Ostrea gregarea, Koppka, Jens, 2015

Koppka, Jens, 2015, Revision of the Bivalvia from the Upper Jurassic Reuchenette Formation, Northwest Switzerland — Ostreoidea, Zootaxa 3927 (1), pp. 1-117 : 50-55

Actinostreon gregareum (J. Sowerby, 1815)

Fig. 20 ; Pls. 16–18; Pl. 19.1–2; Pl. 22

* 1815 Ostrea gregarea n. sp. —J. Sowerby: p. 19, pl. 111, figs. 1, 3.

1815 Ostrea palmetta n. sp. —J. Sowerby: p. 20, pl. 111, fig. 2.

1817 Ostrea crista-galli n. sp. —W. Smith: p. 20, Coral Rag and Pisolite plate, fig. 4. 1822 Ostrea gregaria [sic] Sow.—Young & Bird: p. 238, pl. 9, fig. 16.

1824 Ostrea solitaria n. sp. —J. de C. Sowerby: p. 105, pl. 468, fig. 1. 1825 Ostrea costatum n. sp. —J. de C. Sowerby: p. 143, pl. 488, fig. 3. 1831 Ostrea gregarea Sow. —Deshayes: p. 106, pl. 13, fig. 2.

p 1833b Ostrea gregaria Sow. —Goldfuss: p. 7, pl. 74, figs. 2a – f.

? 1833b Ostrea pulligera nob.—Goldfuss: p. 5, pl. 72, figs. 11a–c.

1835 Ostrea solitaria Sow. —Roemer: p. 58, pl. 3, figs. 2a–c, pl. 13, fig. 4. 1836 Ostrea gregaria [sic] Sow.—Bronn: p. 314, pl. 18, figs. 16a,b.

n 1837 Ostrea gregaria [sic] Goldfuß—Koch & Dunker: p. 50, pl. 6, fig. 2. 1840c Ostrea carinata n. sp. —J. de C. Sowerby: pl. 22, fig. 8.

n 1853 Ostrea gregarea, Sow. , var.—Morris & Lycett: p. 4, pl. 1, fig. 2.? 1853 Ostrea gregarea, Sow. —de Verneuil & Collomb: p. 164, pl. 3, fig. 6.? 1857b Ostrea gregaria [sic] Sow.—Quenstedt: p. 751, pl. 41, fig. 28.

1857b Ostrea pulligera ascendens Quenstedt—Quenstedt : p. 751, pl. 91, fig. 29.? 1859 Ostrea gregaria [sic] Sow.—Trautschold: p. 115, pl. 2, fig. 15.

1861 Ostrea solitaria, Sow. —Thurmann & Etallon: 53.

? 1862 Ostrea semisolitaria, Et. —Etallon in Thurmann & Etallon: p. 279, pl. 40, fig. 1. 1862 Ostrea solitaria, Sow. —Thurmann & Etallon: p. 281, pl. 40, fig. 4.? 1862 Ostrea vallata, Etallon—Thurmann & Etallon : p. 278.

1871 Ostrea gregarea Sow. —Phillips: p. 323, pl. 13, fig. 19.

? 1871 Ostrea gregarea? Sow. —Phillips: p. 181, pl. 10, fig. 4.

1871 Ostrea gregarea, Sow. —Terquem & Jourdy: p. 131.

1872 Ostrea pulligera Goldfuss—de Loriol et al.: p. 402, pl. 24, figs. 1–6. 1875 Ostrea pulligera Goldfuss—de Loriol & Pellat: p. 377, pl. 24, figs. 4–5. 1875 Ostrea Pulligera (Quenst.) —Pillet & Frommentel: p. 133, pl. 14, figs. 24–25. 1878 Alectryonia Potieri, Bayle—Bayle : pl. 131, figs. 2–5.

1878 Actinostreon solitarium, Sowerby , sp.—Bayle: p. 132, figs. 2–6. 1880 Ostrea solitaria Sow. —Damon: pl. 9, fig. 2.

1882 Ostrea gregaria [sic] Sow.—Roeder: pl. 3, figs. 12a,b.

1883 Ostrea (Alectryonia) rastellaris, Münster var. moravica Boehm—Boehm : p. 658, pl. 70, figs. 27–30. 1888 Ostrea (Alectryonia) costata Sow., 1825 —Schlippe: p. 112, pl. 1, figs. 11–12.? 1888 Ostrea (Alectryonia) Marshi Sow., 1814 —Schlippe: p. 114, pl. 1, fig. 14–18. 1892 Ostrea (Alectryonia) Pulligera (Goldfuss) —de Loriol: p. 342, pl. 36, fig. 4. 1892 Ostrea (Alectryonia) solitaria, Sow. —de Loriol: p. 313, pl. 36, figs. 5, 6. 1893 Ostrea solitaria Sow. —Fiebelkorn: p. 396, pl. 13, fig. 14.

1893 Ostrea (Alectryonia) pulligera Goldfuss—Greppin : p. 87, pl. 6, fig. 17, 18. 1894 Ostrea (Alectryonia) vallata Etallon—de Loriol: p. 75, pl. 9, figs. 5, 6. 1897 Ostrea gregaria Sow. —Reed: p. 45.

1897 Ostrea solitaria Sow. —Reed: p. 45.

1900 Ostrea pulligera Goldf. —Müller: p. 532, pl. 18, figs. 13–14.

1900 Ostrea gregarea Sow. var. pterophora , nob.—Cossmann: p. 47, pl. 5, figs. 3, 6. 1900 Alectryonia Asellus, Merian sp.—Greppin: p. 147, pl. 17, fig. 1–2, 5. 1900 Alectryonia cfr. rastellaris (Münster) —Greppin: p. 149, pl. 16, fig. 8. n 1901 Exogyra gregarea Sow. —Raspail: pl. 12, fig. 11.

1901 Alectryonia flabelloides Schloth. —Raspail: pl. 12, fig. 3.

1903 Ostrea (Alectryonia) gregarea Sow. —Remeš: p. 218, pl. 21 (4), figs. 8a,b (Tithonian).

1903 Ostrea (Alectryonia) pulligera ascendens, Qu. —Remeš: p. 218, pl. 21 (4), figs. 6a,b, 7a,b.

1903 Ostrea (Alectryonia) aff. solitaria Sow. —Remeš: p. 217, pl. 21 (4), figs. 5a,b.

1910 Alectryonia gregarea Sowerby—Lissajous : p. 343, pl. 8, fig. 17.

1910 Alectryonia pulligera Goldfuss —Lissajous: p. 334, pl. 8, fig. 18.

1911 Ostrea (Rastellum) gregarea Sow. —Rollier: p. 277.

1911 Ostrea (Exogyra) semisolitaria Etallon—Flamand : p. 924, pl. 9, figs. 2, 2a, 3–4, 5, 5a, 6.

1922 Alectryonia costata (Sowerby) —Cossmann: p. 4, pl. 5, figs. 5–8.

1924 Alectryonia pulligera —Jourdy: pl. 1, fig. 3, no. 2.

1925 Alectryonia pulligera (Goldf.) —Weir: p. 86, pl. 12, fig. 5.

1925 Alectryonia rastellaris (Münster) —Weir: p. 86, pl. 12, figs. 15–17.

1925 Alectryonia solitaria (Sow.) —Weir: p. 85, pl. 12, fig. 9.

1925 Alectryonia aff. solitaria (Sow.) —Weir: p. 86, pl. 12, fig. 8.

1931 Ostrea (Alectryonia) gregaria [sic], Sow.—Yin Tsan-hsun: p. 123, pl. 11, fig. 17.

1931 Ostrea (Alectryonia) solitaria, Sow. —Yin Tsan-hsun: p. 124, pl. 11, fig. 18.

1931 Lopha pulligera (Goldf.) —Diaz-Romero: p. 40, pl. 3, fig. 12, 13.

1933 Lopha gregarea (Sow.) var. solitaria —Oria: p. 34, pl. 2, figs. 7, 1 – 3, pl. 4, figs. 4–6, 8.

1933 Lopha gregarea (J. Sowerby) —Arkell: p. 183, pl. 22, figs. 5, 6, pl. 23, figs. 1–4.

1933 Lopha solitaria (Sowerby) —Arkell: p. 185, pl. 22, fig. 4, pl. 23, figs. 5 – 7.

1935 Lopha solitaria (Sow.) —Cox: p. 171, pl. 17, figs. 9 – 12.

1936 Alectryonia gregarea Sow. —Besairie: pl. 7, fig. 17.

1938 Alectryonia gregarea Sowerby—Chavan & Montocchio : p. 72, fig. 122a.

1939 Lopha Perdalianae (MGH.)—Stefanini: p. 195, pl. 22, figs. 4, 5.

1939 Lopha solitaria (Sow.) —Stefanini: p. 197, pl. 22, figs. 6 – 7.

1952 Lopha gregarea (J. Sowerby) —Cox: p. 96, pl. 4, fig. 2, pl. 10, figs. 7–13.

1956 Lopha gregarea (J. Sow.) —Agrawal: p. 89, pl. 9, fig. 13.

1959 Lopha solitaria (Sowerby) —Jaboli: p. 36, pl. 5, fig. 1.

1960 Lopha solitaria (J. de C. Sowerby)—Joubert: pl. 9, figs. 1, 2a–c.

1960 Lopha gregarea (J. Sowerby) —Tamura: p. 239, pl. 2, fig. 24.

1961 Lopha cf. gregarea (Sowerby, 1815) —Sibiriakova: p. 102, pl. 13, figs. 11–13.

1964 Lopha Solitaria (J. Sowerby) —Maithani: p. 510, pl. 31, fig. 2.

1965 Lopha gregarea (J. Sowerby) —Cox: p. 68, pl. 9, fig. 5.

1965 Lopha solitaria (J. de C. Sowerby)—Cox: p. 69, pl. 9, fig. 4.

1965 Lopha solitaria (Sowerby) s.s. —Freneix: p. 72 (24), pl. 3, figs. 1, 2.

1965 Lopha solitaria (Sowerby) matmatensis n. ssp. —Freneix: p. 73 (25), pl. 3, figs. 4a,b, 5a,b, 6a,b, 7a,b, text-

fig. 7a, c.

1965 Lopha solitaria (Sowerby) subpulligera n. ssp—Freneix: p. 76 (28), pl. 3, figs. 3a,b, 5, 9a,b, 10, 11, 12a,b,

13, 14, text-fig. 7b, d1, d2.

1969 Lopha gregarea (J. Sowerby) —Fischer: p. 96, pl. 10, fig. 28.

1971 Lopha solitaria (J. de C. Sowerby)— Jordan: p. 152, pl. 20, figs. 4a,b, 5a,b.

1971 Alectryonia pulligera (Goldfuss, 1834) —Pugaczewska: p. 234, pl. 8, figs. 1–15.

1971 Alectryonia flabelliformis (Nilson in Goldfuss, 1840)—Pugaczewska: p. 238, pl. 4, figs. 1 – 10.

1971 Alectryonia gregarea (Sowerby, 1816) —Pugaczewska: p. 227, pl. 3, fig. 7, pl. 5, figs. 1–8, pl. 6, figs. 1–8,

pl. 9, figs. 2–3, pl. 10, fig. 3.

1971 Alectryonia rastellaris (Münster, 1833) —Pugaczewska: p. 232, pl. 6, fig. 9, pl. 7, figs. 1–3, 5–7.

1971 Alectryonia solitaria (Sowerby, 1825) —Pugaczewska: p. 230, pl. 3, figs. 1–6, pl. 9, fig. 1.

1971 Alectryonia vallata ( Etallon, 1862) —Pugaczewska: p. 236, pl. 19, fig. 3a–b, 4.

1973 Ostrea solitaria Sow. —Contini & Hantzpergue: p. 150, 152.

1973 Ostrea pulligera Gold. —Contini & Hantzpergue: p. 175.

1976 Lopha solitaria (Sowerby) —Ma Qi-hong in Gu Zhi-wei et al.: p. 323, pl. 35, figs. 34–35.

1977 Lopha (Rastellum) gregarea (Sow.) —Andreeva: pl. 5, figs. 1–5.

1979 Lopha solitaria (Sowerby) —Wen Shi-xuan: p. 303, pl. 92, fig. 8.

1984 Lopha gregarea (Sowerby) —Radulović & Mitrović-Petrović: p. 110, pl. 3, figs. 4–5.

1985 Lopha asellus namtuensis Reed—Zhang Zuo-ming et al.: p. 115, pl. 45, fig. 5.

1985 Lopha cf. gregarea (Sowerby) —Zhang Zuo-ming et al.: p. 115, pl. 45, fig. 3, 4.

1988 Arctostrea gregaria [sic] (Sowerby)—Reiff: pl. 29, fig. 3.

? 1989 Lopha gregarea (Sowerby) —Matyia, Gutowski & Wierzbowski: pl. 3, fig. 4.

1990 Lopha (Actinostreon) gregarea (J. Sow. 1816) —Clausen & Wignall: p. 124, pl. 6, fig. c.

1990 Lopha (Rastellum) gregarea (Sowerby, 1815) —Dykan & Makarenko: p. 83, pl. 16, figs. 13, 15–20.

1990 Lopha (Lopha) pulligera (Goldfuss, 1834) —Dykan & Makarenko: p. 82, pl. 16, figs. 11, 12.? 1994 Actinostreon solitarium (J. de C. Sowerby 1824)—Aberhan: p. 30, pl. 12, figs. 8–10. n 1995 Lopha (Lopha) solitaria (J. de C. Sowerby, 1824)—Monari: p. 166 – 167, pl. 2, fig. 7.

1995 Actinostreon gregareum (J. Sowerby 1815) —Jaitly et al.: p. 186, pl. 13, fig. 13, pl. 14, figs. 1–5.

1997 Lopha gregarea (Sowerby, 1815) —Bernad: p. 14, pl. 2, fig. 4–7.

1998 Actinostreon gregareum (J. Sowerby, 1816) —Machalski: p. 614, fig. 4a–d, g–m.

1998 Actinostreon sp.—Machalski: p. 627, fig. 11A–I.

1998 Lopha solitaria —Breton: pl. 1, fig. 11.

1998 Actinostreon gregareum (J. Sowerby 1815) —Holzapfel: p. 105, pl. 6, figs. 18–19, 21.

1998 Actinostreon costatum (J. de C. Sowerby 1825)—Holzapfel: p. 104, pl. 6, figs. 8–14.

1999 Actinostreon gregareum (J. Sowerby 1815) —Ahmad: p. 15, pl. 6, fig. 3.

2002 Actinostreon gregareum (J. Sowerby 1815) —Gahr: p. 123, pl. 3, fig. 12.

2002 Actinostreon gregareum (J. Sowerby, 1815) —Sha, Smith & Fürsich: p. 433, figs. 6, 7.1–7.14.

2005 Actinostreon solitarium (J. Sowerby, 1824) —Scholz: p. 26, pl.4, figs. 4–7.

2006 Actinostreon gregareum—Hicks: 36.

2006 Actinostreon gregareum (J. Sowerby, 1816) —Richardt: 9, 18.

2011 Actinostreon solitarium (J. de C. Sowerby)—Kiessling et al.: p. 209, fig. 13G.

Lectotype (not seen). Ostrea gregarea J. de Sowerby, 1815: p. 19, pl. 111, fig. 3; subsequent designation by Arkell 1933: p. 185, pl. 22, fig. 5, BM. 44120a (NHMUK). Westbrook near Bromham, Wiltshire, England, Berkshire Oolite Series?, Coral rag, Oxfordian, Upper Jurassic.

Material. More than 1000, mostly articulated specimens, including numerous juvenile specimens, from the Banné Marls of the Reuchenette Formation of Vâ Tche Tchâ near Courtedoux (Ajoie, Switzerland), Lower Kimmeridgian (Appendix, Table 8 ).

Description. Shape, size—LV slightly larger and more inflated than RV; shape largely influenced by attachment size; rather undisturbed growth broadly curved with posteroventral branchitellum; otherwise round, oval, elongated, trigonal to sickle-shaped; umbones small, acute, slightly recurved; opisthogyrate, rarely prosogyrate (e.g., Pl. 16.5a–b, d). Examined specimens between 1.4–7 cm in height (Appendix, Table 8 )

Sculpture—Attached portion of shell often with replicates of overgrown objects (Pls. 16.3a,b, 4; 17.1a, c, 4b; 18.1a, 2a,c, 4a,b). Detached shell margin plicate; plicae growth direction roughly antimarginal, initially often with wavy, later typically with chevron shaped cross section; number of plicae increasing by splitting and intercalation; number variable (ca. 5–35), usually more than 20; plicae become squamous ventrally.

Ligament area—Well developed, initially curved, prosodetic, later growing anteroventrally, bourrelets in LV thick, convex, in adults almost as wide as resilifer; bourrelets in RV less convex, resilifer less sunken, may become convex tending to alivincular-arcuate (see definition in Carter et al. (2012) (Pl. 17.3a–d, Pl. 18.6).

Internal shell characters—Umbonal cavity small to absent. Adductor scar large, weakly raised ventrally, position slightly posterodorsal. Quenstedt muscle scar present in both valves, but rarely observable (Pl. 17.3b–c). Chomata present in all (eco)phenotypes, straight type, rather small (length between 0.3–0.6 mm, width 0.09–0.3 mm) and faint, on anterior and posterior dorsal shell margin, occasionally reaching further ventral than adductor scar, especially in juveniles (Pl. 17.4a).

Microstructure—Both valves with light-weight shell architecture; outermost prismatic shell layer not seen in either valve (eroded?); visible (non-chambered) outer-middle layers homogeneous “mosaic” to complex cross foliated (ca. 500 µm thick); middle-inner layers with many small and medium large chambers, small chambers especially below rib crests, convex or biconvex in cross-section; chambers typically empty (or filled diagenetically with sparry cement), mocret absent or very rare (Pl. 22), chamber walls predominantly regular foliated, walls of void chambers often collapsed.

Prodissoconch, juvenile—Prodissoconch and earliest postlarval shell unknown (but see Pl. 19.4a–d). Small juveniles tend to have a stronger coiled umbo than adults (Pl. 18.4a–b, 5). The PAM of juveniles is oval (Pl. 18.3b); however, it rotates during ontogeny so that the anterior margin of the juvenile PAM becomes the adult dorsal adductor margin.

Paleoecology. Actinostreon gregareum is typical of the marls and marly limestones of the Banné Marls (Ajoie, Switzerland) where specimens are often found articulated. As its name suggests, the species is gregarious, occasionally forming aggregates of dozens of specimens (Pls. 16.2a,b; 17.2a,b; 19.2a–d) (compare with the often solitary growth of the ecomorph “ A. solitarium ”). Individuals or small clusters often settle on large bivalve and gastropod shells. Elongate morphotypes are commonly attached to the spines of the gastropod Harpagodes or to the delicate stems (Pl. 16.3a,b; Pl. 17.4a,b) and thalli of Goniolina (calcareous algae) (Pls. 17.4; 18.1–3) (compare also Pugaczewska 1971, pl. 6, figs. 2a,b, 8a,b; for specimens settling on spines of sea urchins).

Present sedimentary and biogenic evidence suggests that A. gregareum thrived in relatively calm subtidal environments. Arkell (1933, p. 184) associated the species with coral reef settings (the Trigonia hudlestoni Limestones, Corallian , Upper Oxfordian, England). Fürsich (1977) and Sha et al. (2002) reported high-energy conditions as the favoured environment. All settings from which the species has been described indicate fully marine conditions.

Occurrence. In Switzerland, in the Lower Kimmeridgian Vabenau and Banné Members of the Reuchenette Formation, Bathonian–Tithonian of Central and Eastern Europe, Toarcian–Kimmeridgian of Spain, Tithonian of Czech Republic, Bajocian–Kimmeridgian of Israel, Oxfordian–Kimmeridgian of Arabia, Toarcian–Kimmeridgian of East Africa, Bajocian–Bathonian of Iran, Bajocian of Australia, Sinemurian–Aalenian of Chile, Bathonian–Oxfordian of India and China, Oxfordian–Kimmeridgian of Burma, Upper Jurassic of Japan (see Sha et al. 2002, p. 435).

Comparisons. Actinostreon gregareum is remarkably polymorphic even within the rather calm paleoenvironments of the Banné Marls. Because of its many transitional forms with populations described from more turbulent regimes, it is virtually impossible to separate the numerous alleged morphospecies described by Pugaczewska (1971) and previous authors.

The present approach largely agrees with the assessments and extensive synonymies given by Aberhan (1994), Cox (1952), Gahr (2002), Jaitly et al. (1995), Sha et al. (2002), and Siewert (1972). However, this makes A. gregareum a stratigraphically suspiciously wide-ranging species which still requires corroboration. The following list briefly discusses presumably distinct species in alphabetic order and with more doubtful cases towards the end.

Actinostreon marshii (J. Sowerby, 1814) (p. 103, pl. 48)—The species was first described from the Upper Cornbrash (Bathonian) in the neighbourhood of Felmersham near Bedford (Bedfordshire, England), but is also known from the Bajocian to Oxfordian in Europe (Pl. 19.3–4 for specimens of the Callovian of Lithuania) and from the Upper Bathonian to the Kimmeridgian of India (see Cox 1952, for synonymy and occurrence).

The species is characterized by few (7 or 8) strongly developed plicae and reaches a larger adult size with thicker shells than A. gregareum (Pl. 19.3). Adult specimens seem to lack chomata. The figured small specimen from Lithuania also lacks them (Pl. 19.4a–d) but this should be tested for juvenile shells in general. Usually the species does not form clusters, but exceptions are known, e.g., in the Oxfordian of the Vaches Noires (Normandy, France) (Fürsich, pers. comm. 2014). It occurs in relatively calm and, judged by its common association with ammonites, also deeper paleoenvironments.

Actinostreon namtuensis ( Reed, 1936) (p. 9, pl. 1, fig. 1, 1a–b)—The species was originally described as Lopha asellus Merian var. namtuensis from the Bathonian of Burma. Sha et al. (2002) considered it a synonym of A. gregareum . However, unlike A. gregareum , this species has a non-curved shell (despite a small attachment area) and develops more than 30 plications which are much finer than in A. gregareum .

? Actinostreon arietis ( Schäfle, 1929) (p. 63, pl. 6, figs. 2–3)—The species was originally described from the Lower Sinemurian ( Arietites Limestone ) of Vaihingen (Stuttgart, Germany). The only figured specimen is the holotype which lacks the umbo and ventral shell portions. The remaining shell (ca. 6.6 cm high) is not curved and shows about 12 coarse plications ( Schäfle 1929). Internal features and microstructures are unknown. In the light of the poor remains of the species, Schäfle’s allusion to the essentially crescentic genus Arctostrea from the Lower Cretaceous is incomprehensible.

? Actinostreon erucum ( Defrance, 1821) (p. 31)— Defrance (1821) introduced the name as Ostrea eruca without figure and information about the origin of the type material in his oyster chapter of the Dictionaire Scientifique Naturelle. The species is known from the Upper Callovian to Lower Oxfordian of the “falaise du Calvados” (Normandie, France) ( Bigot 1893, 1904; Raspail 1901, pl. 11, fig. 8). Bigot (1893, p. 136, pl. 2, figs. 4–6; 1904, Palaeontologia universalis, 73, 73a) figured the type material of Defrance (1821) and supposed Patrie (= Le Mesnil-Patry?) close to Villers-sur-Mer as the most likely type locality. The species was suggested by Cox (1952, p. 105) as a replacement name for Ostrea hastellata ( Schlotheim, 1820) [itself an invalid short form for Ostracites cristahastellatus Schlotheim, 1820].

The species is narrowly sickle-shaped without being attached to a cylindrical object, thin-shelled, and the central area lacks plicae. This species was attributed to several other oyster genera such as Arctostrea or Rastellum ( Cox, 1952, p. 103 – 106). In fact, the shape and plicae pattern are more reminiscent of the type species of Upper Cretaceous Agerostrea (Flemingostreinae) which is a compact foliated genus ( Malchus, 1990, p. 160, pl. 15, fig. 8) (see also, Klinger & Malchus, 2008; Stenzel, 1971, fig. J133). However, there are no further characters available for a sound assessment.

? Actinostreon pulligerum (Goldfuss, 1833) (p. 5, pl. 72, fig. 11a–c)—The type material, from the Upper Kimmeridgian Corallian facies of Nattheim (Swabian Alb, Germany), compares well with a juvenile, round variation of A. gregareum , attached to a small object (Pl. 16, Figs. 5-6 ) (see also Arkell, 1933, p. 186). Unfortunately, little else is known about this species ( Sha et al. 2002, p. 436).

? Ambigostrea boucaudensis (Choffat) (manuscript name of the unpublished 3rd volume of Choffat’s monograph; according to Fürsich & Werner, 1988, p. 103)—According to Malchus (1990, p. 68–70), the Geological Museum in Lisbon ( Portugal) holds some specimens (nrs. 2593–2598, 2600) from the Kimmeridgian of the Lusitanian Basin which were originally labelled as “ O. ” pulligera var. boucaudensis Choffat. Unlike typical Actinostreon species, this apparently undescribed variant or species is essentially compact foliated, develops nodular plicae, shows plenty of small but well developed relict chomata on its dorsal flanks, and has an ostreoid adductor scar. Malchus (1990) hypothesized that “ O.” pulligera sensu Choffat could be the earliest representative of his newly established genus Ambigostrea ( Malchus 1990, p. 85).

Small straight chomata and an ostreoid adductor scar are also present on the original figure of Goldfuss (pl. 72, fig. 11c) which may suggest that both Choffat’s and Goldfuss’ specimens belong to Ambigostrea rather than Actinostreon .

? Rastellum rusticum ( Defrance, 1821) (p. 31)—The types of Ostrea rustica Defrance, 1821 , are from the Middle Callovian of Gâprée (Basse-Normandie, Department Orne, France) ( Bigot, 1904, Palaeontologia universalis, 72, 72a, figs. C.1–3, P.1–3) (Fig. 21.1–2). The species is identical with Ostrea amata d’Orbigny, 1850 ( Bigot 1904, p. 72a) and is morphologically similar to A. gregareum .

Main differences are a narrower shape, a thinner shell and the larger number of plicae (30–50), covering the whole shell including the umbonal area, absence of chomata, and the more posterodorsally situated oval adductor scar (Fig. 21.3–7). The shell was chambered as indicated by a collapsed shell layer on the inner (depositional) surface of a specimen from Villers-sur-Mer, France (Calvados, Middle Oxfordian, plicatilis Zone) (FPJ-collection, nr. 5369; Fig. 21.5–6) and Liesberg, Switzerland (Middle Callovian, coronatum Zone ) (FPJ, nr. 5367). This type of breakage is typical of specimens with larger (hollow) shell chambers.

Figures

FIGURE 5. Circunula n. gen. cotyledon (Contejean, 1859). 1 – 4. Lectotype: 1, idealized drawing of a bivalved specimen, refigured from Contejean (1859, pl. 24, fig. 15), MC 27 E- 105, Rôce in Montbéliard, Lower Kimmeridgian; 2, anteroventral view of LV attached on a Trichites fragment (refigured from Contejean 1859, pl. 24, fig. 16); 3, external view of RV (with attached paralectotype, revealed during preparation); 4, anteroventral view. 5 – 6. Paralectotype, small LV (MC 27 E- 105 a), attached on lectotype: 5, interior view; 6, prosodetic ligament area. 7. Paralectotype, RV interior, with opisthodetic ligament area, MC 27 E- 104, same locality and age as the lectotype. 8 – 9. Paralectotype, MC 27 E- 108, Arbouans near Montbéliard, France, Upper Oxfordian; 8, thick-shelled LV, idealized drawing refigured from Contejean (1859, pl. 24, fig. 17); 9, same LV, interior view. Scale bars 5 mm and 10 mm.

FIGURE 6. Circunula n. gen. cotyledon (Contejean, 1859). 1 – 3. Drawings of three juvenile specimens originally attached close together on a Trichites - shell (CGN-ALO 009 - 1, see Fig. 8; Pl. 3.2 – 3), Alombre aux Vaches near Courgenay, Lower Kimmeridgian: 1, LV, umbo prosogyrate, ALO 009 - 1 - II; 2, LV, opisthogyrate, ALO 009 - 1 - I; 3, LV, opisthogyrate, ALO 009 - 1 - III. Scale x 5.

FIGURE 20. Actinostreon gregareum (J. Sowerby, 1815). 1. RV, VTT 006 - 77, lateral. 2. LV, VTT 001 - 1455, lateral. 3. LV, VTT 009 - 41, interior. 4. Both valves, VTT 001 - 1700, ventral; all specimens from Vâ Tche Tchâ near Courtedoux, Switzerland, Lower Kimmeridgian.