Mecochirus cenomanicus, Charbonnier & Gilardet & Garassino & Odin, 2023

Charbonnier, Sylvain, Gilardet, Rémy, Garassino, Alessandro & Odin, Giliane P., 2023, A new species of mecochirid lobster from the Late Cretaceous of France, preserved with its eggs, Geodiversitas 45 (23), pp. 681-688 : 682-685

Mecochirus cenomanicus n. sp.

( Fig. 2 )

urn:lsid:zoobank.org:act:F89BFBA8-5958-45AD-820D-D15B56779522

ETYMOLOGY. — The specific epithet refers to the Cenomani, a Gallic tribe dwelling in the modern Sarthe Department, Pays de la Loire region, France, during the Iron Age and the Roman period. The Cenomani tribe is also at the origin of the name of the type locality Le Mans and of the Cenomanian stage.

TYPE MATERIAL. — Holotype by monotypy MNHN.F.B16583 (part and counterpart, Triger coll.). TYPE LOCALITY. — La Butte quarry, Le Mans, Sarthe Department, Pays de la Loire, France. TYPE AGE. — Late Cretaceous (Cenomanian) .

DESCRIPTION

Carapace

Subrectangular carapace (carapace length: 10 mm; carapace height: 0.5 mm).; smooth short rostrum; dorsal margin almost straight; posterior margin slightly sinuous; convex ventral margin until antennal-pterygostomial region with slightly concave ventral margin; shallow narrow orbit; cephalic region with straight raised, and tuberculate orbital and gastro-orbital carinae extending along whole length of cephalic region; deep cervical groove strongly oblique, intercepting dorsal margin at angle of c. 45°, ventrally joined to antennal groove, delimiting narrow cephalic region; short, weak gastro-orbital groove originating as slight median inflexion of cervical groove; shallow postcervical and branchiocardiac grooves parallel, strongly inclined, directed toward posterior margin; postcervical groove joined ventrally to branchiocardiac groove, forming one elongate, straight lobe; short, weak cardiac groove originating as slight dorsal inflexion of postcervical groove; deep hepatic groove, curved toward posterior, surrounding weak subcircular hepatic lobe; regions uniformly covered by small tubercles.

Pleon

Subrectangular s1-s6 equal in size; s1-s5 pleura with longitudinal carina on middle portion; rounded s1-s5 pleura; s1-s6 terga and pleura uniformly covered by small tubercles; subrectangular telson with subovate distal extremity and median part limited by a pair of lateral longitudinal carinae; proximal part with an axial pair of tubercles; tuberculate dorsal surface; distal extremity finely fringed; muscle fibers are preserved at level of s2 and s3.

Cephalic appendages

Small eye; eye-stalk not preserved; a1 not preserved; a2 well preserved; antennal peduncle with three segments: long thin ischiocerite; merocerite shorter than ischiocerite; long carpocerite enlarged distally to which one multi-articulate flagellum (unassessable length) is articulated; triangular scaphocerite with pointed distal extremity.

Thoracic appendages

P1-P4 complete, P5 poorly preserved; achelate P1, relatively long with a thin dactylus; subrectangular P1 merus as long as propodus; subtriangular P1 carpus; subrectangular P1 propodus as long as dactylus; P1 dactylus slightly incurved backward with rimmed ventral margin; P1 merus, carpus, and propodus with smooth dorsal and ventral margins; P1 segments covered by small tubercles; achelate P2-P4 equal in size with smooth segments.

Pleonal appendages

Pleopods covered by eggs; uropodal endopod and exopod not exceed telson length; short subtriangular basipodite; rounded uropodal endopod and exopod finely fringed distally; uropodal endopod and exopod with one longitudinal median carina; uropodal exopod with a diaeresis; diaeresis with straight serrate dorsal margin; outer margin of uropodal exopod strengthened by one row of small tubercles ending with one small distal spine at level of dorsal margin of diaeresis.

Eggs

Spherical smooth eggs (diameter: c. 0.5 mm); 84 eggs visible (probably an underestimated number), joined in clusters and carried by pl1-pl6, mainly pl2 and pl3.

Figures

FIG. 2. — Holotype MNHN.F.B16583 (Triger coll.) of Mecochirus cenomanicus n. sp. from the Cenomanian of La Butte quarry,Le Mans,France:part and counterpart (A, C) and interpretative live drawing (B); white frame corresponds to SEM images and EDS analysis. Abbreviations:a, branchiocardiac groove; a2, antenna; b, antennal groove; ba, basipodite; b1, hepatic groove; c, postcervical groove; cd, cardiac groove; d, gastro-orbital groove; di, diaeresis; e, eye; en, uropodal endopod; ex, uropodal exopod; e1e, cervical groove; gc, gastro-orbital carina; oc, orbital carina; P1-P5, pereiopods 1 to 5; r, rostrum; sc, scaphocerite; s1–s6, pleonal somites 1 to 6; t, telson. Photographs: P. Loubry. Line drawing: R. Gilardet. Scale bars: 5 mm.