Introduction
Although capsulated setae are not uncommon in paguroid hermit crabs, only recently were they reported in fossil forms. Capsulapagurus christiaensi Fraaije et al., Reference Fraaije, Van Bakel, Iserbyt and Jagt2011 from the lower Albian of the Pargny-sur-Saulx clay pit (Haute-Marne, northeastern France) was based on a single right chela. Recently, another paguroid with capsulated setae, Capsulapagurus brocheti Fraaije, Van Bakel, and Jagt, Reference Fraaije, Van Bakel and Jagt2015, was reported from the lower Albian of Laneuville-au-Pont (Haute-Marne), again based only on a single right chela (Fraaije et al., Reference Fraaije, Van Bakel and Jagt2015). According to Osawa (Reference Osawa2012; see also Komai, Reference Komai2003; Komai and Rahayu, Reference Komai and Rahayu2014), eight extant species have close relationships, as established from the possession of capsulated setae on their chelipeds. Recently, Fraaije et al. (Reference Fraaije, Van Bakel and Jagt2015) transferred these eight species to Capsulapagurus. This short report adds another fossil paguroid with capsulated setae, Paracapsulapagurus n. gen., but this time from the Maastrichtian of Senegal.
Fossil decapods of Senegal are poorly known. Tessier (Reference Tessier1952), Remy and Tessier (Reference Remy and Tessier1954), and Gorodiski and Remy (Reference Gorodiski and Remy1959) described several brachyuran species from Maastrichtian, Paleocene, and Eocene Senegalese deposits and reported on some unidentified callianassid claws. Recently, new decapod material from the middle to upper Maastrichtian of the Cap de Naze, Poponguine in Senegal (Fig. 1) has been reported, including a description of a new species of brachyuran genus Costacopluma Collins and Morris, Reference Collins and Morris1975, by Hyžný et al. (Reference Hyžný, Perrier, Robin, Martin and Sarr2016).
Figure 1 Studied area of Cape de Naze, Poponguine, Senegal. The area shaded in gray corresponds to the sediments of late Campanian–Maastrichtian age.
Material and methods
The specimen was studied under binoculars Leica MZ6 and EZ4 and photographed using three different methods: 1) dry and uncoated; 2) coated with ammonium chloride sublimate; and 3) using SEM (Philips XL30ESEM, University of Tartu, Estonia).
Repositories and institutional abbreviations
BSPG: Bayerische Staatssammlung für Paläontologie und Geologie, Munich, Germany; MAB: Oertijdmuseum De Groene Poort, Boxtel, The Netherlands; MNHN: Muséum National d’Histoire Naturelle, Département Histoire de la Terre, Paris, France; SENCN: Laboratoire de Géologie, Université Cheikh Anta Diop, Dakar, Senegal.
Systematic paleontology
Order Decapoda Latreille, Reference Latreille1802
Infraorder Anomura MacLeay, Reference MacLeay1838
Superfamily Paguroidea Latreille, Reference Latreille1802
Remarks
Of all known extant paguroid ingroups, only Parapaguridae Smith, Reference Smith1882, and Pylojacquesidae McLaughlin and Lemaitre, Reference McLaughlin and Lemaitre2001, have not yet been reported from the fossil record (De Grave et al., Reference De Grave2009). The Annuntidiogenidae Fraaije, Reference Fraaije2014, Diogenidae Ortmann, Reference Ortmann1892, Gastrodoridae Van Bakel et al., Reference Van Bakel, Fraaije, Jagt and Artal2008, Parapylochelidae Fraaije et al., Reference Fraaije, Klompmaker and Artal2012, Pilgrimchelidae Fraaije, Reference Fraaije2014, and Pylochelidae Bate, Reference Bate1888, occur predominantly in reefal carbonates of the fossil record, whereas the Paguridae Latreille, Reference Latreille1802 seems to be confined to siliciclastic environments (Fraaije et al., Reference Fraaije, Van Bakel, Iserbyt and Jagt2011, Reference Fraaije, Van Bakel and Jagt2015).
Family Paguridae Latreille, Reference Latreille1802
Genus Paracapsulapagurus new genus
Type species
Paracapsulapagurus poponguinensis n. sp. by original designation and monotypy.
Diagnosis
As for type species by monotypy.
Etymology
From Greek παρά (pará=next to, near) and Capsulapagurus, alluding to the close relationship with Capsulapagurus.
Occurrence
Known only from the middle–upper Maastrichtian of Cap de Naze, Senegal.
Remarks
Paracapsulapagurus n. gen. differs from Capsulapagurus in having platy, scale-like, non-spinose tubercles, in the absence of spines on the dactylus, and in the absence of large embedded setal areas on both fingers. Multiple setal pits of Paracapsulapagurus n. gen. are typically arranged in a curved row, whereas the multiple setal pits of Capsulapagurus spp. are concentrically arranged.
Paracapsulapagurus poponguinensis new species
Figure 2 Paracapsulapagurus poponguinensis n. gen. n. sp. (holotype SENCN-054); middle–upper Maastrichtian of the Cap de Naze Formation, Poponguine, Senegal: (1), outer lateral view; (2), angled view showing the keel on the fixed finger and manus; (3), inner lateral view. Specimen coated with ammonium chloride.
Figure 3 Paracapsulapagurus poponguinensis n. gen. n. sp. (holotype SENCN-054); middle–upper Maastrichtian of the Cap de Naze Formation, Poponguine, Senegal: (1), lateral view of the right cheliped; (2), capsulated setae on the inner lateral surface of merus; (3), inner lateral surface of carpus; note well-developed spines; (4), finger tips in inner lateral view; (5), basal portion of dactylus in inner lateral view; (6, 7), capsulated setal pores on the outer lateral surface of propodus; (8, 9), capsulated setal pores on the inner lateral surface of propodus. All figures are SEM images.
Figure 4 Arrangement of setal pores in all fossil species with capsulated setae known to date: (1), inner lateral surface of the propodus of Paracapsulapagurus poponguinensis n. gen. n. sp. (holotype SENCN-054); middle–upper Maastrichtian of the Cap de Naze Formation, Poponguine, Senegal; (2), outer lateral surface of the propodus of Capsulapagurus christiaensi Fraaije et al., Reference Fraaije, Van Bakel, Iserbyt and Jagt2011 (holotype MAB k. 3158); lower Albian of the Pargny-sur-Saulx clay pit, Département Marne, northeast France; (3), upper portion of the outer lateral surface of the propodus of Capsulapagurus brocheti Fraaije et al., Reference Fraaije, Van Bakel and Jagt2015 (holotype MNHN.F.A52940); lower Albian of the Pargny-sur-Saulx clay pit, Marne, northeast France; (4), upper margin of the propodus of Schobertella simonsenetlangi Schweigert et al., Reference Schweigert, Fraaije, Havlik and Nützel2013 (BSPG 2011 XI 62); lower Pliensbachian of the Amaltheenton Formation, Buttenheim/Franconia. (1) Is a SEM image; (2, 3) are light pictures of specimens coated with ammonium chloride; (4) is a light picture of a specimen without ammonium chloride coating.
Holotype
Right chela consisting of articulated dactylus, propodus, carpus, and merus (Collection n° SENCN-054) (Fig. 2.1–2.3) from the middle to upper Maastrichtian of the Unit 3 of the Cap de Naze Formation, Poponguine, Senegal.
Diagnosis
Right cheliped propodus with concave lower margin at the base of the fixed finger; fixed finger with longitudinal keel extending onto manus; outer surface covered with platy non-spinose tubercles; capsulated setae arranged mostly in a curved row.
Occurrence
Material was collected from the middle to upper Maastrichtian marine sandstones of the Unit 3 of the Cap de Naze Formation outcropping at Cap de Naze, Poponguine, Senegal. The age is based on foraminifers and ammonites from the units 2 and 4, as discussed in detail by Hyžný et al. (Reference Hyžný, Perrier, Robin, Martin and Sarr2016). More details about the geology and subdivisions of the deposits were given by Tessier (Reference Tessier1952), Castelain et al. (Reference Castelain, Jardiné and Monciardini1965), Khatib et al. (Reference Khatib, Ly, Sow and Sarr1990), Sarr (Reference Sarr1995), and Cuny et al. (Reference Cuny, Martin and Sarr2011).
Description
Merus of right chela pressumably subquadrate in outline (as far as it can be inferred from the broken margin) with several transverse rows of tubercles. Carpus with subtrapezoidal outline in lateral view, dorsal margin with distinct spines (Fig. 3.3); distal margin concave, enveloping proximal margin of propodus; outer surface coarsely granular proximally and finely granular distally. Propodus oval in outline (Fig. 3.1), upper margin convex, lower margin initially converging distally and concave at the base of the fixed finger; fixed finger robust, curving inward, with lateral keel running continuously onto the manus (Figs. 2.1, 3.1). Dactylus curving inward, blunt-tipped (Fig. 3.4). Occlusal margins of the fingers armed with subequal molariform denticles. Inner and outer lateral surfaces of all preserved elements more-or-less evenly covered with densely packed platy, scale-like tubercles (Fig. 3.6, 3.8), forming distinct spines on merus and carpus (Fig. 2.3); outer surfaces covered more densely than inner ones. Capsulated setal structures preserved in most tubercles, directed distally; tubercles on the outer lateral surface usually bearing 1–2 setal pits (Fig. 3.6, 3.7), tubercles on the inner lateral surface usually bearing 3–4 setal pits (Fig. 3.8, 3.9).
Etymology
The species epithet refers to the type locality at Poponguine, Senegal.
Remarks
Paracapsulapagurus poponguinensis n. gen. n. sp. differs from Capsulapagurus spp. in several major aspects. The new species possesses a concavity on the lower margin of the propodus, just at the base of the fixed finger. The upper margin of the propodus is strongly convex (Fig. 2). Neither Capsulapagurus christiaensi nor C. brocheti has such a concavity (Fraaije et al., Reference Fraaije, Van Bakel, Iserbyt and Jagt2011, fig. 1B, 1C; Fraaije et al., Reference Fraaije, Van Bakel and Jagt2015, figs. 1B, 1C; respectively), and the upper margin of the latter species is straight (Fraaije et al., Reference Fraaije, Van Bakel and Jagt2015, fig. 1B, 1C). The holotype of C. christiaensi is fragmentary and the upper propodal margin cannot be sufficiently described (Fraaije et al., Reference Fraaije, Van Bakel, Iserbyt and Jagt2011, fig. 1). Both Albian taxa have large tubercles on the upper margin of the propodus, occasionally forming spines. The new material from Senegal has the upper margin of the propodus without such large tubercles, although a few broken spines are present on the proximal-most part of the upper margin; much larger spines are present on the carpus and merus (Figs. 2.3, 3.3). The propodus outline of Paracapsulapagurus poponguinensis n. gen. n. sp. differs strikingly from C. brocheti, which has a more elongated propodus (Fraaije et al., Reference Fraaije, Van Bakel and Jagt2015, fig. 1).
Discussion
Although SEM imaging has been used for documentation of the cuticular surfaces of numerous fossil decapod taxa (in lobsters: e.g., Simpson and Middleton, Reference Simpson and Middleton1985; Feldmann and Tshudy, Reference Feldmann and Tshudy1987; in brachyurans: e.g., Vega et al., Reference Vega, Feldmann and Davila-Alcocer1994; Feldmann and Gaździcki, Reference Feldmann and Gaździcki1998; Haj and Feldmann, Reference Haj and Feldmann2002; Waugh et al., Reference Waugh, Feldmann and Schweitzer2009; Hyžný and Kroh, Reference Hyžný and Kroh2015; Hyžný et al., Reference Hyžný, Perrier, Robin, Martin and Sarr2016), it has only rarely been used to document the morphology of extinct paguroid hermit crabs. Müller (Reference Müller1984, pl. 11, figs. 7–9) used the SEM technique for imaging Anapagurus miocenicus Müller, Reference Müller1984, from the middle Miocene of Hungary. Van Bakel et al. (Reference Van Bakel, Jagt and Fraaije2003) provided a detailed description of Ciliopagurus obesus Van Bakel, Jagt, and Fraaije, Reference Van Bakel, Jagt and Fraaije2003 from the Oligocene (Rupelian) of Belgium based on SEM images. This technique proved invaluable in documenting the stridulatory apparatus of this species (Van Bakel et al., Reference Van Bakel, Jagt and Fraaije2003, figs. 1.1, 2.1).
In this report, SEM imaging provided detailed documentation of capsulated setae of a new paguroid species and helped to identify crucial differences in their development from all hermit crabs with capsulated setae known to date (for a review, see Fraaije et al., Reference Fraaije, Van Bakel and Jagt2015). The setal pores in Paracapsulapagurus poponguinensis n. gen. n. sp. are arranged in curved rows (Fig. 4.1), whereas in representatives of Capsulapagurus they are arranged in more-or-less circular clusters (Fig. 4.2, 4.3). The rows of setal pores in P. poponguinensis n. sp., are best developed on the inner lateral surface of the propodus. Interestingly, some comparable capsulated setal pits are reported here to occur also on the representative of Schobertella simonsenetlangi Schweigert et al., Reference Schweigert, Fraaije, Havlik and Nützel2013 (Fig. 4.4) from the Early Jurassic (Pliensbachian) of France and Germany, indicating that Schobertellidae Schweigert et al., Reference Schweigert, Fraaije, Havlik and Nützel2013, possibly are close to, or even ancestral to Paguridae.
For the possible function of the setae, McLaughlin and Lane (Reference McLaughlin and Lane1975) suggested that they may act both to detect and repel predators. To our knowledge, no further physiological, behavioral, or prey-predator studies of hermit crabs with capsulated setae have been conducted to date. In this respect, the fossil record of taxa with capsulated setae does not offer enough data to analyze.
Acknowledgments
G. Schweigert (Staatliches Museum für Naturkunde, Stuttgart) provided photo of the capsulated setae of Schobertella simonsenetlangi. JEM and RS warmly thank the members of the PaleoSen team for help in the field: L. Hautier, M. Thiam, B. Sambou, S. Adnet, F. Lihoreau, R. Lebrun, and R. Tabuce. Reviewers R. Feldmann and G. Schweigert and associate editor J. Haug are thanked for constructive criticism. This research is part of the PaleoSen project (www.paleosen.com). JEM and RS were supported in the field by ANR PALASIAFRICA (ANR-08-JCJC-0017), PICS-CNRS, the international Exchange Scheme of the Royal Society and the National Geographic Society’s Global Exploration Fund (Northern Europe). The research of MH has been supported by the Slovak Research and Development Agency under contracts no. APVV-0644-10 and APVV-0436-12.
