Cytheridae Baird, 1850

Lord, Alan R., Cabral, M. Cristina & Danielopol, Dan L., 2020, Sieve-type normal pore canals in Jurassic ostracods: A review with description of a new genus, Acta Palaeontologica Polonica 65 (2), pp. 313-349 : 321-323

Family Cytheridae Baird, 1850

Remarks.—The Middle Jurassic species Dolocythere maculosa Bate, 1963 , recognized here as a species of Minyocythere gen. nov., was originally placed by that author in the mid-Cretaceous genus Dolocythere Mertens, 1956 and it is therefore necessary to discuss the suitability of that genus for the new Middle Jurassic species we describe below which are clearly congeners with D. maculosa .

Dolocythere rara Mertens, 1956 is the type species of Dolocythere . We figure paratypes of D. rara ( Fig. 18A, B ) together with Senckenberg material that is conspecific in our opinion ( Fig. 18C–F ). There are clear differences between Albian Dolocythere rara and our Middle Jurassic Minyocythere gen. nov. in, for example, StPC, in muscle scar pattern and in the shape of the mandibular depression (median depression = fulcral point of Van Morkhoven 1962) ( Figs. 4 , 5). Mertens (1956) cites dimorphism (see Appendix 1 for generic diagnosis) but does not mention this for D. rara in text or figures. We have inspected numerous adults and juveniles of D. rara of Aptian–Albian age from NW Germany (Erich Triebel collection in SMF) and find that putative males are difficult to recognize and rather rare. It is clear that revision of the genus is necessary and more than one species is involved, thus we describe Dolocythere amphistiela sp. nov. as distinct from D. rara .

Minyocythere shows differently developed muscle scars and especially the mandibular fulcral depression, both genera have lophodont hingement but less strongly developed in Minyocythere than in Dolocythere and with an accommodation groove on LV. Both genera have StPC but Minyocythere has large and easily recognizable StPC (StPC-M herein; “caps” of Luppold 2012) whereas Dolocythere does not. Minyocythere has two of these StPC-M in a stable antero-dorsal position ( Fig. 6 ) which we consider probably a diagnostic character for Minyocythere as it is common to the four (five?) known species of the genus and it is not present in Dolocythere . Minyocythere macroporosa sp. nov. and M. angulata sp. nov. show pre-adult sexual dimorphism (= “precocious sexual dimorphism”), a feature that is well-known in ostracods (living examples: Heterocythereis albomaculata ( Baird, 1838) and Loxoconcha elliptica Brady, 1868 [ Athersuch et al. 1989: 23–24], Keijcyoidea infralittoralis Tsukagoshi, Okada, and Horne, 2006 [ Okada et al. 2008]; fossil examples: four species of Glyptocythere Brand and Malz, 1962 , Glabellacythere Wienholz, 1967 , Lophocythere Sylvester-Bradley, 1948 [ Whatley and Stephens 1977], Praeschuleridea decorata Bate, 1968 [ Bate 1968]). The important aspects for fossil material are: (i) to check internal fea-

Fig. 5. Comparison of valve morphology and muscle scars in cytherid ostracods Dolocythere (A, B) and Minyocythere (C–G). A. Dolocythere rara Mertens, 1956 from Borehole Lingen 196, 697– 704 m, NW Germany, Lower Albian. Paratype, BGR T.-K. 1300 (Mertens Collection, Hannover), female left valve in internal view (A 1), detail (A 2). B. Dolocythere amphistiela sp. nov. from Borehole Rodewald WA 4, 187 m, NW Germany, lower Middle →

tures carefully to assess full maturity (see Athersuch et al. ble the younger Minyocythere gen. nov. externally but they

1989: fig. 16 with A-1 dimorphs in L. elliptica demonstrating are easily differentiated by hingement which is merodont in simple calcified inner lamella features of the penultimate the former and lophodont in the latter. Differences between moult) and (ii) the problem of time-averaging in micropalae- Minyocythere and Dolocythere are discussed above.

ontological samples which may conceal ecological fluctua- David Horne (personal communication 2019) commented tions reflected in size variation in mature animals over time. on the similarity in valve shape between Minyocythere gen.

In this context larger adults may appear as post-maturation nov. and Cytherissa Sars, 1925 , the latter a living lacustrine

moults although this seems rare, for example, Whittaker in taxon that displays a wide range of morphological variation

his study of The Fleet, Dorset, UK (personal communication ( Danielopol et al. 1990). The hingement of both genera is

to ARL; 1968, 1975) cites Paradoxostoma pulchellum Sars , similar, smooth and tripartite, and both have relatively nar-

1866 with 1700 live adults collected over three years but only row and simple marginal zones but differ in details of StPC

one was 15–20% larger than other adults, and Hirschmannia and muscle scars in addition to the fact that Minyocythere

viridis ( Müller, 1785) with 1500 live and dead adults over is Jurassic, marine and extinct whereas Cytherissa is

three years with only one 15–28% larger.?Paleogene, Pliocene to Recent ( Colin and Carbonel 1990),

Our conclusion is that the suite of Middle Jurassic spe- living, and common in shallow and deep lake environments

cies: Minyocythere macroporosa sp. nov., M. angulata sp. ( Meisch 2000), and is a potential case of homeomorphy or

nov., M. maculosa ( Bate, 1963) and M. tuberculata ( Luppold,

2012) represent a new genus that we erect as Minyocythere convergent evolution. The question arises of family place-

gen. nov. and which differs from Dolocythere in develop- ment. On balance we believe Minyocythere to be closer to ment of hingement, in details of the muscle scar pattern, in living Cythere and the Family Cytheridae than to Cytherissa the nature of the mandibular depression and in the morpho- and the Family Cytherideidae , and also close to Dolocythere logical diversity of the NPC. which is considered a Cytheridae taxon, however, the definition of families of Jurassic ostracods is in need of revision.

Genus Minyocythere nov. Reference is made both above and below to Japanese

ZooBank LCID: urn:lsid:zoobank.org:act:00137DD9-13E3-4ABB- work on NPC of the genus Cythere , especially by Tsukagoshi

8367-8F1865C9D53D and Ikeya (1987), which provides an important compara-

Type species: Minyocythere macroporosa sp. nov., Borehole Hambüh- tive dataset. Cythere , a widespread living and fossil genus ren WA2, NW Germany; Early Bajocian. which gives its name to the family Cytheridae , has heavily

Species included: Minyocythere angulata sp. nov., M. maculosa (Bate, calcified sub-quadrate valves ornamented with pits and/or

1963), M. tuberculata ( Luppold, 2012) . ridges, with internally merodont hingement, broad calcified

Etymology: From Greek, μΙΝΥΟ (minyo), of small dimension and κΥθερα, inner lamella without vestibules and fairly numerous mar-

κΥθερης ( Cythera, Cytherias [Kuthêra, Kuthêrias]), different forms of ginal pore canals especially anteriorly, and is sexually di-

a surname of Aphrodite, derived from the town of Cythera in Crete, or from the island of Cythera , where the goddess was said to have first morphic with females slightly higher than males. Although emerged, and where she had a celebrated temple. Cythere and Minyocythere fall in the same family they are not thought to be closely related.

Diagnosis.—A genus of the Family Cytheridae character- An apparent progression in time of strength of ornament

ized by subtriangular to subrectangular shape, modified lophodont hingement with accommodation groove on LV in Minyocythere species is evident: Minyocythere angulata and up to three types of normal pore canal especially large (almost smooth), M. macroporosa (ranges from weak to round or rarely elongate sieve-type pore canals. strong depressions), M. maculosa (strong depressions), M. tuberculata (strong swollen curving ridges), which, perhaps

Remarks.— Phraterfabanella Whatley and Boomer in Boomer surprisingly, matches the stratigraphic occurrence of these

et al., 2001 (Sinemurian), Camptocythere Triebel, 1950 and species in borehole Hambühren WA2 (although less well

Aphelocythere Triebel and Klingler, 1959 (both Toarcian– in borehole Rodewald WA 2 where occurrences are patchy)

Aalenian) (diagnoses in Appendix 1) are the earliest examples (discussed below).

known to us of StPC in cytheroid ostracods (see “The fossil record of StPC” above). Some species of Aphelocythere, Stratigraphic and geographic range.—Aalenian–Bajocian,

e.g., A. perforata Plumhoff, 1963 ( Fig. 3A 1 ) closely resem- Middle Jurassic; NW Europe.

Albian. Paratype, SMF Xe 23765, male left valve in internal view (B 1), detail (B 2). C, D. Minyocythere maculosa ( Bate, 1963) . C. Topotype, SMF Xe 23743 from Bajocian, Basement Beds; Everthorpe Quarry, South Cave, UK, female left valve in internal view (C 1), detail (C 2), median depression (C 3). D. SMF Xe 23746 from Borehole Hambühren WA2, 171– 174 m, NW Germany, Witchellia laeviuscula Zone (Braun Jura γ), Lower Bajocian, female left valve in internal view (D 1), detail (D 2). E. Minyocythere macroporosa gen. et sp. nov. from Borehole Hambühren WA 2, 166 m, NW Germany, Witchellia laeviuscula Zone (Braun Jura γ), Lower Bajocian. Holotype, SMF Xe 23721, male left valve in internal view (E 1), detail (E 2). F. Minyocythere sp. cf. M. macroporosa gen. et sp. nov. from Borehole Rodewald WA 12, 386 m, NW Germany, Upper Aalenian (Braun Jura β upper). SMF Xe 23724, male right valve in internal view (F 1), detail (F 2). G. Minyocythere angulata gen. et sp. nov. from Borehole Hambühren WA2, 192– 198 m, NW Germany, Upper Aalenian (Braun Jura β). Paratype, SMF Xe 23741, male left valve in internal view (G 1), detail (G 2). Thin white arrows point to median depression; thick white arrows point to frontal scar; black square indicates detail of frontal scar.

Figures

Fig. 18. Cytherid ostracod Dolocythere rara Mertens, 1956 from Borehole Lingen 196, 697–704 m (A, B), Borehole Rodewald WA6, 206 m (C), WA7, 383.7 m (E), Borehole ZW Losser 1, 256.4–258.4 m (F) from NW Germany, Lower Albian and Ziegelei Bekum (D) from NW Germany, Upper Aptian. A. Paratype, BGR T.-K. 1300 (Mertens Collection, Hannover), female left valve in external (A1) and internal (A5) views, ornamentation (A2–A4), muscle scars (A6), hinge (A7), small sieve-type pore canals (StPC) (cf. micro sieve-type normal pore canals StPC-m) (A8). B. Paratype, BGR T.-K. 1300 (Mertens →

Fig. 4. Comparison of muscle scars of Dolocythere Mertens, 1956 and Minyocythere gen. nov. A. Dolocythere rara Mertens, 1956 from Borehole Lingen 196, 697–704 m, NW Germany, Lower Albian. Paratype, BGR T.-K. 1300 (Mertens Collection, Hannover), female left valve in internal view. B. Minyocythere angulata sp. nov. from Borehole Hambühren WA2, 203 m, NW Germany, Upper Aalenian (Braun Jura β). Paratype, SMF Xe 23738, female left valve in internal view. A1, B1, photographs; A2, B2, explanatory drawings.

Fig. 6. Distribution of sieve-type normal pore canals (StPC) and simple normal pore canals (NPC) on the outer side of left valves of cytherid ostracod Minyocythere gen. et spp. nov. A. Minyocythere macroporosa sp. nov. from Borehole Hambühren WA2, 166 m, NW Germany, Witchellia laeviuscula Zone (Braun Jura γ), Lower Bajocian. Holotype, SMF Xe 23721, male left valve (A), detail (A), total area of A, c. 45 μm2. B. Minyocythere angulata 1 2 2 sp. nov. from Borehole Hambühren WA2, 203 m, NW Germany, Upper Aalenian (Braun Jura β). Holotype, SMF Xe 23737, male left valve (B1), detail (B), total area of B, c. 44 μm2. C. Minyocythere sp. cf. M. macroporosa sp. nov. from Borehole Rodewald WA12, 404.5 m, NW Germany, Witchellia 2 2 laeviuscula Zone (Braun Jura γ upper), Lower Bajocian. SMF Xe 23725, male left valve (C1), detail (C2). D. Minyocythere maculosa (Bate, 1963) from Hambühren WA2, 171–174 m, NW Germany, Upper Aalenian (Braun Jura β). SMF Xe 23750, male left valve. E. Minyocythere tuberculata (Luppold, 2012) from Borehole Rodewald WA12, 404.5 m, NW Germany, Witchellia laeviuscula Zone (Braun Jura γ upper), Lower Bajocian. SMF Xe 23754, female left valve. Black dots refer to macro StPC (StPC-M); white arrows point to micro StPC (StPC-m); simple NPC underlined; black arrows indicate position of the two StPC-M characteristic of Minyocythere species. Scale bars 100 μm.

Fig. 3. Sieve-type normal pore canals (StPC) in Aphelocythere and Camptocythere spp. A. Aphelocythere perforata Plumhoff, 1963, from Borehole Wesendorf 51a, 1031–1035 m, NW Germany, Upper Aalenian. SMF Xe 5608 (Plumhoff Collection), carapace in external right view (A1), macro StPC (StPC-M) (A2–A4). B, C. Camptocythere praecox Triebel, 1950 from Borehole Hambühren WA 2, 341 m, NW Germany, Leioceras opalinum Zone, Lower Aalenian (Braun Jura α). B. Paratype, SMF Xe 1448, male right valve in external view (B1), mid-anterior area behind marginal rim, ornamentation and pores (large and small) (B2), StPC-M with a peripheral large pore (B3), micro StPC (StPC-m) (B4). C. Paratype, SMF Xe 1448, male right valve in internal view (C1), hinge (C2), StPC-m (C3). D. Camptocythere media Triebel, 1950 from Borehole Altencelle 1014, 212/16 m, NW Germany, Upper Aalenian (Braun Jura β). Paratype, SMF Xe 1513, female left valve in external view (D1), detail, antero-dorsal area, ornamentation and pores (large and small) (D2), round StPC-M (D3), elongate StPC-M (D4), StPC-m (D5).

Fig. 1. Schematic cross-sections of ostracod valves, exterior to top, interior to bottom. A. NPC classification of Puri and Dickau (1969). B. StPC with sieve plate flush with external surface (1) and sieve plate in funnel-shaped depression (2).