Louisea balssi ( Bott, 1959 )

Mvogo Ndongo, Pierre A., Rintelen, Thomas Von, Albrecht, Christian, Tamesse, Joseph L. & Cumberlidge, Neil, 2018, Lost species in Cameroon: rediscovery of the endangered freshwater crab, Louisea balssi (Bott, 1959) (Brachyura: Potamonautidae), with notes on its ecology and conservation, Zootaxa 4394 (3), pp. 407-416 : 408-413

Louisea balssi ( Bott, 1959)

( Figs. 1–5 )

Globonautes balssi Bott 1959: 999 –1000, fig. 7; Cumberlidge 1987: 2210 –2212; Cumberlidge 1994: 127, 130, figs. 2 a,b, 3 (j– l only), tables 1–2 (ZIM K 3506 only).

Globonautes macropus balssi, Bott 1970: 25 , pl. 1 figs. 6–8.

Louisea balssi Cumberlidge, 1999: 19 , 20, 24, 28, 42, 50–51, 216–217, 227–228, 231–233, 276, 307, 309, 314, 351, figs. 53EE, 54-57, 62G, 68F, tables V, X–XIII, pl. 4 (not figs. 46G, 48F, 49G, 52G, table IX); Mvogo Ndongo et al. 2017a: 273 –274, 278.

Material examined. CAMEROON: 2 adult ♂ (CW 16.2, CL 11.8, CH 7.1, FW 5.5; CW 14.3, CL 10.5, CH 6.1, FW 5.1), Southwest Region, Mount Manengouba Ecological Reserve, Man’s Crater Lake Manengouba (5.032458° N, 9.827178° E), 1,958 m asl, 14 March. 2017, coll. P. A. Mvogo Ndongo ( ZMB Crust. 30319) ; 1 adult ♀ (CW 14.8, CL 10.9, CH 6.4, FW 4.7 mm) Mount Manengouba Ecological Reserve, Man’s Crater Lake Manengouba (5.032458° N, 9.827178° E), 1,958 m asl, 14 March 2017, coll. P. A. Mvogo Ndongo ( ZMB Crust. 30319) ; 2 adult ♂ (CW 13.3, CL 9.7, CH 5.6, FW 4.6; CW 14.8, CL 10.7, CH 6.2, FW 4.9), Mount Manengouba Ecological Reserve, Man’s Crater Lake Manengouba (5.032458° N, 9.827178° E), 1,958 m asl, 14 March 2017, coll. P. A. Mvogo Ndongo ( LZUY 20 ) ; 2 subadult ♂ (CW 11.1, CL 8.6, CH 4.8, FW 4.3; CW 12.7, CL 9.2, CH 5.7, FW 4.3) Mount Manengouba Ecological Reserve, Man’s Crater Lake Manengouba (5.032458° N, 9.827178° E), 1,958 m asl, 14 March 2017, coll. P. A. Mvogo Ndongo ( LZUY 20 ) ; 1 subadult ♀ (CW 11.2, CL 8.2, CH 4.8, FW 4.8) Mount Manengouba Ecological Reserve, Man’s Crater Lake Manengouba (5.032458° N, 9.827178° E), 1,958 m asl, 14 March 2017, coll. P. A. Mvogo Ndongo ( LZUY 20 ) .

Type material examined. CAMEROON. Holotype: juvenile ♂, CW 12.5 mm, Barombi Mbo [formerly Johann Albrechtshöhe (Government Station Johann Albrecht Mountain), Barombi Station] (4.666686° N, 9.392042° E) 323 m asl, 10 September 1909, coll. Carl Rathke ( ZIM K3506) . Paratypes: 3 adult ♀, CWs 22.0, 21.0, 21.0 mm (ovigerous), 1 subadult ♀, CW 13.5 mm, Barombi Mbo [formerly Johann Albrechtshöhe (Government Station Johann Albrecht Mountain), Barombi Station] (4.666686° N, 9.392042° E) 323 m asl, 10 September 1909, coll. Carl Rathke ( SMF 5093 , donated by ZIM K3506).

Diagnosis. Carapace high ( CH /FW 1.24), smooth ( Figs. 1 , 2a ). Postfrontal crest faint but complete, meeting anterolateral margins of carapace ( Fig. 2b ). Exorbital tooth very small, low, epibranchial, intermediate teeth almost undetectable, each reduced to small granule ( Figs. 1 , 2a ). Third maxilliped exopod long, reaching one-third length of merus, exopod completely lacking flagellum, third maxilliped ischium with faint but distinct vertical sulcus ( Fig. 4a ). Mandibular palp with small hard ledge at junction between terminal, subterminal segments, field of long setae at junction between terminal, subterminal segments ( Figs. 4b, c ). Major (right) cheliped of male movable finger (dactylus) highly arched, with single large tooth in middle, single tooth one-third distance from tip, fingers enclosing oval interspace when closed; fixed finger (pollex) with 2 large teeth proximally, single large tooth in middle, single distinct small tooth distally ( Fig. 3a ). Cheliped carpus distal tooth large, wide, proximal tooth large, slim ( Fig. 3c ). Medial inferior margin of merus of cheliped with large jagged tooth one-third from distal margin, followed by six distinct smaller teeth that decrease in size proximally ( Fig. 3d ). G1 terminal article directed outward, broad at base then narrowing sharply, final two-thirds slim, tube-like ( Figs. 5a, b ); G2 terminal article long, flagellum-like, almost as long as G2 subterminal segment ( Fig. 5c ).

Description. Carapace ovoid, high ( CH /FW 1.24), with maximum depth in anterior region ( Figs. 1 , 2a ). Front one third CW (FW/CW = 0.34), deflexed, anterior margin nearly straight ( Figs. 1 , 2a ). Carapace surface, lower orbital margins smooth ( Figs. 1 , 2a, b ). Postfrontal crest well defined, incomplete, ending just before meeting anterolateral margins of carapace ( Fig. 2b ). Epigastric crests, cervical, branchial, cardiac, intestinal, urogastric grooves all either faint or undetectable ( Figs. 2a, b ). Exorbital tooth very small, low; epibranchial tooth granular, almost undetectable ( Figs. 2a, b ). Intermediate tooth on anterolateral margin between exorbital, epibranchial teeth reduced to small granule, almost undetectable ( Figs. 2a, b ). Anterolateral margin of carapace smooth ( Figs. 2a, b ), posterolateral margin curving inward, continuous with anterolateral margin ( Figs. 2a, b ). Carapace posterior margin about 2/3 as wide as CW ( Fig. 2a ). Carapace sidewall with vertical, longitudinal (epimeral) sutures dividing sidewall into suborbital, subhepatic, pterygostomial regions ( Fig. 2b ). Longitudinal suture beginning at respiratory opening, curving backward across sidewall dividing suborbital, subhepatic regions from pterygostomial region ( Fig. 2b ). Vertical suture faint, beginning at epibranchial tooth, curving forward then sharply down, meeting longitudinal suture, dividing suborbital from subhepatic regions ( Figs. 2 a, b ). Thoracic sternite s1 small, pointed distally, s1/s2 suture short but detectable ( Figs. 2c ), s2/s3 suture deep, completely crossing sternum, s3/s4 suture incomplete, reduced to two small notches at each side ( Fig. 2c ). Mandibular palp two-segmented, with small hard ledge with long setae at junction between terminal, subterminal segments ( Figs. 4b, c ). Third maxillipeds ( Fig. 4a ) filling entire buccal cavern, except for transversely oval efferent respiratory openings in superior lateral corners; ischium with faint vertical groove; third maxilliped exopod lacking flagellum ( Fig. 4a ).

Male chelipeds greatly unequal, right larger, longer than left ( Fig.1 ), fixed finger (pollex) with two large teeth proximally, single large tooth in middle, single small tooth distally ( Fig. 3a ); movable finger (dactylus) highly arched, slim, with single large tooth in middle, single tooth one-third distance from tip, closed fingers enclosing oval interspace ( Fig. 3a ). Cheliped carpus distal tooth large, wide, proximal tooth almost same size as distal tooth but slimmer ( Fig. 3c ). Medial inferior margin of merus of cheliped with large jagged tooth one-third from distal margin, followed by six distinct smaller teeth that decrease in size proximally ( Fig. 3d ). Walking legs (pereiopods p2-p5) slender (right p5 missing in adult male figured) ( Fig. 1 ). Dactyli p2-p5 distinctly long, tapering to point, each bearing rows of downward-pointing sharp setae ( Fig. 1 ). Male pleon triangular, sides not indented, telson rounded at distal margin ( Fig. 2c ). G1 terminal article directed outward, broad at base then narrowing sharply, final two-thirds slim, ending in tube-like tip ( Figs. 5a, b ); G1 subterminal segment very wide at base, tapering in central region, distally forming distinctly rounded shoulder at segmental margin; dorsal membrane at segmental/article junction horizontally broad, rectangular ( Figs. 5a, b ,). Ventral face of G1 subterminal segment with raised longitudinal flap extending one third across segment, forming roof of chamber for G2 ( Fig. 5a ); dorsal face of G1 subterminal segment smooth ( Fig. 5b ). G2 subterminal segment wide at base, then tapering sharply to form long, thin, slightly tapering, upright process, terminal article long, flagellum-like, almost as long as G2 subterminal segment ( Fig. 5c ). Female right, left adult chelipeds subequal, fixed, movable fingers of cheliped interspersed with series of small acute teeth along length. Anterolateral margins of carapace with small teeth. Female pleon wide, covering entire sternum, sides reaching bases of coxae of p2-p5.

Size. Louisea balssi is a small species with an adult size range between CWs 13.8 and 22.0 mm, and a pubertal moult that occurs between CWs 12.8 and 13.4 mm.

Color. Carapace and appendages in life reddish brown; preserved specimens ( Fig. 1 ) uniformly light brown.

Type locality. The type locality of L. balssi is in the Bakossi region at Barombi Mbo near Kumba [formerly Johann Albrechtshöhe (Government Station Johann Albrecht Mountain), Barombi Station] (4.666686° N, 9.392042° E) 323 m asl which is situated north of Mount Cameroon in the Bakossi highlands of the Southwest Region of Cameroon. We were unable to locate “Eosung” that is given in the label information of the types ( Cumberlidge 1999), and we have corrected the altitude of Barombi Mbo to 323 m asl (because 1,060 m asl is probably a label transcription error, given that 1,060 feet is approximately 323 m). The present redescription is based on the largest adult male specimen from the stream near Man’s Crater Lake Manengouba, in Manengouba Ecological Reserve.

Distribution. Louisea balssi is endemic to the rainforests of the Southwest Region of Cameroon where it is now known from an expanded range that includes two localities that are both in small streams flowing into lakes: at Barombi Mbo (323 m asl) and at Manengouba (1,958 m asl) that are 63 km apart. Louisea balssi might also occur in other suitable wetland habitats in this part of Cameroon because this region is still poorly surveyed for freshwater crabs.

Remarks. A brief history of the taxonomy of L. edeaensis and L. balssi is available in Mvogo Ndongo et al. (2017a). Louisea balssi (as Globonautes balssi Bott, 1959 ) was originally described from a juvenile male by Bott (1959) who sketched the G1. Cumberlidge (1987) discussed the taxonomic status of G. balssi but was unable to contribute further due to the lack of material. Cumberlidge (1994) assigned museum specimens collected from Yabassi and Yaounde in Cameroon to L. edeaensis , but later ( Cumberlidge 1999) reassigned these specimens to L. balssi and supplemented his redescription of L. balssi with characters of the adult male from Yabassi as well as the juvenile holotype. The subsequent discovery of new material of L. edeaensis by Mvogo Ndongo et al. (2017a) resulted in the transfer of the specimens from Yabassi and Yaounde back to L. edeaensis , thereby reducing the utility of the redescription of L. balssi by Cumberlidge (1999), and leaving the taxonomy of this taxon in confusion.

This unsatisfactory situation has now been resolved with the present availability of new material of L. balssi , including an adult male, making it possible to revise and clarify the diagnosis of Louisea given in Cumberlidge (1999). The specimens of L. balssi from Man’s Crater Lake Manengouba agree well in every respect with the type specimens of L. balssi from Barombi Mbo, although there are small differences in the size of the exorbital and epibranchial teeth that may be attributable to differences between juvenile and adult specimens ( Cumberlidge 1994, 1999, Mvogo Ndongo et al. 2017a). Both species of Louisea share the following characters that justify their continued assignment to this genus. The mandibular palp has a small hard setose process at the junction between the terminal article and subterminal segment ( Fig. 4b ) that is not visible in the posterior view ( Fig. 4c ); the exopod of the third maxilliped lacks a flagellum; s3/s4 is incomplete, and consists of 2 small notches at the sides of the sternum; the G1 terminal article is broad at the base then narrows sharply, and the final two-thirds are slim and end in a tube-like tip ( Figs. 5a, b ); and the G2 terminal article is long, flagellum-like and almost as long as the G2 subterminal segment ( Fig. 5c ).

The following characters distinguish L. balssi from L. edeaensis . The exorbital and epibranchial teeth of L. balssi are barely detectable and the intermediate tooth is undetectable (whereas in L. edeaensis these three teeth are small but distinct); the carapace of L. balssi is high ( CH /FW 1.24) (whereas the carapace of L. edeaensis is of medium height ( CH /FW 1.0-1.1); the cheliped dactylus of L. balssi is highly arched (whereas the cheliped dactylus of L. edeaensis is slim and straight); the cheliped fixed finger of L. balssi has two large teeth proximally (whereas in L. edeaensis the fixed finger has a single large three-peaked proximal tooth); and the cheliped carpus distal tooth of L. balssi is subequal to the proximal tooth (whereas in L. edeaensis the distal tooth is larger and broader than the proximal tooth).

Figures

FIGURE 1. Louisea balssi (Bott, 1959), adult male CW 16.2 mm from Man’s Crater Lake Manengouba, Cameroon (ZMB Crust.30319) (missing left periopod 5). Dorsal view of whole animal showing color when freshly collected.Scale bar equals 8 mm.

FIGURE 2. Louisea balssi (Bott, 1959), adult male CW 16.2 mm from Man’s Crater Lake Manengouba, Cameroon (ZMB Crust.30319). a, carapace dorsal view; b, carapace, frontal view; c,thoracic sternite.Scale bar equals 5 mm (a,b,c).

FIGURE 3. Louisea balssi (Bott, 1959), adult male CW 16.2 mm from Man’s Crater Lake Manengouba, Cameroon (ZMB Crust.30319).a, rightchela frontal view;b, left chela frontalview; c,right chelipedcarpus showingthe first (distal) andsecond (proximal) carpal teeth; d, right cheliped merus showing the inferior margin with the large and prominent distal tooth and the toothed margin.Scale bar equals 5 mm (a,b), 2 mm (c, d).

FIGURE 4. Louisea balssi (Bott, 1959), adult male CW 16.2 mm from Man’s Crater Lake Manengouba, Cameroon (ZMB Crust. 30319). a, third maxilliped showing the faint vertical groove on the ischium, and the absence of a flagellum on the exopod; a, frontal view of right mandible showing small hard setose process at the junction between the palp segments; b, ventral view of the right mandible.Scale bar equals 2 mm (a), 1 mm (c, d).

FIGURE 5. Louisea balssi (Bott, 1959), adult male CW 16.2 mm from Man’s Crater Lake Manengouba, Cameroon (ZMB Crust.30319). a, G1 ventral view; b, G1 dorsal view; c, G2 ventral view.Scale bar equals 1 mm (a,b), 2 mm(c).