Subterranean Fishes of the World

Country

Types

Holotype: ANSP 100891 23.6mm SL. This species is the type‑species by original designation and monotypy of the cave‑restricted genus Stygichthys.

Distribution

Type locality: an undisclosed locality at Jaiba, Minas Gerais State, Brazil (c. 18^oS, 44^oW). Also recorded from xxxxxx.

Habitat

Nothing known. The fish was collected from water brought up from a depth of 30m during a well‑drilling operation.

Systematics

In a large study of the Family Characidae, based solely on morphological characters, Mirande (2010) was unable to draw any meaningful conclusions regarding the phylogeny of this species: "The position of this genus within Characidae is completely enigmatic; even its assignment to the Characidae can not be considered to be well justified. The single species of this genus, Stygichthys typhlops Brittan and Böhlke, has hypogean habits and some unique or much unusual features among the Characidae (Géry 1977). The presence in this species of a very short anal fin with only eight rays is unique within the Characidae. No information relevant to a hypothesis about the relationships of this genus is available and Stygichthys is maintained as incertae sedis within the Characidae."

Oliveira et al. (2011) made an extensive ingroup study of the Family Characidae. Their results strongly support a sister group relationship between S. typhlops and the monotypic Coptobrycon bilineatus (Ellis 1911) (redescribed by Langeani and Serra 2010, see also Serra, Carvalho and Langeani 2007 and Buckup 2011), and a sister group relationship between these two species and a group consisting of Probolodus heterostomus, Deuterodon iguape and Myxiops aphos (Figure below). All of these species are currently incertae sedis within Characidae. [Stygichthys typhlops specimen studied: LBP 8107, 37558, location Cacimba fazenda Lajeado, Jaíba, MG, Brazil, 15°24'41.7' S 43°45'19.7' W. Genbank accession numbers: 16S HQ171407, CytB HQ289694, Myh6 HQ289115, Rag1 HQ289308, Rag2 HQ289500].

In a study based on morphological and molecular data (Mirande 2018) the monotypic genus Stygichthys was placed in the Tribe Grundulini within the subfamily Stethaprioninae. Significantly, the four species shown to be sister species by Oliveira et al.2011 (see above and Figure) are also found close to Stygichthys within this tribe and it may be that we can now begin to explore the evolution of Stygichthys from its epigean ancestor.

The most recent study of the Family Characidae (Teran et al. 2020) has S. typhlops in a tree with Phycocharax rasbora, Cyanogaster noctivaga, "Hyphessobrycon" elachys and, again, Coptobrycon bilineatus.

Museum Holdings

Non-type specimens: all from Rio Verde Grande system, Rio Sao Francisco basin, Minas Gerais, município de Jaíba, Brazil. MZUSP 87677 (4: 29·3–39·7 mmLS) well at Fazenda do Seu Roque, c´orrego (stream) Escuro, 15◦ 24 41·7 S; 43◦ 45 19·7 W, C. Moreira, E. Trajano, M. de Pinna, O. Oyakawa, M. E. Bichuette & F. Passos, 27 April 2004. MZUSP 87678 (21: 22·8–45·8 mm LS; 4 CS) shallow well at Fazenda do Lajeado (also known as Fazenda do Mandioqueu), c´orrego Escuro, 15◦ 27 05·8 S; 43◦ 45 09·2 W, C. Moreira, M. E. Bichuette, O. Oyakawa, M. de Pinna, E. Trajano & F. Passos, 28 April 2004 (Moreira et al. 2010)

As above plus: LBP 8107, 37558. LESCI 000230/002, 38.9 mm SL (Pastana et al. 2019)