21.07.2022

It depends on the horn!

Recently we received from Steven Schramm an exuvia of a tarantula from Africa which he had received on 15.06.2022 from Ümit Inan under the name Ceratogyrus brachycephalus. He asked for an identification of the Spider, because he suspected that it might not be this species. A look into the Ceratogyrus revision of De Wet & Dippenaar-Schoeman (1991) showed then very fast that the assumption of Steven Schramm was absolutely correct. Several characteristics did not agree with C. brachycephalus in the Spider. The genus Ceratogyrus from Africa is characterized in many species by the fact that they mostly have a distinct elevation or horn in the thoracic fovea. The shape and direction of growth of this horn is essential for species identification. In the present animal it was only an elevation, but by no means a distinctly raised horn, as can be seen in Pics 1 & 2. A comparison with the structure of the thoracic fovea of other Ceratogyrus species clearly shows that the present animal cannot be C. brachycephalus, because this Species has a distinct elongated and forward directed horn in the thoracic fovea, which is much larger than the elevation in the present exuvium (Pic 3 & 4 from De Wet & Dippenaar-Schoeman).

A comparison with the thorax forms of other Ceratogyrus species led to the assumption that the present exuvia is probably a Ceratogyrus sanderi (Pic 5).

• The posterior sternal sigillae, which are not positioned marginally, in contrast to those of C. brachycephalus, also lead to this assumption (Pic 6, compare with Pics 4 & 5).

• Similarly, the structure of the spermathecae from the exuvium shows significantly more similarity to that of Ceratogyrus sanderi than to C. brachycephalus [Pics 7 & 8 (green circle)].

Resumé:

Comparing the characters of the present exuvium with the descriptions of the known Ceratogyrus species and especially with the revision of De Wet & Dippenaar-Schoeman of 1991, one comes to the conclusion that the exuvium will not be Ceratogyrus brachycephalus - under this name the spider was sold - , but that it is probably Ceratogyrus sanderi. According to Steven Schramm the living female (in the meantime it unfortunately died) had a bright band above the epigastric furrow. Also this observation speaks for C. sanderi, because De Wet & Dippenaar-Schoeman could observe that in C. sanderi the "... epigastric area and posterior pair booklungs (...) are yellowish-cream", whereas this area in C. brachycephalus is described as "paler brown". Whether ALL Ceratogyrus brachycephalus in the "hobby" are actually Ceratogyrus sanderi is not known. Nonetheless, therefore, there appear to be misidentified spiders in the community in this genus as well.

Reference:

De Wet, J. I. & Dippenaar-Schoeman, A. S. (1991). A revision of the genus Ceratogyrus Pocock (Araneae: Theraphosidae). Koedoe 34: 39-68.