Worms by number.

This paper investigates alternation patterns in length, shape and orientation of dorsal cirri (fleshy segmental appendages) of phyllodocidans, a large group of polychaete worms (Annelida). We document the alternation patterns in several families of Phyllodocida (Syllidae, Hesionidae, Sigalionidae, Polynoidae, Aphroditidae and Acoetidae) and identify the simple mathematical rule bases that describe the progression of these sequences. Two fundamentally different binary alternation patterns were found on the first four segments: 1011 for nereidiform families and 1010 for aphroditiform families. The alternation pattern in all aphroditiform families matches a simple one-dimensional cellular automaton and that for Syllidae (nereidiform) matches the Fibonacci string sequence. Hesionidae (nereidiform) showed the greatest variation in alternation patterns, but all corresponded to various known substitution rules. Comparison of binary patterns of the first 22 segments using a distance measure supports the current ideas on phylogeny within Phyllodocida. These results suggest that gene(s) involved in post-larval segmental growth employ a switching sequence that corresponds to simple mathematical substitution rules.

Least-inclusive taxonomic unit: a new taxonomic concept for biology.

Phylogenetic taxonomy has been introduced as a replacement for the Linnaean system. It differs from traditional nomenclature in defining taxon names with reference to phylogenetic trees and in not employing ranks for supraspecific taxa. However, 'species' are currently kept distinct. Within a system of phylogenetic taxonomy we believe that taxon names should refer to monophyletic groups only and that species should not be recognized as taxa. To distinguish the smallest identified taxa, we here introduce the least-inclusive taxonomic unit (LITU), which are differentiated from more inclusive taxa by initial lower-case letters. LITUs imply nothing absolute about inclusiveness, only that subdivisions are not presently recognized.