Panopeus lacustris Desbonne in Desbonne & Schramm, 1867

Jarquin-Gonzalez, Jani, Valdez-Moreno, Martha & Rosas-Luis, Rigoberto, 2023, Taxonomic insights into Panopeus lacustris Desbonne (Crustacea, Decapoda, Brachyura) based on morphological and molecular data, ZooKeys 1179, pp. 107-122 : 107

Panopeus lacustris Desbonne in Desbonne & Schramm, 1867

Figs 2 , 3 , 4 , 5

Material examined.

Mexico • non-ovigerous female, 28.9 mm; Mexico, Quintana Roo, El Uvero ; 18°57.240'N, 87°36.900'W; depth 0.5 m; 28 Jan. 2021; collectors Víctor Conde, Astrid Te leg.; in coralline rocks under Thalassia testudinum ; ECOSUR-C1117 • non-ovigerous female, 9.5 mm; same collection data as for preceding; ECOSUR-C1195 • one male, 19.3 mm; same collection data as for preceding; ECOSUR-C1196 • one male, 12.5 mm; same collection data as for preceding; ECOSUR-C1197 .

Diagnosis

(emended for Williams, 1983). Carapace smooth or with a few setae, with transverse lines of granules, coarse granules on ocular and hepatic regions and along anterolateral margins. With five lateral teeth, the first two coalesced, separated by a shallow rounded notch (variable in depth). The second tooth is broader than the first, but the tips are almost equally prominent (variable in form). Third, fourth and fifth lateral teeth with prominent or semi-prominent acute tips. Third, maxilliped with one red or orange spot on the ventral surface side of the ischium. Cheliped with two distal spines in merus. The palm of chelipeds with a reticulated pattern of small purple granules. The reticulate pattern of color on the outer surface of the palm is continuous or not on its lower half. With random dark spots below the midline of the palm, ventral side of the palm, and ventral side of the cheliped merus. Dactylus of cheliped with a prominent proximal tooth. Pereopods are setose. Female: Abdomen setose, with six pereonites. Male: Abdomen with five pereonites. Gonopod 1 has two distal rows of conic spines that increase in thickness as they approach the anterior part of the outer margin, with six subdistal slender spinules on the inner margin.

Description.

Non-ovigerous female, ECOSUR-C1117, 28.9 mm (Fig. 2A, B ). Carapace reddish-brown with creamy-white areas, smooth, surface finely granulate, hexagonal, convex, feebly areolated, with some lines of granules on hepatic and epigastric regions.

The frontal margin is sinuous and granulose, with a median closed fissure and rounded outer angles. First and second lateral teeth coalescent, separated by a shallow rounded notch. The first tooth is small, triangular, and has a prominent tip. The second tooth is broader than the first, convex, with a semi-prominent acute tip. The third tooth is convex, not outstanding, with semi-prominent acute tip. The fourth tooth is convex and outstanding, with a prominent acute tip. The fifth tooth is smaller than the fourth, outstanding spiniform (Fig. 2C-E ).

Orbits suboval, wide; orbital region granular; dorsal inner orbital angle separated from the front by a shallow notch. Eyestalk stout, covered with fine granules. Antennular fossettes (Fig. 2F ) are subrectangular and flattened; antennules are stout, folding transversely. The basal segment of the antenna is subrectangular; the flagellum is slender, tip reaches an exorbital angle. Epistome broad at base and pointed distally. Posterior margin of endostome with oblique ridges.

First and second maxillipeds with a few monochromatic chromatophores (Fig. 2G, H ). The third maxilliped (Fig. 2I, J ) completely covers the buccal orifice. Ischium subrectangular, granular, with a medial groove on dorsal surface; inner margin crenulated and setose; outer margin with rounded proximal projection; with one proximal orange spot on the ventral surface. Merus subquadrate, granular. Exopod narrow, longer than broad; inner margin with subdistal projection rounded and setose; outer margin with short distal setae.

Abdomen setose, with all pleonites well defined; first, second and third pleonite longer than broad fourth and fifth pleonites similar, broader than long; sixth pleonite is the largest, sinuous. Telson is subtriangular, broad, with rounded angles and a similar length to the sixth pleonite.

Chelipeds are unequal, robust, and finely granulate. Merus is broader than carpus, with two distal spines, no setose, and few dark spots ventrally (Fig. 3A, B ). Carpus without groove parallel to the distal margin; reticulated pattern present only dorsolaterally; with one pointed tooth on the inner side. Palm with subdistal broad and triangular lobe near dactylus articulation; the reticulate pattern of color present dorsolaterally and does not continue on its lower half; with random dark spots below the midline of the palm, also present on its ventral side. The dark color of pollex does not continue on the palm. Major chela (Fig. 3C ), pollex with seven teeth; with cusps raised above a straight line drawn between the angle at the juncture of a finger with anterior margin of palm and tip of the finger; first four teeth very broad; first and second teeth flattened, not separated, with blunt cusp probably due to wear; the third tooth is the largest of all, with a pointed cusp; fourth article broader than following teeth, with blunt cusp; fifth and seventh teeth smaller than sixth tooth, with blunt cusp each one. Dactylus of major chela, with one proximal tooth, prominent, longer than broad, with blunt cusp; with two reduced teeth; with one medial pointed process.

Minor chela (Fig. 3D ) with a few small proximal teeth on the inner margin of the pollex. Pollex and dactylus of both chelipeds with white tips.

Ambulatory legs all setose dorsodistally; with dactylus small, broad, and orange tip. Second, third, and fourth pereopods with merus shorter than carpus; carpus inflated, longer than broad; propodus longer than merus, less inflated than carpus. Fifth pereopod is shorter than all, with merus and carpus of similar width; with propodus as long as merus.

Male, ECOSUR-C1197, 12.5 mm (Fig. 4A-C, E ). The male morphology is like the female, but there are still some differences. The color of the carapace is dark-brown with creamy-white areas.

The frontal margin is rectilinear (Fig. 4D ). With a row of setae on the posterolateral and hind margins. Abdomen with five pereonites (the third, fourth and fifth pereonites fused), with a few small setae.

The third pleonite with similar width but is shorter than the fourth pleonite; the fourth pleonite is shorter than the fifth pleonite; the fifth pleonite is twice as long as broad. Chelipeds (Fig. 4E ), merus with similar length of the carpus; the reticulate pattern does not continue on its lower half, except in the minor chela, which slightly exceeds. Ambulatory legs are less setose than in females. Gonopod 1 (Fig. 5A-D ), long and slender; slightly curving laterally; outer margin with two distal rows of conic spines that increase in thickness as they approach the anterior part of the outer margin; inner margin with six subdistal slender spinules. An accessory process long; dorsally expanded, with numerous ventrolateral spinules; anterior part narrow, ringed. The medial process is slightly sigmoidal, with subdistal spinules on the outer margin and robust proximal setae on the outer margin. Lateral approach bifid, with both teeth well developed. Gonopod 2 (Fig. 5E ) is small, slightly sigmoidal.

Remarks.

Comparing morphological descriptions between specimens of Panopeus lacustris from Mexico, the USA, and the Virgin Islands, these were similar because they have a transverse line of granules on the carapace, the front margin of the carapace is granular and finely divided, the first two anterolateral carapace teeth are coalesced and separated by a round notch, the cheliped has broad proximal teeth on the pollex, and the pereopods are setose. Even so, there are some structural differences between them: P. lacustris from El Uvero, Mexico has a dark-brown or reddish-brown with creamy-white areas color pattern, while P. lacustris from Guadeloupe is dirty purple, and for Florida, USA, and St. Croix, VI the specimens are greyish; in P. lacustris from El Uvero, the carapace has some setae, whereas in P. lacustris from Guadeloupe, Florida, and St. Croix it is generally smooth. Table 2 provides more morphological comparisons.

Molecular analysis

Molecular analysis based on the COI gene for specimens of P. lacustris from the Southern Mexican Caribbean (El Uvero, Quintana Roo), Western Atlantic (Bocas del Toro, Panama), and Central Pacific (Hawaii, USA) shows that they belong to the same taxonomic identity because their intraspecific divergence value was 0.27% (N = 11), which according to Matzen da Silva et al. (2011) and Jarquín-González et al. (2022), remains below the range of intraspecific divergence (3.7-4.9%) reported in decapods. Additionally, P. lacustris showed an interspecific genetic variation of 5.78% with P. herbstii and 7.57% with P. occidentalis , confirming that they are distinct taxonomic entities (Fig. 6 ).

Figures

Figure 2. Panopeus lacustris. ECOSUR-C 1117, non-ovigerous female, 28.9 mm A body, dorsal view B body, ventral view C frontal margin D first two coalescent teeth E lateral teeth of the carapace F frontal view. ECOSUR C 1195, non-ovigerous female, 9.5 mm G maxilliped H maxilliped 2 I maxilliped 3 J spot on isquium of maxilliped 3.

Figure 3. Panopeus lacustris. ECOSUR-C 1117, non-ovigerous female, 28.9 mm A, B spots and spines in merus of chelipeds C major chela D minor chela.

Figure 4. Panopeus lacustris. ECOSUR-C 1197, male, 12.5 mm A body, dorsal view B body, dorsal view C frontal view D frontal margin E first two coalescent teeth F pollex and dactylus of chelipeds.

Figure 5. Panopeus lacustris. ECOSUR-C 1197, male, 12.5 mm A, B gonopods 1 C detail of right gonopod 1 D detail of left gonopod 1 E gonopods 2.

Figure 6. COI identification tree shows the clustering of P. lacustris, P. herbstii and P. occidentalis from the Southern Mexican Caribbean, Western Atlantic and Central Pacific. Numbers on the branches indicate bootstrap support after 500 replications. The numbers after the names are BINs.