Ammopylocheles robertboreki, Fraaije & Krzemiński & Van Bakel & Krzemińska & Jagt, 2012

Fraaije, René H. B., Krzemiński, Wiesław, Van Bakel, Barry W. M., Krzemińska, Ewa & Jagt, John W. M., 2012, The earliest record of pylochelid hermit crabs from the Late Jurassic of southern Poland, with notes on paguroid carapace terminology, Acta Palaeontologica Polonica 57 (3), pp. 647-654 : 650-652

Ammopylocheles robertboreki sp. nov.

Fig. 4A–D.

Etymology: Named after Robert Borek, who collected the majority of specimens used in the present study, in the company of his wife Iwona and daughter Karolina.

Holotype: ISEA I−F / MP/2745 /1530/08 is a near−complete carapace (maximum length 11.5 mm, maximum width 8 mm).

Type locality: Wysoka, southern Poland.

Type horizon: Perisphinctes plicatilis Zone and base of Gregoriceras transversarium Zone (Middle Oxfordian; see Głowniak 2002).

Referred material.—ISEA I−F/MP/6199/1577/10, a near−complete shield (maximum length 3.5 mm, maximum width 3 mm) from Ogrodzieniec; ISEA I−F/MP/6198/1577/10, a near−complete shield (maximum length 5 mm, maximum width 4 mm) from the same locality; ISEA I−F/MP/6197/ 1577/10, a near−complete shield (maximum length 7 mm, maximum width 4.5 mm) from Kroczyce.

Fig. 4. Pylochelid hermit crabs from Oxfordian (Jurassic) of southern Poland. A–D. Ammopylocheles robertboreki sp. nov. A. Holotype, ISEA Ą 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, ISEA I−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.

http://dx.doi.org/10.4202/app.2011.0002

Diagnosis.—Carapace longer than broad, shield as long as wide, broadest at centre of undivided massetic regions and clearly tapering posteriorly; small rostrum; distinct sinuous cervical furrow, central gastric groove and post−frontal ridge.

Description.—Carapace markedly longer than broad (W/L ratio 0.68), strongly convex in transverse section, convex in longitudinal section, markedly tapering posteriorly. Shield width and length approximately equal (W/L ratio 1.03); cervical groove prominent, a separate linea transversalis is absent; ornament of dorsal surface of gastric region consisting of small, imbricated granules on anterior and posterior sides; long longitudinal ridges at sides, bounded by lateral gastric grooves which tend to converge axially.

Small transverse post−rostral region with obscure rostrum; transverse, markedly convex, post−rostral ridge medially subdivided by a deep, central gastric groove; post−antennal projections obtuse. Lateral margins sloping, with highly globose, undivided massetic region. Posterior carapace shorter than shield, less well calcified, smooth, strongly tapering posteriorly.

Remarks.—The new species, of Middle Oxfordian age, differs from its Kimmeridgian congener, Ammopylocheles mclaughlinae (holotype: MAB k.2454), in having a transversely more convex, cylindrical and markedly posteriorly tapering carapace. The shift from a more cylindrical towards a more flattened carapace could be indicative of a change in hiding strategy. Currently, A. robertboreki sp. nov. is known from three localities at which the deeper, intra−reefal layered sponge limestone ( Förster and Matyja 1986; Krobicki and Zatoń 2008) are exposed, while A. mclaughlinae inhabited areas closer to and within the shallower sponge reefs ( Van Bakel et al. 2008). The absence of fragments of wood, scaphopods, larger serpulids and rock fragments at the type locality would suggest a possible mutualistic mode of life (pylochelid/ sponge) for A. robertboreki sp. nov., while A. mclauglinae also had reefal debris available to hide in as well as under.

Geographic and stratigraphic range.—To date, known only from the southern Polish Uplands, northwest of Kraków, all material stemming from the Middle to Late Oxfordian.

Mixtopagurinae Forest, 1987a

Genus Jurapylocheles Van Bakel, Fraaije, Jagt, and Artal, 2008

Type species: Jurapylocheles malutka Van Bakel, Fraaije, Jagt, and Artal, 2008 (by original designation). Algal limestone of the “Riff−fazies” of the Kimmeridgian Untere Felsenkalke Formation (“Weissjura delta”, early Late Kimmeridgian, Aulacostephanoides mutabilis / Aspidoceras acanthicum Zone ) exposed in a quarry north of the village of Geisingen, southern Germany.