Eoparanaxia, Ferratges & Domínguez & Ossó & Zamora, 2023

Genus EOPARANAXIA View in CoL n. gen.

Figure 3 View FIGURE 3

zoobank.org/ 07B9F785-4E4A-4018-9D7B-50B3576421F4

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Type species. Eoparanaxia eocenica View in CoL n. gen. n. sp. by monotypy and present designation. Gender feminine.

Diagnosis. Carapace pyriform, longer than wide; rostrum axially sulcate, with two fused, long pseudorostral spines, length 0.53 times CW. Hepatic region with small spine, directed anterolaterally. Intestinal tubercle strong, protruding beyond posterior carapace margin; carapace regions well defined with metagastric and urogastric regions narrower than mesogastric and cardiac regions; mesobranchial region with posteriorly directed large spine. Dorsal regions armed with long spines.

Etymology. The generic name derives from the prefix Eo- (from ɳως (gr.)= aurora), to generically indicate an ancestral form, in arbitrary combination with the generic name Paranaxia Rathbun, 1924 , to refer to its morphological affinities with the new genus.

Remarks. The material herein described is referred to the subfamily Pisinae Dana, 1851 . Species of this subfamily possess elongated carapaces; elongated pseudorostral spines; orbits always with postorbital spine or lobe, usually cupped, sometimes with antorbital spine; carapace triangular, sometimes with posterior spine (see Schweitzer et al., 2020). The new genus possesses all these characteristics and is therefore referred to this subfamily.

The new genus Eoparanaxia has similarities with Paranaxia , in the general outline of the carapace, showing a very elongated pseudorostral spines, parallel and distally bifid, slightly differentiated dorsal regions, with aligned spines in the dorsal part of the mesobranchial region, and well developed mesobranchial and intestinal spines (i.e., Windsor and Felder, 2014), sometimes beyond posterior carapace margin (see Rathbun, 1924, and Hosie and Hara, 2016, p. 128, figure 2; p. 129, figure 3).

However, Paranaxia presents the pseudorostral spines separated from their base, a supraorbital eave with a pronounced spine at the preorbital lobe, postorbital angle with a spine separated from the anterior lobe by a notch. In addition, Eoparanaxia n. gen. exhibits a postorbital spine between abbreviations employed in Table 2.

the gastric region and the hepatic region, which is not present in Paranaxia .

The studied material has similar characteristics with the modern genus Sphenocarcinus A. Milne-Edwards, 1875 , Oxypleurodon Miers, 1885 , and Rhinocarcinus de Forges and Ng, 2009 , including the shape of the rostrum with two long and coalescent cylindrical spines with slightly diverging sharp tips, and the shape and location of the orbits. However, Eoparanaxia n. gen. shows a different distribution of dorsal regions, with shallower dorsal grooves than in Sphenocarcinus , Oxypleurodon , and Rhinocacinus; intestinal region with a prominent conical spine unlike in Sphenocarcinus , Oxypleurodon , and Rhinocacinus, which lack such conical expansion; sinuous posterior margin; longitudinal antennal pits, parallel to the axis of the body unlike in the other three genera, which are oblique.

The modern genera Pisa Leach, 1815 , Leptopisa Stimpson, 1871 (both included in Pisinae Dana, 1851 ), and Oregonia Dana, 1851 ( Oregoniidae Garth, 1958 ) also show similarities with the new genus in the shape of the rostrum and orbits (i.e., Zariquiey-Álvarez, 1968; p.449, figure 151; Carmona-Suárez and Poupin, 2016, p. 369, figure 5). However, the shape and distribution of dorsal regions, posterior margin, dorsal surface with elevated regions, without spines, are clearly different in the modern genus. Furthermore, Eoparanaxia n. gen. presents the pseudorostrum fused throughout its length, only diverging at the tip, (while in the three mentioned taxa it separates from the base); presents a strong and long intestinal spine, a long branchial spines and spiny ridges on the dorsal surface (of which are absent in the three taxa). In addition, Pisa has anterolateral margins generally straight or slightly concave, with fewer or without spines and lacks the strong and prominent spine in the intestinal region that the new genus possesses.

Other modern genera, Rochinia A. Milne-Edwards, 1875 , Scyramathia A. Milne-Edwards, 1880 , Minyorhyncha Tavares and Santana, 2018 , and Anamathia Smith, 1885 share with the new genus the general outline of the carapace, distribution of spines in the posterolateral and posterior margins, especially in juvenile stages (see Tavares and Santana, 2018; p. 206-214, figures 1-9). However, all these genera have clearly separated and divergent pseudorostral spines unlike in Eoparanaxia n. gen., which presents parallel and fused spines. Some species of Doclea Leach, 1815 , show similarities with the new genus, for instance a fused bilobed pseudorostrum only diverging at the tip, a long and acute intestinal spine, a row of axial spines, oblique carinae, paralleling anterolateral margin, and also in the branchial regions. However, the modern genus Doclea differs from Eoparanaxia n. gen. in having a shorter pseudorostrum, a notch in the supraorbital eave, and mostly rounded or less elongated outline.

The material studied here also shows a certain resemblance to some representatives of Inachoididae Dana, 1851 , in view of the general outline of the carapace (see Santana, 2008; Lima et al., 2022). However, Inachoididae have usually a shorter pseudorostral spine, strongly fused, and generally ended in a single tip, concave posterior margin, and less spinose/tuberculate dorsal surface.