Wladysagitta, Voichyshyn, 2006

Voichyshyn, Victor, 2006, New osteostracans from the Lower Devonian terrigenous deposits of Podolia, Ukraine, Acta Palaeontologica Polonica 51 (1), pp. 131-142 : 136-138

Genus Wladysagitta gen. nov.

Type species: Wladysagitta janvieri gen. et sp. nov.

Derivation of the name: In honour of the late Dr. Władysław Zych (1899–1981), and from the Latin sagitta, arrow, referring to the arrow−shaped rostral margin of the headshield.

Diagnosis.—Osteostracans of small size. The length of the headshield (40–60 mm) is more or less the same or somewhat smaller than its width (L/S = 0.8–1.0). The anterior margin of the headshield formes the elongated to triangle−shaped rostral process. The lateral fields are long, somewhat broadened in their posterior third. Their rounded anterior ends are closely approaching the base of the rostral process, and their sharp posterior ends reach to the middle parts of the cornual processes. The cornual processes are relatively short and narrow. The ornamentation of the exoskeleton consists of tiny elongated tubercles.

Comparison.—According to the classification of the Osteostraci proposed by Afanassieva (1991), Wladysagitta gen. nov. differs from the genera referred to the Benneviaspidoidei by the shape of the headshield and the presence of tubercles on the exoskeleton (and from some superficially similar representatives of the Boreaspididae , in particular Dicranaspis , by having one, instead of two pairs of lateral fields, and by its considerably greater general size). It differs from the known genera of the Zenaspidida by the presence of a rostral process.

Taking into account the proportions of the shield, the relative size, shape and orientation of the cornual processes, and the extent of the lateral fields, Wladysagitta gen. nov. appears to be similar to several representatives of Pattenaspis that have a rostral lobe [most developed in P. eurhynchus ( Wängsjö, 1952) ], although this lobe does not extend into a rostrum. However, this general resemblance does not answer the question of the position of the species relative to the genus Pattenaspis , since this genus includes a wide diversity of forms, and is possibly not a clade (Afanassieva and Voichyshyn 1991), and may not even belong to the Cephalaspididae ( Janvier 1985b) . One of the features that throw doubts on this assignment may be present in species of Pattenaspis from Spitsbergen and Great Britain. These species possess an extensive exoskeletal ornamentation, usually consisting of thorn−like tubercles, contrary to the original descriptions by Wängsjö (1952) (Philippe Janvier, personal communication 1998). Typical cephalaspidids, such as Cephalaspis , Parameteoraspis , and Mimetaspis have practically no ornamentation, or their ornamentation consists of very small tubercles. Except for the rostral process, Wladysagitta gen. nov. differs from Pattenaspis by the shape of lateral fields that are slightly broadened in their posterior third, possibly, by the shape and smaller size of the tubercles of the exoskeletal ornamentation, and by lacking denticles on the inner margin of cornual processes.

In contrast, Wladysagitta gen. nov. resembles primitive zenaspidids, in particular the genus Zychaspis , by its exoskeletal ornamentation. It should be noted that Zychaspis is also characterized by having a slight rostral lobe ( Janvier 1985 b; Voichyshyn and Solodkyi 2004). In sum, and considering the available data, Wladysagitta gen. nov. may be regarded as morphologically intermediate between Pattenaspis and primitive zenaspidids.

Species included.— Besides the type species, W. acutirostris ( Stensiö, 1932) , from the Lower Devonian of Great Britain .

Occurence.—Lower Devonian of Podolia and Great Britain.