Atryparia (Costatrypa), 1973

Baliński, Andrzej, 2006, Brachiopods and their response to the Early-Middle Frasnian biogeochemical perturbations on the South Polish carbonate shelf, Acta Palaeontologica Polonica 51 (4), pp. 647-678 : 668

Atryparia (Costatrypa) sp.

Figs. 17 , 18B .

Material.—Five complete, 10 slightly damaged, and 16 fragmentary shells from Wietrznia Id−W (beds 4 and 14) and Ie (beds 44–45) sections. In addition, two specimens were recovered from loose blocks found between Id−W and Ie sections. Majority of available specimens represent neanic stage.

Description.—Shell medium sized, dorsibiconvex to planoconvex, usually shield shaped, with long, recti−linear hinge margin and rounded hinge corners, slightly wider than long to subequal, widest near hinge; anterior commissure weakly to rarely strongly uniplicate.

Ventral valve gently convex to almost flat, flanks concave; beak strongly incurved, adpressed; presence of pedicle foramen not clear due to damaged apical region of the beak; sulcus weak but in some large specimens producing long and narrow tongue. Dorsal valve more convex to inflated; fold usually weak, observed near the anterior commissure only.

Ribs rather low, 5–9 per 5 mm, sometimes variable in thickness along shell length, thinner near commissure; growth lamellae spaced at 1–3.5 mm, more crowded anteriorly.

Interior of the ventral valve with strong, massive teeth; dental lamellae lacking; thick pedicle callist. Inside the dorsal valve distinct, comblike cardinal process lining inner socket ridges and cardinal pit ( Fig. 17 ); brachial apparatus not preserved in sectioned specimen.

Remarks.—General shell form, its ornamentation and details of the internal structure suggest that described specimens belong to Atryparia (Costatrypa) Copper, 1973 . However, the studied collection, in which neanic specimens predominate, seems to be not sufficient for specific determination. They show general similarity to several species from the early part of the Frasnian of Western Europe and North America. It seems that they are closest to the highly variable externally A. (Costatrypa) variabilis ( Godefroid, 1970) from de Neuville Formation, Belgium ( Godefroid 1970, 1998). Some large specimens from Wietrznia are almost identical morphologically to Atryparia rubra Cooper and Dutro, 1982 from the Oñate Formation of New Mexico ( Cooper and Dutro 1982).

Occurrence.—This is uncommon species in lower part of the set C in Wietrznia Id−W and Ie sections representing Palmatolepis transitans conodont Zone (Figs. 2, 3).

Figures

Fig. 17. Serial sections of the shell of Atryparia (Costatrypa) sp., GIUS 4−273 Wt/EB−5, middle Wietrznia Beds of Wietrznia Id−W. Numbers refer to distance in mm from ventral umbo.

Fig. 18. Athyridid and atrypid brachiopods from the Frasnian of Wietrznia and Dębnik. A. Biernatella lentiformis Baliński, 1995, ZPAL Bp 60/5, complete shell from the middle Wietrznia Beds of Wietrznia Ie in dorsal (A1), ventral (A2), lateral (A3), posterior (A4), and anterior (A5) views. B. Atryparia (Costatrypa) sp., GIUS 4−273 Wt/IM−5, from the middle Wietrznia Beds of Wietrznia Id−W in dorsal (B1), ventral (B2), and lateral (B3) views. C, D. Spinatrypina (Exatrypa) cf. explanata (Schlotheim, 1820) GIUS 4−273 Wt/IM−10 (C) and GIUS 4−273 Wt/IM−13 (D) from the middle Wietrznia Beds of Wietrznia Id−W, in dorsal (C1, D1), ventral (C2, D2), and lateral (C3, D3) views. E, F. Spinatrypa semilukiana Ljaschenko, 1959 from the Nodular Limestone (Palmatolepis hassi Zone) of Dębnik. E. Shell ZPAL Bp 60/20 in dorsal (E1) and ventral (E2) views. F. Complete shell ZPAL Bp 60/8 in dorsal (F1), ventral (F2), lateral (F3), posterior (F4), and anterior (F5) views.