Petralycus obtusicornis, Uusitalo, 2025

Petralycus obtusicornis sp. nov

( Figs. 48A–E, 49A–F)

Description. Dorsum (n= 1 male, Fig. 48B). Single male broken badly and total length cannot be measured; holotrichous number of plumose dorsal setae with a slightly elongated and swollen shaft tapering apically, setae on microplates; lamellae inserted densely at regular intervals on continuous striae of integument; on TN prodorsum: naso long (21 µm), narrow and rounded at tip, setae vi and in multiciliate, setae sce reduced in size, setae exp and eyes absent, sensilla sci filiform with short cilia, sensilla ve oval, obovate and barbed, all inserted on hard integument.

Venter ( Fig. 48D–F). Ventral side neotrichous with stellate setae; 17 genital setae per valve, 8–9 pairs eugenital setae; 3 and 5 anal setae per valve.

Gnathosoma ( Fig. 48C). Three pairs of setae on subcapitulum; chelicerae chelate-dentate, robust, and elongated with one pair of nude setae dorsally; large palpal solenidion reaching over two nude and apical eupathidia.

Legs ( Fig. 49A–D). Solenidial formula for tarsi, tibiae, genua and femora on legs I, II, III and IV, respectively: 1-1-0-0, 2-2-2-2, 9-2-2-5, 12-3-1-3+1; famulus I placed abaxially, near distal end of tarsus I.

Tritonymph (n=2, Figs. 48A, 49 E­, F). Lengths 330 µm and 360 µm; like adult, but dehiscence line δ present; 3 pairs of genital papillae but no eugenital setae; 10–11 genital setae per valve; one anal seta per valve; solenidial formula for tarsi, tibiae, genua and femora on legs I, II, III and IV, respectively: 1-1-0-0, 2-2-2-2, 7-2-2-3, 7-2-1- 2+0.

Type material. Holotype male and 2 paratype tritonymphs from litter back dunes, brushy area, Sea Pines, Hilton Head Island , Beaufort Co., South Carolina, 15 August 1997, VE LaRoche, 3 slides with collection number AL 5210, at Acarology Laboratory, Museum of Biological Diversity , Ohio State University; holotype male on slide NA35.

Differential diagnosis. Petralycus obtusicornis is most similar to P. celtisacinus McDaniel & Bolen, 1983 by having one pair of cheliceral setae. They differ by having ciliated setae in different (bushy in P. obtusicornis and cilia along elongated shaft in P. celtisacinus , Figs. 48A versus Fig. 45A) and solenidial formulae (Table in Differential diagnosis of P. celtisacinus ). These American species (including P. caryapecaus McDaniel & Bolen, 1983 ) with an elongated and blunt tipped naso are closely related to the European species P. unicornis Grandjean, 1943 which, however, has a tapering and pointed naso. They differ from the South African neotrichous species P. longicornis Theron, 1977 and P. brevicornis Theron, 1977 by having a holotrichous pattern of dorsal setae and a unique solenidial pattern.

Remark. P. obtusicornis was coded as ‘pet’ in Uusitalo (2010).

Etymology. The specific name is the masculine gender of two Latin words obtusus and cornu meaning blunt and horn, respectively, and refers to the form of the naso of the species.

Summary

The tribe Alycini was divided into three genera based on the shapes of the chelicerae, that is, the different-shaped chelicerae suggest each genus is pursuing a different food target ( Uusitalo 2010). The robust, non-elongated and sparsely toothed chelicera of Alycus C.L. Koch 1842 presumably represent the most plesiomorphic pattern. A new genus proposed herein, Odontoalycus gen. nov. is characterized by stout and non-elongated chelicera with a considerable increase in teeth, suggesting a shift in diet.

Also, among the alycids with robust and elongated chelicera, two different lines in lifestyles can be seen. The larger group, Amphialycus (sensu str.) Zachvatkin, 1949, is made up of species with a normal range of senses: naso is present, prodorsal setae resemble dorsal setae and pair of setae vi are far apart. In addition, the legs are normal in size and shape and the anus is on the ventral side. On the other hand, there are the small species with reduced prodorsal setae, lost naso and setae vi are exceptionally close to each other. The legs are also atrophied and bent, and the anus is caudal ( Fig. 54). This combination of characteristics suggests an adaptation to a very edaphic life and the group Orthacarus Zachvatkin, 1949 has been re-elevated to genus level, although this was not still obvious in the phylogenetic analysis of the family Alycidae due to the incomplete investigation of the South African species ” clu ” ( Fig. 54) and erroneous markings in the data matrix ( Uusitalo 2010: 19).

As for the tribe Bimichaeliini , division of the clade IV, or the genus Bimichaelia sensu lato Thor, 1902, into genera was based on the phylogenetic analysis ( Uusitalo 2010). The genus Bimichaelia (sensu str.) Thor, 1902 (clade VII) with small granulae of secondary pattern was represented by two species in the European fauna. The terminals of the clade VIII included material from other continents as well, forming several clades. Thus, the terminal ” gra ” is still waiting for review of the Polynesian material, but three other terminal clades included European species. The new genus Laminamichaelia (sensu lato) was established for the species with small, transverse lamellae on the integument but splitting of the European species into new monotypic genera seemed unfounded and premature, because the species of other continents remained undescribed. However, the clades, which included the European species, were named and treated as species groups ( subnuda -group, setigera -group, arbusculosa -group) to show off the conspicuous differences, especially in the sensory areas ( Uusitalo 2010). The small-sized specimens with poorly differentiated, holotrichous prodorsum, densely barbed sensilla ve, two baculiform solenidia on tarsus I, and with non-reticulate dorsal pattern belonged to subnuda -group. Two groups with reticulated dorsal patterns had clearly differentiated prodorsums, i.e. lateral parts were soft but the central area or crista and area of sensilla were sclerotised. The middle-sized specimens with additional setae only on soft prodorsum and two twisted baculiform solenidia on tarsi I belonged to the setigera -group. The specimens with additional setae both on soft and sclerotised parts of prodorsum and three baculiform solenidia on tarsi I were mostly large in size and grouped into the arbusculosa -group. Dorsal reticulation also occurs in the genus Bimichaelia and does not necessarily indicate a close relationship.

The original phylogenetic tree ( Uusitalo 2010: fig. 1) contained material only from one collection. Three new collections were added for this review. The biggest change in the interpretation of the tribes happened in the tribe Bimichaeliini : A new species that didn’t have lamellae, five species that had characteristics that qualified them for the setigera -group, two for the arbusculosa -group, and one for the subnuda -group were found. The groups were no longer monotypic and were named their own genera as indicated by the tree. Laminae are also present outside Laminamichaelia (e.g. in the genera Bimichaelia , Nanorchestes and Proterorhagia ) and laminae can be absent ( Glabromichaelia ) so that the mere existence of laminae is not enough to prove kinship, but the laminae must have arisen several times. It seemed reasonable to bring up also the differences in the sensory areas rather than similarities in the skin structures only, and to replace the subnuda -group by Minimamichaelia gen. nov. (2 species, worldwide), setigera -group by Quartusmichaelia gen. nov. (5 species) and arbusculosa -group by Laminamichaelia sensu stricto (3 sp. worldwide), which was actually visible and suggested in the original tree. The new taxa that were not known or available for the original the tree, will be taken into account in the final version of the tree when the Polynesian and Australian materials have also been reviewed.

Tribe Petralycini got one new, holotrichous species in addition to the other two. So far, the distribution of each Petralycus species is limited to only one continent, and neotrichy has arisen independently in South Africa.