Bathynomus civisi, Hyžný & Campos & Carretero, 2020

Hyžný, Matúš, Campos, Ildefonso Bajo & Carretero, Joaquín Cárdenas, 2020, A new species of Bathynomus A. Milne-Edwards, 1879 (Malacostraca: Peracarida Isopoda: Cirolanidae) from the upper Miocene of the Guadalquivir Basin (Spain), Zootaxa 4819 (1), pp. 159-169 : 163-165

Bathynomus civisi sp. nov.

Figs 4–6

urn:lsid:zoobank.org:act:268B0BA1-02CD-4DE8-A5CD-02DBADAFD152

Material examined: The species is so far represented by the only specimen (measurements: 70.0 x 51.6 mm). The holotype (MGM-6636M) represents the posterior moult consisting of pereonites 5–7, pleonites 1–5, and pleotelson; uropods were exposed with further preparation. The specimen consists of part and counterpart ( Figs 4B , 5 A–B) and was collected by the authors JCC and IBC. GPS coordinates of the type locality (see below): 37°37’1.85”N, 5°47’38.42”W.

Diagnosis: Pleotelson approximately 0.7 as long as wide with indistinct carina and 7 broad, short, straight pleotelsonic spines plus 2 lateral spines; central spine longest, not bifid; gap between second and third side spines wider than between other spines. Uropod with oval exopod and subtriangular endopod, distolateral corners of both elements distinctly produced into tips.

Description: Pereonites 5–7 poorly preserved, pereonite 5 longer than pereonites 6 and 7 (possibly due to last pereonites being overlapped by preceding ones). Pleonites of approximately same length; pleonite 4 slightly overlapping pleonite 5 laterally; pleonites 3–5 reaching to almost same posterior level. Pleotelson subcircular in outline, approximately 0.7 as long as wide, dorsal surface finely granulated; posterior margin with 7 broad, short, straight pleotelsonic spines, and 2 smaller lateral spines; central spine longest, simple (not bifid); gap between second and third side spines wider than between other spines ( Fig. 6 ). Uropodal exopod with elongate oval outline, lateral margin convex, distolateral corner obtuse with pointed tip, distomedial corner rounded, medial margin straight; uropodal endopod broadly subtriangular, distolateral corner obtuse, distinctly produced into sharp tip, distomedial corner broadly rounded, median margin straight.

Etymology: In Memoriam of Dr. Jorge Civis, professor of Palaeontology at the University of Salamanca and great promoter of Palaeontology in the Neogene of the Guadalquivir Basin.

Remarks: Although the only known specimen is incomplete, there are taxonomically important characters preserved supporting a designation of a new species. Lowry & Dempsey (2006) noted that the shape of the lateral, medial, and distal margins of the uropodal endopods and exopods and the distal corners are important for species identification. The number of pleotelsonic spines are relevant in this matter, especially when combined with the shape of uropod rami ( Shipley et al. 2016; Hyžný et al. 2019). These characters (pleotelsonic spines and uropod rami) are indeed present in the holotype of Bathynomus civisi sp. nov. and they allow distinguishing the new species from other congeners.

The new species clearly differs from a number of extant taxa with lanceolate uropod rami, including Bathyno- mus affinis Richardson, 1910; B. bruscai Lowry & Dempsey, 2006 ; B. decemspinosus Bruce, 1986 ; B. doederleini Ortmann, 1894 ; B. immanis Bruce, 1986 ; B. kapala Griffin, 1975 ; B. maxeyorum Shipley, Brooks & Bruce in Shipley et al., 2016 ; B. obtusus Magalhaes & Young, 2003 ; and B. pelor Bruce, 1986 . From congeners with oval uropod rami, B. c ivisi sp. nov. is morphologically close to several of them. Bathynomus brucei Lowry & Dempsey, 2006 shares the number of pleotelsonic spines ( Lowry & Dempsey 2006: fig. 4F); it, however, does not have a wide gap between second and third side distal spines as the new species has. Additionally, the uropodal exopod of B. civisi sp. nov. is more oval in outline than that of B. brucei ( Lowry & Dempsey 2006: fig. 5D–E). In this respect, the new species is close to the type species, B. giganteus A. Milne-Edwards, 1879 , but differs in the number and shape of pleotelsonic spines ( Soto & Mincarone 2001: fig. 5; Magalhaes & Young 2003: fig. 1A). The same holds for Bathynomus jamesi Kou, Chen, Li, He & Wang, 2017 , which is close to B. civisi sp. nov. as far as the uropod rami concerns ( Lowry & Dempsey 2006: fig. 22A–B; Kou et al. 2017: fig. 3d, e), but differs in the development of pleotelsonic spines ( Kou et al. 2017: fig. 4). Concerning the pleotelson outline and the number and development of pleotelsonic spines, the closest extant congener is Bathynomus miyarei Lemos de Castro, 1978 ; it, however, differs with uropodal endopod having distal margin straight ( Soto & Mincarone 2001: fig. 5; Magalhaes & Young 2003: fig. 10B), whereas its outline is slightly concave close to distolateral corner ( Figs 5C , 6 ).

Bathynomus civisi sp. nov. differs from the fossil congeners; Bathynomus sismondai ( Ristori, 1891) from the Plio-Pleistocene of Italy has more pleotelsonic spines and uropodal exopod with less obtuse distolateral corner ( Hyžný et al. 2019: figs. 6A3–A4). Bathynomus kominatoensis Kato & Tokita in Kato et al., 2016 from the Miocene of Japan has proportionally wider pleotelson and higher number of pleotelsonic spines (figs. 3.5, 4.1) than B. civisi sp. nov. No fossil species of Bathynomus known to date has a wide gap between second and third side distal spines as the new species has.

Occurrence: Bathynomus civisi sp. nov. is so far known only from the upper Tortonian marls of the Écija Formation, exposed at the type locality, an old quarry located in the close vicinity of Arroyo Trujillo (Seville, Spain) .

Figures

FIGURE 4. Marls of the Écija Formation exposed at the studied section of Arroyo Trujillo. A, marls with bivalve fossils; B, The holotype of Bathynomus civisi sp. nov. at the time of its finding.

FIGURE 5. Bathynomus civisi sp. nov., holotype MGM-6636M. A, part with applied Paraloid B-72 preservative; B, counterpart with applied Paraloid B-72 preservative (numerals 1–5 refer to pleonites). C, part with exposed uropods (en = endopod, ex = exopod) after subsequent preparation; D, counterpart at the time of finding (lateral spine is still present: see the text for more details). Scale bars equal 10 mm.

FIGURE 6. Bathynomus civisi sp. nov., reconstruction of the pleotelson outline (left) and the shape of uropod rami (right).