Wladysagitta janvieri, Voichyshyn, 2006

Voichyshyn, Victor, 2006, New osteostracans from the Lower Devonian terrigenous deposits of Podolia, Ukraine, Acta Palaeontologica Polonica 51 (1), pp. 131-142 : 138-139

publication ID	https://doi.org/ 10.5281/zenodo.13643619
persistent identifier	https://treatment.plazi.org/id/780FDC4B-6D14-FFDF-FCD0-F6A9FB07FE12
treatment provided by	Felipe
scientific name	Wladysagitta janvieri
status	sp. nov.

Treatment

Wladysagitta janvieri sp. nov.

Figs. 7 View Fig , 8 View Fig , 9B–D View Fig .

1985 “ Cephalaspis ” cf. acutirostris ( Stensiö, 1932) ; Janvier 1985 b: 331, fig. 20A.

Derivation of the name: In honour of Dr. Philippe Janvier (Laboratoire de Paléontologie, Muséum National d’Histoire Naturelle, Paris).

Holotype: SMNH BP.102, fragmentary mould of the headshield from the dorsal side and its imprint ( Fig. 7A View Fig ).

Type lolcality: Ukraine, Podolia, Ustechko, left bank of Dniester ( Fig. 1C View Fig ).

Type horizon: Old Red Formation (Dniester Series, the lowest part of its Khmeleva Member).

Material.— Besides the holotype, a fragment of the headshield exposed in ventral view, SMNH BP.100 ( Fig. 7B View Fig ) .

Diagnosis.—A moderately large Wladysagitta species with asymmetrical pectoral sinuses and with narrowed anterior and posterior ends of lateral fields.

Description.—The headshield is narrow (L about 50 mm; S = 55–58 mm; Lrc about 60 mm). The rostral part of the shield is produced into a clearly outlined process (about 10 mm in length) with rather concave lateral sides and a rounded distal end ( Fig. 7A View Fig 3 View Fig , B 2 View Fig ). The lateral margins of the shield are moderately convex with an irregular curvature. The maximum width of the shield is either in the middle part of the cornual processes or at their tips. The cornual processes are relatively short, not very broad at their base, and conspicuously narrow in their distal half. They start to point caudally at the level of their middle part. The lateral margin of the cornual processes is straight or feebly convex, whereas its medial margin is slightly concave. The abdominal part is narrow (Si/S = 0.47). The pectoral sinuses are asymmetrical ( Fig. 7A View Fig 1 View Fig , A 2 View Fig ), their tips (anterior margin) lying closer to the body axis. The lateral fields are slightly broader in their posterior third, with sharpened posterior ends. The surface of the headshield is relatively evenly covered with oval to elongated, closely set tubercles, the length of which ranges from 0.3 mm in the preorbital region (0.3–0.5 mm on the interzonal part) to 0.6 mm along the medial margin of the proximal part of the cornual processes.

Comparison.—In contrast to Wladysagitta acutirostris ( Fig. 9A View Fig ), W. janvieri sp. nov. ( Figs. 8 View Fig , 9B–D View Fig ) has proximally broader and relatively longer cornual processes (Lrc/Lc of W. janvieri sp. nov. is 3.2–3.6 whereas it is 4.0 in W. acutirostris ), a narrower abdominal part of the shield, different shape and greater width of pectoral sinuses, larger overall size, and a possibly wider headshield ( Stensiö 1932 considered that the specimen of W. acutirostris was somewhat flattened and that it must have originally been higher and narrower). The two species are similar in their general contours of the headshield, in particular by the curvature of their lateral headshield margins. Nevertheless, the imperfectly preserved rostral part of W. acutirostris and, as a whole, the poor preservation of the material examined does not allow to resolve more precisely the relationship among them.

Remarks.—The two specimens of W. janvieri sp. nov. housed in SMNH originate from a taphonomic assemblage containing few well−preserved carapaces mainly of osteostracans ( Benneviaspis whitei Belles−Isles and Janvier, 1984 , Stensiopelta pustulata Janvier, 1985b , Pattenaspis rogalai ( Balabai, 1962) , and Zychaspis granulata Voichyshyn, 1998 ). Among heterostracans Zascinaspis heintzi ( Brotzen, 1936) and Weigeltaspis brotzeni Tarlo, 1964 are recorded for this assemblage. Since the sediment is fine−grained with an admixture of argillaceous fractions, the assemblage may have formed under quiet hydrodynamic conditions. The relatively good preservation of the carapaces seems to indicate that this assemblage is autochtonous ( Voichyshyn 1997).

One of the specimens ( Fig. 9D View Fig ) referred here to W. janvieri, BM(NH) P.20508 ( Janvier 1985 b: fig. 20A) from Horodnytsia, differs from the holotype by somewhat longer and thinner cornual processes of more or less caudal direction, whereas the cornual processes of the holotype are gently curved. Another specimen ( Figs. 7B View Fig , 9C View Fig ) from the same locality and layer as the holotype, is represented by a fragment of the shield exposed in ventral view, with preserved rostral and cornual processes. The contours and proportions of the cornual processes, lateral margins of the shield and rostral process in this specimen are practically the same as in the holotype, but its cornual processes seem to be somewhat more diverging, i.e., the maximum width of the shield is found at the tips of the cornual processes. Possibly, all these differences are either due to individual variation, or postmortem distortions of the shields .