A comparison of phenetic and phylogenetic methods applied to the systematics of Oligochaeta

A comparative study of naidid subfamilies shows that a combination of ordination, Jaccard/Average Linkage cluster analysis and Wagner parsimony provides a useful basis for a rational phylogeny but that this does not differ markedly from the original proposed by Sperber nearly four decades ago. Hennig rules, modified by Wiley, permit a preliminary phylogeny and classification of the Annelida to be made by hand. An error in earlier versions suggested that the Dorydrilidae lacked prostate glands, and this is corrected.     

Did the lumbriculids provide the ancestors of the branchiobdellidans,acanthobdellidans and leeches?

Revision of the literature concerning Agriodrilus (Oligochaeta, Lumbriculidae) and Acanthobdella (Acanthobdellida), both supposedly intermediate links in the traditional single line of evolution between lumbriculids, branchiobdellidans, and leeches, supports the alternative hypothesis of an independent origin of most if not all of these groups. Discovery of Phagodrilus, a lumbriculid that is clearly convergent with Agriodrilus in terms of the pharynx, lends further support to this concept. No decision as to the rankings of the various taxa can be made until new material of Acanthobdella is examined and all variable characters are used to determine synapomorphic character states and monophyletic groupings within this complex.     

Hair today,gone tomorrow: induced chaetal changes in tubificid oligochaetes

Laboratory experiments were conducted to determine the extent of chaetal variation in the tubificids Tubifex tubifex and Ilyodrilus frantzi and the naidids Specaria fraseri and Nais communis under varying environmental conditions. Univariate exposures were carried out using different levels of pH, salinity, water hardness and mercury. We were not able to induce chaetal changes in the two naidids tested. However, we were able to reduce the hairs and pectinations of T. tubifex with exposure to pH, salinity and to hard water such that the bergi form was produced. Prolonged exposure to low or high pH resulted in the total loss of hairs and pectinates such that the blanchardi form was produced. We were able to eliminate the hairs and pectinates of I. frantzi (capillatus) in soft, freshwater exposures such that the bifidus form of I. frantzi was produced. Conversely, in hard or saline water we were able to induce formation of hairs and pectinates on the bifidus form such that the capillatus form was produced. These changes occurred at time intervals ranging from a few days to two months.     

Comments on the evolution of the Annelida

The structure of the male ducts and their relative positions are significant indicators of the fact that the Lumbriculidae do not represent the stem forms of the Oligochaeta, confirming the recently expressed opinion of Hrab (1983). However, the same arguments provide the basis for the separation of Dorydrilus in the family Dorydrilidae.     

Assimilation by Aquatic Oligochaeta

Aquatic oligochaetes selectively ingest material from sediments given as food. Determinations of the quantity of organic material presented, left in the residue, and voided as feces enabled estimation of assimilation. These figures were not significantly different from those obtained by summing growth as observed in the experiment with respiration determined independently. Short term experiments yield estimates of assimilation of 77 to 181 cals/g dry wt/day, long term experiments yield an estimate of 232 cals/g dry wt/day, both for mixed populations of Tubifex tubifex and Limnodrilus hoffmeisteri.     

The position of the Haplotaxidae in the evolution of oligochaete annelids

The Haplotaxidae have all the characteristics to support the hypothesis that they are the living descendents of the stem forms from which all of the Oligochaeta Clitellata (Orders Lumbriculida, Haplotaxida, Lumbricida, Tubificida) can be derived. The Aphanoneura are distinct from the Clitellata and are raised to a separate Class. There is no evidence to support the view that the elaborate setae of many Tubificida are derived from a polychaete ancestry; both are held to be independent modifications to aquatic life derived from a simple burrowing protoannelid with lumbricine setae.     

A taxonomic revision of the family Haplotaxidae (Oligochaeta)

The family Haplotaxidae is re-defined and the genera Pelodrilus, Heterochaetella and Adenodrilus are merged in the single genus Haplotaxis. Haplotaxis dubius and Haplotaxis ascaridoides are recognized as subspecies of Haplotaxis gordioides, and H. forbesi is regarded as synonymous with H. gordioides following a re-examination of the type material. The absence of the gizzard in H. smithii is reported for the first time, and the presence of both pairs of male pores in the same segment in H. violaceus is confirmed, the type material of both species having been examined. Pelodrilus monticola, P. tuberculatus and P. darlingensis are merged in Haplotaxis africanus (n. comb.), Pelodrilus aucklandicus is recognized as a synonym of H. hologynus hologynus (n. comb.), but P. bipapillatus is recognized as a subspecies of hologynus.