Hallocinetus? arvernus (Piton, 1940) Spasojevic & Broad & Klopfstein, 2022

Spasojevic, Tamara, Broad, Gavin R. & Klopfstein, Seraina, 2022, Revision of 18 ichneumonid fossil species (Hymenoptera, Ichneumonidae) highlights the need for open nomenclature in palaeontology, Fossil Record 25 (1), pp. 187-212 : 187

Hallocinetus? arvernus (Piton, 1940) comb. nov.

Fig. 2

* Phaenolobus arvernus Piton, 1940

Material.

Holotype (part only, MNHN.F. A57301 ) examined at MNHN.F.

Stratum.

Menat Formation, Puy-de-Dôme, France. Late Palaeocene (Thanetian), 58.7-55.8 Ma.

Description.

Sex unknown. Holotype in lateral view, rather poorly preserved, with head, outline of mesosoma and partial metasoma, partial fore wing and outline of hind legs. Body length ~10 mm.

Dark brown including wing venation, legs and posterior part of metasoma lighter brown or reddish.

Head rather large and high, compound eye about 0.7-0.8 × head height in lateral view. Antennae incomplete, scape rather short. Mesosoma rather short, without any details preserved. Fore wing 7.2 mm; areolet obliquely quadrate and strongly petiolate, 2 + 3M longer than 4M; 1cu-a meeting M + Cu nearly opposite of 1M & 1Rs; 3Cu a bit longer than 2cu-a; cell 2R1 3.2 × longer than wide; 2m-cu without bullae in posterior half, potentially with one or two bullae in anterior half. Hind legs rather stout; femur 3.5 ×, tibia 5.2 × longer than wide; hind tarsi with first segment much longer than second and third, which are about as long as wide. Metasoma with T1 elongate, probably with a dorso-lateral carina; sternites rather well sclerotized; tip not well preserved.

Interpretation.

This is a rather poorly preserved fossil, from which not many characters can be discerned. Comparing the holotype and its high-resolution photograph with the drawing in the original description (p. 228, fig. 94, Piton 1940), we found that the latter shows a considerable amount of artistic freedom. The antennae are drawn as very short and apically expanded, while they are incomplete and parallel-sided in the fossil. The head shows a beak-like structure not discernible clearly in the fossil and unknown in extant representatives of the subfamily, and the small eyes appear around 0.5 × as long as the head length in profile, compared to 0.7-0.8 × in the fossil. The areolet is depicted as being open, while we found it to be closed and strongly petiolate in the fossil. The tarsi of the fore and hind legs appear complete with claws present in the drawing, while at most the first tarsal segments are visible in the fossil. The femora of all legs are much thinner in the drawing than in the fossil, and the drawing of the posterior half of the fore wing, which largely overlaps the metasoma, contains veins not found in any ichneumonid wasp. Piton also drew the elongate-triangular hypopygium typical for the subfamily Acaenitinae ; we are more cautious, noting that the apical part of the metasoma is too poorly preserved to draw conclusions about the shape of the hypopygium. Additional characters that could help subfamily placement, such as the shape of T1 and position of its spiracle, the propodeal carination and length of the ovipositor are indiscernible. The general habitus of the fossil, especially the shape of the metasoma in profile and stout legs, does resemble Acaenitinae , but in a rather vague fashion. Other characters are somewhat at odds with this placement, although not completely so. For instance, most Acaenitinae have 2m-cu with two bullae, one in the anterior and one in the posterior half, which would disagree with the fossil; however, some genera in former Acaenitini , such as Hieroceryx Tosquinet, 1896 and Prosacron Townes, 1971, have both bullae in the anterior half and separated by a very short tubular part of the vein. Moreover, Phaenolobus and Phorotrophus Saussure, 1892 can in fact have a single bulla, in the former located in the dorsal half of 2m-cu. However, all former Acaenitini have an open areolet, while a closed and petiolate areolet occurs only in the former tribe Coleocentrini , which has turned out paraphyletic with respect to the former Acaenitini ( Wahl and Gauld 1998; Quicke et al. 2009; Klopfstein et al. 2019; Spasojevic et al. 2021). The characters for generic placement within the former Coleocentrini , such as the shape of the clypeus, size and shape of the hypopygium and modifications on tarsal claws ( Townes 1971) are not visible in the fossil. Since we also have no character evidence for placing the fossil in a different subfamily, we tentatively place it in Hallocinetus Viktorov, 1962, to which it superficially resembles in the shape of the anterior margin of the mesoscutum and stout and large hind legs. However, we acknowledge the uncertainty in its placement by placing a question mark after the genus and subfamily names.

Cremastinae Förster, 1869

Dimophora ? Förster, 1869

Figures

Figure 2. Hallocinetus? arvernus (Piton, 1940) comb. nov. A. Photograph of the holotype obtained from MNHN. F; B. Our interpretative drawing of the fossil. Thicker lines indicate outlines of body structures, thinner lines show characters inside these outlines, and dotted lines represent uncertain interpretations.