Paranecrocarcinus balla, Van Bakel & Guinot & Artal & Fraaije & Jagt, 2012

Van Bakel, Barry W. M., Guinot, Danièle, Artal, Pedro, Fraaije, René H. B. & Jagt, John W. M., 2012, A revision of the Palaeocorystoidea and the phylogeny of raninoidian crabs (Crustacea, Decapoda, Brachyura, Podotremata) 3215, Zootaxa 3215 (1), pp. 1-216 : 60-62

Paranecrocarcinus balla n. sp.

( Fig. 19A, C, E, G )

Necrocarcinus minutus Milne-Edwards in Guillier 1886: 244 [nomen nudum].

Necrocarcinus minutus A. Milne-Edwards , nomen nudum, in Guillier (1886: 244) — Guinot & Breton 2006: 610. Necrocarcinus labeschii — Breton & Collins 2007: 18, fig. 6. — Breton 2008: 53, pl. 1, figs. 1–3.

Diagnosis. Carapace small, rounded subhexagonal, weakly convex both longitudinally, transversely; orbitofrontal width less than posterior margin; rather short, downturned rostrum, broadly sulcate; orbits close together, deep, upturned; supraorbital margin with 2 fissures; anterolateral margin slightly convex, with at least 6 spines of varying sizes; posterolateral margin straight; posterior margin broadly concave, thin; cervical groove indistinct; 2 pairs of post-rostral slits; small to large rounded tubercles on mesogastric, protogastric, epigastric, cardiac lobes; distinct epibranchial spine; test finely pitted, otherwise smooth.

Derivation of name. After the Old High German balla (ball, balloon), in allusion to the Marnes de Ballon Formation; noun used in apposition.

Material examined. Holotype is MNH LM 3807 [ex Guéranger Collection]; paratype is MNH LM 3808 [ex Guéranger Collection]. The holotype was in sample B16563, together with an isolated major cheliped of a necrocarcinid crab, probably Necrocarcinus labeschii , with a label reading, ‘ Necrocarcinus minutus M. Edw., Cénomanien de la Sarthe, 1902 -3’, from Ballon, Sarthe ( France). The holotype is from the Marnes de Ballon Formation (lower Cenomanian, carcitanense and basal saxbii zones), whereas the paratype comes from the Sables du Perche Formation at Le Mans (middle–upper Cenomanian, jukesbrownei to guerangeri zones) (for details see Collins & Breton 2009).

Description. Carapace small (see Table 6), rounded subhexagonal in outline, carapace width exceeding length, weakly convex both longitudinally, transversely; orbitofrontal width (5.8 mm) smaller than posterior margin (7.6 mm); front produced as a rather short, downturned rostrum, broadly sulcate with sides upturned, widely rimmed; only partially preserved, thus no spines visible; orbits close together, deep, upturned, with thin margins, lacking spines; supraorbital margin with 2 fissures, relatively short, the upper slightly longer; anterolateral margin slightly convex, with at least 6 spines of varying sizes; posterolateral margin straight, with a slightly tuberculate, undulating ridge running from the epibranchial tubercles to just in front of posterior margin; posterior margin broadly concave, thin; no rim. Cervical groove indistinct, but two small longitudinal pits visible on either side of a wide medial gap; level with supraorbital rim with 2 pairs of slits, the anterior short, curved, positioned obliquely left, right of the posterior pair; posterior pair straight, elongated, close together, on either side of carapace mid-line, followed by a pair of small tubercles on the mesogastric lobe; single, small tubercle on each protogastric lobe; cardiac lobe with single, large, low, rounded tubercle, 3 small elevations in triangle behind it; distinct epibranchial spine, single, large tubercles on epigastric lobes; test finely pitted between tubercles, otherwise smooth; hepatic region depressed in lateral view, with a single small tubercle, the subhepatic relatively small, only slightly inflated.

Remarks. Breton & Collins (2007: 18, fig. 6) considered this specimen to represent a young individual of N. labeschii , a taxon recorded from the upper Aptian to Cenomanian in southern England, northern France ( Wright & Collins 1972) and the upper Albian of southwestern Crimea (= N. bodrakensis Levitskyi, 1974 ; Ilyin 2005: 199). N. labeschii lacks the characteristic postfrontal fissures, however, and the carapace regions and ornament are clearly different.

Wright & Collins (1972: 71, text-fig. 10b; pl. 22, fig. 6) recorded only a single paranecrocarcinine, Paranecrocarcinus biscissus , based on a single specimen with two slits from correlative strata (lower Cenomanian, mantelli Zone ) at Wilmington, Devon (southwestern England), (holotype, NHM In. 61166, ex Collins Collection). This species differs from the co-occurring P. digitatus (see below) in having a flatter carapace, with straighter margins, more numerous tubercles on the dorsal surface and two post-rostral slits. Paranecrocarcinus digitatus Wright & Collins, 1972 ( 1972: 69, text-fig. 10a; pl. 12, fig. 7a–c) from the lower Cenomanian ( mantelli Zone ) of Wilmington is easily differentiated from congeners by its elongated radiating ridges or bosses on the protogastric lobe ( Wright & Collins 1972: 70, text-fig. 10a). Paranecrocarcinus foersteri Wright & Collins, 1972 ( 1972: 70, pl. 22, fig. 5a– c), from the lower-middle Cenomanian ( mantelli and rhotomagense zones), is distinguished from other species of Paranecrocarcinus by having long and straight granular posterolateral margins and a longitudinally ridged dorsal surface. Three fragmentary specimens (MNHN A29412a–c [ex Pépin Collection; labelled Paranecrocarcinus ( hexagonalis ?) V. Straelen 1936]), all from the Craie Glauconieuse Formation (lower Cenomanian, carcitanense and saxbii zones) from Le Billot, are probably conspecific with P. foersteri .

Paranecrocarcinus hexagonalis Van Straelen, 1936 ( 1936: 36, pl. 4, figs. 6–7), from the Neocomian (lower Cretaceous, Hauterivian) of Migraine, near Auxerre (Yonne, France), appears to be closely related to P. balla n. sp. in size, the width of the orbitofrontal margin, carapace outline and ornament, but has a better-developed epibranchial spine as well as transversely elongated tubercles (rather than rounded ones) on the mesogastric and epigastric lobes. Only one pair of post-rostral slits is preserved in the type specimen ( Van Straelen, 1936: pl. 4, fig. 7), but the rostral region is damaged, precluding observation of a second pair, if at all present.

Paranecrocarcinus milbournei Collins, 2010 ( 2010: 16, figs. 1.5–1.8), from the Cenomanian (Odukpani Formation) of Nigeria, has a subpentagonal carapace outline, with a narrow orbito-frontal margin and only one pair of post-rostral slits, as well as tumid protogastric, epibranchial, mesobranchial and cardiac lobes and a longitudinal ridge on the metabranchial lobes.

Paranecrocarcinus balla n. sp. differs from congeners by its rounded subhexagonal outline, apparently simple rostrum, paucity of tubercles on the dorsal surface and a finely tuberculate ridge on the posterior carapace half; from species which lack these, it is easily distinguished by the presence of two pairs of post-rostral slits. Paranecrocarcinus quadriscissus , from the upper Maastrichtian of northeastern Belgium and southeastern Netherlands ( Fig. 19B, D, F, H ), also has four slits, but the anterior pair are short and straight and the carapace ornamentation (tubercules, granules) is clearly different from the pitted ornament of P. balla n. sp. ( Fraaije 2002; Jagt et al. 2010).

Figures

FIGURE 19. A, C, E, G, Paranecrocarcinus balla n. sp. (Necrocarcinidae, Paranecrocarcininae), MNH LM 3807 (holotype; ex Guéranger Collection), Cenomanian, Ballon (Sarthe, northwestern France); detail of orbitofrontal region showing frontal slits; right lateral view; frontal view, and dorsal view of carapace; B, D, F, H, Paranecrocarcinus quadriscissus (Noetling, 1881), MAB k. 2913 (indeterminate sex), upper Maastrichtian, Maastricht, the Netherlands; detail of orbitofrontal region showing frontal slits; dorsal view of carapace; right lateral and frontal views. cg, cervical groove; iol, infraorbital lobe. Scale bars: A, B: 2mm; C-H: 5mm.