This species is relatively rare in the ornamental trade where it is also known as 'sparkling eartheater' and 'four-spot eartheater'.
It is sometimes confused with its similarly-patterned congeners S. daemon and S. lilith. These three species all possess 1-3 dark blotches on the side of the body and a relatively large ocellus on the upper caudal-fin base, characters that immediately separate them from the remainder of the genus which lack blotches on the body and have a relatively small ocellus on the upper caudal-fin base.
S. acuticeps is unique in possessing three flank blotches (vs. two in S. daemon, one in S. lilith), and also differs in a number of morphological characters (see below).
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.
The monophyly of the S. acuticeps group is well-supported in phylogenetic studies, although there appears to be some geographic genetic diversity, with a degree of separation between populations from the rios Maués and Purus, for example.
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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