Stylogastropoda Frýda and Bandel, 1997

Jagt-Yazykova, Elena, Krawczyński, Wojciech & Rakociński, Michał, 2006, Molluscs from the Early Frasnian Goniatite Level at Kostomłoty in the Holy Cross Mountains, Poland, Acta Palaeontologica Polonica 51 (4), pp. 707-718 : 714-715

Order Stylogastropoda Frýda and Bandel, 1997 Family Palaeozygopleuridae Horný, 1955 Genus Palaeozygopleura Horný, 1955

Type species: Zygopleura alinae Perner, 1907 ( Perner 1907: 352, pl. 110: 5, 6), Early Devonian, Czech Republic.

Palaeozygopleura (Bohemozyga) pyritica sp. nov. Fig. 5F–J .

Holotype: GIUS 4−2284 Kos−14 ( Fig. 5H ).

Type horizon: Goniatite Level in the uppermost Szydłówek Beds; Palmatolepis transitans conodont Zone, Early Frasnian.

Type locality: Active quarry Kostomłoty II (Małe Górki).

Derivation of the name: Alluding to the shells’ preservation in pyrite.

Diagnosis.—Ornamentation consists of strong collabral ribs, which clearly differentiate this species from the similar Palaeozygopleura (Bohemozyga) kettneri Horný, 1955 , which has more delicate, and more closely spaced, collabral furrows. P. (Bohemozyga) pyritica sp. nov. also differs by the more convex shape of the whorls and deeper sutures.

Material.—Five pyritised fragments of shells with well−preserved ornamentation ( GIUS 4−2284–2287 Kos−14–17).

Description.—Shell is turriculate (to 15 mm in length), dextral, with evolute whorls, which have clearly convex profile. Sutures are moderately deep. Aperture elongate oval. External and internal lips are not preserved. Ornamentation consists of comparably strong collabral ribs, which are orthocline near the upper suture and then continue to strongly opisthocline ribs to the rounded base where they turn into a prosocline course. Collabral ribs are rounded on the external side of the shell, have a small trench on the internal side, and number 30–32 per whorl. Protoconch not preserved. Axial angle is 20–23°.

Discussion.— Frýda and Bandel (1997) erected a new subgenus for palaeozygopleurids with characteristic ornamentation consisting of strongly opisthocline collabral ribs, reflecting the shape of the internal lip. In contrast to shells of Katoptychia Perner, 1907 , with a similarly strong opisthocline external lip, Palaeozygopleura (Bohemozyga) is characterised by the appearance of ornamentation already at the earliest stages of ontogeny in teleoconchs, a more convex profile of the whorls, and a smaller−sized protoconch (see Horný 1955; Frýda and Bandel 1997).

Occurrence.— At the type locality, Kostomłoty II quarry ( Małe Górki ) and also from the Early Frasnian Kadzielnia limestones from Jaźwica (set J; see Krawczyński 2006) near Kielce (Holy Cross Mountains, Poland) .

Figures

Fig. 5. Gastropods from the Early Frasnian Goniatite Level (uppermost Szydłówek Beds) at Kostomłoty, Holy Cross Mountains, Poland. A–C. Lahnospira taeniata (Sandberger, 1842). A. GIUS 4−2282 Kos−12 in apertural view. B, C. GIUS 4−2276 Kos−6 (B) and GIUS 4−2277 Kos−7 (C) in lateral views. D. Subulitidae indet., GIUS 4−2289 Kos−19, in apertural (D1) and lateral (D2) views, with protoconch visible. E, K. Naticopsis aff. N. kayseri Holzapfel, 1895. E. GIUS 4−1164 Kos−2 in pertural (E1), lateral (E2), and apical (E3) views and cycloneritid−type protoconch (E4). K. GIUS 4−2288 Kos−18 in apertural (K1) and lateral (K2) views. F–J. Palaeozygopleura (Bohemozyga) pyritica sp. nov. H. GIUS 4−2284 Kos−14 in apertural (H1) and lateral (H2) views of holotype. F, G, I. GIUS 4−2287 Kos−17 (F). GIUS 4−2285 Kos−15/1 (G), and GIUS 4−2286 Kos−16 (I), lateral views with opisthoclinal ornamentation visible. J. GIUS 4−2285 Kos−15/1, apertural view of shell fragment.