Higher level relationships of leeches (Annelida : Clitellata : Euhirudinea) based on morphology and gene sequences

The evolutionary patterns of divergence of seven euhirudinean families were investigated by cladistic analysis of 33 euhirudinean species. Oligochaete s, Acanthobdella peledina, and branchiobdellidans were included as outgroup taxa. Cladistic analysis employed 1.8 kb of nuclear 18S ribosomal DNA and 651 bp of mitochondrial cytochrome c oxidase subunit I in addition to morph ological data. The use of two molecular data sets, one nuclear gene and one mitochondrial gene, as well as morphological data combined historical info rmation evolving under a variety of different constraints and therefore was less susceptible to the biases that could confound the use of only one typ e of data. Results suggest that the nuclear 18S rDNA gene yields a meaningf ul historical signal for determining higher level relationships. The more r apidly evolving CO-I gene was informative for recent or local areas of the evolutionary hypothesis, such as within-family relationships. Analyses comb ining all data from the three character sets yielded one most-parsimonious tree. Most of the higher taxa in recent leech systematics were well corrobo rated in the resulting topology. However, these results suggested paraphyly of the order Rhynchobdellida, which contradicts the presence of a probosci s as a synapomorphy. The medicinal leech family Hirudinidae was polyphyleti c because Haemadipsidae and Haemopidae each have a hirudinid ancestor. In a ddition, all but one of the genera within the family Erpobdellidae must be either abandoned or renamed. Unusual findings included compelling evidence of historical plasticity in blood-feeding behavior, having been lost at lea st four times in the course of euhirudinean evolution. Biogeographic patter ns supported a New World origin for Arhynchobdellida. (C) 1999 Academic Pre ss.