Louisea cataracta, Mvogo Ndongo & Rintelen & Clark & Cumberlidge, 2025

Mvogo Ndongo, Pierre A., Rintelen, Thomas Von, Clark, Paul F. & Cumberlidge, Neil, 2025, A new species of Louisea Cumberlidge, 1994, a freshwater crab from the Ekom-Nkam Waterfall, Cameroon (Brachyura: Potamonautidae: Liberonautinae), Zootaxa 5590 (1), pp. 113-123 : 115-121

Louisea cataracta sp. nov.

( Figs. 1B , 2A–D , 3A–H , 4 )

Type material. Holotype: ZMB Crust. 33410, adult ♂ (CW 17.5, CL 13.0, CH 7.7, FW 6.2 mm), southwestern Cameroon, Nkam River below the Ekom Nkam Waterfalls , near Melong (5.061728°N, 10.030878°E, 498 m ASL), coll. P.A. Mvogo Ndongo & Kuate Simo, 31 January 2023 . Paratypes: ZMB Crust. 33411, adult ♀ (CW 16.6, CL 12.7, 12.3, CH 8.3, FW 5.4 mm) ; CARC 20X , 3 adult ♂♂ (CW 17.4, 17.3, 14.6; CL 12.7, 12.4, 11.3; CH 7.6, 7.9, 6.4; FW 5.6, 5.6, 5.5 mm) ; CARC 21X , 3 adult ♀♀ (CW 16.9, 15.1, 14.9; CL 12.3, 11.4, 10.8; CH 7.7, 6. 7, 6.4, FW 5.5, 5.1, 4.7 mm), all same data as holotype .

Diagnosis. Carapace postfrontal crest distinct, prominent, complete, ends meeting carapace margin behind intermediate tooth ( Figs. 1B , 2A, D ); exorbital, intermediate teeth small, distinct; epibranchial tooth undetectable ( Figs. 1B , 2A, D ). Mandibular palp consisting of basis plus two articles; terminal article undivided, with small anterior lobe arising at junction between articles ( Fig. 3H ). Third maxilliped exopod completely lacking flagellum; ischium lacking vertical sulcus ( Fig. 3G ). Sternal sulcus S2/3 deep, incomplete, not traversing sternum; S3/4 incomplete, reduced to 2 short lateral notches ( Fig. 2C ). Male right (major) chela dactylus distinctly arched, broad, with 4 large pointed teeth (2 distal, 2 proximal) ( Fig. 3D ); propodus with 4 large teeth (3 proximal, 1 distal) ( Fig. 3D ); both fingers touching at tip when chela closed, enclosing long oval interspace; cheliped carpus inner margin distal tooth long, pointed; proximal tooth subequal ( Fig. 3F ); merus medial inferior margin with large jagged distal tooth followed by 5 distinct smaller teeth ( Fig. 3F ). G1 TA short (TA/SA = 0.35), directed outwards, proximal one third distinctly broad, distal two-thirds abruptly narrow, slim, tube-like ( Fig. 3A, B ). G1 SA tapering slightly from broad basal margin to relatively wide distal margin; dorsal face with broad dorsal membrane at TA/SA junction (maximum width 0.1× SS length) ( Fig. 2A, B ). G2 TA medium length (TA/SA = 0.44), flagellum-like, less than half as long as G2 SA ( Fig. 3C ).

Description. Carapace surface smooth, ovoid, widest in anterior third (CW/FW = 2.8, n=8), medium height ( CH /FW = 1.2, n = 8) ( Figs. 1A, B , 2A ), semi-circular, urogastric grooves deep; cardiac region weakly marked, cervical grooves short, faint; transverse branchial grooves faint ( Fig. 1A, B ). Front deflexed slightly, about 1/3 carapace width (FW/CW = 0.4, n=8); frontal margin straight ( Figs. 1B , 2B, D ); postfrontal crest sharply defined, complete, traversing entire carapace; meeting anterolateral margin of carapace behind intermediate tooth ( Figs. 1B , 2B, D ); exorbital, intermediate teeth small, distinct, epibranchial tooth undetectable carapace lateral margin posterior to epibranchial tooth smooth ( Figs. 1B , 2A, D ). Branchiostegal sidewall with vertical, longitudinal sutures dividing it into three regions (suborbital, subhepatic, pterygostomial) ( Fig. 2C ); longitudinal suture beginning at respiratory opening, curving backward across sidewall dividing suborbital, subhepatic from pterygostomial regions ( Fig. 2C ); vertical sulcus on branchiostegal wall curving backward to meet anterolateral margin at epibranchial tooth ( Fig. 2C ), dividing suborbital from subhepatic regions ( Fig. 2C ).

Mandibular palp consisting of basis plus two articles; terminal article with small anterior lobe at junction between endopod articles ( Fig. 3H ).

Third maxillipeds filling entire oral field, except for transversely oval efferent respiratory openings at superior lateral corners; third maxilliped exopod completely lacking flagellum; third maxilliped ischium with faint vertical sulcus ( Fig. 3G ).

Thoracic sternal sulcus S1/2 completely traversing sternum; thoracic sternal sulcus S3/4 incomplete, not traversing sternum, represented by short sections at lateral ends, with wide obscure mid-section ( Fig. 2C ); episternal sulci S4/E4, S5/E5, S6/E6, S7/E7 complete ( Fig. 2C ).

Male right (major) chela dactylus slightly curved leaving long narrow interspace when chelae tips touching; dactylus with 4 small teeth (2 distal, 2 proximal) ( Fig. 2D , 3D, E ); major chela propodus with 4 teeth (3 large proximally, 1 small distally) ( Fig. 3D, E ); both fingers touching at tip when chelae closed, enclosing long oval interspace; cheliped carpus inner margin distal tooth long, pointed; proximal tooth subequal ( Fig. 3F ); dactylus, propodus of male left (minor) chela straight, with small teeth on occluding margin ( Fig. 3D, E ); merus medial inferior margin with large jagged distal tooth followed by 5 distinct smaller teeth ( Fig. 3F ).

Ambulatory legs P2–5 stout, distal articles (merus, carpus, propodus, dactylus) not elongated; dactylus of P2–5 tapering to point, each bearing four rows of downward-pointing sharp bristles ( Fig. 1A ).

Male pleon and telson together forming slim triangle; pleon edges distinctly concave lined by small setae; telson triangular, apex rounded, base broadest, sides outwardly sloping; PL1–6 rectangular, wider than long; PL6 longest, more than 1/2 as long as wide, remaining pleomeres short, less than 1/3 as long as wide ( Fig. 2C ). G1 TA, stout, distinctly sinuous, short, about one-quarter length of G1 SA (TA/SA = 0.25), directed outwards, proximal one-third distinctly broad, distal two-thirds abruptly narrow, distally forming slim tube ( Fig. 3A, B ). G1 SA tapering slightly from broad basal margin to wide distal margin; dorsal face with broad oval dorsal membrane at TA/SA junction ( Fig. 3B ). G2 TA long, subequal to G2 SA length (TA/SA = 0.44), flagellum-like ( Fig. 3C ).

Colour. Carapace of living specimens red-brown. Chelipeds dark yellow, tips of fingers are white. Ambulatory legs (P2–5) purple ( Fig. 2B ).

Type locality. Nkam River below the Ekom Nkam Waterfalls, near Melong (5.061728°N, 10.030878°E, 498 m ASL), southwestern Cameroon.

Etymology. The species name, cataracta , is derived from the Latin for waterfall in reference to the Ekom Nkam waterfalls where the specimens were collected. The specific epithet is used as a Latin noun in apposition.

Distribution. Louisea cataracta sp. nov. is known from a single locality below the Nkom Ekam waterfalls in southwestern Cameroon.

Habitat. This small colourful species of Central African freshwater crab is only found in the humid rainforest zone of southwestern Cameroon. Louisea cataracta sp. nov. was collected in the Nkam River below the Ekom Nkan Waterfalls, where it lives a semi-terrestrial existence under rocks in the extremely humid spray zone ( Fig. 1A ). The Ekom Nkam Waterfalls are located in tropical rainforest about 15 km from the village of Melong. At the falls, the river drops 80 m over a cliff. There are two main waterfalls here, one flows year-round, while the other one (and several smaller ones) only flow during the rainy season.

Remarks. Louisea now comprises five species, all endemic to southwestern Cameroon ( Cumberlidge 1994, 1999; Mvogo Ndongo et al. 2017 a, 2019). Louisea cataracta sp. nov. is assigned to this genus because it conforms to the diagnosis provided by Cumberlidge & Daniels (2022: 1291). For example, there is an intermediate tooth on the anterolateral margin between the exorbital and epibranchial teeth, and the epibranchial tooth is small and granular; the mandibular palp consists of the basis plus two articles, and the terminal article has small anterior lobe at the junction between the endopod articles ( Fig. 3H ); the third maxilliped exopod completely lacks a flagellum, and the ischium has only a faint vertical sulcus ( Fig. 3G ); the cheliped merus medial inferior margin has a large jagged distal tooth followed by 5 distinct smaller teeth ( Fig. 3F ); the G1 TA is stout and distinctly sinuous and short, about one-quarter the length of the G1 SA; the G1 TA dorsal face has a broad oval dorsal membrane at the TA/SA junction; and the G2 TA is long and flagellum-like. In addition, species of Louisea are all small, with an adult size range beginning at CW 16–18 mm ( Cumberlidge 1994, 1999; Mvogo Ndongo et al. 2017 a, 2019).

Comparisons. Louisea cataracta sp. nov. can be distinguished from the other four species of this genus by examination of thoracic sternal sulcus S2/3 which is deep, incomplete, and does not traverse the entire sternum because its lateral ends do not meet the side margins ( Fig. 2C ) (vs a thoracic sternal sulcus S2/3 that is either deep or faint but always traverses the thoracic sternum in the other four Louisea species; Mvogo Ndongo et al. 2019: fig. 6a–d).

Louisea cataracta sp. nov. can be distinguished from L. nkongsamba as follows. The thoracic sternal sulcus S3/ 4 in both species is incomplete and does not traverse the sternum, but is represented only by short sections at the lateral ends with a wide obscure mid-section in L. cataracta sp. nov. ( Fig. 2C ) (vs a thoracic sternal sulcus S3/4 that is represented by long side sections and just a short obscure mid-section in L. nkongsamba ; Mvogo Ndongo et al. 2019: fig. 6d). In addition, the thoracic sternal side margins of both S3 and S4 are flat in L. cataracta sp. nov. ( Fig. 2C ) (vs thoracic sternal side margins of S3 and S4 that are raised and thickened in L. nkongsamba ; Mvogo Ndongo et al. 2019: fig. 6d).

Louisea cataracta sp. nov. can be distinguished from L. balssi as follows. The major chela dactylus is slightly curved, leaving a long narrow interspace when the chelae tips are touching in L. cataracta sp. nov. ( Fig. 3D ) (vs a major chela dactylus that is highly arched, leaving oval interspace when the chelae tips are touching in L. balssi ; Mvogo Ndongo et al. 2019: fig. 8c). In addition, the major chela propodus has three teeth proximally and one tooth distally in L. cataracta sp. nov. ( Fig. 3D ) (vs a major chela propodus has two teeth proximally and two teeth distally in L. balssi ; Mvogo Ndongo et al. 2019: fig. 8c). Furthermore, the cheliped carpus inner margin has a long, pointed distal tooth and a subequal proximal tooth in L. cataracta sp. nov. ( Fig. 3D ) (vs a cheliped carpus inner margin that has a small & blunt distal tooth and a subequal proximal tooth in L. balssi ; Mvogo Ndongo et al. 2019: fig. 10b). Furthermore, the cheliped carpus inner margin has a small granular tooth between the distal & proximal teeth in L. cataracta sp. nov. ( Fig. 3F ) (vs a cheliped carpus inner margin that lacks a small granular tooth between the distal and proximal teeth in L. balssi, Mvogo Ndongo et al. 2019 : fig. 10b).

Louisea cataracta sp. nov. can be distinguished from L. edeaensis as follows. The thoracic sternal sulcus S3/ 4 in both species is incomplete and does not traverse the sternum, but is represented only by short sections at the lateral ends with a wide obscure mid-section in L. cataracta sp. nov. ( Fig. 2C ) (vs a thoracic sternal sulcus S3/4 that is represented by long side sections and just a short obscure mid-section in L. edeaensis ; Mvogo Ndongo et al. 2019: fig. 6a). Finally, L. cataracta sp. nov. can be distinguished from L. yabassi as follows. The thoracic sternal sulcus S2/3 is incomplete, does not traverse the entire sternum, and its lateral ends do not meet the sternal side margins in L. cataracta sp. nov. ( Fig. 2C ) (vs an S2/3 that is complete (traverses the entire sternum), and its lateral ends meet the sternal side margins in L. yabassi ; Mvogo Ndongo et al. 2019: fig. 6c).

Details of the distribution of these differences in characters between L. cataracta sp. nov. and the other species of the genus are listed in Table 2 .

Conservation. The Ekom-Nkam Waterfalls are a popular tourist attraction with a high number of visitors. Surveys around the waterfall revealed a large number of dead freshwater crabs and frogs that had apparently been trampled by visitors to this attraction. These included L. cataracta sp. nov., as well as several larger species, Sudanonautes africanus (A. Milne-Edwards, 1869) , S. aubryi (H. Milne Edwards, 1853) and S. floweri (De Man, 1901) that are actively fished by local people for consumption. In summary, L. cataracta sp. nov. is vulnerable to habitat disturbance and trampling by tourists, as well as being captured by local fishermen seeking the larger species. The recent discovery date of L. cataracta sp. nov. means that little is known about its population levels and trends, distribution, reproductive cycle, potential predators, habitat preferences and threats. These data are required to accurately assess its extinction risk using the International Union for Conservation of Nature (IUCN) Red List protocols, but given the low number of specimens known and the presence of immediate threats to this species, it is likely to place it in a threatened category when an extinction risk assessment has been completed. Further research is urgently required aimed at assessing the conservation status of L. cataracta sp. nov., devising a plan of action, and then implementing conservation measures to protect this potentially threatened species.

The conservation status of the other four species is also a concern because L. edeaensis and L. balssi are currently listed on the IUCN Red List as endangered species (IUCN 2003; Cumberlidge 2008a, 2008b; Cumberlidge et al. 2009; Mvogo Ndongo et al. 2017 a, 2019). The other two species, L. yabassi and L. nkongsamba , are still awaiting a conservation assessment and so are not yet included on the IUCN Red List, but both of these little-known species face anthropogenic impacts that include habitat destruction, pollution, and pollution from the release of harmful chemicals into the water as has been reported for other species of freshwater crabs living in this part of Cameroon ( Mvogo Ndongo et al. 2017a, b, 2018, 2019, 2021a, b, 2022, 2023, 2024a).

Molecular analysis. Separate phylogenetic analyses for the two mtDNA genes did not result in different topologies. The phylogenetic tree derived from using a combination of COI and 16S RNA mitochondrial DNA sequences with confidence values derived from BI and ML analyses recovered all species of Louisea as a single monophyletic clade ( Fig. 4 ). Each of the five Louisea species ( L. balssi , L. edeaensis , L. nkongsamba , L. yabassi and L. cataracta sp. nov.) was found to be represented by a well-supported independent lineage. Uncorrected p-distances based on COI sequence data were 2.20–10.46% among the species of Louisea included in the present study, and 0–0.8% within species. The four new species are distinct from their congeners ( Table 3 ). Within the clade of Louisea , L. cataracta sp. nov. (from the Ekom-Nkam waterfalls) and L. nkongsamba (from the nearby Mt. Nlonako Ecological Reserve) were sister species.

Figures

FIGURE 2. Louisea cataracta sp. nov. adult male holotype, CW 17.5 mm, Ekom-Nkam Waterfalls, Cameroon, ZMB Crust. 33410: A, carapace, frontal view; B, whole animal, dorsal view showing natural colour; C, cephalothorax, ventral view; D, carapace, dorsal view.

FIGURE 3. Louisea cataracta sp. nov. adult male holotype, CW 17.5 mm, Ekom-Nkam Waterfalls, Cameroon, ZMB Crust. 33410: A, right G1 ventral view; B, right G1 dorsal view; C, right G2 ventral view; D: right chela frontal view; E, left chela frontal view; F, right cheliped carpus and merus, dorsal view; G, left third maxilliped frontal view; H, left mandibular palp removed from mandible, frontal view.

FIGURE 4. ML topology for species of Louisea from Cameroon studied herein based on mtDNA sequences (16S rRNA and COI). Statistical values at nodes indicate posterior probabilities (BI) and bootstrap support (ML), respectively.

FIGURE 1. A, Ekom-Nkam Waterfalls, the type locality of Louisea cataracta sp. nov. B, Louisea cataracta sp. nov. adult male holotype, CW 17.5 mm, Ekom-Nkam Waterfalls, Cameroon, ZMB Crust. 33410: whole animal, dorsal view.