Abyssophthalmus, Schweitzer and Feldmann, 2009

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 : 16-17

Abyssophthalmus cf. A. spinosus (von Meyer, 1842)

Figure 8

1842 Prosopon spinosum von Meyer , p. 71, pl. 15.1- 15.2.

1858 Prosopon marginatum von Meyer ; Quenstedt, p. 779, pl. 95.35.

1860 Prosopon spinosum von Meyer ; von Meyer, p. 196, pl. 23.6-23.7.

1867 Prosopon personatum Quenstedt , p. 315, pl. 26.10.

1936 Prosopon spinosum von Meyer ; Kuhn, p. 122, fig. 2.

1969 Nodoprosopon spinosum (von Meyer) ; Förster, p. 53, pl. 2.2.

1983 Nodoprosopon spinosum (von Meyer) ; Meyer and Schmidt-Kaler, fig. 21.6(8).

1985 Nodoprosopon spinosum (von Meyer) ; Collins and Wierzbowski, p. 80, pl. 1.6.

1988 Nodoprosopon spinosum (von Meyer) ; Wehner, p. 44, pls. 2.9, 3.1, 3.2.

2000 Nodoprosopon spinosum (von Meyer) ; Müller et al., fig. 17f.

2009d Abyssophthalmus spinosus (von Meyer) ; Schweitzer and Feldmann, p. 108, fig. 8.1, 8.5- 8.7. 2012 b Abyssophthalmus spinosus (von Meyer) ; Schweitzer et al., fig. 9.1.

2018 Abyssophthalmus spinosus (von Meyer) ; Schweigert and Kuschel, p. 20, fig. 11.

2018 Abyssophthalmus spinosus (von Meyer) ; Schweitzer et al., fig. 18.1.

Diagnosis. See Wehner (1988, p. 45).

Material studied. MAB k3607-3612, from the sponge-microbial limestones at the Plettenberg quarry near Schömberg (Google Earth coordinates: 48.21, 8.81), SW Germany, Late Jurassic (late Oxfordian-early Kimmeridgian); NHMW 2014/ 0194/0952, from the coral reef Ernstbrunn Limestone of the Ernstbrunn quarries (Google Earth coordinates: 48.54, 16.35), Austria, Late Jurassic (Tithonian) (Schweitzer and Feldmann, 2009d; Schneider et al., 2013).

Occurrence. Late Jurassic (Oxfordian-Tithonian) of Europe ( Austria, Germany, and Poland).

Dimensions. (In mm) NHMW 2014/0194/0952: max. length excl. rostrum (L)=39.1, max. width excl. projections (W)=30.1; MAB k3607: L=12.0, W=9.5; k3608: L=-, W=11.8; k3609: L=10.1, W=7.6; k3610: L=10.3, W=8.2; k3611: L=9.0, W=7.3; k3612: L=-, W=10.2.

Description. See von Meyer (1860, p. 196) and its translation and emended description in Schweitzer and Feldmann 2009d, p. 110-111).

Remarks. The specimen represents an unusually large individual with a length width ratio of 1.30; we have found no smaller individuals in the Ernstbrunn collection that may be conspecific to this specimen. The specimen closely resembles Abyssophthalmus spinosus in many ways: the overall pattern and depth of grooves, carapace outline, the rostrum with a wide concavity axially in dorsal view, the spinose character of the anterior carapace, distinct spines on the epibranchial region, the uro-/ metagastric region that is much narrower axially, and the tubercles on the meso-metabranchial region. However, some differences also exist such as the lack of a true mesogastric process (it is a groove instead), the seemingly proportionally wider meso-metabranchial region, and the somewhat more spinose character on the anterior carapace. Moreover, the length-width ratio of the Oxfordian material appears to increase as the animal grows from ~1.3 for small specimens to ~1.4-1.5 (carapace lengths of ~ 12-19 mm) (Schweitzer and Feldmann, 2009d, table 8), but this trend is not supported by data in Wehner (1988, p. 45). We refrain from erecting a new species because we cannot exclude the possibility that the differences are caused by ontogenetic change. The carapace herein is nearly twice as large as the largest one reported in Wehner (1988): 22.1 mm vs 39.1 mm length. Therefore, we tentatively assign the specimen to A. spinosus .

This specimen is the first record of this species from the Tithonian, if our assignment is correct. To our knowledge, this specimen represents the largest complete reported brachyuran carapace identified to the species-level from the Jurassic thus far [compare to data in Klompmaker et al. (2015a)]. The right orbital cavity bears a vertical ridge in frontal view ( Figure 8E , left side), a feature often seen in Late Jurassic crabs (e.g., Schweitzer and Feldmann, 2009d; Starzyk, 2013; herein). Of note is that the cuticle is fully present in one part ( Figure 8E , left side, middle part), but nearly absent in another part ( Figure 8E , left side, lower part); this ridge becomes much less prominent in the latter case, implying that this ridge may become difficult to recognize for internal molds of some brachyurans.

Figures

FIGURE 8. Specimen of the crab Abyssophthalmus cf. A. spinosus (von Meyer, 1842) from the Late Jurassic (Tithonian) of Ernstbrunn, eastern Austria (all except B and C) and specimens of A. spinosus from the Late Jurassic (late Oxfordian-early Kimmeridgian) of the Plettenberg quarry, Germany (B, C). A, D-H, dorsal, ventral, right-orbital (shown upside down to better see depth), frontal, left-lateral, and right-lateral views, resp. (NHMW 2014/0194/0952). B, C, dorsal views (MAB k3611 and k3607). Scale bar width is 10.0 mm, except for E (1.0 mm).