Hirudinea

Euhirudinea


Hirudo medicinalis

Leeches

Mark E. Siddall & E. M. Burreson * 



        ,____________________Acanthobdella peledina
        |
        |
________|
        |      ,_________Branchiobdellida
        |      |
        `______|
               |    ,_______________Glossiphoniidae 'RYNCHOBDELLIDA'  (proboscis-bearing)
               |    |
               `____|
                    |        ,_____________Piscicolidae 'RYNCHOBDELLIDA'  (proboscis-bearing)
                    `________|
                             |
                             `_______________ARHYNCHOBDELLIDA (jawed)

Based on: results of combined 18S rDNA, CO-I and morphology by Apakupakul et al. 1998

Table of Contents

Introduction
Discussion of Phylogenetic Relationships
Characteristics of the Group
Sources of Information on the Internet
References

Introduction

Leeches are oligochaetes which have adopted a carnivorous mode of nutrition in place of the detritus-feeding habits of their ancestors. They possess the general characteristics of clitellates in that they are hermaphroditic, have a cocoon-secreting clitellum, and exhibit somatic metamerism, though there are varying degrees of coelomic reduction. Synapomorphies delimiting the Euhirudinea are, in part, apparently related to feeding behaviour, such as the presence of an oral and a caudal sucker used both in locomotion and in feeding (either by grasping prey by the macrophagous leeches or for attachment to a host by the ectoparasitic species).

Although leeches are more commonly thought of in relation to the sanguivorous habits of some taxa, particularly those that form intimate relationships with humans in freshwater environments, euhirudinid taxa exploit a wide range of adaptive zones. In freshwater systems, macrophagous leeches that prey on invertebrates are more common, both in terms of number of species and absolute abundance, than are species that blood-feed (Sawyer, 1986). In marine systems, the reverse is true, in that most are ectoparasitic on elasmobranchs and perciformes.

Etymology: The word "leech" came into use early in the history of the English language and for most of its history has had two distinct meanings: the blood-sucking worm often used for medical purposes, and a physician. Use of the leech for medicinal purposes did, of course antedate its mention in Old English (the Anglo-Saxon) language: its first occurrence in such a context seems to be that found in a medical poem by Nicander of Colophon who died ca. 132 B.C. The close association of the leech and a physician was therefore early established and lasted well into the eighteenth century. It seems natural that the "leech" became a synonym for doctor early in the history of the word. Despite this synonomization, "leech" for worm and "leech" for physician are two different words, with two separate entries in etymological dictionaries. Briefly, the Old English "læce", meaning the worm, came into use sometime before 900 A.D., and was a cognate with Middle Dutch "lieke", leech. The other Old English word "læce", meaning physician, came from Germanic languages, including Old Frisian "letza", meaning physician, Old Saxon "laki", and Old High German "lakki". The joining or relating of the two different meanings seems to be an artificial development.

Discussion of Phylogenetic Relationships

Acanthobdella pelidina as sister-group. The notion that Acanthobdella pelidina is the sister taxon to the euhirudinids is well established. Livanow (1906) was the first to suggest this phylogenetic affinity, considering Acanthobdella pelidina as an ancient hirudinean (Livanow 1906, 1931). The presence of chaetae on anterior somites which aid in attachment to their fish hosts, a compelling functional precursor to the oral sucker of leeches, has been thought of as indicative of group-membership with the oligochaetes (Michaelson 1919). In constrast, the constant number of somites, caudal sucker, partial reduction of the coelom, and fusion of female gonopores has led most to include Acanthobdella pelidina in the Hirudinea (Selensky 1907, Wendrowsky 1928, Livanow 1931, Scriban and Autrum 1934, Autrum 1939, Mann 1962, Sawyer 1986). Debate has also surrounded the relationship of the Branchiobdellida including arguments for membership in the Hirudinida (Odier 1823, Sawyer 1986), in the Oligochaeta (Vejdowsky 1884, Michaelson 1919), or a separate status equivalent to the Euhirudinea and Oligochaeta (Holt 1953, Ferraguti and Gelder 1991, Brinkhurst and Gelder 1989).

Characteristics of the Euhirudinea

Synapomorphies for leeches are:

In so far as leeches are clitellates they are also characterized by:

Sources of Information on the Internet

References

About This Page

Mark E. Siddall & Gene M. Burreson
Email: mes@vims.edu or gene@vims.edu
Virginia Institute of Marine Science
School of Marine Science
College of William and Mary
Gloucester Point, Virginia 23062, USA

Page copyright © 1995 Mark E. Siddall
Last modified 30 April, 1996