<p><strong><span style="font-family: Times New Roman;">Morphological ontogeny, distribution and ecology of <em>Edwardzetes edwardsii</em> and <em>Sphaerozetes orbicularis </em>(Acari: Oribatida: Ceratozetidae)</span></strong></p>

Abstract

In this study the morphological ontogeny, distribution and ecology of Edwardzetes edwardsii (Nicolet, 1855) and Sphaerozetes orbicularis (C.L. Koch, 1835) were investigated. The latter species looks strikingly similar to S. piriformis (Nicolet, 1855), and was recognized by a rounded distal part of lamellar cusp, which in S. orbicularis had an outer spine. However, the shape of the lamellar cusp varies in Norwegian adults of S. orbicularis being rounded or with one or two spines, which puts in question the validity of S. piriformis. Our study on the morphology of juveniles of these two morphological forms of S. orbicularis also indicates that they are identical, so we provisionally consider S. piriformis as a junior synonym of S. orbicularis (syn. nov.). The juveniles of E. edwardsii and S. orbicularis have a humeral organ and a humeral macrosclerite, which is common in Sphaerozetinae, and carry seta c1 on the humeral macrosclerite. In the juveniles of E. edwardsii most gastronotal setae are of medium size and blunt, but the gastronotal shield of the larva is divided in two parts, whereas in the nymphs this shield is uniform. In all juvenile stages of S. orbicularis the gastronotal setae are short and the gastronotal shield is uniform. The adult of E. edwardsii has a rounded rostrum and 10 pairs of long notogastral setae, including c2, whereas that of S. orbicularis has rostrum with two deep incisions and 11 pairs of short notogastral setae, including c2 and c3, which is typical of Sphaerozetes Berlese, 1885, but unique in Sphaerozetinae. Edwardzetes edwardsii has a holarctic distribution, whereas S. orbicularis is a Palaearctic species. The former species prefers forest litter, whereas the latter species prefers moss.