Presence of a stridulatory apparatus in the manca stages of isopods (Crustacea, Isopoda, Oniscidea)

Armadillo officinalis Duméril, 1816 (Armadillidae) is a widespread terrestrial isopod species in the Mediterranean basin and on the western coasts of the Black Sea. The species is adapted to live in xeric environments and has mainly nocturnal habits. This species is capable of producing stridulations, which is nowadays recognized as a synapomorphy of the genus. In both sexes, these vibrations are produced by a line of scales on the propodus of pereopod 4 and 5. The main goals of this study are: to describe the manca stages of Armadillo officinalis; to detect the presence of the stridulatory apparatus in the manca stages; to evaluate the differences of such apparatus in the various manca stages. The manca stages (I, II, III) of Armadillo officinalis are described for the first time showing: i, the shortest duration (known in literature) of the manca stage I (approximately 30 minutes); ii, the presence of a rudimental stridulatory organ that may be of great importance in terms of evolutionary aspects and adaptation to terrestrial life. Notes on the reproductive biology are also reported. Furthermore, some considerations on future perspectives for A. officinalis as a model species in biotremology are also discussed.