Laeviprosopon joecollinsi, 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 : 14-15

Laeviprosopon joecollinsi n. sp.

Figures 1 , 9

zoobank.org/ C569B457-C53E-4130-88E9-2DD874756F88

Diagnosis. Carapace longer than wide, widest on branchial region (length of holotype from epigastric region to posterior margin: 6.7 mm), strongly vaulted transversally and moderately vaulted longitudinally. Epigastric, protogastric and hepatic regions separated by transverse grooves. Internal mold of carapace densely covered with granules posteriorly, sparsely so in anterior part; granules also visible on cuticle. Shallow grooves laying parallel to branchial groove.

Etymology. The name joecollinsi is dedicated to Joseph (Joe) S.H. Collins (1927–2019), a specialist of fossil crustaceans, especially decapods.

Comparisons. The carapaces of L. laeve are less convex. Laeviprosopon joecollinsi n. sp. also differs from L. laeve in the absence of the symmetrical tubercles on the mesogastric region and in having a narrower posterior part of this region. The mesogastric region of L. joecollinsi n. sp. is not divided in the middle as in L. punctatum , L. laeve and L. musialiki . It has a distinct narrow anterior and broad posterior part more or less the same length unlike in L. lazarae , L. sublaeve , L. grandicentrum , L. laculatum , L. edoi , L. hispanicum , L. planum and L. crassum . The species has round epigastric regions, not short and wide as in L. sublaeve , L. fraasi , L. edoi , L. planum and L. hispanicum . The species does not have a transverse groove from the cervical to the branchio-cardiac groove as in L. sublaeve , L. fraasi , L. musialiki and L. icaunensis . The species does not have any large tubercles on the carapace as in L. musialiki , L. lanceatum n. sp. and L. lazarae . The epigastric, protogastric and hepatic regions are separated by transverse grooves as in L. laeve , L. lazarae , L. sublaeve , L. fraasi , L. ewakrzeminskae n. sp. and L. lanceatum n. sp.

Material Examined

Type material. Holotype: I-F/ MP/6264 /1599/12; type locality: Niegowonice ; age: middle – late Oxfordian (upper Elizabethae Subzone – upper Wartae Subzone).

Paratypes. I-F/ MP/5061 /1543/09; type locality: Niegowonice; age: middle – late Oxfordian; I-F/ MP/ 741 /1502/08; type locality: Ogrodzieniec; age: early–middle Oxfordian; UF272115 , UF272119 ; type locality: Szklary; age: middle Oxfordian .

Additional material. Niegowonice: I-F/ MP /3037/ 1532/08; I-F/ MP /3038/1532/08; I-F/ MP / 3873/1533/08; I-F/ MP /4623/1534/08.

Dimensions. The state of preservation of the material is not good enough to take most of the measurements. The length of the holotype from the epigastric region to the posterior margin is 6.7 mm, 9.5 mm for paratype UF272115 . The maximum width of paratype 5061 in the epibranchial region is 5.3 mm. The length of the mesogastric region of paratypes 5061 and 741 is 3.4 mm and 2.7 mm, respectively .

Description. The carapace is longer than wide, widest in the branchial region, strongly vaulted transversally and moderately vaulted longitudinally ( Figure 9A, E , G-H).

The rostrum is not preserved on any specimen. The orbital margin is rounded, with a flattened suborbital spine ( Figure 9A , marked with a black arrow). The anterior groove is distinct.

The epigastric regions are rounded and lay in front of the mesogastric region, which is distinctly bordered by grooves. The length of the anterior (narrow) part of this region is about 0.6x the posterior (wide) part, and the posterior part is the highest point of the carapace. There is no incision in the posterior border of this region. It is covered with many granules on the internal mold and the cuticle; gastric spines are absent. Epigastric, protogastric and hepatic regions are separated by transverse grooves ( Figure 9C, E ). A pair of small, elongated gastric pits is present in the cervical groove ( Figure 9B ).

The urogastric region is convex and divided into two parts by an incision, which connects to the postcervical groove ( Figure 9A , D-E, H). Incisions laying on the epibranchial region, with the postcervical and branchial groove, bound surfaces directed to the cardiac region. The cardiac region is not distinctly bordered, widening anteriorly.

The grooves are very deep and wide. The cervical groove is the deepest. The branchiocardiac groove reaches the posterior margin of the carapace.

The posterior border of the carapace is rimmed and concave in the middle ( Figure 9A, C ). The whole surface of the carapace is covered with granules, which occur both on the internal mold and on the cuticle. In the anterior part, they are sparsely present, but they are denser in the posterior part. On the branchial region, they are positioned in lines parallel to the branchial groove ( Figure 9 C-D).

Figures

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

FIGURE 9. Laeviprosopon joecollinsi n. sp. A - carapace (paratype, UF272115, Szklary); B - carapace (I-F/MP/ 30381532/08, Niegowonice) gp – gastric pits; C - lateral left view (paratype, UF272115) groove parallel to the branchio-cardiac groove; D - carapace (I-F/MP/741/1502/08, paratype, Ogrodzieniec) groove parallel to the branchio-cardiac groove; E - carapace (I-F/MP/6264/1599/12, holotype, Niegowonice); F - anterior view (paratype, UF272115); G - lateral right view (I-F/MP/741/1502/08); H - carapace (paratype, UF272119, Szklary). Scale bars equal 1.0 mm.