magalhães and Türkay (2008: 187 – as D. septemdentatus ) as deposited in the then carcinological collection of Universidade Santa Úrsula (Rio de Janeiro, Brazil). This collection was later transferred to MZUSP and the lots were catalogued as follows: USU 514 (2 ♂ 2 ♀♀) = MZUSP 17440 (1 ♂) and MZUSP 42728 (1 ♂ 2 ♀♀); USU 510 (1 ♂) = MZUSP 44033.

Although Dilocarcinus montinavis sp. n. (Lineage 3) was retrieved as a sister species of D. spinifer (Lineage 2) in the concatenated tree using ML and IB analyzes (Fig. 2 ), morphologically it shows a closer resemblance with D. septemdentatus , as indicated by the morphology of their G 1 distal portion (characterized by the strong curvature towards the lateral side) and that of the frontal margin (clearly bilobed versus near straight in D. spinifer ).

The very short apex of the G 1 of Dilocarcinus montinavis sp. n. is also found in the G 1 of Dilocarcinus truncatus Rodríguez, 1992 . Both species can be morphologically distinguished from each other by the orientation of the G 1 distal portion, which is sinuous and distinctly curved laterally in the former (Fig. 7 E, F ) and nearly straight in the latter (see Rodríguez 1992: 112, fig. 39). Dilocarcinus truncatus was based on a single male specimen from the Beni River (province of Beni, Bolivia). Unfortunately, without the inclusion of molecular tools, the phylogenetic affinities between this species and those studied herein could not be properly evaluated.

Figures

Figure 1. Computerized nano-tomography of the distal portion of the male right first gonopod of Dilocarcinus septemdentatus, INPA 1470 (A), D. spinifer, MPEG 697 (B), and D. montinavis sp. n., paratype, INPA 584 (C), photographed in ventromesial view. Outline of the frontal margin of D. septemdentatus (D) and D. spinifer (E). — Abbreviations: a = apex; sl = subdistal lobe. Scale bars: 1 mm (A – C), 5 mm (D, E).

Figure 2. Phylogram generated by the Bayesian Inference method, based on concatenated alignments of the COI and 16 S genes of specimens belonging to the Dilocarcinus septemdentatus sensu Magalhães and Türkay (2008) species complex. The values in the branches correspond to posterior probability (left) and 1000 bootstrap replicates (right). We considered the recovered branches, in both approaches (ML and IB) and with high support value (≥ 95 %), showing the recovered lineages. * = bootstrap values < 95 %. L 1, L 2, and L 3 = strains 1, 2, and 3, respectively.

Figure 6. Map of the geographic distribution of Dilocarcinus septemdentatus and D. montinavis sp. n. (A) and D. spinifer (B).

Figure 7. Dilocarcinus montinavis sp. n., holotype male (cw 39.5, cl 32.7), MZUSP 17440. Habitus, dorsal view (A), ventral view (B), frontal view (C), buccal frame and pterygostomial region (D); left G 1, ventromesial view (E); left G 1, detail of distal portion, ventrodorsal view (F); left G 2, ventrolateral view. — Abbreviations: a = apex; ms = marginal suture, sl = subdistal lobe. Scale bars = 1 mm. Photo credits: J. Colavite, S. Bueno.