Erimetopus vandenbrandeni ( Balss, 1936 ) Cumberlidge & Reed, 2004

Cumberlidge, Neil & Reed, Sadie K., 2004, Erimetopus vandenbrandeni (Balss, 1936) n. comb., with notes on the taxonomy of the genus Erimetopus Rathbun, 1894 (Brachyura: Potamoidea: Potamonautidae) from Central Africa, Zootaxa 422 (1), pp. 1-27 : 14-24

2. Erimetopus vandenbrandeni ( Balss, 1936) n. comb. ( Figs. 18–45 )

Potamon (Potamonautes) vandenbrandeni Balss, 1936: 190 , fig. 26.

Potamon vandenbrandeni: Chace, 1942: 223 .

Potamonautes (Longipotamonautes) vandenbrandeni: Bott, 1955: 240–241 , fig. 22A, 69A,a–b, pl. III, fig. 3a–b.

Type material: Democratic Republic of Congo (formerly Zaire): Lectotype (here designated), male subadult (cw 16.8, cl 12.4, ch 4, fw 4.4 mm) Kinshasa, 04°17’60”S, 15°18’ E, coll. G. F. de Witte, 31.viii.1930 ( MRAC 1273 ) . Paratypes, 2 females, both ovigerous (cws 30.4, 28.5 mm) Kinshasa S 04°19’, E 015°19’, 1926, coll. Dr. van den Branden ( MRAC 247­248 ) . Paratype, female, ovigerous (cw 35.5 mm) coll. Dr. van den Branden, 1926 ( MRAC 251); paratype, female, ovigerous (cw 29.8 mm), Kinshasa, coll. Dr. van den Branden, 1926 ( MRAC 252 ) ; paratype, female, ovigerous, Kinshasa, 1931, coll. C. Henrard ( MRAC 1640 ) .

Additional material. Democratic Republic of Congo: female, ovigerous (cw 30 mm) Kinshasa , coll. Dr. van den Branden, 1926 ( MRAC 249 ) ; female, ovigerous (cw 33.8 mm), Kinshasa , coll. Dr. van den Branden, 1926 ( MRAC 250 ) ; female, ovigerous (cw 35.1 mm), Kinshasa , coll. Dr. van den Branden, 1926 ( MRAC 253 ) ; female, ovigerous (cw 38 mm), Kinshasa , coll. Dr. van den Branden, 1925 ( MRAC 1557 ) ; female, ovigerous (cw 35.2 mm), Kinshasa , coll. Dr. van den Branden, 1925 ( MRAC 1559 ) ; 3 females, all ovigerous (cws 24.9, 22.7 mm, one damaged), Kinshasa , coll. Dr. van den Branden, 1930 ( MRAC 1566–1568 ) ; 2 females, both ovigerous (cws 24, 22.6 mm), Kinshasa , coll. C. Henrard, 1931 ( MRAC 1634–1635 ) ; 4 females, all ovigerous (cws 31.2, 25.8, 25.8, 22.6 mm), Kinshasa , coll. C. Henrard, 1931 ( MRAC 1636–1639 ) .

Diagnosis. Frontal margin smooth; either straight or only faintly indented in center; eyestalk normal length, not tapering distally; cornea not reduced, pigment dorsal and ventral; margin of meri of P2–P5 lined by dense hair­like setae; second carpal tooth of P1 reduced (much smaller than first carpal tooth); carapace very flat (ch/fw 0.9); carapace height less than front width; anterolateral margin between exorbital, epibranchial teeth very long, straight, directed outward then curving sharply inward, forming deep sinus before meeting epibranchial tooth; terminal article of gonopod 1 one­third as long as subterminal segment, terminal article tubular with parallel sides, medial and lateral folds low and even throughout length, tip of terminal article broad, with distinct triangular medial corner; distal margin of subterminal segment of gonopod 1 distinctly indented in middle; dorsal membrane broadest in middle, tapering sharply at both sides, narrowest at lateral and medial margins; gonopod 2 long, terminal article long, slender, flagellum­like.

Redescription. Carapace outline subhexagonal/rounded. Frontal margin smooth, either straight or faintly indented in center; front horizontal or only slighlty deflexed; front narrow (fw/cw 0.3); postfrontal crest incomplete, epigastric lobes continuous with postorbital crests, but lateral ends of postorbital crests not meeting anterolateral margins. Exorbital tooth small, pointed; epibranchial tooth large, sharp, directed forward, positioned well behind postfrontal crest. Eyestalks normal length, not tapering distally; cornea not reduced, pigment dorsal and ventral; orbit narrow (1/7 cw), upper orbital margin semi­circular; carapace flat, height less than front width (ch/fw 0.9). Anterolateral margin of carapace between exorbital and epibranchial teeth lacking intermediate tooth; margin granulated, very long, straight, directed outward, then curving sharply backward, forming deep sinus before meeting epibranchial tooth; anterolateral margin of carapace posterior to epibranchial tooth with two small teeth behind epibranchial tooth; margin continuous with posterolateral margin. Carapace sidewall with vertical sulcus, curving upward from longitudinal groove to meet anterolateral margin at exorbital tooth, dividing sidewall into three parts. Second antennal segments broad, filling lateral margins of antennular fossae.

Exopod of third maxilliped with long flagellum, ischium smooth, lacking vertical sulcus. Thoracic sternal sulcus s1/s2 either faint or absent; thoracic sternal sulcus s2/s3 deep, slightly curved, running horizontally across sternum; thoracic sternal sulcus s3/s4 reduced to two small side notches. Episternal sulci s4/e4, s5/e5, s6/e6, s7/e7 each marked by visible groove.

Chelipeds of adult female and subadult male lectotype slim, slightly heterochelous, with long narrow fingers (dactylus, propodus), dactylus not arched, teeth of both fingers small, even. First carpal tooth on inner margin of carpus of cheliped large, slender, pointed, curving forward, second carpal tooth very small (0.25 x first carpal tooth); series of small teeth on outer margin of carpus of P1. Lateral, medial inferior margins of merus of cheliped faintly granular, single small pointed distal meral tooth superior surface of merus granular. Carpi of P2–P4 with spines on anterior margins, posterior margins smooth; carpus of P5 with single spine on anterior margin, posterior margin smooth; propodi of P2–P4 with spines on anterior margins, posterior margins smooth; propodus of P5 with spines on anterior and posterior margins; meri of P2–P5 with two sharp pointed distal teeth; margins of dactyli of P2–P5 with rows of strong spines. P5 shortest walking leg, propodus P5 broad, dactylus P5 very short, about half as long a dactyli of P2–P4. Terminal article of gonopod 1 one­third as long as subterminal segment, terminal article tubular with parallel sides, medial and lateral folds low and even throughout length, tip of terminal article broad, with distinct triangular medial corner; distal margin of subterminal segment of gonopod 1 distinctly indented in middle; dorsal membrane broadest in middle, tapering sharply at both sides, narrowest at lateral, medial margins. Subterminal segment of gonopod 2 broad­based, tapering sharply to long slim process, terminal article of gonopod 2 long, slender, flagellum­like. Erimetopus vandenbrandeni is a small species with an adult size between cw 22.6 and 38 mm. For more details, and illustrations of the type material see Balss (1936, fig. 26 ), for a description, photographs, and illustrations of other specimens see Bott (1955).

Distribution. Erimetopus vandenbrandeni is found either in, or near, the Congo River in the vicinity of Kinshasa, D. R. Congo ( Fig. 45 ). Balss (1936) based his description on three lots of specimens, all from Kinshasa, and Bott (1955) reported on two female specimens from Kalima (near Kinshasa) collected by E. Dartevelle in 1948 (MRAC 31998, 32910). This species has a relatively narrow distribution, is not well represented in museum collections, and has not been collected (to our knowledge) since 1935. For these reasons we would judge its conservation status to be in the Critically Endangered category (Red List Criteria A2) of the Red List Assessment ( IUCN 2001).

Relationships. Erimetopus vandenbrandeni is close to E. brazzae and has a similar subhexagonal carapace outline, similar tooth patterns on the carapace margins and walking legs, a large epibranchial tooth, and a long, toothed anterolateral margin of the carapace between the exorbital and epibranchial teeth. Erimetopus vandenbrandeni differs from E. brazzae as follows. The carapace of E. vandenbrandeni is conspicuously flattened (it is of medium height in E. brazzae ), the second carpal tooth on the inner margin of the carpus of the cheliped of E. vandenbrandeni is small (this tooth is large in E. brazzae ), and the superior margins of the meri of the walking legs P2–P5 have dense hair­like setae (these margins lack setae in E. brazzae ). In addition, the vertical groove on the carapace sidewall of E. vandenbrandeni meets the base of the epibranchial tooth (this groove is not directed toward the epibranchial tooth in E. brazzae ); there is a deep sinus on the anterolateral margin just anterior to the epibranchial tooth in E. vandenbrandeni (this sinus is lacking in E. brazzae ), and the frontal margin of of E. vandenbrandeni is straight (this margin is distinctly indented in E. brazzae ). Erimetopus vandenbrandeni shares characters such as a straight frontal margin, and a row of hair­like setae on the meri of P2–P5 with P. (E.) b. frontospinulosa. However, E. vandenbrandeni can be easily distinguished from P. (E.) b. frontospinulosa by the same characters outlined above that distinguish E. vandenbrandeni from E. brazzae .

Remarks. Only a single subadult male specimen (cw 16.8 mm) of E. vandenbrandeni is known ( Figs. 27–35 , 39–45). The gonopods of E. vandenbrandeni were not illustrated by Balss (1936) in the original description of this species, but gonopod 1 of the male of E. vandenbrandeni was sketched by Bott (1955: 22 A), although Bott did not list this specimen in the material examined section of his work. Gonopod 1 of the male of E. vandenbrandeni from Kinshasa is shown in more detail in the present study ( Figs. 31–33 , 42–44), and gonopod 2 of this species is illustrated here for the first time ( Figs. 34–35 ).

The general form of gonopods 1 and 2 of E. vandenbrandeni is the same as that found in the Old World potamonautid and potamid freshwater crabs ( Bott 1955, 1970; Cumberlidge 1999). For example, gonopod one is in four parts that include a relatively well­developed terminal article and a broad dorsal membrane. This also describes the general organization of the first gonopod of a number of African genera such as Potamonautes , Liberonautes , Sudanonautes , Potamonemus , Louisea , Afrithelphusa , Globonautes , Platythelphusa , and Deckenia (Cumberlidge 1999) . Similarly, gonopod two is in four parts that include a relatively well­developed flagellum­like terminal article. These characteristics also describe the general organization of the second gonopod of African genera such as Potamonautes , Liberonautes , Louisea , Afrithelphusa , Platythelphusa and Deckenia (Cumberlidge 1999) .

Bott (1955) assigned E. vandenbrandeni to Potamonautes (Longipotamonautes) on the basis of perceived similarities between the shape of the terminal article of gonopod 1 in E. vandenbrandeni and Potamonautes ballayi (A. Milne­Edwards, 1887) (the type­species of the subgenus Longipotamonautes Bott, 1955 ). Although the terminal article of gonopod 1 of P. ballayi has a broad tip that is somewhat similar to that of E. vandenbrandeni , the terminal article in P. ballayi is distinctly tapered (which is typical of Potamonautes ), rather than tubular and hose­like, as in E. vandenbrandeni . Moreover, the first gonopod of E. vandenbrandeni ( Figs. 31–33 , 42–44) differs from P. ballayi in other characters such as the shape of the dorsal membrane, the shape of the distal margin of the subterminal segment, and the position and definition of the longitudinal (seminal) groove of the terminal article ( Capart 1954; Bott 1955, fig. 23 ).

It should be noted that the hose­like terminal article of the first gonopod of E. vandenbrandeni is neither identical to, nor close in organization to, the strongly­tapered terminal article of the more than 60 species of Potamonautes that we are familiar with. Moreover, P. ballayi (which is the species of Potamonautes that is closest to E. vandenbrandeni according to Bott (1955)) is in fact distinctly different from Erimetopus when non­gonopod diagnostic characters of the carapace, pereopods and mouthparts are considered ( Bott 1955). For example, like all species of Potamonautes , P. ballayi lacks teeth on the anterolateral margin of the carapace between the exorbital and epibranchial teeth, lacks teeth on the outer margin of the carpus of the cheliped, and lacks teeth or setae on the margins of the carpi and propodi of the walking legs (P2–P4). In addition, P. ballayi can be further distinguished from Erimetopus by the former taxon’s lack of teeth on the anterolateral margin behind the epibranchial tooth, by a distinctly arched dactylus of the major cheliped, and by a complete and deep sternal sulcus s3/s4.

There are only a few other species of freshwater crabs in Africa with a noticeably flat carapace similar to that found in E. vandenbrandeni . Examples include the completely aquatic lake­living crab Platythelphusa maculata (ch/fw 0.9) and the West African river crab Liberonautes chaperi (ch/fw 0.9) (Cumberlidge et al. 1999; Cumberlidge 1999). In general, African freshwater crabs with a flat carapace tend to be completely aquatic river or lake dwellers that rarely, if ever, breathe air at any point in their life cycle (Cumberlidge 1999). It remains to be seen whether this generalization applies to E. vandenbrandeni , and the answer to questions such as this must await data from new field collections in the lower Congo River. Given the current long­term political unrest in Central Africa, it may be a very long time before anyone is in a position to collect thoroughly enough to obtain a series of male specimens of any species of this interesting genus.

Figures

FIGURE 45. Summary of the distribution of Erimetopus brazzae (A. Milne­Edwards, 1886) (large grey circles) and E. vandenbrandeni (Balss, 1936) (small black circle). Locality data are from the present study and from the literature (Rathbun 1905, 1921; Balss 1936; Bott 1955).

Figures 18–26. Erimetopus vandenbrandeni n.comb. (Balss, 1936) adult female paratype (cw 29.5 mm), MRAC 1273. 18, carapace and eyes, dorsal view; 19, cephalothorax, carapace and eyes, frontal view; 20, carpus. propodus, and dactylus of right cheliped, frontal view; 21, carpus. propodus, and dactylus of left cheliped, frontal view; 22, carpus of cheliped, superior view; 23, carpus and merus of right cheliped, dorsal view; 24, merus of right cheliped, inferior view; 25, right pereopod 3; 26, right pereopod 5. Scale = 5 mm (18–19, 22, 25–26); 10 mm (20–21, 23–24).

Figures 27–35. Erimetopus vandenbrandeni n. comb. (Balss, 1936). 27–29, 31–35, subadult male lectotype, cw 16.8 mm, MRAC 1273. 30, adult female paratype (cw 29.5 mm), MRAC 252. 27, abdomen; 28, left third maxilliped; 29, anterior sternum (male); 30, anterior sternum (female); 31, left gonopod 1, ventral aspect; 32, left gonopod 1, dorsal aspect; 33, left gonopod 1 terminal article, dorsal aspect, detail; 34, left gonopod 2, ventral aspect; 35, left gonopod 2, dorsal aspect. Scale = 5 mm (27–30); 3 mm (31–32, 34–35); 1 mm (33).

FIGURES 36–38. Erimetopus vandenbrandeni n. comb. (Balss, 1936), photographs of adult female paratype (cw 29.5 mm), MRAC 252. 36, frontal view; 37, dorsal view; 38, underside, ventral view.

FIGURES 39–41. Erimetopus vandenbrandeni n. comb. (Balss, 1936), photographs of subadult male lectotype (cw 16.5 mm), MRAC 1273. 39, frontal view; 40, dorsal view; 41, underside, ventral view.

FIGURES 42–44. Erimetopus vandenbrandeni n. comb. (Balss, 1936), photographs of subadult male lectotype (cw 16.5 mm), MRAC 1273. 42, first gonopod ventral view; 43, first gonopod dorsal view; 44, first gonopod terminal article, dorsal view.