SYSTEMATICS AND PHYLOGENY OF THE SPIONIFORM POLYCHAETA
Blake, J. A.1 & Arnofsky, P. L.2
1ENSR, 89 Water Street, Woods Hole, Massachusetts, 02543 USA. 2Woods Hole Oceanographic Institution, Woods Hole, MA 02543 USA
A cladistic analysis of the genera of the spioniform Polychaeta using reproductive, larval, and adult morphology was conducted. Most of the genera of Spionidae, Apistobranchidae, Longosomatidae (=Heterospionidae), Poecilochaetidae, Trochochaetidae, and Uncispionidae were included, with the exception of Australospio, Lauberiellus, Orthoprionospio, Uncopherusa, and Xandaros. The Chaetopteridae and Magelonidae were excluded. A total of 52 characters were included in an initial analysis of 36 spioniform genera. Reproductive characters included features of the egg envelope, cortical alveoli, egg masses, egg capsules, brood pouches, sperm type, spermatophores, copulatory structures, and interparapodial pouches. Larval morphology included the peristomial umbrella, ciliated pit, larval eyes, gastrotrochs, nototrochs, and larval prostomial features. Adult characters focused on the diversity of branchiae, prostomium, and setae. Apistobranchus consistently behaved as a root and this genus along with a paraonid (Cirrophorus) and cirratulid (Aphelochaeta) were used as outgroups. The data matrix was edited in MacClade version 3.01 and analyzed with PAUP version 3.1.1. Results suggest that the Spionidae as currently defined, is paraphyletic. Two large clades are defined: (1) Spio, Microspio, Pygospio, and all the polydorid genera, traditionally assigned to the subfamily Spioninae and (2) a large clade comprised of several smaller clades. The "Spioninae" is monophyletic, however, the Polydora-complex may be paraphyletic. One smaller clade within (2) includes the genera: (A) Uncispio, Trochochaeta, Heterospio, and Poecilochaetus, which in this analysis, suggest that this clade is clearly derived from spionids having thickened and honeycombed egg envelopes. This suggests that the family status of Unicispionidae, Trochochaetidae, Longosomatidae, and Poecilochaetidae and the definition of the Spionidae as a whole needs to be reconsidered. Other smaller clades included in (2) are: (B) the entire Prionospio-complex including Streblospio, and (C) twelve remaining genera forming smaller clades. Within these smaller clades, relationships among genera follow traditional groupings. Pygospiopsis may represent an additional clade that separates basally and behaves as an outgoup.