Iowatrypa, Copper, 1973

Ma, Xue-Ping, Sun, Yuan-Lin, Hao, Wei-Cheng & Liao, Wei-Hua, 2002, Rugose corals and brachiopods across the Frasnian- Famennian boundary in central Hunan, South China, Acta Palaeontologica Polonica 47 (2), pp. 373-396 : 388-390

Iowatrypa ? shaodongensis sp. nov.

Figs. 11F–O , 12 .

Costatrypa sp. ; Ma 1998: 353–354, fig. 8B–F,?figs. 7, 8G–K.

Holotype: PUM 00004 , complete shell, illustrated in Fig. 11J–N .

Type locality: Daoshitang, Heyi village , Yangqiao Township , Shaodong County, central Hunan Province .

Type horizon: Upper Shetianqiao Formation at a horizon corresponding to basal part of bed 25 of the Shetianqiao Formation ( Hou and Wang 1988:132), latest Frasnian (probably Palmatolepis linguiformis Zone ).

Derivation of the name: a county name in central Hunan from where the specimens were collected.

Material.—Over 150 well preserved complete specimens of various growth stages.

Diagnosis.—Large sized Iowatrypa ? with long straight hinge line, tubular−imbricate ribs, conjunct deltidial plates, the presence of dental nucleus in stead of dental cavity, pedicle layer or collar, dorsal median septum, and 12 whirls of spiralium.

Description.—Adult shells generally ranging from 15 to 25 mm in width (largest shell over 25 mm), most shells wider than long, about equibiconvex; greatest width at hinge or slightly anteriorly or at midlength; surface marked by 50 to 70 tubular−imbricate ribs (more imbricate and less tubular ribs) of both bifurcation and implantation (chiefly by bifurcation on both valves); growth lamellae variously spaced, from 0.5 to 2 mm, generally 1 mm; anterior commissure uniplicate.

Ventral beak generally suberect to slightly incurved, but straight in young specimens; deltidial plates conjunct, minute foramen commonly infilled by pedicle structures.

Internally ventral valve with pedicle collar well−developed, partly fused to shell wall and dental nucleus, shell thickened posteriorly. Dorsal valve with knobbed cardinal process sitting on inner socket ridges and the median pit; ball−like crural bases developing anteriorly to feathered crura, disjunct jugum, 12 whorls of spiralium; with low and strong median septum.

Remarks.—This species has been reported as Costatrypa sp. from the Pa. linguiformis Zone of the Chongshanpu section of central Hunan ( Ma 1998), but differs from true Costatrypa Copper, 1973 in having conjunct deltidial plates ( Ma 1998: 354). Numerous new specimens from the Shetianqiao section show that this species is characterized by numerous well−developed fine more imbricate and less tubular ribs which suggests a generic assignment to Spinatrypina Rzhonsnitskaya, 1964 or Iowatrypa . However, the present species is different from species of Spinatrypina in lacking dental cavities. Therefore the species is tentatively assigned to Iowatrypa , but it is different from species of Iowatrypa Copper, 1973 in its larger size and having more numerous whorls of spiralium.

The new species is similar to Middle Devonian Atrypa douvillii Mansuy, 1912 from eastern Yunnan Province, which was later assigned into Spinatrypina by Chen (1983). The new species is different from S. douvillii by its larger size, wider and straighter hinge, more numerous plications (about 50 to 60 vs. about 44–48 for a similar−sized shell), and internally absence of dental cavities and more whorls (up to 12 vs. seven in S. douvillii ) of spiralium. It is distinct from Iowatrypa ? qidongensis Ma, 1998 by its larger size, coarser ribs, prominent ventral beak, and more whorls of spiralium. The present species is different from Iowatrypa timanica and I. nalivkini figured by Rzhonsnitskaya et al. (1998: fig. 21F–J) and Anatrypa timanica var. markovskii figured by Lyashenko (1959: pl. 26: 5–6) in its closely spaced and more imbricate lamellae. The new species is similar to? Waiotrypa pluvia figured by Godefroid and Helsen (1998: fig. 8A–M) in general shell form and some internal structures (presence of a pedicle collar, cardinal process etc.). However, the latter has dental cavities and thick deltidial plates, and lacks a dorsal median septum. It is distinct from I. rotundicollis of Godefroid (1994) by its large shell size, more densely spaced lamellae, more prominent beak, presence of a pedicle collar, and more whorls of spiralium.

Occurrence.—Central Hunan Province, in the Shetianqiao and Chongshanpu sections; late Frasnian.

Figures

Fig. 11. A–E. Spinatrypa subkwangsiensis (Tien, 1938), sample S−Y−4. A–C. Posterior, ventral and lateral views of PUM 00016; × 2. D, E. Dorsal and posterior views of PUM 00020; × 2. F–O. Iowatrypa? shaodongensis sp. nov., S−Y−4.F–I. Posterior, dorsal, lateral, and ventral views of paratype PUM 00003; × 2. J–N. Posterior, lateral, dorsal, anterior and ventral views of holotype PUM 00004; × 2. O. Ventral view of paratype PUM 00001, × 1.5. P, Q. Iowatrypa? qidongensis Ma, 1998, sample S−Y−4, posterior and ventral views of PUM 00008; × 1.5.

Fig. 12. Transverse serial sections of Iowatrypa? shaodongensis sp. nov. from the Shetianqiao section (sample S−Y−4). Numbers refer to distance in mm from the ventral apex. A. Specimen PUM 00069 (specimen of acetate peel – 00A). B. Transverse section showing the spiralium at its maximum number at a distance of 9.8 mm from the ventral apex. Specimen PUM 00070 (00B).