Evaluating the use of the anterior ceratohyal morphology to diagnose Laetacara Kullander , 1986 , with comments on other cichlid genera ( Cichlidae : Cichlasomatini )

The morphology of the anterior ceratohyal is herein analyzed in all the species of Laetacara currently known, and in some species of the tribes Cichlasomatini and Heroini, evaluating the use of this structure morphology to diagnose Laetacara as well as a key character to the classification of the tribe Cichlasomatini. It was concluded that the morphology of the anterior ceratohyal is not useful to diagnose species of Laetacara by being quite polymorphic among species of the genus. We can also conclude that the traditional use of this bone morphology in the taxonomy of the tribe Cichlasomatini at present stage of knowledge seems not to be appropriate due to the polymorphism occurring in the species analyzed herein, and until a similar work is done for the whole tribe.


Introduction
Osteology has been an important source of character states for taxonomic studies of the Teleostei.Several cichlid genera have osteological character states as diagnostic features, as well as, osteological characters are widely used in the classification of Cichlidae (see Kullander, 1986Kullander, , 1998;;Kullander & nijssen, 1989).Despite of using osteological diagnostic features, exhaustive studies about description, morphology and variation of osteological structures are scarce among cichlids.
Although these studies report controversial records about the use of the anterior ceratohyal morphology as generic diagnostic feature, this structure was never exhaustively analyzed for species of Laetacara.The objective of this paper is to provide a comprehensive analysis of variation of the morphology of the anterior ceratohyal among species of Laetacara, in order of assessing its validity as a diagnostic character state of Laetacara.

Material and Methods
Osteological studies were made on cleared and counterstained (C&S) specimens prepared according to taylOr & van dyKe (1985); the osteological nomenclature follows cOsta (2006).The medial view of the hyoids was preferably illustrated, because it is clear to observe this character in this view.Scale bar = 1 mm.
The three morphological patterns of the dorsal margin of the anterior ceratohyal are herein minutely re-characterized to facilitate the comprehension of the three distinguish patterns.
Material is deposited in the following institutions: IEPA -Instituto de Pesquisas Científicas e Tecnológicas do Estado do Amapá, Macapá; MNRJ -Museu Nacional, Universidade Federal do Rio de Janeiro, Rio de Janeiro; MZUSP -Museu de Zoologia, Universidade de São Paulo, São Paulo; and UFRJ -Instituto de Biologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro.

Cichlasoma araguaiense
The distinguishing morphological patterns of the anterior ceratohyal found in each species of Laetacara herein examined are presented in Table 1, and in other Ci chlasomatini and Heroini species are presented in Table 2.

Discussion
The three morphological patterns of the anterior ceratohyal previously described in the literature (e. g.Kullander, 1986;Kullander & nijssen, 1989), and herein re-characterized, were variable among species and specimens of the Cichlasomatini.Among species of Laetacara all the three morphological patterns were found (Figs. 2 and 3; Table 1), and variability was recorded even in the same specimen, which had hyoids of  and C ;and OttOni et al., 2009).In addition, intermediate stages among the three morphological patterns of the anterior ceratohyal were also frequently recorded among specimens herein analyzed: some specimens exhibited a slight notch, very inconspicuous in some cases, instead of a clear deep notch, being difficult to classify it on patterns 1 or 2 (an intermediate stage between patterns 1 and 2) (e.g.Fig. 3E); and others specimens exhibited laminar ledge only reaching or slightly surpassing the margin of notch, being difficult to classify it on patterns 2 or 3 (an intermediate stage between patterns 2 and 3) (e.g.Figs.2B and C).In some of the other genera of Cichlasomatini this character was also polymorphic.The results proposed by Kullander (1986) and Kullander & nijssen (1989) were herein confirmed for Acaronia nassa (Fig. 1A), Bujurquina vittata (Fig. 1B), and Cleithracara maronii (Fig. 1C).However, it was not confirmed for Krobia guianensis (Figs.1G and H) due to pattern 1 was also recorded for this species.In addition, Nannacara aureocephalus exhibited patterns 1 and 2 (Fig. 1I and J), and "Aequidens" hoehnei exhibited patterns 1(Fig.1D) and 2, however the notch was less evident, in some cases very inconspicuous.Both cases also do not corroborate the information presented by Kullander (1986) and Kullander & nijssen (1989).In Cichlasoma araguaiense the presence of morphological pattern 1 was confirmed (Fig. 1 F), however the anterior ceratohyal was also recorded exhibiting a total irregular shape of dorsal margin (Fig. 1E), making classification in any of the three morphological pattern described above impossible.Some species of the tribe Heroini were also examined in the present work.The results proposed by Kullander (1986) and Kullander & nijssen (1989) were herein confirmed for Australoheros autrani, Mesonauta sp., Petenia splendia and Symphysodon sp.(Figs. 4 A, B, D  and D).However, it was not confirmed for Pterophyllum sp.(Figs. 4 E, F and G).Kullander (1986;p. 321) affirmed for Laetacara: "A synapomorphy of these species is the shape of the hyoid, with a deep notch in the dorsal margin of the anterior ceratohyal, which is not margined by laminar ledges" and "The particular ceratohyal notch is shared only with 'Aequidens' maronii (steindachner) among cichlids."However, after the exhaustive comparison of the shape of the anterior ceratohyal among species of Laetacara, it can be concluded that it is not a useful character to diagnose Laetacara.This character is highly polymorphic in this genus, exhibiting all three morphological patterns.
We can also conclude that the traditional use of

Table 1 .
Occurrence of morphological patterns of the anterior ceratohyal among species of Laetacara.LH = left hyoid; RH = right hyoid; BH = both hyoids.thisbone morphology in the taxonomy of the tribe Cichlasomatini at present stage of knowledge seems not to be appropriate due to the polymorphism occurring in the species analyzed herein, and until a similar work is done for the whole tribe.Better and more embracing investigations of transformation series of this character among different linages of Cichlidae and ontogenetic stages are highly recommended.

Table 2 .
Occurrence of morphological patterns of the anterior ceratohyal among species of Heroini and Cichlasomatini.LH = left hyoid, RH = right hyoid, and BH = both hyoids.