Four terebellines (Polychaeta, Terebellidae) with problematic taxonomic histories

Four taxa of terebellines with problematic taxonomic histories are redescribed. One is a new species that has been mis-identified for the last 37 years and one is allocated to a different genus from that to which it was previously assigned. Pista corrientis McIntosh, 1885 was described from Argentina and has been reported from several localities along the Brazilian coast. Examination of the holotype of P. corrientis revealed that the Brazilian specimens belong to a separate species, herein described as P. nonatoi sp. nov., and a redescription of the holotype of P. corrientis is provided. Pista sombreriana (McIntosh, 1885) was considered indeterminable due to the poor condition of the holotype. Our examination of the holotype showed that although it is poorly preserved most taxonomic characters are visible. The morphology of the lobes on anterior segments, especially those of segments 3-4, is closer to Lanicides than to Pista but considering that Lanicides is also poorly defined we redescribe P. sombreriana under its original designation. Finally, Eupolymnia turgidula (Ehlers, 1887) has been considered as a junior synonym of E. crassicornis (Schmarda, 1861) but a recent study resurrected it as a valid species of Terebella, which was the original generic designation. According to our examination of the holotype, E. turgidula does belong to Eupolymnia, but it is uncertain as to whether it is a valid species or a synonym of either E. crassicornis or E. magnifica (Webster, 1884).

The competing roles of extensional viscosity and normal stress differences in complex flows of elastic liquids

In various attempts to relate the behaviour of highly-elastic liquids in complex flows to their rheometrical behaviour, obvious candidates for study have been the variation of shear viscosity with shear rate, the two normal stress differences N(1) and N(2) especially N(1), and the extensional viscosity eta(E). In this paper, we shall be mainly interested in `constant-viscosity` Boger fluids, and, accordingly, we shall limit attention to N(1) and eta(E). We shall concentrate on two important flows - axisymmetric contraction flow and ""splashing"" (particularly that which arises when a liquid drop falls onto the free Surface of the same liquid). Modem numerical techniques are employed to provide the theoretical predictions. It is shown that the two obvious manifestations of viscoelastic rheometrical behaviour can sometimes be opposing influences in determining flow characteristics. Specifically, in an axisymmetric contraction flow, high eta(E) , can retard the flow, whereas high N(1) can have the opposite effect. In the splashing experiment, high eta(E) can certainly reduce the height of the so-called Worthington jet, thus confirming some early suggestions, but, again, other rheometrical influences can also have a role to play and the overall picture may not be as clear as it was once envisaged.