Wallaciia, Varella & Kullander & Menezes & Oliveira & López-Fernández, 2023

Varella, Henrique R, Kullander, Sven O, Menezes, Naércio A, Oliveira, Claudio & López-Fernández, Hernán, 2023, Revision of the generic classification of pike cichlids using an integrative phylogenetic approach (Cichlidae: tribe Geophagini: subtribe Crenicichlina), Zoological Journal of the Linnean Society 198 (4), pp. 982-1034 : 1015-1016

Node 183— Wallaciia , new genus u r n: l s i d: z o o b a n k. o r g: a c t: 9 7 8 0 B 3 3 1 - 2 5 8 7 -

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Type species: Crenicichla wallacii Regan, 1905 .

The genus Wallaciia is recovered in the ML and BI analyses, as well as in the parsimony analysis, under extended implied weighting (XIW/ DiscreteMatrixTE and XIW/ContinuousMatrixTE). However, it is not recovered in the parsimony analyses under equal weighiting (EW/DiscreteMatrix and EW/ ContinuousMatrixTE). We hypothesize that the discordance is a result of long-branch attraction caused by convergence in characters associated with specializations to rheophily (see Remarks). Such convergence clustered W. heckeli and W. urosema , two species that inabit rapids and were represented by morphological characters only, with Teleocichla . Although the node corresponding to the genus Wallaciia was moderately supported in the ML tree (BS 71%; Table 6), it shows high support in the BI tree (PP 100%) and is recovered as monophyletic in all previous molecular studies ( Kullander et al. 2010; Piálek et al. 2012; Burress et al. 2017, 2018; Fig. 3). Moreover, three of the five unambiguous morphological synapomorphies optimized for the group ( Table 13) are congruent with characters used to diagnose the C. wallacii group in previous studies and also to diagnose the genus Wallaciia as proposed herein.

Diagnosis: Wallaciia includes small-sized species (max. SL 52–85 mm) that differ from all pike cichlids by the following combination of traits: large eyes (orbital diameter 7.8–12.6% of SL); presence of serrations on the posterior margins of the supracleithrum; posterior margin of preopercle with prominent, spine-like serrations; pectoral fin with 13–14 rays (vs. 15–18; in modal values); reduced predorsal squamation (not extending on to the NFL0; see char. 28); and pelvic fin rounded with second ray longest and all post-lachrymal infraorbitals autogenous (vs. infraorbitals 4 and 5 co-ossified, forming a median opening). Wallaciia heckeli deviates from the typical Wallaciia morphology by having some characters convergently shared with Teleocichla , another small-bodied genus. For example, W. heckeli has smooth preopercle and suprachleitrum, jaws not prognathous, and the pattern of fixation of oral teeth and configuration of the lower pharyngeal jaw is different from the typical Wallaciia species. Also, it can be distinguished from other Wallaciia species by having smaller eyes, infraorbitals co-ossified forming a median opening (vs. 4 and 5 autogenous), and pelvic fin pointed, with third ray longest (vs. rounded). Besides, Wallaciia differs from Teleocichla by lacking several other osteological modifications associated to life in rapids and diagnostic of the later (see below).

Species of Wallaciia are additionally distinguished from Saxatilia by the absence of a humeral blotch and suborbital marking, from Lugubria by having fewer scales in the E1 series (52–64 vs. 88–123 scales) and fewer vertebrae (31–34 vs. 38–42), from Hemeraia by having most scales on the flanks ctenoid (combination of patterns 1 and 2 on dorsal portion and pattern B2 on ventral portion of the flank) vs. most flank scales cycloid (combination of patterns 3 and B3). Wallaciia are additionally distinguished from the subgenus Crenicichla of Crenicichla , by cycloid (vs. ctenoid) scales on the cheek and on the chest. Wallaciia differs from the subgenus Batrachops of Crenicichla by the absence of a reticulate colour pattern on the flank (vs. reticulate pattern on flanks formed with the dark pigmentation on the base of the scales), and from the subgenus Lacustria of Crenicichla by the absence of a suborbital marking (vs. presence of dark puntulations more or less scattered on the cheek forming different patterns of suborbitals markings).

Distribution: As proposed here, Wallaciia includes eight species that are distributed in the Amazon basin, Río Orinoco, and Essequibo river basins. Species of Wallaciia are present in almost all major rivers of the Amazon basin from the Río Madeira to the Río Tocantins, but are not found in the Western portion of the Amazon basin, i.e. tributaries and main channel of the Amazon basin west of Santo Antonônio do Içá.

Remarks: This is the first phylogenetic study of pike cichlids that includes Wallaciia heckeli and W. urosema , two rheophilic species that inhabit rapids of the Río Trombetas and Río Tapajós basins, respectively. In the two parsimony analyses of the combined datasets under the equal weighting scheme, these species cluster with Teleocichla , as successive sister-groups. This is probaby a result of long-branch attraction of some convergences shared by W. heckeli and Teleocichla , resulting in synapomorphies of an expanded Teleocichla (including W. heckeli and W. urosema ) or of the group Teleocichla + W. heckeli in the aforementioned parsimony trees. Many of these convergent characters are correlated with specializations for rheophilic habitats and specialized benthic diets (e.g. Kullander 1988; Varella et al. 2016), including reduced cheek squamation, differences in number of precaudal and caudal vertebrae, acute mouth with narrow gape, ridged vomer (linked with a downturned mouth), and modifications on the format and teeth of the lower pharyngeal jaw (char. 19: 0=>2; char. 113: 0=>1; char. 128: 0=>1; char. 159: 1=>2 A; char. 205: 2=>3; char. 206: 0=>1). Interestingly, these characters are shared between Teleocichla and three species of Wallaciia instead of two—the third being W. compresiceps, also a rheophilic species that inhabits rapids in the Río Tocantins. Further study is needed to help clarify the relationships of rheophilic Wallaciia species, because W. compressiceps is the only taxon in our matrix represented by both molecular and morphological data, whereas the others are represented by morphology only, which is probaby the reason why W. compressiceps grouped with Wallaciia instead of Teleocichla , as did the two species with only morphological data.