Friularachne rigoi, Dalla Vecchia & Selden, 2013

Dalla Vecchia, Fabio M. & Selden, Paul A., 2013, A Triassic spider from Italy, Acta Palaeontologica Polonica 58 (2), pp. 325-330 : 327-328

Friularachne rigoi sp. nov.

Figs. 2 , 3 .

Etymology: In honour of the finder, Roberto Rigo, Udine, Italy.

Holotype: MFSN40302 a (part) and MFSN40302 b (counterpart), moderately well preserved adult male.

Type locality: Rovadia Brook valley, Forni di Sopra municipality, Udine Province, Friuli Venezia Giulia Region, Italy.

Type horizon: Dolomia di Forni Formation, upper Alaunian–lower Sevatian (upper middle–lower upper Norian).

Diagnosis.—As for the genus.

Description.—Adult male. Body length (excluding chelicerae) 3.48 mm; carapace length 1.41 mm, width 1.27 mm (L/W ratio 1.11); broad, straight anterior margin with frontal (ocular?) lobes. Chelicera length 0.78 mm; subelliptical shape in dorsoventral view; fang emerging from distal end, apparently at least half length of paturon; denticles possibly present on paturon adjacent to fang. Pedipalp length 1.05 mm; proximal podomeres slender, swollen tarsus (adult male). Leg podomere lengths: leg 1 femur 1.44 mm, patella 0.28 mm; leg 2 femur 1.18 mm, patella 0.41 mm, tibia 0.62 mm; leg 3 femur 1.10 mm, patella 0.32 mm, tibia 0.67 mm, metatarsus 0.83 mm, tarsus 0.56 mm; leg 4 femur 1.13 mm, patella 0.35 mm, tibia 0.60 mm, metatarsus 0.96 mm, tarsus 0.55 mm. Leg formula (longest to shortest) 1243? Opisthosoma length 2.10 mm, width 1.13 mm (L/W ratio 1.87); single,

http://dx.doi.org/10.4202/app.2011.0132

oval scutum, length 1.17 mm, width 0.74 mm (L/W ratio 1.59), anteriorly positioned on opisthosoma, and extending more than half its length.

Remarks.—Distinctive features of the fossil spider which might aid identification are: large, porrect chelicerae, subequal leg lengths, and probable dorsal opisthosomal scutum. Few spiders have chelicerae nearly as long as the carapace, and these include the archaeids and related families, tetragnathids, some desids, gallieniellids, and atypoids. Of these, the third leg is much shorter than the others in the web−weaving families Tetragnathidae and Archaeidae , so the other three families are more likely candidates.

Gallieniellidae is a small family of 11 genera and 57 species ( Platnick 2011) of southern−hemisphere ground spiders which commonly occur among ants. They have no fossil record. There are no fossil ants earlier than the Cretaceous, so if the association with ants is obligate, then gallieniellids would not be expected in strata as old as the Triassic. The same reasoning holds for a number of other myrmecomorphous spiders with enlarged chelicerae, e.g. salticids, corinnids, and zodariine zodariids, the last of which have enlarged chelicerae, opisthosomal scuta, and are obligate ant feeders ( Jocqué 1991). Gallieniellids are thought to be plesiomorphic among gnaphosoids ( Platnick 1984), but the fossil differs from gallieniellids in their lack of a dorsal opisthosomal scutum.

Desid genera which have large, porrect chelicerae are Desis , Matachia , and Notomatachia in both sexes, and in the males of the subfamily Myroninae ( Jocqué and Dippenaar−Schoeman 2007) . Some desids live in intertidal habitats, which could make them more susceptible to fossilization in marine habitats than terrestrial forms. However, desids do not bear a dorsal opisthosomal scutum.

When Millot (1947) described the first gallieniellid, Gallieniella mygaloides , he was struck by the similarity between the new species and mygalomorphs, as the specific epithet attests. The superfamily Atypoidea consists of three families: Atypidae , Antrodiaetidae , and Mecicobothriidae . The inclusion of Mecicobothriidae in Atypoidea has been controversial, but molecular systematic analyses have shown strong support for this composition of the superfamily (see Ayoub et al. 2007, and references therein). Males in the atypoid families Atypidae and Antrodiaetidae have extremely elongated chelicerae, similar to those Millot found in Gallieniella . In addition, atypid and antrodiaetid males have slen− der legs with inconspicuous setation, and they bear a dorsal scutum on the anterior part of the opisthosoma. For these reasons, the fossil is considered likely to belong to the Atypoidea .

Most atypoid males bear one or more dorsal tergites anterodorsally on the opisthosoma; see e.g., Coyle (1971: figs. 109–113, 1975: figs. 45–48; Antrodiaetidae ), Kaston (1978: figs. 150, 154, 156, 158), Gertsch and Platnick (1979; Mecicobothriidae ), Jocqué and Dippenaar−Schoeman (2007: figs. 12a, 18a, 58a). A single scutum, when present, is generally rather short, but a few atypids bear relatively large, single scuta, such Atypus suthepicus and A. dorsualis , both from northern Thailand and adjacent parts of Myanmar ( Schwendinger 1989), several Atypus species from Korea ( Namkung 2003; Kim et al. 2006), and the mainly European A. piceus ( Sauer and Wunderlich 1997: 31) . In some of these, the scutum bears a distinct tergite within, which is a different arrangement from that seen in the fossil. The habitus of the fossil resembles that of the atypid Calommata (e.g., Jocqué and Dippenaar−Schoeman 2007: fig. 18a) more than other atypoid genera. Nevertheless, it would be unwise to attempt to assign the fossil to an extant family with such poor preservation of details.

Geographic and stratigraphic distribution.— Type locality and horizon only.

Figures

Fig. 2. Mygalomorph spider Friularachne rigoi gen. et sp. nov., holotype MFSN40302, Rovadia Brook valley, Friuli, Italy, late middle to early late Norian (Late Triassic); Dolomia del Forni Formation. Part (MFSN40302a) (A), and counterpart (MFSN40302b) (B). Photographs (A1, B1) and explanatory drawings (A2, B2). 1–4, walking legs 1–4.

Fig. 3. Mygalomorph spider Friularachne rigoi gen. et sp. nov., holotype counterpart MFSN 40302b, Rovadia Brook valley, Friuli, Italy, late middle to early late Norian (Late Triassic); Dolomia del Forni Formation. Photograph (A) and explanatory drawing (B) of anterior part of prosoma showing anterior border of carapace, chelicerae and pedipalps.