Introduction

At the present day, pylochelid hermit crabs inhabit the Indo-West Pacific with the western Atlantic oceans, their vertical distribution in subtropical to tropical waters ranging from 30 to 2,149 metres. Occurrences above 100 metres are rare with the maximum number of species having been recorded from depths between 200 and 500 metres (Forest 1987b; McLaughlin and Lemaitre 2009). Unlike most paguroids, all extant pylochelids have well-calcified carapaces and abdominal tergites, in particular the sixth abdominal tergite. This group of “symmetrical” paguroids, so named because their chelipeds are of near-similar size, seek protection in hollow objects, with the sixth abdominal tergite functioning as an operculum to close off the posterior opening of their abode. Dependent of availability, pylochelids use cavities in pieces of wood (e.g., bamboo), rock (conglomerate, limestone and tuff/pumice) or empty shells of molluscs (mainly scaphopods, but also gastropods) and serpulid worms, while some species carry living sponges. A number of species of the genera Trizocheles Forest, 1987a and Pylocheles Milne-Edwards, 1880 demonstrate a mutualistic relationship with thin-walled dictyonin hexactinellids or more massively built lithistid and haplosclerid demosponges (Forest 1987b; McLaughlin and Lemaitre 2009).

In general, there are only few studies on Late Jurassic decapod crustaceans from Poland, and most of them are devoted to brachyuran crabs, e.g., Radwański (1972), Collins and Wierzbowski (1985), Krobicki and Müller (2000), Müller et al. (2000), Krobicki and Zatoń (2008) and Starzyk et al. (2011), or describe remains of macrurans, e.g., Förster and Matyja (1986) and Garassino and Krobicki (2002). The first paper in which anomurans from Jurassic strata in Poland were recorded was that by Van Bakel et al. (2008), in which a species of the gastrodorid genus Gastrodorus von Meyer, 1864 (see also Klompmaker et al. 2011) was described and illustrated. Van Bakel et al. (2008) were the first to recognise and document a wide range of paguroid carapaces, including two species of pylochelid, from the Late Jurassic of southern Germany. They also were able to place these specimens within the present classification of the Paguroidea. For reasons unknown to us, Schweitzer et al. (2010: 53) listed the four new genera erected by Van Bakel et al. (2008) as “Family uncertain” within the superfamily Paguroidea Latreille, 1802.

Fig. 1.

Localities with paguroid-bearing strata of Middle—Late Oxfordian age in southern Poland (see inset), as follows: G, Grabowa; K, Kroczyce; N, Niegowonice; O, Ogrodzieniec; W, Wysoka (modified after Głowniak 2006: fig. 2).

Following this, the Borek family from the village of Dąbrowa Górnicza (southern Poland) succeeded in collecting, over a period of two years, in excess of 7,000 specimens of decapod crustaceans from six localities within the southern Polish Uplands, northwest of Kraków (Fig. 1). This impressive collection now forms the basis of the present note as well as of several ongoing studies on anomurans, brachyurans (Starzyk et al. 2011) and macrurans.

Microfossil assemblages from the Oxfordian sponge facies of the Kraków Upland comprise mainly foraminifera, ostracods and sponge spicules. The commonest spicules can be assigned to the Choristida, Lithistida, and Lyssakida (Olszewska and Wieczorek 1988). Other associated macrofossil groups in this facies are ammonites, belemnites, echinoids, crinoids, and brachiopods, while bivalves, gastropods, and fish remains occur rather sporadically.

Institutional abbreviations.—ISEA, Institute of Systematics and Evolution of Animals, Polish Academy of Sciences, Kraków, Poland; MAB, Oertijdmuseum De Groene Poort, Boxtel, the Netherlands.

Geographic and stratigraphic setting

The paguroids described below most probably lived between and/or within sponge buildups, which formed in neritic environments along the southernmost part of the epicontinental Peri-Tethyan sea, which was connected with the northernmost shelf of the Tethys Ocean during Oxfordian times. Originally, sponge accumulations formed sponge-microbial bioherms surrounded by soft muddy bottoms, the latter now represented by thin-bedded, micritic, chert-free, platy limestone with thin marly intercalations, full of nektonic ammonites and rare decapod crustaceans (Müller et al. 2000; Garassino and Krobicki 2002; Krobicki and Krzemiński 2010). The Upper Oxfordian massive limestone and thick-bedded, sponge-microbial chert-bearing limestone are relatively decapod-rich deposits as typical type of sponge mega-facies limestone across the whole of Europe, in particular the Jurassic of the Fränkische and Schwäbische Alb in southern Germany (see Wehner 1988; Müller et al. 2000). The depth of deposition of these Oxfordian limestone rocks has been hotly disputed (Matyja and Wierzbowski 1996, 2004; Matyszkiewicz 1999), which is related to the lack of both bathymetrically diagnostic fossils and sedimentary structures, but most probably carbonate buildups originated at depths of one to a few hundred metres (Leinfelder 1993; Leinfelder et al. 1994; Matyja and Wierzbowski 1996, 2004; Matyszkiewicz 2008). After the global Callovian transgression, which allowed the formation of bioherms and reefs in Late Jurassic Peri-Tethyan basins, this created a palaeoenvironment which was conducive to the rapidly evolving decapod crustaceans (Müller et al. 2000; Van Bakel et al. 2008). When the first Oxfordian cyanobacteria-sponge buildups appeared in Europe, decapod crustaceans began to flourish and inhabited these biostructures in great numbers, expanded practically over the whole of Europe during the Oxfordian, from Portugal through Spain and France and to Germany, Poland, and Romania (Müller et al. 2000; Feldmann et al. 2006; Krobicki and Zatoń 2008). In turn, the latest Jurassic regression in the Peri-Tethyan area resulted in the disappearance of the sponge megafacies and led to changes of habitat, migration and colonisation of primitive crabs, for instance in the Štramberk coral reefs along the northernmost margin of the Tethys Ocean, where these crabs probably reached an acme (Müller et al. 2000; Krobicki and Zatoń 2008).

The material described below originates from six localities in the southern Polish Uplands, northwest of Kraków (Fig. 1), as follows:

Ogrodzieniec.—On ammonite evidence, the section exposed at Ogrodzieniec Quarry can be dated as Early and Middle Oxfordian. With the exception of the discontinuous Quenstedtoceras mariae Zone, all zones and subzones from the Cardioceras cordatum to the Gregoriceras transversarium zones, have been documented (Głowniak 2006).

Bzów.—This pit, the northerly portion of which is in the village of Bzów, represents a prolongation of the large quarry at Ogrodzieniec. Ammonites (Ochetoceras canaliculatum [von Buch, 1831], Trimarginites trimarginatus [Oppel, 1863], Dichotomosphinctes sp., Glochinoceras subclausum [Oppel, 1863]) collected at this locality have recently been identified by Günter Schweigert (personal communication 2011) (Staatliches Museum für Naturkunde, Stuttgart, Germany) and indicate the Gregoriceras transversarium Zone of the Middle Oxfordian. A single specimen in this lot might represent Cardioceras tenuiserratum Oppel, 1863, which would indicate the upper Perisphinctes plicatilis Zone (see also Matyja and Wierzbowski 1994).

Niegowonice.—The sequence exposed at this quarry ranges from the upper Peltoceratoides elisabethae Subzone to the upper Dichotomoceras wartae Subzone, i.e., is of Middle and Late Oxfordian age (Głowniak 2006).

Grabowa.—The quarry is east to the quarry of Niegowonice and very close to it. The age of these sediments was until now not known from the literature. One accompanying ammonite was recently determined by Ewa Głowniak and Andrzej Wierzbowski (personal communication 2011) as Taramelliceras externnodosum (Dorn, 1930), which correlates with the Upper Oxfordian zone of the uppermost Perisphinctes bifurcatus to the lowermost Epipeltoceras bimammatum (Euaspidoceras hypselum Subzone) (according to Glłwniak and Wierzbowski 2007: fig. 2).

Kroczyce.—As above, the age of these sediments has been recently determined by Głowniak and Wierzbowski (2007) as Late Oxfordian (uppermost Perisphinctes bifurcatus to the lowermost Epipeltoceras bimammatum (Subzone: Euaspidoceras hypselum) zones, on the basis of accompanying ammonites: Taramelliceras externnodosum, Glochiceras (Glochiceras) tectum Ziegler, 1958, Glochiceras (Coryceras) aff. canale (Quenstedt, 1848) and Taramelliceras (Richeiceras) jaeggii Quereilhac, 2009. The biohermal basin of Kroczyce is c. 20 km long and extends in a NE-SW direction. It belongs to a complex of bioherms occupying over c. 100 km from NW to SE of the Polish Jurassic Chain (Matyja and Wierzbowski 2004).

Wysoka.—Głowniak (2002) documented the Perisphinctes plicatilis Zone and the base of the Gregoriceras transversarium Zone at this quarry, i.e., the Middle Oxfordian.

Fig. 2.

Pylochelid carapace terminology employed in the present paper.

Paguroid carapace terminology

Despite the fact that paguroid carapaces very often display clearly developed and diverse morphological features, comparatively little attention has been paid to these features by neontologists. Carapace morphology amongst pylochelids is highly diagnostic (Fig. 2), as was demonstrated in a landmark study of this family by Forest (1987a: 17), who noted [translated from French], “The definitions and descriptions of the different taxa of Pylochelidae are based on numerous characters of external morphology. The shape, the proportions, and the lines and grooves of the cephalothoracic carapace and of the abdomen are probably the elements allowing an immediate generic identification….”. Unfortunately, in that particular paper, as well as in all subsequent work on pylochelids, descriptions of shield and carapace merely mention their size and the presence of a cervical groove and linea transversalis. Even in the most recent classification of the Pylochelidae (McLaughlin and Lemaitre 2009: 162), the part of the diagnosis of the family which deals with carapace features is very meagre, “Carapace usually well calcified, at least anteriorly; incompletely or completely divided into shield and posterior carapace by linea transversalis; cervical groove contiguous or not with linea transversalis. Rostrum present or absent.”

In recent years, the number of fossil paguroid carapaces on record has steadily grown (e.g., Fraaije et al. 2008; Van Bakel et al. 2008; the present study). Data obtained from the study of these carapaces are a welcome addition to our understanding of phylogenetic relationships within the Paguroidea (Lemaitre and McLaughlin 2009). In order to assess properly the phylogenetic “signal” preserved in these carapaces, a uniform descriptive terminology is called for and this would also allow the recognition of homologous structures or carapace regions. However, a survey of the biological literature has revealed an omission in the standard terminology of a particular region in a paguroid carapace, which is often very pronounced. In brachyuran crabs, the equivalent of this is referred to as the hepatic region, this area more or less reflecting the position of the underlying hepatic caeca (Stachowitsch 1992). In a detailed study of the internal muscular anatomy of the Recent Pagurus bernhardus (Linnaeus, 1758), Pilgrim (1973) demonstrated the presence of two areas of attachment of mandible muscles to the carapace. A large, powerful external adductor occupies and is attached to a large elongated-oval area of the anterolateral gastric region, whereas the much smaller external abductor is located posteriorly of the adductor within the same area. This region is at the same position of the hepatic region in brachyurans, but, in view of the fact that it does not reflect the location of the liver in paguroids, this should be named differently. Here we introduce the term “massetic region” (New Latin massētēr, from Greek masētēr, massētēr, to masticate or chew) for this morphologically clearly distinct region on the carapace, which constitutes the site of attachment of the mandibular adductor and abductor muscles.

Fig. 3.

The position of the massetic region (new term) in various paguroid families and subfamilies.

This homologous region cannot be overlooked in representatives of nearly all paguroid families (Fig. 3). In some groups, it usually appears as an undivided, elongated-oval region (e.g., in the Pylochelinae), whereas in others (e.g., in the Parapylochelinae and Parapaguridae) there is a markedly larger anterior and a smaller posterior portion which are divided by a clear groove. It would appear that in all major taxonomic studies of the Pylochelidae, drawings rather than photographs are contained to illustrate the species described. While comparing line drawings of the same species in different studies, it seems that the massetic region was either interpreted differently, or even ignored, by the artist. For that reason, we strongly recommend the use of photographs in all future studies of paguroids, and of pylochelids in particular. To stress this fact, one example will suffice here: compare e.g., Trizocheles s. spinosus in Forest (1987a: 203, fig. 70) and Forest et al. (2000: 46, fig. 11).

Amongst other extinct decapod crustaceans, there is only one group which has pronounced massetic regions. This is the closely related family Gastrodoridae (see Van Bakel et al. 2008: 149, figs. 9, 10b, d; Klompmaker et al. 2011: fig. 6). This observation also makes it highly probable that in the equally closely related Galatheoidea (e.g., Klompmaker et al. 2011), the term hepatic should also be replaced by massetic. Thorough studies, along the lines of Pilgrim's 1973 paper, are needed to resolve this matter.

Systematic palaeontology

The classification proposed by McLaughlin et al. (2010) is adopted here pending further refinements.

Fig. 4.

Pylochelid hermit crabs from Oxfordian (Jurassic) of southern Poland. A–D. Ammopylocheles robertboreki sp. nov. A. Holotype, ISEA I-F/MP/2745/ 1530/08 from Wysoka. B. ISEA I-F/MP/6198/1577/10 from Ogrodzieniec. C. ISEA I-F/MP/6197/1577/10 from Kroczyce. D. ISEA I-F/MP/6199/1577/10 from Ogrodzieniec. E–F. Jurapylocheles iwonae sp. nov. E. Holotype, ISEAI-F/MP/3956/1533/08 from Bzów. F. Paratype, ISEA I-F/MP/6193/1577/10 from Ogrodzieniec. Scale bars: A–C 5 mm, D–F 2 mm.

Conclusions

The present pylochelid faunule from the Oxfordian of the southern Polish Uplands matches well that of the Kimmeridgian in southern Germany (see Van Bakel et al. 2008), with the same subfamilies and genera being represented. Probably as a result of the rise of brachyuran crabs and galatheoid anomurans, which led to increased competition within shallow-marine near-reefal environments, pylochelids migrated from near-reefal environments to deeper-water settings during the Late Jurassic and have remained there ever since.