Tanidromites weinschenki, Klompmaker & Starzyk & Fraaije & Schweigert, 2020

Klompmaker, Adiël A., Starzyk, Natalia, Fraaije, René H. B. & Schweigert, Günter, 2020, Systematics and convergent evolution of multiple reef-associated Jurassic and Cretaceous crabs (Decapoda, Brachyura), Palaeontologia Electronica (a 32) 23 (2), pp. 1-54 : 32-33

Tanidromites weinschenki sp. nov.

Figure 18

zoobank.org/ A85AA221-E934-4F93-BCC8-C1106D489F9D

2011 Tanidromites sculpta (Quenstedt, 1858) ; Schweigert and Koppka, p. 229, fig. 7C.

Diagnosis. Species with relatively low length/width ratio, deep grooves, with coarse pustulate ornamentation diminishing in strength posteriorly.

Etymology. After Alwin Weinschenk (Aalen-Wasseralfingen, Germany), who found and donated the specimen.

Material studied. Holotype and sole specimen: SMNS 77338 .

Occurrence. Braunenberg quarry area near Aalen-Wasseralfingen, eastern Swabian Alb, Germany (Google Earth coordinates: 48.86, 10.12), calcareous spongiolithic mudstone of the Upper Jurassic Oberjura-Massenkalk Formation, Lochen Member (lower Kimmeridgian, planula Zone, galar Subzone).

Dimensions. (In mm) SMNS 77338: 6.5 mm long incl. rostrum, 6.0 mm maximum width.

Description. Carapace outline pentagonal, weakly to moderately convex transversely and longitudinally, slightly longer than wide, with subtriangular anterior part bearing a forwardly directed, incomplete rostrum. Augenrest appears shallow, slightly concave, bordered by dense pustules. True orbits not exposed. Distance between cervical groove and outer orbital edge short (~1.0 mm). Hepatic and protogastric regions confluent. Mesogastric region triangular to pyriform, appears least marked medially, with narrow anterior process. Uro-/metagastric region narrow, confluent with epibranchial regions. Cardiac region not elevated, posteriorly grading into confluent meso-metabranchial areas. Cervical and branchiocardiac grooves strong, equally deep and well-developed, except near longitudinal axis for latter; both run parallel laterally. Post-cervical grooves short and very shallow. Posterior margin of carapace concave, with smooth rim. Cuticular ornamentation coarser and wider spaced in anterior part of carapace and denser and finer in branchial areas, least prominent on axial part posterior carapace. Appendages, ventral side, abdomen, and ornamentation on internal mold not known.

Remarks. The general outline of Tanidromites weinschenki sp. nov. best resembles T. sculpta . Schweigert and Koppka (2011, figure 7C) referred this specimen with cuticle to T. sculpta , but this specimen has many distinct tubercles all over the carapace unlike the smooth internal molds of T. sculpta they figured. It is possible for internal molds of brachyurans to show less or no ornamentation than on the cuticular layers (e.g., Klompmaker et al., 2015c), but this is not common. Von Meyer (1860, p. 205) described Prosopon lingulata , now considered to be a junior synonym of T. sculpta (Schweigert and Koppka, 2011) , based on two specimens that were mentioned to have no ornamentation. Whether these specimens had cuticle preserved is unclear. The specimens of T. sculpta from Ernstbrunn do have cuticle preserved in some specimens, but the cuticle does not display any pustules or other ornamentation. Moreover, specimens of the congeneric T. muelleri show both cuticle and the internal mold on the same specimen for multiple specimens (Krobicki and Zatoń, 2016), yielding about equal-sized and spaced tubercles on both surfaces, and the same applies to T. maerteni (Fraaije et al., 2013) and T. montreuilense (Crônier and Boursicot, 2009) . Thus, it seems likely that ornamentation or lack thereof is fairly similar on the cuticle versus internals molds for Tanidromites spp. Thus, we use this character to distinguish T. weinschenki sp. nov. from T. sculpta . Tanidromites muelleri also bears ornamentation, but this species has some exceptionally strong tubercles/ spines not seen in T. weinschenki sp. nov. and weaker ornamentation on the gastric region. Tanidromites maerteni , T. lithuanicus , T. montreuilense , and T. pustulosa appear to have weaker tubercles anterior to the cardiac region. Tanidromites aequilatus , T. alexandrae , T. etalloni , T. hyznyi , T. insignis , T. longinosa , T. nightwishorum sp. nov., T. raboeufi , T. richardsoni , T. scheffnerae , T. schweitzerae , and T. starzykae all appear to have no or very limited ornamentation. To back up differences in ornamentation between T. weinschenki sp. nov. and congenerics, some additional key differences are also given. Tanidromites aequilatus , T. alexandrae , and T. hyznyi exhibit deeper augenrests; the carapace of Tanidromites etalloni is more rounded; T. insignis , T. richardsoni , and T. scheffnerae are proportionally longer (e.g., Schweitzer and Feldmann, 2008a, plate 6; Schweigert and Koppka, 2011, figures 5, 6, 8; Hyžný et al., 2011, figure 2A; Starzyk, 2013, figures 4, 6; Figure 18 ); the cardiac region of T. lithuanicus is outlined more pronounced than in T. weinschenki sp. nov.; T. nightwishorum sp. nov. has much more swollen epibranchial regions; T. longinosa and T. raboeufi have a proportionally longer gastric region; T. maerteni bears at least two tubercles on the lateral margin, not seen in the new species; T. montreuilense widens more posteriorly; the postcervical grooves are deeper in T. muelleri ; the rostrum of T. pustulosa is less prominent in dorsal view (Schweitzer and Feldmann, 2010c, figure 1.13-1.14; Hyžný and Zorn, 2016, plate 2.4-2.5, incorrectly referred to Eodromites rostratus ); the cervical groove of T. schweitzerae is oriented more obliquely on the flank; the curve in the cervical groove at the position of the posterior edges of the mesogastric region is more pronounced in T. sculpta ; and the grooves of T. starzykae are less prominent and largely lacking for the mesogastric region.

Figures

FIGURE 18. Holotype and sole specimen of the crab Tanidromites weinschenki sp. nov. (SMNS 77338) from the Late Jurassic (early Kimmeridgian) of Aalen-Wasseralfingen (Braunenberg quarry area), southwestern Germany. A, dorsal view of carapace. B, frontal view. C, left-lateral view. Scale bar width equals 2.0 mm.