Galatea schwabi (Clench, 1929)

Kondakov, Alexander V., Konopleva, Ekaterina S., Adesanya, Abiona J., Bespalaya, Yulia V., Braun, Jean J., Gofarov, Mikhail Y., Lyubas, Artem A., Tomilova, Alena A., Vikhrev, Ilya V., Pokrovsky, Oleg S. & Bolotov, Ivan N., 2020, The global freshwater bivalve checklist’s extension: Freshwater occurrences and phylogenetic position of Galatea clams from West Africa (Venerida: Donacidae), Ecologica Montenegrina 35, pp. 144-158 : 150-152

Galatea schwabi (Clench, 1929)

= Egeria schwabi Clench (1929) : 122, pl. 1, figs. 1-2; Purchon (1963): 251; Daget (1998): 227. = Egeria paradoxa hermaphrodita Clench (1929) : 121 [non Gmelin (1791): 3278].

= Galatea schwabi Huber (2010): 692 .

Figs. 1-3 , Table 1.

Type: Holotype MCZ 78.072 [ Museum of Comparative Zoology , Harvard University, Cambridge, Massachusetts, USA].

Type locality: “Lobetal, lower Sanaga River” [ CAMEROON: Sanaga River at Lobetal (lower reaches, slightly brackish section), 3.6322°N, 9.7704°E, altitude 5-6 m a.s.l., Littoral Province] (Clench 1929) .

Topotypes examined: CAMEROON: Sanaga River near Mouanko (lower reaches, slightly brackish section), 3.6360°N, 9.8100°E, altitude 5-6 m a.s.l., Littoral Province, 19-21.iii.2019, 5 specimens [ RMBH biv800: 2 shells; 5 ethanol-preserved tissue snips], Oleg Pokrovsky leg. The topotypes were collected 4 km east (upstream) of the type locality .

Other material examined: CAMEROON: Sanaga River at Monatélé (middle reaches, freshwater section), 4.2710°N, 11.1990°E, altitude 380 m a.s.l., Central Province, 19-21.iii.2019, 2 specimens [ RMBH biv801: 2 shells; one ethanol-preserved tissue snip], Oleg Pokrovsky leg.

Conchological re-description: Shell triangular, rather thick and strong. Specific trait is radial rays running from the umbones to the ventral margin, which can vary in number and width on both valves. These rays are purplish and impregnated into prismatic layer, visible also in the inner side of the shell, but mainly along the margin, especially in the ventral and anterior edges. Umbones high, almost in the center of the shell, eroded. Periostracum smooth, thin, have a propensity for scaling off. Nacre whitish, not shining; muscle scars and basal areas of pseudocardinal teeth can be tinted in purple. Young specimens with greenish yellow coloration, which turning to dark brown or black in adult individuals. Hinge plate strong and well-developed. The right valve with one median, dissected pseudocardinal tooth and short, flat lateral tooth; tubercular tooth-like structure is also above anterior muscle scar. The left valve with three pseudocardinal teeth, intermediate tooth usually smaller than the other two, and serves to articulate into hollow space of dissected teeth from the right valve. Umbo cavity very deep. Muscle attachment scars are well-developed, anterior scar oval-shaped, posterior scar more circular.

Habitats: This species inhabits freshwater and slightly brackish sections of a large river (see Fig. 2 for a freshwater section). Its type locality is situated approximately 20 km upstream of the river mouth, “just beyond tide water” (Clench 1929) but we recorded Galatea schwabi from the middle reaches of the Sanaga River at altitude 380 m a.s.l. The Edea Hydroelectric Power Station’s dam separates this part of its population from the downstream stock ( Fig. 1 ).

Distribution: Sanaga River in Cameroon ( Fig. 1 and Table 2).

Comments: This species may represent a separate taxon or a local population of the widespread Galatea paradoxa . DNA sequences of Galatea paradoxa samples from Ghana and Nigeria are urgently needed to produce a final solution on the status of these taxa.

Figures

Figure 1. Occurrences of Galatea schwabi (red stars) and Galatea paradoxa (light green stars). The locality data is given in Table 2. Freshwater basins are colored as follows: Sanaga (1), Cross (2), Niger (3), and Volta (4). The red dash indicates the Edea Hydroelectric Power Station’s dam on the Sanaga River. (Map: Mikhail Y. Gofarov).

Figure 2. Sanaga River in Cameroon, habitat of Galatea schwabi. (Photo: Jean J. Braun).

Figure 3. Shells of Galatea schwabi from Sanaga River, Cameroon. (A-B) Topotypes RMBH biv800, Mouanko (lower reaches, slightly brackish section). (C-D) Specimens RMBH biv801, Monatélé (middle reaches, freshwater section). Red arrows show well-developed muscle attachment scars. Scale bar = 10 mm. (Photos: Artem A. Lyubas).