Bechleja brevirostris Mazancourt, Wappler & Wedmann, 2022, n. sp.
Creators: name: de Mazancourt, Valentin
name: Wappler, Torsten
name: Wedmann, Sonja
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Palaemonidae
Bechleja
Bechleja brevirostris

description: Bechleja brevirostris n. sp. (Figs. 2, 3, 4, 5, 6, 7, 8 and 9).
Type material: SF-MeI 5933, holotype, plate (A) and counterplate (B); SF-MeI 13611, plate (A) and counterplate (B); SF-MeI14640, plate (A) and counterplate (B), SF-MeI 16018, plate (A) and counterplate (B), HLMD-Me 10684, HLMD-Me 13919, HLMD-Me 13920, paratypes.
Type locality: Grube Messel, near Darmstadt, Hesse, Germany (Fig. 1).
Stratigraphic information: Holotype SF-MeI 5933: grid square G8; 0.1 m below to 0.3 m above local stratigraphic marker level alpha; SF-MeI 13611: grid square E8/9; 2.5 m above to 3.5 m above local stratigraphic marker level alpha; SF-MeI 14640: grid square i14; 0.95 m above to 1.75 m above local stratigraphic marker level M; SF-MeI 16018: grid square F9; 2.5 m above to 3.5 m above local stratigraphic marker level alpha; HLMD-Me-10684: grid square H/ I7; 1.86 m below stratigraphic marker gamma; HLMD-Me-13919: grid square H/ I7; 1.57 m below to 2.09 m below stratigraphic marker gamma; HLMD-Me-13920: grid square H/ I7; 1.63 m below stratigraphic marker gamma (marked in Fig. 1 with red dots).
Derivation of epithet: From the Latin words “ brevis ” (short) and “ rostrum ” (beak) referring to the distinctively short rostrum of this species in comparison to its congeners.
Diagnosis: Small shrimp with a short dorsally serrate rostrum and long second pereiopods with strong chela.
Description: Small sized shrimp (Figs. 2, 3, 4, 5, 6), total body length 14–19 mm, carapace post-orbital length 5.0– 8.5 mm, maximum length about 1.6 of maximum height, laterally compressed, dorsal margin straight, ventral and posterior margin both smooth and convex, no spines discernable besides antennal spine in one paratype (HLMD-Me-13919; Figs. 4F, 6B). Rostrum (Figs. 3, 4F, 7B) short, about one fifth of carapace length, straight, laterally compressed, with an acute distal end, bearing 6–8 spines of equal size on dorsal margin all placed distally to the post-orbital margin and one tooth on ventral margin. Eyes developed, with a globular cornea, broader than eyestalk. Antennules seemingly biflagellate, antennular peduncle about half as long as carapace length. Antennae long, basal segments shorter than the antennular peduncle, with a well-developed scaphocerite about 4 times as long as broad. Left mandible preserved in the holotype (Fig. 7A), incisor process well developed, with three strong teeth, reduced molar process, no evidence of a palp being present. Pereiopods long and slender, first two pairs chelate. Chela of first pereiopod rounded, about three times as long as high, with sharp dactylus twice as long as its maximum height, about the same length as the palmar portion. Second pereiopod much longer and bigger than first, chela about four times as long as high, shorter than carpus, dactylus slightly shorter than palmar portion. Possible sexual dimorphism, with males having longer second pereiopods than females (see remarks below). Last three pairs of pereiopods similar in length and shape. Pleopods poorly preserved. Abdomen smooth, six-segmented, somites with a convex dorsal margin, pleura well developed, first somite reduced, second pleura overlapping both first and third, fourth and fifth somites smallest, similar in shape and size, sixth somite longest. Long telson, about half of carapace length, slightly shorter than uropods. Uropods flabellate, exopod about the same length as endopod, with no diaeresis discernable.
Remarks: Internal organs are visible in at least four of the specimens (holotype SF-MeI 5933 and paratypes SF-MeI 13611, HLMD-Me 13919 and HLMD-Me 13920), the holotype being the one with the most of its anatomy preserved (Figs. 2, 3). Just above the mandible (Fig. 7A) is a chitinous structure identified as the stomach (Fig. 9A). Near its posterior end, three hard smaller structures seemingly distinct from the stomach cuticle could be identified with some doubt as gastric ossicles, the largest being likely the mesocardiac ossicle, the one in the middle a zygocardiac ossicle and the bottom one a pterocardiac ossicle. The discovery of new fossils with a similar state of preservation could confirm the presence of such ossicles in this species. Directly posterior to the stomach, a large dark patch is interpreted as the mature ovary, allowing to identify the holotype as an adult female specimen. Near the dorsal margin of the third somite of the holotype, a portion of the intestine has been preserved (Fig. 9B) with two dark pellets interpreted as feces. In the specimen HLMD-Me 13919, the four last pleurobranchiae are preserved (Figs. 4F, 6B).
An additional specimen (HLMD-Me 10646: grid square H/ I7; 2.80 m below stratigraphic marker gamma; Fig. 10) shows a different morphology with a seemingly long upcurved rostrum which could suggest that it belongs to a different species. It is thus excluded from the paratypes of B. brevirostris n. sp. Due to the absence of several important characters in that fossil, we deem it safer to wait until more specimens are discovered before describing it as a new species.
description: Published as part of de Mazancourt, Valentin, Wappler, Torsten & Wedmann, Sonja, 2022, Exceptional preservation of internal organs in a new fossil species of freshwater shrimp (Caridea: Palaemonoidea) from the Eocene of Messel (Germany), pp. 18114 in Scientific Reports 12 (1) on pages 9-12, DOI: 10.1038/s41598-022-23125-9, http://zenodo.org/record/15118930