The first record of a paguroid shield (Decapoda, Anomura, Annuntidiogenidae) from the Miocene of Cyprus

For the first time, a paguroid shield is recorded from upper Miocene reefal strata (Koronia Member, Pakhna Formation) that crop out along the northern margin of the Troodos Massif, north of the village of Mitsero, Cyprus. Described here as Paguristes joecollinsi sp. nov., it constitutes the first paguroid shield known from Miocene deposits. The paucity of Cenozoic paguroid shields can probably be linked to a collecting bias in view of their relatively small size; in addition, suitable gastropod shells and internal moulds of such should be screened for ‘hidden’ hermit crabs.


Introduction
Up to now, abundant paguroid shield material has been recorded only from Jurassic reefal deposits (e.g., Van Bakel et al., 2008;Fraaije, 2014a;Fraaije et al., 2019) and mid-and Upper Cretaceous strata of comparable lithologies (e.g., Fraaije et al., 2008Fraaije et al., , 2009Fraaije et al., , 2012. In stark contrast is the current record of just a single hermit crab shield from Eocene coral-algal limestones in northern Italy as recorded by Beschin et al. (2016Beschin et al. ( , 2017 and of an individual of Dardanus colosseus, preserved in situ in an internal mould of a gastropod from the Eocene of Austria (Fraaije & Polkowsky, 2016). Recently, six partially preserved shields have been briefly described and illustrated on the internet by a private collector, who had recovered them from reefal strata of Danian age at a quarry near Vigny (Paris Basin, France) (Buridan.over-blog.com 2018). All of the above constitute the current meagre record of paguroid shields of Paleogene and Neogene age that we are aware of.
Although relatively common in the fossil record, hermit crabs rarely become fossilised within the empty gastropod shells they usually inhab-it, probably because the animals abandon these when under stress (Dunbar & Nyborg, 2003). Alternative hypotheses are that the hard parts fall out of the gastropod shell upon decay of the hermit crab and not all Mesozoic hermit crabs inhabited gastropods (e.g., Fraaije, 2003). A recent study by Klompmaker et al. (2017) has revealed that the decay of complete paguroid animals is a rapid process, in comparison to other decapod crustaceans such as lobsters and crabs. They also demonstrated that, in addition to paguroid claws, anterior carapaces (shields) also have a relatively high preservational potential compared to the less calcified posterior shield. This result suggests that the paucity of extinct paguroid carapaces/shields might be a matter having been overlooked by collectors in the field on account of their small to diminutive size in comparison to other associated decapod crustaceans. Additionally, extensive checking of the content of gastropod shells or their internal moulds is likely to yield more paguroid specimens.
The new specimen described here was collected in May 2017 by one of us (RHBF) while doing fieldwork together with the fourth author (AAK) in upper Miocene reefal deposits at Mitsero, Cyprus (Figs. 1, 2). Following the record of a new, shallow-water munidopsid anomuran by Fraaije (2014b), this is only the second study on decapod crustaceans from the Miocene of Cyprus. More material from various localities in Cyprus is now contained in the collections of the Oertijdmuseum at Boxtel (the Netherlands). Below we adopt the morphological terminology of paguroid carapaces as described by Fraaije et al. (2019).
Material: The holotype and sole known specimen to date (MAB 10456a,b: part and counter-part) is an anterior part of the carapace with a maximum length of 3.8 mm and a maximum width of 3.3 mm.
Etymology: The species is named after our recently departed friend and colleague, Joseph ('Joe') S.H. Collins of London (England), who did so much to stimulate decapod crustacean studies by three of us (RHBF, BWMvB and JWMJ). We owe him a great deal.
Locality and stratigraphy: To the west of Kreatos Hill, about one kilometre to the northnorth-west of the village of Mitsero, in coral-reef talus of the upper Miocene (Tortonian, 11.6-7.2 Ma) Koronia Member (Pakhna Formation; see Fig. 1). The shield was recovered from a block of bioclastic rock measuring about one square metre. The sedimentology and stratigraphy of this region have been described in detail by Robertson et al. (1991) and Follows (1992).
Description: Shield elongated (L/W ratio c. 1.15), convex transversely, almost straight longitudinally, divided into distinct regions by grooves (as shown in Fig. 3); broad, rimmed and shallow orbital cavity, broad, slightly convex postrostral ridges centrally indented by central gastric furrow, extending posteriorly in faint central line; pronounced, very globose and spinose massetic region, posteriorly covered with finely spinose ridges; tiny reniform but clear keraial region; narrow and spinose lateral branchial area; anterior gastric region alongside central furrow with transversely crenulated ornament; V-shaped cervical groove; shield irregularly covered with large (setal) pores.

Remarks:
The new species is assigned to Paguristes because the shape of the anterior shield, the grooves such as a central gastric groove, and the regional definition conform well with those of many modern species (e.g., Forest et al., 2000). Numerous representatives of Paguristes have been described from the fossil record, from the Albian (late Early Cretaceous) onwards (see Fraaije et al., 2015, table 1), but nearly all of these are based exclusively on chelae, with the exception of two, namely a partial shield from the upper Pleistocene of southern Italy, referred to Paguristes cf. syrtensis de Saint Laurent, 1971, by Garassino et al. (2014 and a specifically indeterminate form, Paguristes sp., from the lower Eocene of northern Italy (Beschin et al., 2016). A comparison with this specimen is not made here, because this species will be placed in a different genus (Fraaije et al., 2020). Paguristes joecollinsi sp. nov. differs from P. cf. syrtensis in having less convex orbital cavities, a much more globose massetic region, less convex upper orbital margins and substantially fewer (setal) pores across the shield, although the cuticle is less well preserved. We have also compared the species to extant representatives from the same geographical region, the Mediterranean, which was a nearly enclosed basin during the Tortonian (e.g., Rögl, 1999). After all, decapods crustaceans with stratigraphical ranges of 10 million years or more have been reported occasionally (Klompmaker et al., 2012, p. 792-793;Hyžný, 2016, table 1). This region may also harbour one or more descend-ants of the species in the present study. However, the shields of extant Mediterranean species of Paguristes are not morphologically identical or very close to the new species. Paguristes joecollinsi sp. nov. differs from P. eremita (Linnaeus, 1767) [= P. oculatus (Fabricius, 1775) and P. maculatus (Risso, 1827)] (see Pipitone, 1998;Koçak et al. 2005, for drawings and images), P. streaensis Pastore, 1984 and P. syrtensis in that the general shape is more triangular and the massetic region is more pronounced in the new species. The shield appears to show impressions of the anterior gastric muscles (sensu Klompmaker et al., 2019, fig. 14F) in the anterior portion.
The assemblage from Mitsero also contains paguroid appendage fragments, but more research is needed to check whether one or more specimens might be ascribed to P. joecollinsi sp. nov. Ascribing disarticulated paguroid elements to one species is difficult, but it is essential to evaluate the true diversity of paguroids within assemblages. For example,  have attempted to link sixth abdominal tergites to shield-based species based on the relative abundance of these isolated elements. None of the propodi within the Mitsero assemblage known to date is comparable to another Miocene Paguristes, P. cserhatensis Müller, 1984, from the middle Miocene of Hungary, or with Paguristes gagnaisoni from the middle Miocene of France (Gagnaison, 2012).