REVIEW OF SCOLECODONTS ASSIGNED TO ARABELLITES, BASED ON HINDE'S (1879) TYPE MATERIAL

SCOLECODONTS ARE the mouth pieces of jaw-bearing polychaete annelid worms that occur in abundance as microfossils in the fossil record. Historical scolecodont collections (e.g., Hinde, 1879, 1880, 1882; Stauffer, 1933, 1939; Eller, 1934, 1936, 1940, 1942) are of crucial importance for the taxonomy of fossil polychaetes because they often include taxa with nomenclatural priority over more recently established ones. One significant problem, however, is that most publications dealing with these collections have rudimentary hand-drawings of the fossils that do not allow unambiguous identifications. In this study, all specimens assigned to Arabellites by Hinde (1879) have been re-examined and photographed. Over the years Arabellites has been used for a plethora of morphologically variable scolecodonts of uncertain taxonomic affinity, rendering its status questionable (e.g., KielanJaworowska, 1962, 1966; Kozur, 1970; Jansonius and Craig, 1971; Szaniawski and Wrona, 1973; Eriksson and Bergman, 2003). However, first-hand studies of the type material have allowed new discussions of this genus. Moreover, Glycerites Hinde, 1879, is briefly discussed as it proved to be intimately linked to Arabellites.

ARABELLITES AND THE NAME-BEARING TYPE

The genus Arabellites was established by Hinde (1879) in his paper on Paleozoic, predominantly Ordovician and Silurian, scolecodonts from Canada and Scotland. In the description, Hinde (1879, p. 377) noted that "I propose to include in this genus jaws of widely different form, which have a general resemblance to those of the existing genus Arabella Grube." The nomenclatural use of already existing generic names of extant polychaetes with the addition of the suffix -ites, for fossil ones, was not uncommon by Hinde and his contemporaries. It has, however, been criticized (e.g., Sylvester, 1959; Kielan-Jaworowska, 1966) because it causes confusion and implies phylogenetic relationships that do not necessarily exist. Moreover, the International Code of Zoological Nomenclature (IZCN) recommends that such name constructions be avoided (see Article 20). Nonetheless, in this particular case members of the genus Arabellites are in fact similar to, and possibly ancestral of, Arabella Grube, 1850.

Hinde ( 1879) subdivided the different morphotypes included in Arabellites into three categories: 1. jaws with a prominent, pointed anterior hook and smaller denticles on a wide base (i.e., the first maxillae or MI); 2. sickle-shaped jaws and allied forms (which could be the MII-MIV); and 3. subquadrate jaws with a straight, denticulated upper edge (which according to his figured specimens are equivalent to the basal plate). However, the 26 specimens Hinde (1879) assigned to different species of Arabellites not only comprise jaws of different positions in the apparatus but also belong to a wide range of higher taxa.

Similarly as with his other genera (Oenonites Hinde, 1879, Glycerites Hinde, 1879, and Staurocephalites Hinde, 1879) Hinde did not designate a type species for Arabellites (nor did he select any holotypes for his species). During the late 19th and first half of the 20th centuries, scolecodonts of various taxa were assigned to Arabellites (e.g., Foerste, 1888; Hinde, 1882; Eller, 1934, 1942; Zebera, 1935; Stauffer, 1933; Seidel, 1959) but no revisions of this taxon were made. As noted by Jansonius and Craig (1971, p. 264), Sylvester (1959, p. 40) selected a left MI described as A. hamatus Hinde, 1879, as lectotype (see below). Sylvester emended the genus concept and proposed that Arabellites should include only the MI and MIL

In 1962 Kielan-Jaworowska erected, among other genera, Atraktoprion, Kalloprion, and Skalenoprion based on more or less complete, articulated jaw apparatuses from erratic boulders of Ordovician and Silurian age, collected in Poland. She noted that various isolated jaws of these genera had been previously described under scolecodont-based genus names, including Arabellites (see also Edgar, 1984). Tasch and Stude (1965) made one of the most conspicuous revisions of fossil jawed polychaetes in which they lumped several higher taxonomic names (criticized by Kielan-Jaworowska, 1968) as junior synonyms to Eunicites Ehlers, 1868 (but see discussion of the status of that genus name by Jansonius and Craig, 1971). Tasch and Stude (1965, p. 649) argued that 'Arabellites species, regardless of shape variations, may all belong to the genus Eunicites'. One year later, however, Tasch and Stude (1966) assigned several Permian scolecodonts to species of Arabellites.

In 1967, Eller reviewed Hinde's (1879) scolecodonts from the Cincinnatian of Canada and argued that because Hinde's descriptions apparently were based on his drawings and not on the actual specimens, they were largely inaccurate (Eller, 1967a). Although it is true that the illustrations do not match the specimens particularly well (see below) I find it difficult to believe that Hinde based his descriptions entirely on the drawings, considering the lack of details in his sketches, compared to those provided in (some of) the descriptions. Nonetheless, Eller (1967a, p. 117-118) re-described TArabellites hamulus [sic] and synonymized it with A. cornutus, Hinde, 1879 (see also below). It is puzzling that Eller (1967a, p. 118) noted that 'species of Arabellites do not have a shank on the outer margin' and therefore questioned the genus affinity, as indicated by the question mark.