Palaeosynaxes montserratae, Fraaije & van Bakel & Jagt & Krobicki & Ossó & Palero & Wallaard, 2023

Fraaije, René H. B., van Bakel, Barry W. M., Jagt, John W. M., Krobicki, Michał, Ossó, Àlex, Palero, Ferran & Wallaard, Jonathan J. W., 2023, A reconsideration of the palinuroid family Synaxidae (Crustacea, Decapoda), with a new member from the Upper Jurassic of southern Poland, Palaeontologia Electronica (a 19) 26 (2), pp. 1-9 : 4-6

Palaeosynaxes montserratae nov. gen., nov. sp.

Figure 4

zoobank.org/ 23EEB842-EF06-4A28-8DE9-D5EDCFA00C5D

Diagnosis. As for genus.

Repository of the type specimen. MAB - Oertijdmuseum , Boxtel, The Netherlands.

Type material. The holotype MAB13942, and sole specimen known to date, is an incomplete carapace with a maximum preserved length of 9.5 mm and a maximum preserved width of 6.0 mm, collected in June 2013 by one of us (À.O.) during a field trip to the 5th Symposium on Mesozoic and Cenozoic Decapod Crustaceans , Kraków ( Poland). Etymology. Dedicated to Montserrat Batet, partner of one of us (À.O.), as a token of thanks for her support and understanding.

Locality and stratigraphy. A road cutting on a small hill close to the village of Szklary, southern Poland, exposing upper middle Oxfordian ( Gregoryceras transversarium ammonite Zone) reefal strata ( Figures 1 , 2 ).

Description. Carapace small, oval, tubular, convex in transverse section; base of rostrum broad, tuberculate and concave; cervical groove Vshaped centrally, obscure laterally; carapace densely covered with coarse, blunt, forwardly directed tubercles, most robust on two postrostral ridges on anterior part; another less pronounced ridge of tubercles extending centrally on mesogastric with double circular tubercle arrangement forming a figure 8 on mesogastric area; cervical groove forming wide V in central third of carapace and extending obliquely (c. 45 degrees) toward anterolateral border; posterior part of carapace densely covered with coarse, blunt, forwardly directed tubercles, largest around cervical groove; maximum length of preserved posterior part about 35 per cent of total preserved carapace length.

Remarks. The type of ornament, general shape of the anterior carapace and length of the posterior portion, rules out assignment to the families Palinuridae , Cancrinidae , or Scyllaridae and places the present Late Jurassic taxon in the Synaxidae . The two postrostral ridges of larger tubercles on the anterior carapace of Palaeosynaxes nov. gen. could be taken as a prelude of the postfrontal horns of members of the Palinuridae . These two rows of forwardly directed tubercles and the subcircular tubercular arrangements on the central gastric area make Palaeosynaxes nov. gen. easily differentiated from all other known synaxids.

The Middle Triassic Yunnanopalinura schrami Feldmann, Schweitzer, and Zhang in Feldmann, et al., 2012 shows some similarities to synaxids according to Feldmann et al. (2012), but a more detailed comparison is impossible because the Chinese taxon is based on two specimens in which preservation of parts of the cephalothorax is too poor ( Fraaije et al., 2020).

Figures

FIGURE 1. Lithostratigraphical column of Oxfordian strata in the Kraków area (southern Poland), with indication of the Szklarka valley locality (modified after Matyszkiewicz, 1996; Matyszkiewicz et al., 2012).

FIGURE 2. Sedimentology, palaeoecology, and presence of decapod crustaceans in the Szklarka valley outcrop (see Figure 1 after Müller et al., 2000; supplemented by Fraaije et al., 2022). The black star denotes the approximate level of provenance of the holotype of Palaeosynaxes montserratae nov. gen., nov. sp. (Figure 4).

FIGURE 4. Palaeosynaxes montserratae nov. gen., nov. sp., holotype (MAB k3781), in left lateral and dorsal views, scale bar equals 5 mm.