Liberonautes constantini, Cumberlidge & Fitch & Clark, 2023

Cumberlidge, Neil, Fitch, Rebecca L. & Clark, Paul F., 2023, A checklist and key to the Ivorian freshwater crabs, with the description of a new species of Liberonautes Bott, 1955 (Brachyura: Potamoidea: Potamonautidae), Zootaxa 5278 (1), pp. 119-130 : 120-127

Liberonautes constantini n. sp.

Constantin’s freshwater crab

( Figs. 1–3 , Tabs. 1 , 2 )

Holotype. MNHN-IU-2022-3213. Adult male ( CW 21.8 , CL 13.2, CH 6.7, FW 6.4 mm), Côte d’Ivoire, from torrents de Tonkoui (7.450997°N, 7.551561°W), near Mt. Tonkoui (740 m asl), coll. M. Lamotte, 24 August 1960.

Paratype. MNHN-IU-2022-3214. Subadult male, ( CW 20.8 , CL 14.5, CH 7.4, FW 7.4 mm) Côte d’Ivoire, from torrents de Tonkoui (7.450997°N, 7.551561°W), near Mt. Tonkoui (740 m asl), coll. M. Lamotte, 19 August 1960 .

Diagnosis. Third maxilliped ischium with faint vertical sulcus; exopod lacking flagellum. Exorbital, intermediate teeth low; epibranchial tooth small, granule sized. Thoracic sternal sulcus Sl/2 obscure; episternal sulci S4/E4–S6/ E6 clearly visible. Cheliped dactylus not arched, enclosing long narrow interspace when fingertips touching.

Description. Carapace transversely oval, wide (CW/CL l.7), moderately high ( CH /FW l.1). Front slightly indented, wide (FW/CW 0.3). Both epibranchial, branchial regions of carapace with rows of carinae, remaining carapace surface smooth; semi-circular, urogastric, cardiac, cervical, transverse branchial grooves shallow, faint. Postfrontal crest distinct, incomplete, consisting of fused epigastric, postorbital crests, not traversing entire carapace, lateral ends fading out in fields of carinae before meeting anterolateral margins; mid-groove on postfrontal crest short, forked. Exorbital angle, intermediate tooth low, epibranchial tooth small, low, granule sized. Lateral margin posterior to epibranchial tooth raised, marked by row of small granules; lateral margin curving inward over carapace posteriorly, not continuous with posterolateral margin. Width of posterior margin of carapace subequal to FW.

Suborbital, pterygostomial, subhepatic regions of branchiostegite smooth; distinct vertical sulcus from base of epibranchial tooth to epimeral sulcus.

Third maxilliped ischium as wide as merus; vertical sulcus on ischium faint. Exopod longer than ischium, reaching halfway along merus, lacking flagellum. Mandibular palp consisting of basis followed by 2 articles; terminal article bilobed, with small small rounded lobe on anterior side, arising near article junction.

Thoracic sternal sulcus Sl/2 short, distinct, S2/3 deep, straight, completely traversing sternum, S3/4 reduced to 2 short notches laterally; episternal sulci S4/E4–S6/E6 clearly visible; S7 /E7 not visible.

Chelipeds unequal: major (left) longer, higher than minor; dactylus of left chela slim (0.25 × propodus palm height), upper margin smooth, dactylus not arched, enclosing long narrow interspace; finger of propodus broad (0.3 × propodus palm height), lower margin of chela propodus almost straight, with small curved indentation. Dactylus of right chela slim, slightly arched, enclosing long interspace when fingertips touching; fingers of right chela with two large pointed teeth along margins interspersed with several smaller teeth. Distal tooth on inner margin of cheliped carpus large, pointed, directed forward, proximal carpal tooth small, followed by two small granules. Lateral, medial inferior margins of cheliped merus lined by small pointed teeth, distal meral tooth small; superior margin of cheliped merus with field of large raised granules. Ambulatory legs P2–5 smooth with slightly serrated superior margins.

Pleomeres PLl–6 four sided; PL7 (telson) triangular, with rounded distal margin; PL3 broadest, PL3–7 forming slim triangle with indented sides, tapering towards telson. G1 TA long (about two-thirds as long as G1 SA), distinctly curved, tapering gradually, distally elongted, narrow; G1 TA lateral, medial folds both narrow, low; longitudinal groove on ventral face not visible on dorsal face; entire G1 TA directed inward. G1 SA long, slim, lateral margin with distinct inward curve, base broad; G2 longer than G1; G2 TA long, flagellum-like.

Size. This small species is known only from two specimens (CWs 21.8 and 20.8 mm).

Type locality. West Africa. Côte d’Ivoire, from mountain stream draining Mt. Tonkoui, a tributary of the River Ko that flows through the city of Man, western Côte d’Ivoire, Montagnes District, Tonkpi Region ( Fig. 3 : 3). This fast-moving mountain stream (torrent) feeds the nearby Ypou waterfall near Zadépleu where it flows over a series of layered staircase-like rock formations, at the bottom of which are the stream and several natural pools. Stream flow is strongest during the wet season (November to June) and declines during the dry season (July to October). Mt. Tonkoui is covered by Guinean montane forest, which is an upland evergreen forest dominated by Parinari excelsa trees.

Ecology. Liberonautes constantini n. sp. is found in the Upper Guinea Forest zone of West Africa that extends from southern Guinea into eastern Sierra Leone, Liberia, Côte d’Ivoire, Ghana, and western Togo, and is regarded as a global biodiversity hotspot ( Myers et al. 2000). This forested region includes several highland areas including the Fouta Jallon Mountains in Guinea, the Nimba Mountains in Liberia, and Mount Tonkoui in Côte d’Ivoire. Liberonautes constantini n. sp. is found in a forested mountain stream. The only other species that is known from a similar highland stream habitat is L.rubigimanus Cumberlidge & Sachs, 1989 from Liberia and Guinea ( Cumberlidge 1999; Cumberlidge & Huguet 2003; Daniels et al. 2016). Other species of Liberonautes occupy a variety of habitats within the Upper Guinea Forest zone, including lowland streams ( L. latidactylus , L. lugbe Cumberlidge, 1999 and L. grandbassa Cumberlidge, 1999 ), high altitude savanna grasslands ( L. nimba Cumberlidge, 1999 ), lowland wetlands and marshes ( L. paludicolis ), and large rivers ( L. nanoides Cumberlidge & Sachs, 1989 ). Liberonautes latidactylus is also found outside of the forested areas in the dry savannas of northern Ghana, Burkina Faso, Mali and Senegal.

Distribution. Liberonautes constantini n. sp. is known only from Côte d’Ivoire, from a mountain stream draining Mount Tonkoui close to the village of Zadépleu near the city of Man ( Fig. 3 : 3).

Etymology. The species is named for Constantin Georg Pockberger to mark his baptism on 20 August 2022 in Cyprus, who is the son of crustacean biologist Dr. Magdalini Christodoulou and her husband Maurice Pockberger.

Remarks. The freshwater habitats of Côte d’Ivoire include four West African major rivers that drain south into the Gulf of Guinea (the Cavally, Sassandra, Bandama, and Comoé) and Lake Kossou on the Bandama River in the center of the country. The six species of freshwater crabs currently known to occur in Côte d’Ivoire belong to three genera, Liberonautes , Sudanonautes , and Occidensonautes ( Cumberlidge 1999; Cumberlidge & Daniels 2022).

Liberonautes constantini n. sp. is the ninth species of Liberonautes to be described. In addition to the four species of this genus found in Côte d’Ivoire, the other five are L. rubigimanus , L. nanoides , L. lugbe , L. grandbassa and L. nimba . Liberonautes reaches its highest species diversity in Liberia (eight species) with Côte d’Ivoire now the second most species-rich country where this genus is found. It is likely that there are other species of Liberonautes still to be described given that recent molecular systematic studies by Daniels et al. (2016) and Cumberlidge & Daniels (2022) indicate the presence of unidentified lineages within L. latidactylus and L. rubigimanus from Liberia and Guinea.

Liberonautes constantini n. sp. is assigned to Liberonautes on the basis of the following characters. The G1 TA is long and curves inward; the G2 TA is a long flagellum; the postfrontal crest is incomplete and does not meet the lateral carapace margins; there is an intermediate tooth on the anterolateral margin between the epibranchial and exorbital teeth; the branchiostegite is divided into three parts by the epimeral and vertical sulci; the mandibular palp consists of the basis followed by 2 articles; the terminal article is bilobed, with a small rounded lobe on the anterior side, arising near the article junction, sternal sulcus S2/3 is deep, straight, and completely crosses the sternum, S3/4 is incomplete and is represented only by two short notches at the lateral ends; and episternal sulcus S7/E7 is obscure.

Species of Liberonautes can be distinguished from those of Sudanonautes by examination of the characters of the gonopods (see key below). For example, the G1 TA of Liberonautes is directed inward toward the midline, and the G2 TA is long and flagellum-like ( Cumberlidge 1999), whereas in Sudanonautes the G1 TA is directed outward away from the midline, and the G2 TA is reduced to a short stub ( Cumberlidge 1999). Both Liberonautes and Sudanonautes can be distinguished from Occidensonautes by the anterolateral margin of the carapace, which has an intermediate tooth between the exorbital and epibranchial tooth in the former two genera, and lacks an intermediate tooth in the latter ( Cumberlidge 1999; Cumberlidge & Daniels 2022)

The distributional ranges of Liberonautes and Sudanonautes overlap in Ghana and Côte d’Ivoire ( Fig. 3 ). Ghana is the eastern limit of the distribution of the nine species of Liberonautes in West Africa, whose range includes Senegal, Mali, Guinea, Guinea Bissau, Burkina Faso, Sierra Leone, Liberia, Ghana, and Côte d’Ivoire ( Cumberlidge 1999; Daniels et al. 2016). Côte d’Ivoire is the western limit of the 14 species of Sudanonautes ( Cumberlidge 1999; Cumberlidge & Daniels 2022) that are found in West Africa from Côte d’Ivoire east to Nigeria, as well as in a number of countries in Central Africa ( Cameroon, D.R. Congo, Gabon, Equatorial Guinea, Central African Republic, Republic of the Congo and Cabinda ( Angola) and East Africa ( South Sudan and northern Uganda).

Occidensonautes is assigned to the Potamonautinae Bott, 1970, a subfamily it shares with nine other African genera, while Liberonautes is assigned to the Liberonautinae Cumberlidge & Daniels, 2022 which it shares with Sudanonautes , and three other genera that are all endemic to Cameroon: Buea Cumberlidge, Mvogo Ndongo, Clark & Daniels, 2019 , Louisea Cumberlidge, 1994 , and Potamonemus Cumberlidge & Clark, 1992 ( Cumberlidge & Daniels 2022). Liberonautinae and Potamonautinae diverged ca. 30.14 Mya during the Eocene-Oligocene, while Liberonautes diverged from the other Liberon au tinae genera ca. 27.65 MYA, also during the Eocene-Oligocene ( Cumberlidge & Daniels 2022).

Comparisons. Liberonautes constantini n. sp. is most similar to the other four small Liberonautes species, e.g., L. lugbe , L. nimba , L. grandbassa and L. nanoides , which all have a similar adult size range of CW 20–24.5 mm. These species can be distinguished from the four large bodied species e.g., L. latidactylus , L. rubigimanus , L. paludicolis and L. chaperi , because specimens of any of these species with a CW of 25 mm would not be adult.

Liberonautes constantini n. sp. is closest to L. lugbe but can be distinguished from this species as follows. In L. constantini n. sp. the ischium of the third maxilliped has a faint vertical sulcus; Fig. 2F (vs a deep vertical sulcus in L. lugbe ; Cumberlidge 1999: fig. 23H), episternal sulci S4/E4, S5/E5, and S6/E6 of L. constantini n. sp. are all clearly visible; Fig. 1C (vs episternal sulci S4/E4, S5/E5, and S6/E6 are all faint and incomplete in L. lugbe ; Cumberlidge 1999: fig. 21H), the distal tooth of the cheliped carpus is large and pointed; Fig. 2C (vs the distal tooth of the cheliped carpus is small, blunt and low in L. lugbe ; Cumberlidge 1999: fig. 25H, HH), the exorbital, intermediate, and epibranchial teeth are all small and granular; Fig. 1B (vs the exorbital, intermediate, and epibranchial teeth are small, pointed, and distinct in L. lugbe ; Cumberlidge 1999: fig. 20H) and the dactylus of the major (left) cheliped is not arched and encloses a long narrow interspace when the fingers are touching; Fig. 2A (vs the dactylus of the major (left) cheliped is slightly arched and the closed chela encloses a long, broad rectangular interspace in L. lugbe ; Cumberlidge 1999: fig. 24H).

Liberonautes constantini n. sp. is distinguished from L. grandbassa , L. nimba , and L. nanoides by the lack of a third maxilliped exopod flagellum; Fig. 2E (vs a long third maxilliped exopod flagellum in L. grandbassa , L. nimba , and L. nanoides ; Cumberlidge 1999: fig. 23G, Cumberlidge 1999: fig. 23E and Cumberlidge 1999: fig. 23B, respectively). Liberonautes constantini n. sp. can be further distinguished from L. nimba by episternal sulci S4/E4, S5/E5, and S6/E6 which are all distinct in the new species; Fig. 1C (vs S4/E4, S5/E5, and S6/E6 that are all obscure in L. nimba Cumberlidge 1999 : fig. 21B). Liberonautes constantini n. sp. can be further distinguished from L. nanoides by the carapace height, which is greater than the front width; Fig. 1B (vs a carapace height less than the front width in L. nanoides ; Cumberlidge 1999: 157). Finally, L. constantini n. sp. is one of only two species of Liberonautes that occurs in rainforest mountain streams, the other one being the large species, L. rubigimanus . Interestingly, each of these mountain stream species lacks a flagellum on the exopod of the third maxilliped ( Fig. 2E ; Cumberlidge 1999: 160).

Checklist of the Côte d’Ivoire freshwater crabs. The addition of L constantini n. sp. from Mt. Tonkori to the checklist of Côte d’Ivoire freshwater crabs ( Table 1 ) makes this species only the second member of this fauna (together with S. koudougou ) that is endemic to this country. The other Ivorian species are also found elsewhere in West Africa. For example, O. ecorssei is found in the Niger River and its tributaries from Mali to Nigeria, L. latidactylus ranges from Senegal to Ghana in rainforests and savannas, L. paludicolis is mainly reported in the forests of Liberia, northeast Guinea, and northwest Côte d’Ivoire. Liberonautes chaperi is also found in major rivers in Ghana and Liberia, and S. aubryi has a wide distribution east of Côte d’Ivoire in Ghana, Togo, Benin, Nigeria, Cameroon, Gabon and Equatorial Guinea ( Table 1 ; Cumberlidge 1999).

The comparatively short checklist of freshwater crabs from Côte d’Ivoire (a relatively large country (322,463 km 2) with abundant freshwater habitats is probably an artifact of under-collecting, rather than a reflection of the actual species richness ( Fig. 3 ; Cumberlidge 1999). The species numbers in this country have slowly increased over the years, with the new additions to this fauna being the result of either taxonomic revisions or range extensions of species that occur in neighboring countries, rather than descriptions of new taxa ( Table 1 ; Bott 1955; Cumberlidge 1999; Cumberlidge et al. 2021). In addition, the species richness in Côte d’Ivoire has not been helped by the lack of a reliable identification key for the freshwater crabs of this country, or the lack of systematic biological inventories over the years ( Cumberlidge 1999). It is, therefore, likely that there are still additional species of freshwater crabs yet to be discovered in Côte d’Ivoire, given the large amounts of unexplored suitable habitat in that country’s watersheds, lakes, and highland streams.

Conservation. The extinction risk of the new species, and S. koudougou (both endemic to Côte d’Ivoire), has yet to be determined. The three species of Liberonautes found in Côte d’Ivoire ( L. chaperi , L. latidactylus , and L. paludicolis ) are all listed in the International Union for Conservation of Nature (IUCN) Red List as LC ( Cumberlidge 1999; Cumberlidge et al. 2009; Cumberlidge & Daniels 2020a –c), as are S. aubryi and O. ecorssei ( Cumberlidge & Daniels 2020d –e; Table 1 ). While this is encouraging, the Upper Guinea Forests in Côte d’Ivoire, Guinea, Sierra Leone and Liberia are still threatened by ongoing habitat loss and degradation. Significant increases in human populations accompanied by intensive slash and burn agricultural practices have negatively affected water quality and habitat availability for freshwater species, including crabs, and their continued survival in this threatened region is not guaranteed. Freshwater crabs (mainly the large-bodied species such as L. latidactylus and L. paludicolis ) are also frequently consumed as a source of inexpensive protein by rural communities although the impact on the populations of these species remains unquantified. As far as the new species is concerned, the high conservation value of Mt. Tonkoui as a biodiversity ‘hotspot’ has led to the proposal that it be declared as a new protected area: The Nature Reserve of Mt. Tonkoui ( Moretto et al. 2021), which is also recommended here.

Medical Importance. Côte d’Ivoire, Liberia and Guinea are all countries where human lung fluke disease (paragonimiasis) caused by the trematode Paragonimus uterobilateralis Voelker & Vogel, 1965 , is endemic ( Cumberlidge et al. 2018; Rabone et al. 2021). Freshwater crabs serve as second intermediate hosts of this parasite, and parasitologists working on paragonimiasis in Africa have focused a lot of their attention on the easily accessible freshwater crabs. A species of freshwater crab is considered to be a second intermediate host of Paragonimus if the parasite’s metacercariae can be isolated from it. In this way, four species of Liberonautes have been shown to be second intermediate hosts of P. uterobilateralis , three of which are found in Côte d’Ivoire ( L. latidactylus , L. paludicolis , and L. chaperi ) ( Fig. 3 : 1, 2, 4; Cumberlidge & Sachs 1989; Sachs & Cumberlidge 1990, 1991; Cumberlidge et al. 2020; Rabone et al. 2021), but the status of the new species is unknown. In Côte d’Ivoire, foci of paragonimiasis are found in the Upper Guinea Western Focus in Woroba District near the border with Guinea, and in Gôh-Djiboua District Lakota, Ouagalilie, at Gagnoa in the Gôh Region ( Coulibaly et al. 1975; Nozais et al. 1980; Traoré et al. 2001, 2011; Aka et al. 2008 a, b, 2009).

Key to the Ivorian freshwater crab genera and species

(adapted from Cumberlidge 1999)

1. Anterolateral margin with intermediate tooth between exorbital, epibranchial teeth; sternal sulcus S1 / 2 not visible; S3 / 4 reduced to two side notches; G1 TA long (about two-thirds as long as the G1 SA)......................................... 2

– Anterolateral margin always lacking intermediate tooth between exorbital, epibranchial teeth; sternal sulcus Sl/2 clearly visible; S3/4 completely traversing sternum; G1 TA short (about one-quarter to one-third as long as the G1 SA)................................................................................................ Occidensonautes ecorssei

2. G1 TA directed outward: G2 TA short (about 0.05–0.07 times as long as the G2 SA). Postfrontal crest complete always meeting anterolateral margins either at, or behind, the epibranchial teeth................................................ 3

– G1 TA directed inward. G2 TA long, flagellum-like (about 0.5–0.75 times as long as G2 SA). Postfrontal crest incomplete, not meeting carapace lateral margins........................................................................ 4

3. Postfrontal crest always meeting lateral margins behind epibranchial teeth........................ Sudanonautes aubryi

– Postfrontal crest always meeting lateral margins at epibranchial teeth........................ Sudanonautes koudougou

4. Lateral carapace margin behind epibranchial tooth smooth or lined by small granulations; intermediate, epibranchial teeth small.............................................................................................. 5

– Lateral carapace margin behind epibranchial tooth with three or more large, pointed teeth; intermediate tooth large, triangular, pointed; epibranchial tooth large, pointed.................................................. Liberonautes chaperi

5. Exopod of third maxilliped with long flagellum............................................................. 6

– Exopod of third maxilliped lacking flagellum …..................................... Liberonautes constantini n. sp.

6. Carapace height equal to front width ( CH /FW 1.0). Episternal sulci S4/E4, S5/E5 obscure, S6/E6 clearly visible …....................................................................................... Liberonautes latidactylus

– Carapace height greater than front width ( CH /FW 1.1). Episternal sulci S4/E4, S5/E, S6/E6 all clearly visible ….......................................................................................... Liberonautes paludicolis

Figures

FIGURE 1. Liberonautes constantini n. sp., holotype, adult ♁ CW 21.8 mm, from Mt. Tonkoui, Côte d’Ivoire (MNHN-IU- 2022-3213). (A) whole animal, dorsal view; (B) carapace, frontal view; (C) thoracic sternum, ventral view. Scale bar: A = 6.3 mm, B = 2.5 mm, C = 3.1 mm.

FIGURE 2. Liberonautes constantini n. sp., holotype, adult ♁ CW 21.8 mm, from Mt. Tonkoui, Côte d’Ivoire (MNHN-IU- 2022-3213). (A) frontal view of right chela; (B) frontal view of left chela; (C) right cheliped carpus and merus dorsal view; (D) right cheliped merus underside; (E) third maxilliped, frontal view; (F) right G1 ventral view; (G) right G1 dorsal view; (H) left mandible, frontal view. Scale bar: A = 4.9 mm, B = 3.6 mm, C = 3.3, D = 4.0 mm, E = 1.7 mm, F = 1.0 mm, G = 1.1 mm, H = 1.2 mm.

FIGURE 3. Map of West Africa showing the geographic distribution of the seven species of freshwater crabs found in Côte d’Ivoire. Black circles = species of Liberonautes; white squares = species of Sudanonautes; black triangles = species of Occidensonautes. 1 = Liberonautes latidactylus, 2 = L. paludicolis, 3 = L. constantini n. sp., 4 = L. chaperi, 5 = Sudanonautes aubryi, 6 = S. koudougou, 7 = Occidensonautes ecorssei. Scale bar = 220 km. See Table 2 for exact localities.