Shillukia, Linnavuori, 1977

The genus Shillukia can be recognized by the combination of the following set of characters:

- body form elongated;

- coarse punctation of the dorsal part of the body; - reduced chetotaxy (submarginal hair-like setae on head, thorax, abdomen);

- absence of apical seta on eyes, or if present (rarely) only as a minute seta;

- genus-specific shape of the vestibule of the metathoracic glands;

- evaporatorium occupying large area on meso- and metapleura;

- laterotergites 8 connected mediodorsally;

- spermathecal duct wide and long, strongly coiled, devoid of definite dilation or invagination.

As pointed by Linnavuori (1993), the genus Shillukia superficially resembles certain Geotomus species (now transferred to the genus Fromundus ; see Lis, 1994, 1999) in general appearance. All the above characters (excepting the spermatheca) are indeed shared by several other geotomine genera.

The genus is best characterized by its spermatheca. In Cydnidae , the spermathecal characters are of great value at species, genus and suprageneric levels.

According to Linnavuori (1993), Shillukia , an endemic African geotomine genus, could be a taxon representing an evolutionary lineage of its own. We essentially agree with this opinion. This kind of spermatheca, although clearly of geotomine facies, is indeed unique within Geotomini. With its very long and wide spermathecal duct, it does not fit any of the three geotomine species groups recently defined ( Pluot-Sigwalt and Lis, 2008) on the basis of the structure of the spermathecal duct:

- group I: spermathecal duct with spherical dilation more or less developed (most genera such as Aethus , Geotomus , Fromundus, Macroscytus);

- group II: spermathecal duct with a large pumkinlike dilation (such as Teabooma, Cydnotomus);

- group III: duct with a sausage-like dilation (such as Hiverus, Katakadia, Scoparipes).