Chaceus guajiraensis, Campos & Puerta, 2023

Campos, Martha R. & Puerta, Dario A., 2023, A new species of freshwater crab of the genus Chaceus Pretzmann, 1965 (Brachyura: Decapoda: Pseudothelphusidae) from La Guajira, including distribution and a key to the species of the genus, Zootaxa 5306 (4), pp. 463-472 : 464-468

Chaceus guajiraensis , new species

( Figs. 1–3 )

Material examined. Holotype. Male (cl 15.4 mm, cw 26.1 mm), ICN-CR 3576 Colombia, La Guajira Department, Municipio Fonseca, corregimiento Conejo , vereda Las Colonias , Regional Natural Park Serranía de Perijá , Los Saltos Creek , elevation 980 m, 10°43’25.3”N, 72°43’51.7”W, 3 Dec 2022, leg. Darío A. Puerta. Paratypes. 2 males (cl 14.3 mm, 16.2 mm, cw 23.9 mm, 27.4 mm) , 2 juveniles, ICN-CR 3577, same locality data as for holotype .

Additional material examined: Colombia, La Guajira Department, Municipio Fonseca, corregimiento Conejo, vereda Las Colonias , Regional Natural Park Serranía de Perijá , Los Saltos Creek , elevation 1320 m, 10°43’11.9”N, 72°43’42.8”W, 14 Feb 2023, leg. Darío A. Puerta, 2 males (cl 16.4 mm, 16.6 mm, cw 28.1mm, 28.4 mm), 2 females (cl 16.6 mm, 17.2 mm, cw 28.6 mm, 29.0 mm), ICN-CR 3578 .

Diagnosis. First male gonopod with lateral process lanceolate, borders thickened, outer margin festooned, caudal surface rough with a conspicuous ridge on lateral side, concave internal, failing to reach apex of gonopod; apex with mesial process rounded basally, cylindrical, rounded distally, directed cephalically; marginal process narrow, elongated, half turn twisted in cephalad direction, with acute ending, and juxtaposed to mesial process on caudal surface; apex semicircular distally. Third maxilliped with exopod 0.60–0.62 times length of ischium; orifice of efferent branchial channel ovate and completely closed by spine of jugal angle and extensions of lateral lobe of epistome.

Description of holotype. Carapace ( Fig. 1A ) with straight, narrow, shallow cervical grooves, ending near lateral margin; antero-lateral margins with shallow depression behind outer orbital angle, devoid of papillae before cervical grooves; lateral margins with approximately 15 tubercles, diminishing in size posteriorly; postfrontal lobes low, oval; median groove shallow, narrow; front lacking distinct upper border, frontal area regularly sloping downwards, bilobed in dorsal view, lower margin sinuous in frontal view, visible in dorsal view, conspicuously thickened; lower orbital margins each fringed with tubercles ( Fig. 2B ); epistome narrow, lower margin moderately arched, epistomial tooth inconspicuous, rounded distally; buccal frame sub-square; pterygostomial region pubescent, devoid of papillae; thoracic sternum ovate, bent anteriorly. Third maxilliped with external margin of merus nearly straight, exopod 0.60 times length of ischium ( Fig. 1E ). Orifice of efferent branchial channel ovate, completely closed by spine of jugal angle and extensions of lateral lobe of epistome ( Fig.1B, C ).

First pereopods heterochelous ( Fig. 1A ); right cheliped larger than left, merus with 3 crests as follows: upper crest with rows of tubercles of different sizes, internal lower crest with 2 tight rows of large tubercles, diminishing in size proximally, external lower crest with row of papillae; carpus with blunt subdistal spine, followed by 4 rounded tubercles; palms of both chelipeds smooth, palm of larger (right) cheliped strongly swollen, fingers 1.3 length of palm, gaping when closed, tips crossing ( Fig. 1A, D ); palm of smaller cheliped moderately swollen, fingers 1.2 length of palm, not gaping when closed, tips crossing. Walking legs (second to fifth pereopods) slender ( Fig. 1A ), dactyli each about 1.2 times as long as propodi, with 5 longitudinal rows of large spines diminishing in size proximally, arrangement of spines on dactylus of left second pereopod as follows: antero-lateral, antero-ventral rows each with 5 spines, external row with 5 spines, 2 proximal papillae, posteroventral, posterolateral rows each with 4 spines.

Episternites sub-triangular, partially fused with sternites, suture lines well defined, extended to mesial region; sterno-abdominal cavity concave, midline of sternum short, deep, restricted to sternite VIII, sternites V, VI with a shallow concavity that receive distal processes of G1; abdomen subtriangular, margin with fine pubescence, somites well-differentiated, suture lines nearly straight, first abdominal segment narrow, increasing in size towards 6; telson subtriangular, margin smooth, pubescent; dorsal surface of carapace smooth, covered by small papillae, regions not well demarcated.

G 1 in caudal view, recurved in caudocephalic direction, lateral side expanded with rounded protuberance in the mid-basal portion. Lateral process lanceolate, concave internally, borders thickened, outer margin festooned, caudal surface rough with conspicuous ridge on lateral side, directed distally in caudal view and failing to reach apex of gonopod. Mesial process rounded basally, cylindrical, rounded distally, directed cephalically. Marginal process narrow, elongated, half turn twisted in cephalad direction with acute ending ( Fig. 2A–D ). Apex consists of mesial cylindrical process and narrow, elongated marginal process. Mesial and marginal processes not surrounded by lateral process in distal view; distal orifice of spermatic channel surrounded by few minute spines ( Fig. 2E ); mid-basal portion with distinct lateral protuberance bearing rows of long plumose setae; mesial side with spinules. Marginal suture situated along caudal surface, slightly sinuous, with conspicuous long setae along proximal portion ( Fig. 2A ). Lateral suture incomplete, marked by distinct sulcus on proximal half of caudal side extending as a low ridge along lateral process ( Fig. 2A ).

Colouration. The freshly-alcohol preserved holotype is beige (near Tawny Olive, 223D) with brown triangular design anteriorly and circular posteriorly (near Verona Brown, 223B) on the dorsal surface of the carapace. The walking legs are brown dorsally and ventrally (near Mars Brown, 223A). The chelae are beige dorsally and ventrally (near Tawny Olive, 223D). The ventral surface of the carapace is light brown (near Sayal Brown, 223C).

Habitat. The specimens were collected by hand under the rocks and leaf litter in Los Saltos Creek. The stream was surrounded by a gallery forest and the water was characterized as crystal clear with sandy-clay soil and limestone substrate. The biome is a Tropical dry forest with a transition to the Andean Forest.

Etymology. The species is named after La Guajira Department where the type locality of the new species was found.

Remarks. Chaceus guajiraensis n. sp. shows similarity in the shape of the G1 to Chaceus turikensis Rodríguez & Herrera, 1994 (see Rodríguez & Herrera 1994: figs. 2A–E). The main distinguishing features between the two species for their G1 are (1) in C. guajiraensis n. sp. the lateral process is lanceolate and concave internally, the borders are thickened, and the outer margin is festooned, the caudal surface is rough with a conspicuous ridge on the lateral side, directed distally in caudal view, not reaching the apex of gonopod ( Fig. 2A–E ); C. turikensis has a well-developed lateral process, foliose, implanted transversely to the main axis of the appendage in caudal view with a conspicuous row of stout spines on the lateral side, reaching the apex of the gonopod ( Rodríguez & Herrera 1994: fig. 2A, C); (2) the mesial process is cylindrical in C. guajiraensis n. sp. ( Fig. 3A–E ), whereas it is ellipsoidal in C. turikensis ( Rodríguez & Herrera 1994, fig. 2A, C); (3) the marginal process is narrow and elongated in C. guajiraensis n. sp. ( Fig. 3A–E ), whereas it is triangular in C. turikensis ( Rodríguez & Herrera 1994: fig. 2A, C). The two species also differed in the length of the exopod of the third maxilliped, which is 0.60 to 0.62 in C. guajiraensis n. sp. ( Fig. 2E ) and 0.77 in C. turikensis ( Rodríguez & Herrera 1994: fig. 2D); in C. guajiraensis n. sp. ( Fig. 1C ) the orifice of the efferent branchial channel is completely closed by the spine of jugal angle and the extensions of the lateral lobe of the epistome; in C. turikensis ( Rodríguez & Herrera 1994: fig. 2E) it is not completely closed. Until now C haceus guajiraensis n. sp. was found in epigean environments, while C. turikensis specimens were collected most of the time in caves and in the Apón River in epigean environments.

Rodriìguez (1982) theorized about the possible derivation of the genus, Hypolobocera Ortmann, 1897 , from an ancestral Chaceus , based on the homology of the finger-like mesial processes in Chaceus and the triangular caudal processes with the two papillae found near the spermatic channel in Hypolobocera . The morphology of the first male gonopod in Chaceus davidi supports this theory since the mesial and the caudal processes are surrounded by a ridge that resembles the apex shape in the species of Hypolobocera (Rodriìguez & Campos 1989) . In addition, a recent robust molecular phylogeny reconstructed by Álvarez et al. (2021) corroborates this morphological hypothesis and the close relationship with genera Strengeriana Pretzmann, 1971 , Neostrengeria Pretzmann, 1965 , and Moritschus Pretzmann, 1965 .

Figures

FIGURE 1. Chaceus guajiraensis n. sp., male holotype (cl 15.4 mm, cw 26.1 mm), ICN-CR 3576. A.,Habitus, dorsal view; B, Frontal view of carapace; C, Opening of left efferent branchial channel, external view; D, Chela of large cheliped, external view; E. Left third maxilliped, external view.

FIGURE 2. Chaceus guajiraensis n. sp., male holotype, ICN-CR 3576, first male gonopod. A,Left first gonopod, caudal view; B, Same, lateral view;C, Same, cephalic view; D, Same, mesial view; E, Apex distal view: 1. lateral process; 2. mesial process; 3. marginal process; 4. spermatic channel.

FIGURE 3. Chaceus guajiraensis n. sp., male holotype, ICN-CR 3576.