Sicarius Thomisoides

''Sicarius thomisoides'' is a species of spider in the family Sicariidae, found in Chile. It is the type species of the genus '' Sicarius''. Its correct name has been the source of confusion. It has often been known by the synonym ''Sicarius terrosus'', a name which has also often been used incorrectly for other species.

Taxonomy

There has been confusion over the correct name for this species. In 1847, Charles Athanase Walckenaer published the name ''Sicarius thomisoides'', also erecting the genus '' Sicarius''. He based the name on illustrations he had seen in a work still in preparation and so not then published, namely a section on spiders by Hercule Nicolet in the multivolume ''Historia física y política de Chile''. It was finally published in 1849. Nicolet called the species ''Thomisoides terrosus''. In his earlier publication, Walckenaer had argued that ''Thomisoides'' was inappropriate as a genus name, as the species was not related to '' Thomisus'', a crab spider. Although Walckenaer's name has priority, ''Thomisoides terrosus'' was used in subsequent descriptions, and even when the generic name ''Thomisoides'' was abandoned in favour of ''Sicarius'', the specific name ''terrosus'' continued to be employed (e.g. in the World Spider Catalog in 2015). F.O. Pickard-Cambridge had argued in 1899 that if Walckenaer's ''Sicarius'' is used as the generic name, his specific name should be too. This argument was reinforced in 2017, and is now accepted, so that ''Sicarius thomisoides'' is the correct name for the species, which is the type species of the genus.

Adding to the confusion, the specific name ''terrosus'' "was very seldom used in the literature to refer to the correct Chilean species", so that descriptions under this name may actually refer to species such as '' Sicarius levii''.

Description and behavior

It can grow between 12 and 20 mm in length, lives in desert areas of northern and central Chile and has nocturnal habits, building shelters under rocks on sandy substrate in northern Chile, it is extremely common in urban regions with a lot of household waste.

''Sicarius'' spiders have already been observed feeding on insects, scorpions and other spiders, but recently, a 20 mm long specimen of ''S. thomisoides'' was recorded in Mamiña, in northern Chile, preying on a 28 mm gecko ('' Phyllodactylus gerrhopygus'') long. The spider was reported feeding on the fluids of the lizard's digested body, the lizard's skin was damaged and dark, indicating possible dermonecrotic effects, since enzymes of hemolytic and dermonecrotic activity were reported in ''Sicarius'', with an action similar to that of ''Loxosceles''.

Venom

A recent study showed that the species ''S. thomisoides'' has active sphingomyelinase D, which has effects and intensity similar to that of the dangerous '' Chilean recluse spider'' (''Loxosceles laeta'').

The venom is capable of causing complement-dependent hemolysis and cytotoxic activity against human skin fibroblasts in concentrations of 10 µg, and 50 µg induces progressive dermonecrosis, basically induces hemolysis, cytotoxicity and dermonecrosis. Therefore, like '' Sicarius ornatus'' and ''Loxosceles laeta'', ''S. thomisoides'' fulfils the toxic parameters to cause damage in humans. The concentration of 50 µg of ''S. thomisoides'' venom seems to be enough to produce dermonecrosis. Thus, higher doses of venom inoculated by adults of ''S. thomisoides'' could cause more seious lesions, since adults possess up to eight times the concentration assayed. ''Sicarius thomisoides'' venom also has extremely fibrinogenolytic activity and cleaved all Aα-Chains most rapidly, while ''Loxosceles reclusa'' and ''L. laeta'' took longer to cleave.

References

{{Taxonbar, from=Q55692223

Sicariidae
Spiders of South America
Spiders described in 1847
Endemic fauna of Chile