Orbiniella Day 1954

Genus Orbiniella Day, 1954

Type-species: Orbiniella minuta Day, 1954, by monotypy.

Synonym: Falklandiella Hartman, 1967. Fide Buzhinskaja 1992: 76. Type species: Falklandiella annulata Hartman, 1967, by monotypy.

Diagnosis. Body elongate, with separation between thorax and abdomen indistinct, anterior segments may be narrower than more posterior segments, but size changing gradually over several segments, or no change in appearance between anterior and posterior segments; prostomium broad or elongate with paired nuchal organs usually present, these sometimes pigmented, eyespots present or absent; peristomium with 1–2 asetigerous rings. Noto- and neuropodia poorly developed, consisting of low tori from which setae emerge; with only simple postsetal lamellae, or these entirely absent; posterior parapodia not elevated and shifted dorsally as in genera of the Orbiniinae. Capillary noto- and neurosetae always crenulated or weakly camerated with pointed bristles apparent at relatively low magnification (100x); prominent acicular spines present or absent in noto- and neuropodia, or entirely absent; furcate setae absent. Branchiae entirely absent.

Remarks. Species of Orbiniella are generally small and with a simple morphology, resulting in a taxonomy that is largely based on negative characters. In this respect, it is highly likely that several of the described species are in fact juveniles or post-larval stages of other species of Orbiniidae. This is, however, very difficult to demonstrate without a good growth sequence documenting morphological change. An examination of one of the SEM images of O. marionensis in Gillet (1999: Fig. 2 D) clearly shows that furcate setae are present in the last notopodium on the right side. This suggests that this species at least, is likely a juvenile of another orbiniid.

Table 2 provides a list of 13 species of Orbiniella and main morphology. Two other species do not belong in the genus: O. drakei is transferred to Leitoscoloplos (see above) and O. branchiata does not agree with the definition of the genus because it has branchiae, elongate postsetal lamellae, and may be a juvenile of another orbiniid (see below). Of the 13 species listed in Table 2, four occur in deep water and nine occur in shallow water.

The four deep-water species all have noto- and neuropodial acicular spines. Of these, O. hobsonae has crenulated acicular spines instead of smooth and O. petersenae is the only one to have four anal cirri. For the two remaining species, O. andeepia has short notopodial postsetal lamellae while O. aciculata has none.

Of the nine shallow-water species, both O. landrumae n. sp. and O. marionensis have furcate setae and with further assessment may not belong in Orbiniella at all. In addition, O. landrumae appears to have notopodial flail setae, another character not associated with Orbiniella and its generic assignment is thus provisional. For the remaining seven species, O. dayi has small noto- and neuropodial postsetal lobes that are absent in the other six species. The remaining six species all have noto- and neuropodial acicular spines or short emergent aciculae. Of these, O. spinosa n. sp. has unusual barbed or finely hirsute spines (see below). Apart from eyespots being are reported for O. nuda, O. plumisetosa, and O. annulata, and absent in O. minuta and O. uniformis, these remaining five species are similar in morphology and apart from overall body shape, prostomial shape, and the development of the two peristomial rings are separated with difficulty. The main taxonomic characters for species of Orbiniella are presented in Table 2. Five species, two new are treated below, with “ Orbiniella ” branchiata treated separately.