Laeviprosopon ewakrzeminskae, Starzyk & Van Bakel & Klompmaker & Schweigert & Fraaije, 2023

Starzyk, Natalia, Van Bakel, Barry W. M., Klompmaker, Adiël A., Schweigert, Günter & Fraaije, René H. B., 2023, A new approach to the systematics of Laeviprosopon (Brachyura: Homolidae), with remarks on the molting process of early brachyurans, Palaeontologia Electronica (a 10) 26 (1), pp. 1-24 : 11-12

Laeviprosopon ewakrzeminskae n. sp.

Figures 1 , 7

zoobank.org/ 004C6A33-3FC4-45B7-8C5A-D3002EC6B540

Diagnosis. Carapace very elongate, narrowing anteriorly, strongly vaulted transversally and moderately vaulted longitudinally. Orbits not differentiated. Very long and narrow mesogastric region. Two tubercles on each side of mesogastric region present. Branchial region ornamented with very small tubercles.

Etymology. The species name is dedicated to Ewa Krzemińska (ISEA PAS), with a deep gratitude for being an advisor and a mentor of Natalia Starzyk. Ewa is a renowned specialist of recent and fossil Diptera, also working on fossil Brachyura and Anomura.

Comparisons. Specimens of Laeviprosopon ewakrzeminskae n. sp. are narrowing anteriorly as in L. joecollinsi , L. lazarae and L. grandicentrum . The carapace is elongated unlike in L. planum and L. crassum . It has a long and narrow mesogastric region unlike in L. joecollinsi , L. musialiki , L. lanceatum , L. laeve , L. punctatum , L. sublaeve , L. laculatum , L. fraasi , L. icaunensis , L. hispanicum and L. crassum . Symmetric tubercles on the mesogastric region present in L. laeve are absent in L. ewakrzeminskae n. sp., but there are two tubercles on each side of the mesogastric region which are absent in L. joecollinsi , L. laeve , L. punctatum , L. laculatum , L. fraasi , L. icaunensis , L. edoi , L. planum , L. hispanicum and L. crassum . Epigastric, protogastric and hepatic regions are separated by transverse grooves as in L. laeve .

Material Examined

Type material. Holotype: NHMW 1990 /0041/ 2744a; type locality: Ernstbrunn; age: Tithonian.

Paratypes. NHMW 1990 /0041/5179, NHMW 2014 / 0194/0978; locality: Ernstbrunn; age: Tithonian.

Additional material. NHMW 1990/0041/3959b; locality: Ernstbrunn; age: Tithonian.

Dimensions. The state of preservation of the material from the NHMW collection is not good enough to take measurements of all specimens. The length of the mesogastric region of the holotype is 1.4 mm, and that of the paratypes are 1.7 and 1.4 mm, respectively. The width at the hepatic region of the holotype is 2.4 mm. The width of the branchial region of the holotype is 2.3 mm. As the posterior margin is not preserved on any of the specimens, it is not possible to measure the length of the carapace .

Description. The carapace is longer than wide, widest on the branchial region, strongly vaulted transversally and moderately vaulted longitudinally ( Figure 7 ).

Only the base of the rostrum is preserved in specimen NHMW 2014/0194/0978 ( Figure 7B ). The anterior groove is deep, visible at the intersection of the rostrum and the upper orbital margin ( Figure 7 ). The epigastric regions are rounded. The mesogastric region is very long, flattened with a very narrow anterior part. There is no separation between the anterior and posterior part of this region ( Figure 7 ). The posterior gastric muscle scars are absent.

Gastric pits and mesogastric groove tubercles are absent. There are two hepatic tubercles on each side of the mesogastric region ( Figure 7A, C ). The epigastric, protogastric and hepatic regions are separated by transverse grooves ( Figure 7B , D-E).

The urogastric region is undivided ( Figure 7C ). The cardiac region is distinctly bordered by the branchiocardiac groove, narrowing posteriorly, with two tubercles in the anterior part and a tubercle in the posterior part ( Figure 7C ).

The carapace is covered with granules only in its posterior part. They are visible on the internal mold and in places with the cuticle preserved. The grooves are wide and deep. The lateral parts of the postcervical groove are connected with the branchial groove. The branchiocardiac groove reaches the posterior margin of the carapace. The posterior margin of the carapace is not preserved in any of the specimens.

All of the specimens are almost complete carapaces not showing any traces of molting lines.

Figures

FIGURE 1. Stratigraphic range of the species herein considered within Laeviprosopon with schematic drawings of all the species.

FIGURE 7. Laeviprosopon ewakrzeminskae n. sp. A - carapace (NHMW 1990/0041/5179, paratype, Ernstbrunn); B - carapace, rostrum marked by an arrow (NHMW 2014/0194/0978, paratype, Ernstbrunn); C - carapace, spines on the epibranchial region marked by an arrow (NHMW 1990/0041/2744a, holotype, Ernstbrunn); D - lateral right view (NHMW 1990/0041/2744a); E - lateral right view (NHMW 1990/0041/2744a). ht – hepatic tubercle. Scale bars equal 1.0 mm.