Plutonium zwierleini


Plutonium zwierleini, in the monotypic genus Plutonium, is one of the largest scolopendromorph centipedes in Europe, and one of the few potentially harmful to humans. Nevertheless, it has been rarely reported, only from the southern part of the Iberian and Italian peninsulas, Sardinia and Sicily.

Morphology

The body is mainly brown-orange, slightly darker on the head and the most posterior part of the body, including the ultimate pair of appendages. Conversely, the antennae and the walking legs are paler. The body length may surpasses 12 cm, which is the maximum measured from the anterior margin of the head to the posterior tip of the trunk, among the few specimens collected. Even higher measures have been reported in the past.
P. zwierleini is fully blind, without trace of eyes. As in all other centipedes, the first appendages of the trunk are a pair of piercing fangs, which are used to grasp and poison prey. Two denticulate plates project forwards between the fangs, which have also a small tubercle on their mesal side.
A total of 20 walking legs are present on both sides of the body. In addition to short setae that are sparse on the entire body surface, including the appendages, the ventral side of the basal articles of the legs are covered with remarkably dense and long setae, which is unusual among centipedes. The function of these unusual setae is unknown. The tergites covering the body trunk, one every pair of legs, are alternatively slightly longer and slightly shorter, as common in scolopendromorph centipedes.

Distribution and habitat

P. zwierleini was first described upon specimens collected around year 1878 near Taormina, in Sicily. Soon after, the species was reported also from Sardinia and near Sorrento in the Italian peninsula. However, despite the large size and the distinctive morphological characters, P. zwierleini has been found only rarely. Up to 2017, less than 50 records have been documented. Dedicated field campaigns carried on by different zoologists turned out often unsuccessful, while most records have been obtained by occasional findings by speleologists, amateurs and common citizens.

Evolutionary relationships

Both morphological and molecular analyses suggest that P. zwierleini belongs to the so-called “blind clade” of scolopendromorph centipedes and is strictly related to Theatops. In the past, the evolutionary affinities of Plutonium have been a matter of speculations, within the more general debates on the evolution of the segmental anatomy of the Arthropoda.