Subterranean Fishes of the World

Country

Systematics

All four species of Mastacembelus included in this list are troglomorphic Lower Congo River residents (Alter et al. 2015, Day et al. 2017). Phylogenetic studies by these authors have shown conclusively that the sister species of M. brichardi is the epigean and non-troglomorphic M. brachyrhinus Boulenger 1899 and that this pair are the furthest from the root of the Family and the latest to evolve. M. crassus and M. aviceps are each other’s sister species and the sister of this pair is the epigean and non-troglomorphic M. simbi Vreven and Stiassny 2009. Clearly the evolution of troglomorphy in the Lower Congo has occurred twice independently and is a clear case of convergent evolution. See Vreven (2005) for further phylogenetic information on the Family Mastacembelidae. M. latens was not available for these studies but is almost certainly a third instance of the evolution of troglomorphy.

Diversification dynamics of the African Mastacembelus radiation inferred using BAMM. Top: Phylorate plot shows speciation rate along each branch (‘linear’ plot); warmer colours indicate faster rates; scale bar represents speciation rate per Ma. Bottom: Evolutionary rate variation through time (RTT plot); shading denotes confidence on rate reconstructions at any point in time. [Figure 2 from Day et al 2017, used with permission].

Biological Notes

The lower Congo River, and especially the northern and southern rapids below Pool Malebo, are home to many endemic species (Roberts and Stewart 1976, Bailey 1986, Thieme et al. 2005, Mamonekene 2005, Alter et al. 2015, Alter et al. 2017, Stiassny 2016). In particular there are at least eleven species, in five Families, which exhibit the troglomorphic features of reduced eyes and pigment:

Clariidae

Channallabes apus (Günther 1873) Teugels 1986

Dolichallabes microphthalmus Poll 1942

Gymnallabes nops Roberts and Stewart 1976

Platyallabes tihoni (Poll 1944) Poll 1977

Claroteidae

Notoglanidium pallidum Roberts and Stewart 1976

Mastacembelidae

Mastacembelus aviceps Roberts and Stewart 1976

Mastacembelus brichardi (Poll 1958) Vreven 2005

Mastacembelus crassus Roberts and Stewart 1976

Mastacembelus latens Roberts and Stewart 1976

Cichlidae

Lamprologus lethops Roberts and Stewart 1976

Mormyridae

Stomatorhinus microps Boulenger 1898

These features probably evolved because these species live at depth within the rapids and spend their whole lives in permanent darkness, analagous to life in caves. The ocular and craniofacial anatomy of several of these species have been studied (Schobert et al. 2010, 2011, 2013) but almost nothing else is known about these animals.