Much debate has ensued during the past decade on the positive and negative aspects of the three major approaches to biological classification: cladistics, evolutionary classification (=phy- letics), and phenetics. Most of the discussion has taken place between practitioners of cladistics and phenetics with claims being made for the supremacy of one or the other. Evolutionary classification has not been central to the discussion because of the lack of explicit approaches. Having such avenues would be useful to allow focus on the merits and deficiencies of evolutionary classification relative to phenetics and cladistics. Further, it would also allow for more informative comparisons of classifications being produced by the majority of practicing systematists. This paper presents several approaches toward explicit evolutionary classification, involving different combinations of cladistic, patristic, and phenetic information. Different kinds of phylograms and two-dimensional plots are suggested, all of which are explicitly derived. An example of these approaches is given from the genus Lagascea (Compositae).

Explicit Approaches for Evolutionary Classification

Cladistic methods are used to analyse phylogenetic relationships within the Phoronida. Eleven characters, which may be present in an apomorphic or derived condition, are as follows: ecological habit; shape of longitudinal muscle; number of giant nerve fibres; number of coelomic funnels of nephridia; number of nephridial branches; development of nephridial epithelium; type of lophophoral organs; collar fold; gonads; developmental patterns, and larva. Some of the other characters need further investigation to establish their phylogenetic usefulness. These 11 characters have been used for constructing a tree of phylogenetic interrelationships of phoronid species. Two sister-groups are recognized, one of boring species and the other of soft-sediment living species. Phoronis ovalis and P. muelleri are considered to be primitive in each group respectively, and the genus Phoronopsis as the most advanced among the sediment-dewellers.



Zusammenfassung

Vorscblag fur ein pbylogenetisches System der Pboronida (Lopbopborata)



Unter Heranziehung von 11 Merkmalen, die jeweils bezuglich ihrer Plesiomorphie oder Apomorphie bewertet werden, wird ein kladistisches System der Phoronida entworfen. Die herangezogenen Merkmale sind: Habitat (Weichbodenbewohner oder Besiedler harter Substrate), Ausbildung der Langsmuskulatur, Langsnerven in einfacher oder doppelter Ausbildung, Zahl der Nephrostome an den Metanephridien, Form des Nephridialkanals, Vorhandensein oder Fehlen des Nephridialepitheliums, Form der Lophophore, Ausbildung oder Fehlen einer Ringfalte unter dem Lophophor, Geschlechtsverhaltnisse (Gonochorismus oder Hermaphroditismus) und Entwicklun (Eier und Larven). Um weitere Merkmale fur eine phylogenetische Auswertung zu benutzen, bedarf es noch entsprechender Untersuchungen und Analysen. Nach den 11 ausgewerteten Merkmalen lassen sich die Phoroniden in zwei durck eine Anzahl von Apomorphien charakterisierte Schwestergruppen aufteilen. Die eine Gruppe umfast die Weichbodenbewohner, die andere die in harteren Substrat bohrenden Vertreter. Phoronis ovalis kann als der urspriinglichste Vertreter der einen, Phoronis muelleri als der ursprunglichste der anderen Gruppe gelten. Die Ganung Phoronopsis stellt die am meisten abgeleitete Gruppe der Phoronida dar.

Phylogenetic systematics in Phoronida (Lophophorata)

When constructing a tree according to Wagner's groundplan divergence analysis (Wiley, 1981), the single available value for plotting each taxon on the graph is the Divergence Index (DI), which just allows the investigator to place the taxon somewhere on a concentric semicircle that equals its DI (Fig. la). However, the position on the semicircle cannot be determined for actual taxa or for hypothetical common ancestors. Therefore, it is desirable for a second parameter to be introduced on the graph to avoid such subjectivity. In this paper, I develop a technique for representing on such a graph the number of characters that have been used in the analysis as this second parameter. This technique can be used in conjunction with any method of phylogenetic character analysis to construct a tree, showing in summary form more of the information in the data matrix.

Christian Charles Emig

Papers

A New Method for Representing Trees