S. rhynchitis was previously referred to S. jurupari and known as S. sp. 'red lips' in the ornamental trade.
It can be distinguished from congeners by the following combination of characters: lips red in live adult specimens; absence of dark blotches or bands on the sides of the body; absence of white spots or vermiculations on sides of head; 8-10, modally 9, soft dorsal-fin rays (vs. 12-14 in other Satanoperca species); 25-27, modally 26, scales in the E1 row above the lateral line (vs. 27-31); 12-14, modally 14, ceratobranchial gill rakers (vs. 17-23).
Among the described species S. rhynchitis is most similar to S. jurupari but can be distinguished by possession of: a modal dorsal-fin count of XV.9 (vs. XV.10); 26 (vs. 27) scales in the E1 row above the lateral line; 13-15, usually 13-14 gill rakers (vs. 14-18, usually 16-17); gill blade narrower (vs. wider) than ceratobranchial; snout generally longer, measuring 14.3-19.4 % SL (vs. generally shorter, 11.3-15.9 % SL).
The precise identity of S. jurupari is a confusing issue, however, with differences in colour pattern and morphological characters observed across its range. In addition, a red-lipped form similar to S. rhynchitis occurs to the immediate south of its range, in Amapá state, northeastern Brazil, but specimens from the rio Araguari in Amapá were not recovered as genetically distinct from S. jurupari in phylogenetic analyses, and in morphological terms they appear intermediate between S. jurupari and S. rhynchitis.
It is still unclear whether these intermediate fish (1) are natural hybrids between S. jurupari and S. rhynchitis, (2) represent a distinct species themselves, (3) signify a clinal gradient of variation between populations from Amapá and French Guiana, or (4) S. rhynchitis is a rheophilic phenotype of a more widespread species.
There is also a possibility that populations from the Río Orinoco watershed in Colombia and Venezuela, currently referred to as S. mapiritensis (Fernández-Yépez 1950), may turn out to be conspecific with S. jurupari. There appears to be no clear genetic separation between these two putative species nor a form known to aquarists as S. sp. 'Negro-Alto Orinoco'. It is also worth noting that both S. mapiritensis and a form from the Río Madre de Dios watershed in Peru both have orange-coloured lips as adults.
Based on current knowledge, it thus remains impossible to deduce whether the group of putative species currently comprising S. jurupari, S. mapiritensis, and S. rhynchitis, plus populations from Amapá and the upper Negro/upper Orinoco region, represent distinct taxa or a single meta-population which can be referred to as S. jurupari sensu lato. Here on SF we include the named species separately, since they continue to be considered valid.
Satanoperca was considered a synonym of Geophagus for a number of decades before being revalidated by Kullander (1986). It is separated from all other members of the putative cichlid subfamily Geophaginae by presence of a small ocellated spot at the upper caudal-fin base, and from Geophagus by a number of morphological characters as follows: equal numbers of abdominal and caudal vertebrae or one more abdominal vertebra (vs. more caudal than abdominal vertebrae in Geophagus); no ribs on caudal vertebrae and no postabdominal swimbladder extensions (vs. presence of both in Geophagus; cheek scaled rostrally to centre (vs. naked on anterior half; dorsal and anal fins naked (vs. scaled); external gill rakers on lower limb of first gill arch attached to the skin covering the gill filaments (vs. attached to ceratobranchial skin); jaw dentition reduced to one or two short series in each jaw (vs. pluriseriate with wide band of inner teeth); absence (vs. presence) of tooth plates on 4th ceratobranchial; presence (vs. absence) of an ocellus on caudal-fin base; both or only upper lip fold continuous (vs. both interrupted anteriorly); preoperculum and supracleithrum frequently serrated (vs. entire); absence (vs. presence) of median hypural cartilage; 3 (vs. 4) infraorbitals.
The genus is likely to contain additional species, and has been separated into three groups with distinctive morphology, namely the S. jurupari group, the S. daemon group, and the monotypic S. acuticeps group.
Among these, members of the S. jurupari group are characterised by a colour pattern comprising a dark lateral stripe or row of blotches along the side of the body, normally XV.10 (XIV-XVII.8-11) dorsal-fin rays, normally 27 (26-28) E1 scales (the longitudinal row immediately above the lower lateral line, excluding the pectoral girdle), and 12-18 rakers on the first gill arch.
S. daemon group members grow larger than other congeners, possess one or two large dark blotches on the side of the body and a prominent ocellus at the upper caudal-fin base, usually XIX.13 (XII-XIV.12-14) dorsal-fin rays, 29-31 E1 scales, and 18-22 gill rakers. S. acuticeps is unique in that it has a relatively more terminal mouth than all other genus members, normally XIII.12 (XIII.11-12) dorsal-fin rays, 27-28 E1 scales, and 17-20 gill rakers.
The groups also differ in reproductive strategy, with the S. daemon and S. acuticeps assemblages being substrate spawners, and the S. jurupari group mouthbrooders.
Satanoperca and a number of related genera are often included in the putative subfamily Geophaginae, and Kullander (1998) conducted a morphology-based phylogenetic study in which the neotropical Cichlidae was divided into six subfamilies of which the Geophaginae contained 16 genera divided among three 'tribes':
Acarichthyini - Acarichthys and Guianacara.
Crenicaratini - Biotoecus, Crenicara, Dicrossus and Mazarunia.
Geophagini - Geophagus, Mikrogeophagus, 'Geophagus' brasiliensis group, 'Geophagus' steindachneri group, Gymnogeophagus, Satanoperca, Biotodoma, Apistogramma, Apistogrammoides and Taeniacara.
Later molecular studies by Farias et al. (1999, 2000, 2001) resulted in the additions of Crenicichla and Teleocichla to the Geophaginae, a result supported by López-Fernández et al. (2005) who conducted the most detailed molecular analysis of the grouping to date including 16 of the 18 genera and 30 species.
However their conclusions regarding interrelationships between genera did vary somewhat from previous hypotheses and can be summarised by the following loosely-defined groups:
- a weakly-supported sister group relationship between Acarichthys and Guianacara.
- a well-supported 'Satanoperca clade' comprising Satanoperca, Apistogramma, Apistogrammoides and Taeniacara.
- a 'big clade' with Geophagus, Mikrogeophagus, 'Geophagus' brasiliensis group, 'Geophagus' steindachneri group, Gymnogeophagus, Biotodoma, Crenicara and Dicrossus.
- a 'crenicarine clade' with Biotoecus and Crenicichla.
No representatives of Teleocichla or Mazarunia were included in the study but the former is well-established as sister to Crenicichla while the latter has grouped closely with Dicrossus and Crenicara in earlier works.
The other main conclusions of the paper are confirmation that Geophaginae is a monophyletic group exhibiting strong signs of having undergone rapid adaptive radiation.
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