Platoecobius Chamberlin & Ivie, 1935

Santos, Adalberto J. & Gonzaga, Marcelo O., 2008, Two new Neotropical spiders of the genera Oecobius and Platoecobius (Araneae: Oecobiidae), Zootaxa 1786 (1), pp. 61-68 : 63-65

Platoecobius Chamberlin & Ivie, 1935

Platoecobius Chamberlin & Ivie, 1935: 270 .

Type species. Thalamia floridanus Banks, 1893 , by monotypy.

Diagnosis (emended from Chamberlin & Ivie 1935 and Shear 1970). Platoecobius resembles Oecobius Lucas, 1846 and Paroecobius Lamoral, 1981 by the presence of a cribellum and a calamistrum. It can be distinguished from those genera by the flattened cephalic area and the ocular quadrangle which is wider than long ( Chamberlin & Ivie 1935, figs. 22, 23, 28). Specimens of the remaining cribellate oecobiid genera have the cephalic area elevated and domed and the ocular quadrangle usually as wide as long (see Chamberlin & Ivie 1935, figs. 4, 5, 6, 11). The female epigynum is remarkably simple, without sclerotised areas, projecting scape-like structures or deep depressions, as are common in other genera (see Shear 1970; Baum 1972; 1980; Santos & Gonzaga 2003; Rheims et al. 2007). The only female genitalic structure present externally in Platoecobius is a transverse septum delimiting the copulatory openings and an anterior pit ( Fig. 11 ). Internally, the copulatory and fertilization ducts are both sclerotised and relatively short and, unlike several species of Oecobius , the sclerotised capsules of the fertilisation ducts are large and contiguous ( Figs. 9, 10 ; Shear 1970, figs. 46, 47). Males are known only for P. floridanus , which has no tegular lobes and oecobiid tegular apophysis small, rounded and with an acuminated, curved ventral projection (indicated as “s” in Shear 1970, figs. 11, 12). Shear (1970) listed two additional diagnostic characters: the legs comparatively shorter and stouter than in Oecobius and the calamistrum occupying the entire length of metatarsus IV. However, the size of legs in Platoecobius are within the range of variation in other small oecobiids and the calamistrum of P. kooch sp.nov., as described below, is as long as those observed in Oecobius .

Composition. Two species, Platoecobius floridanus (Banks, 1893) from Florida ( USA) and P. kooch sp.nov., from Argentina.

Remarks. The absence of a comprehensive phylogenetic analysis for the Oecobiidae prevents a detailed discussion on monophyly and relationships among its members. In this study we provide preliminary evidence for the monophyly of Platoecobius , but a complete phylogenetic test is still required to determine the relationships between species of Platoecobius and the large and extremely variable genus Oecobius . Certainly, the presence of the cribellum is not evidence of a relationship between Oecobius , Paroecobius and Platoecobius , since it is primitive and repeatedly lost in araneomorph spiders ( Griswold et al. 2005). However, Platoecobius is similar to at least some species of Oecobius (like Oecobius navus , O. cellariorum and O. eberhardi sp.nov.), with which it shares the presence of sclerotised capsules on the fertilization ducts ( Baum 1972; 1980; this study). Two putative synapomorphies for the genus Platoecobius emerge from a comparison with other oecobiids ( Baum 1972; 1980; Shear 1970; Rheims et al. 2007) and members of the closely related families Eresidae and Hersiliidae ( Kraus & Kraus 1988; Baehr & Baehr 1993; Rheims & Brescovit 2004; Griswold et al. 2005). This genus can be provisionally considered monophyletic based on the simplified female epigynum, without a distinction between a median field and lateral lobes ( Fig. 10 ), and the contiguous sclerotised capsules ( Fig. 9 ).

Additional material examined. Platoecobius floridanus : USA: Florida: Highlands Hammock State Park , 27 o 16’N, 81 o 19’W, 20.XII.1962, W. Ivie coll., 2♂ 2♀ ( AMNH) .

Figures

FIGURE 11. Platoecobius kooch sp.nov. Scanning electron micrograph of female epigynum, ventral view (paratype from General Roca, Argentina, MACN). Abbreviations: AP, anterior pit of epigynum; CO, copulatory openings. Scale bar = 0.1 mm.

FIGURES 8–10. Platoecobius kooch sp.nov. 8, female habitus, dorsal view (paratype, IBSP 79531); 9-10, female epigynum (paratype, AMNH): 9, ventral view; 10, internal genitalia, dorsal view. Abbreviations: CD, copulatory ducts; FD, fertilisation ducts; S, spermathecae; SC, scletotised capsule. Scale bars: 7 = 0.5 mm; 8–9 = 0.1 mm.