Pionosyllis Malmgren, 1867 is revised based on a cladistic analysis of the 41 species considered herein as valid, two newly described species in this paper (Basidiosyllis victoriae and Opisthodonta russelli), 11 species from other genera actually belonging, or related to, Pionosyllis, and 13 syllid species from different subfamilies. The phylogenetic analysis is based on 55 characters; a strict consensus of 1200 equally parsimonious trees (length = 314 steps) was obtained. The clades containing species usually included within Pionosyllis are newly named within the frame of a new Linnean classification of the group (except for one, belonging to another subfamily). The diagnosis of Pionosyllis is emended, and five new genera are proposed: Synmerosyllis, Basidiosyllis, Westheidesyllis, Perkinsyllis and Brevicirrosyllis. Paraehlersia San Martín, 2003, proved to be closely related to Pionosyllis. Seven species are transferred to Opisthodonta Langerhans, 1879, here emended, and three transferred to Nudisyllis Knox & Cameron, 1970 (according to San Martín & Hutchings, 2006). Opisthodonta uraga (Imajima, 1966) comb. nov. and Perkinsyllis longisetosa comb. nov. are redescribed. Pionosyllis compacta Malmgren, 1867, P. stylifera Ehlers, 1913, P. gigantea Moore, 1908, P. enigmatica (Wesenberg-Lund, 1950), and Nudisyllis magnidens (Day, 1953) comb. nov., are redescribed. Pionosyllis marquesensis Monro, 1939 and P. procera Hartman, 1965 likely belong to the Syllinae, thus they are not treated in the taxonomic account.

We present a new phylogenetic analysis of 15 primate Plasmodium species based on 18S rDNA sequences including new sequences of Plasmodium coatneyi, P. fieldi, P. gonderi, P. hylobati and P. simium. The results are discussed in the context of the parasite host species and their geographical distribution. Contrary to other phylogenies constructed with this 18S rDNA molecule, we observed that the topology of phylogenetic trees was not affected either by the quality of the nucleotide matrices, or by the species present in the outgroup. This analysis showed the following. (1) The polyphyly of human Plasmodium is confirmed. (2) The monophyly of Plasmodium from Old World monkeys is confirmed by the new added sequences and P. gonderi, an African species, possibly could be at the root of this group. (3) The most parsimonious biogeographical hypothesis is that P. vivax originated in Asia; thus, its related species P. simium appears to be derived through a transfer from the human P. vivax to New World monkey species in South America. (4) Sampling efforts of non-human primate Plasmodium could permit improvement of the knowledge of primate Plasmodium phylogeny and also consideration of the risks of malaria emergence from monkey reservoirs.

A new genus and species of primitive echinozoan, Bromidechinus rimaporus, is described from the Upper Ordovician of Oklahoma, USA. This has a unique plate arrangement. There is a single perradial series of imperforate plates bounded on either side by a column of perforate ambulacral plates. A double column of interambulacral plates separates ambulacral zones. The sparse record of Ordovician echinozoans is reviewed and cladistic analysis suggests that Bromidechinus represents a lineage that diverged prior to the split between bothriocidarids and main-line echinoids. This leads to a revised interpretation of the earliest stages of morphological evolution of echinoids.

The fossil of a second primitive snake from Cretaceous marine sediments is identified and redescribed: Pachyophis woodwardi Nopcsa. This snake was similar to Pachyrhachis in having pachyostotic vertebrae, a slender neck and a small head. However, Pachyophis differed from Pachyrhachis in being even more aquatically adapted: the mid-dorsal vertebrae and ribs are more swollen (pachyostotic), the body was more laterally compressed, and the dentary contains more teeth. The hindlimb (well developed in Pachyrhachis) cannot be confirmed as present or absent in Pachyophis. A cladistic analysis demonstrates that Pachyophis and Pachyrhachis form a clade. This grouping, here termed the Pachyophiidae, forms the most basal group of snakes so far known and is the sister group to all other well-known snakes.

Two African genera of the Gesneriaceae, Saintpaulia and Streptocarpus, are similar in many respects. Both genera have blue to purple flowers, pollen of similar shape and exine sculpting, embryos with one-celled, uninucleate chalazal haustoria, shared vegetative structures among some species, and are among the few genera in the Gesneriaceae which include species with chromosome counts of n = 15. The similarity of these features has indicated that the two genera are likely to be closely related.

Resemblance between animal taxa may be due to convergence rather than to recent common ancestry. Constraints on biological materials and adaptation to particular habits or habitats will produce widespread convergence. How may we distinguish the two causes of resemblance? The relationship between convergence and taxonomy is discussed, demonstrating that the choice of taxonomic method will itself determine the extent to which convergence is perceived. In particular, cladistic analysis based on parsimony will tend to minimise and thus conceal convergence: neither the resulting cladogram nor a consistency index derived from it can be used to assess the prevalence of convergence. With any taxonomic system, there can be no substitute for evaluation of the morphological characters used. Complementary use of molecular characters shows promise: we wait further understanding of constraints in genetic evolution and of the possibilities of convergence at this level also.

These general principles are illustrated with a range of examples from within and between invertebrate phyla: the phylogeny of Cnidaria and Platyhelminthes cannot be traced with certainty, but where the fossil record allows clear rooting, as for the echinoderms and in particular the echinoids, combination of morphological and molecular methods has made much progress. Sub-groups within a phylum, for example opisthobranch molluscs and the dipteran Phoridae, may show an uncontested phylogeny, and here studies have precisely identified convergence and shown that it may be the commoner cause of resemblance. Adaptation to exacting environments shown by terrestial and freshwater nemertines may also result in a predominance of convergent resemblance.

Traditional grouping of phyla breaks down on re-examination of supposedly key characters, such as segmentation, body cavities, germ layers and symmetry, each of which must have had multiple origins: nor are developmental stages (especially not larvae) a reliable guide to relationships. Demarcation of phyla may be difficult, as with arthropods, and location of phyla is even more difficult, due to their early and rapid radiation. Over-simplified definition of characters has bedevilled invertebrate classification and the use of molecular data has not yet resolved the major controversies.

The question ‘How common is convergence?’ remains unanswered and may be unanswerable. Our examples indicate that even the minimum detectable levels of convergence are often high, and we conclude that at all levels convergence has been greatly underestimated.

The subfamily Koneprusiinae is revised as part of a larger study of the Odontopleuridae, and Laethoprusia gen. nov. is described. The type species L. salax sp. nov. is from the Wenlock of Gotland, Sweden, and the genus is known also from the Wenlock of the Montagne Noire in south France, and from the Lower Devonian of Australia. The type species is most unusual among trilobites in possessing large fenestrae perforating the exoskeleton on segmental boundaries from the cephalic posterior margin to within the pygidium. The fenestrae were probably covered with soft tissues. Their function is enigmatic. Laethoprusia gen. nov. is the sister taxon to Isoprusia and/or Koneprusia. These genera are revised, and a review of all species assigned to them is given. A cladistic analysis of the best known taxa of Laethoprusia, Isoprusia, and Koneprusia is presented. Laethoprusia is the most derived genus of the subfamily, although stratigraphically it is the earliest.