Laxitextella laxitexta ( Jones, 1890 )

Olempska, Ewa, 2004, Late Triassic spinicaudatan crustaceans from southwestern Poland, Acta Palaeontologica Polonica 49 (3), pp. 429-442 : 435-436

Laxitextella laxitexta ( Jones, 1890)

Figs. 5A , 7 .

Estheria minuta, Alberti ; Jones 1862: 57, pl. 2: 1–7.

Estheria laxitexta Sandberger ; Sandberger 1871: 48 (nomen nudum). Estheria minuta Alberti ( E. laxitexta Sandberger ); Jones 1890: 387– 388, pl. 12: 8.

Euestheria laxitecta (Jones) ; Raymond 1946: 242.

Euestheria laxitecta (Sandberger) ; Kobayashi 1954: 54, 98.

Isaura laxitexta laxitexta ( Jones, 1890) ; Reible 1962: 210–212, fig. 15, pl. 8: 3, 4.

Isaura hausmanni ( Schmidt, 1938) ; Reible 1962: 214–215, fig. 17, pl. 9: 3.

Palaeestheria laxitexta ( Jones, 1890) ; Warth 1969: 137, fig. 7, pl. 3: 5.

Laxitextella laxitexta ( Sandberger, 1871) ; Kozur 1982: 378–379.

Material.—18 complete or slightly damaged valves and 20 damaged specimens.

Description.—Carapace of moderate size, varying in outline from elongate ovoidal to subquadrate, up to 9.0 mm long and up to 5.5 mm high; lateral convexity greatest just behind and below the umbo in anterior third of valve; dorsal margin almost straight, varies in relative length; anterior margin broadly rounded, posterior ventrally truncated, ventral margin more or less convex; umbo small, situated close to anterior end of dorsal margin, protruding above dorsal margin; growth bands approximately 28 in largest specimens, ventral growth bands closely spaced in adult specimens, median widely spaced; surface of growth bands ornamented by polygonal reticulation, in largest specimens usually 2–3 meshes (0.026 –0.039 mm in diameter) are present in growth bands in ventral part, 4 in mid−ventral part and 5–6 (0.065 –0.091 mm in diameter) in median part of the carapace.

Remarks.— Laxitextella laxitexta is similar in ornamentation pattern to Laxitextella sp. sensu Seegis (1997) from the Lehrberg Beds of southern Germany.

The described species is also similar in surface ornament pattern to Loxomegaglypta wetlugiana Novojilov, 1958 from the Early Triassic of the Volga region (see Novojilov 1960: fig. 504) but differs from the latter in having the umbo situated close to the anterior end of the dorsal margin. Laxitextella laxitexta laxitexta illustrated by Reible (1962: pl. 8: 5, 6) probably represents Howellisaura fimbriata ( Warth, 1969) . Estheria minuta illustrated by Roemer (1870: pl.15: 10) from the Late Triassic of the Upper Silesia (Hellewalder Estherien−Schichten), probably belongs to a new species, closely related to the Laxitextella laxitexta .

Occurrence.—Gipskeuper of South Germany;?Late Triassic of England; late Carnian, Krasiejów, Poland.

Figures

Fig. 5. A. Laxitextella laxitexta (Jones, 1890). Left valve ZPAL Cr. 6/2 in oblique dorsal view (A1), and details of shell structure showing layers of cuticle (A2–A4). B. Menucoestheria? sp. Right valve ZPAL Cr. 6/3 with details showing layers of cuticle in mid−dorsal area. C, D. Menucoestheria bocki sp. nov. C. Specimen ZPAL Cr. 6/28, showing growth bands ornamentation (C1), and details of shell structure showing layers of cuticle in median area (C2). D. Specimen ZPAL Cr. 6/15, showing growth band reticulate ornamentation in mid−dorsal part (D1), and details of cuticle layers in mid−dorsal area (D2).

Fig. 7. Laxitextella laxitexta (Jones, 1890). A. Left valve ZPAL Cr. 6/2 in oblique lateral view (A1), in dorsal view (A2), the same with details of reticulate growth band ornamentation (A3, A4). B. Right valve ZPAL Cr. 6/4 in oblique ventral view (B1), in lateral view (B2), and the same with details of growth bands reticulate ornamentation (B3). C. Left valve ZPAL Cr. 6/52 in lateral view. D. Right valve ZPAL Cr. 6/50 in lateral view.