11.11.2022

About the difficulties in determining a species of Tliltocatl

Recently we received a male of a Tliltocatl species, which Lucas Riebe bought on 24.06.2019 in a Petstore as "Tliltocatl vagans". In the meantime, the then juvenile animal had molted into the adult stage and had died of old age in the meantime and was sent to us for identification. The identification turned out to be extremely difficult, which again shows how poorly processed and complicated this genus actually is.

First it had to be clarified whether it is a Tliltocatl at all. For this, and for further diagnosis of the species status, the revision of the genus Brachypelma by Mendoza & Francke (2020) was consulted. Based on the morphology of the bulb and the structure of the keels on the bulb as well as the coloration of the male, the affiliation to the genus Tliltocatl could be confirmed. Now it was necessary to locate the correct species, which turned out to be rather difficult.

The present male, whose exact locality is unfortunately not known, differs from Tliltocatl schroederi according to Rudloff 2003 by the bright, reddish hairs on the opisthosoma (Pic 1) and by the "apical keel" (AK), which is shallower in T. schroederi (Pic 2) than in the present male (Pic 3). Also, T. schroederi possesses two spines on the prolateral tibial apophysis (Pic 4, green arrows) while in the studied male there is only one spine on this tibial apophysis (Pic 5, green arrow).

The examined male differs from Tliltocatl verdezi by the width of the embolus, which is not as wide in T. verdezi (Pic 6) as in the present male (Pic 3) (see Schmidt 2003). In addition, there is no spine on patella I in T. verdezi (see Mendoza & Francke 2020), whereas the examined male has a spine there (Pic 7, green arrow).

The examined male differs from Tliltocatl kahlenbergi by the different number of spines on the retrolateral tibial apophysis (see Rudloff 2008). In T. kahlenbergi there are 2 spines on this tibial apophysis (Pic 8, green circle), whereas in the examined male there is only one large spine (Pic 9, green arrow).

The present male is clearly distinguished from Tliltocatl albopilosus by the absence of the dense, light brown curly hairs on the opisthosoma and extremities. Also, the bulb of T. albopilosus is narrower overall and the "prolateral superior keel" (PS) and "apical keel" (AK) are not as pronounced (Pic 10) as in the examined male (Pic 3 & 11) (see Mendoza & Francke 2020).

In the end, this leaves three species that could be considered. They are then also those three species which form a sister group relationship in the phylogenetic analysis in Mendoza & Francke (2020) as terminal taxa (Pic 23, green circle), namely Tliltocatl epicureanus, Tliltocatl sabulosus and Tliltocatl vagans. Unfortunately, the genus Tliltocatl was only established and defined in this publication, but the individual species were not (re)described and morphologically differentiated from each other, which makes a taxonomic classification and determination of the three species now remaining here very difficult. Nevertheless, there is a possibility to filter out a few useful characters for the differentiation of the three mentioned species from the phylogenetic analysis. For this purpose, we downloaded the character matrix to the mentioned publication by Mendoza & Francke 2020 from the server of the Zoological Journal of the Linnean Society, where the paper was published (Appendix 1). We then filtered out the characters under consideration for the differentiation of the three species, coded by numbers in the consensus phylogenetic tree, from the character matrix and compared them to the respective coded character state from Table 1 in the referenced paper by Mendoza & Francke 2020. We then included this coded value as well as the useful distinguishing characters in a matrix (Pic 12) and compared it with the characters of the studied male and coded these characters for this one as well.

Resume:

As can be seen in the matrix in Pic 12 there is a slight tendency that the examined male fits better to Tliltocatl vagans. Whereby especially the characters concerning spination have to be considered with caution, because - as Mendoza and Francke themselves write - "Spination is very variable in tarantulas, with the same specimen sometimes having a different number on left and right appendages.". Genital morphological characters are usually more informative than somatic characters, but should never be the main factor for taxonomic identification, but should always be considered and evaluated in combination with all available and useful characters. Looking at the structure of the bulb in Tliltocatl epicureanus (Pic 19) compared to that of Tliltocatl vagans (Pic 20), the high similarity in the structure of the bulbs is striking. However, the embolus of T. epicureanus clearly differs in the shape of the "apical keel" (AK) compared to T. vagans. In T. epicureanus the AK runs somewhat more shallowly and is much closer to the embolus tip than in T. vagans. In the present male, the shape of the AK is even slightly more pronounced (Pic 21) than in T. vagans and is similarly well distanced from the embolus apex (Pic 22) as in T. vagans. From the evaluation of the available characters and the agreement regarding the expression of the "apical keel" (AK) as well as the congruence of some somatic characters, we would designate the examined male as Tliltocatl cf vagans.

One more word about Tliltocatl sabulosus. This species is so far known only in the female sex. However, Mendoza and Francke 2020 obviously had males of this species available for their phylogenetic analysis, because T. sabulosus was also coded with respect to male characters, as can be seen in Table 1 in Mendoza and Francke 2020. Similarly, 3 males of this species were used for genetic analysis (Appendix 2). We then included these characters from the morphological analysis in our matrix (Pic 12) as well. Officially, the male of this species has not been described yet.

Reference:

Mendoza, J. & O. Francke (2020). Systematic revision of Mexican threatened tarantulas Brachypelma (Araneae: Theraphosidae: Theraphosinae), with a description of a new genus, and implications on the conservation. Zoological Journal of the Linnean Society 188(1): 82-147.

Rudloff, J.-P. (2008b). Eine neue Brachypelma-Art aus Mexiko (Araneae: Mygalomorphae: Theraphosidae: Theraphosinae). Arthropoda 16(2): 26-30.

Rudloff, J.-P. (2003). Eine neue Brachypelma-Art aus Mexiko, Brachypelma schroederi sp. n. (Araneae: Mygalomorphae: Theraphosidae: Theraphosinae). Arthropoda 11(3): 2-15.

Schmidt, G. (2003). Das Männchen von Brachypelma verdezi sp. n. (Araneae: Theraphosidae: Theraphosinae), einer häufig mit Aphonopelma pallidum verwechselten Vogelspinnenart aus Mexico. Tarantulas of the World 86: 4-9. (also 87: 4-9)