A new early brachyuran (Crustacea, Decapoda) from the Middle Jurassic of northwest France, epibionts and ecological considerations

Abstract

The earliest known crabs are of Early and Middle Jurassic age; in general, they are rare. Here we describe a new species of homolodromioid from the late Bathonian of Sarthe (France), based on a single dorsal carapace, Tanidromites raboeufi n. sp. This specimen has mostly well-preserved cuticle, and shows two episkeletozoans (bryozoan colonies) on its dorsal side, which is unique amongst early brachyurans (Early and Middle Jurassic). These bryozoans are identified as juvenile colonies of the morphogenus Berenicea (sheet-like tubuluporines), typical encrusters of hard substrates. Their presence directly on the carapace crab shows that they were closely cohabitating with this early brachyuran in its palaeoenvironment. One of these colonies appears to have attached to the internal carapace surface, indicative of post-mortem settlement and growth. Colony sizes suggest a growth phase of at least several months on the sea floor, implying a certain resistance to decomposition of the crab carapace. This is of note in the light of extant homolodromioids which are known to have extremely fragile carapaces. This association demonstrates that post-mortem associations may yield palaeoecological insights into both substrate and colonising organisms.

Systematics and convergent evolution of multiple reef-associated Jurassic and Cretaceous crabs (Decapoda, Brachyura)

“…In many brachyurans, the hepatic region does not border the mesogastric region (e.g., Glaessner, 1969, figure 220;Davie et al, 2015, figure 71-2.6). Such mesogastric groove tubercles can be found on the internal mold and on the cuticle in representatives of Tanidromites (Starzyk, 2016(Starzyk, , 2013herein), but also in specimens of Distefania Checchia-Rispoli, 1917, Eodromites Patrulius, 1959, Gabriella Collins et al, 2006, and Pithonoton von Meyer, 1842 Gastric pits have been used extensively to describe two pits on the gastric region close to the longitudinal axis of decapods (e.g., Jakobsen and Collins, 1997;Blow, 2003;Hyzný and Müller, 2010;Klompmaker et al, 2012), but cervical pits have been used instead recently (Starzyk, 2013(Starzyk, , 2016Robin et al, 2015;Hyžný et al, 2015). We here use gastric pits because not all such pits are located clearly within the cervical groove (e.g., Dakoticancridae; Nitotacarcinus Schweitzer et al, 2007; some Etyidae) or a clear cervical groove is not always present (Paranecrocarcinidae, Zanthopsidae, some Raninoida).…”

“…montreuilense Crônier and Boursicot, 2009; T. muelleri Krobicki and Zatoń, 2016; T. nightwishorum sp. nov.; T. pustulosa (von Meyer, 1860), as Pithonoton; T. raboeufi Robin, Van Bakel, d'Hondt, and Charbonnier, 2015; T. richardsoni (Woodward, 1907), as Prosopon; T. scheffnerae Schweigert and Koppka, 2011 (=T. wysokaensis Starzyk, 2016); T. sculpta (Quenstedt, 1858), as Prosopon (=Prosopon lingulata von Meyer, 1858; Prosopon wuergauensis Kuhn, 1939); T. schweitzerae Starzyk, 2016;T.…”

Three new species of the genus Tanidromites (Decapoda: Brachyura: Tanidromitidae) from the Late Jurassic (Oxfordian) of Poland

“…montreuilense Crônier and Boursicot, 2009;T. pustulosa (von Meyer, 1840), as Pithonoton; T. raboeufi Robin et al, 2015; T. richardsoni (Woodward, 1907), as Prosopon; T. scheffnerae Schweigert and Koppka, 2011;T. sculpta (Quenstedt, 1857), as Prosopon; T. longinosa n.…”

“…The epibranchial TABLE 2. All species of the genus Tanidromites with their respective habitats (information from Crônier and Boursicot, 2009;Fraaije et al, 2013;Hyžný et al, 2011;Müller et al, 2000;Robin et al, 2015;Schweigert and Koppka, 2011;Schweitzer and Feldmann, 2010;Starzyk, 2015a region is much shorter than branchial and hepatic regions. The cervical groove is deep.…”

New early Paleocene (Danian) paguroids from deep-water coral/bryozoan mounds at Faxe, eastern Denmark

“…The quarry at Faxe comprises the best-studied Danian decapod crustacean fauna worldwide (Jakobsen & Collins, 1997). Studies dealing with such taxa, in chronological order, are the follow- ing: von Schlotheim (1820), Reuss (1859), von Fischer-Benzon (1866), Segerberg (1900), Woodward (1901), Rasmussen (1973), Förster (1975), Jagt et al (1993), Collins & Jakobsen (1994), Jakobsen & Collins (1997), Fraaije (2003), Jakobsen (2003), Jakobsen & Feldmann (2004), Collins (2010), Robin et al (2015) and Klompmaker et al (2015Klompmaker et al ( , 2016. However, in none of these are any paguroid remains recorded, so that our present note is the first formal description of middle Danian hermit crab taxa from Faxe.…”