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Phylogenetic Relationships of the Triclads (Platyhelminthes, Seriata

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Phylogenetic Relationships of the Triclads (Platyhelminthes, Seriata Bijdragen tot de Dierkunde, 59 (1) 3-25 (1989) SPB Academic Publishing bv, The Hague Phylogenetic relationships of the triclads (Platyhelminthes, Seriata, Tricladida) Ronald Sluys Institute of Taxonomic Zoology, University of Amsterdam, P.O. Box 4766, 1009 AT Amsterdam, The Netherlands Keywords: Plathyhelminthes, Tricladida, phylogeny la Abstract da; parmi ceux-ci, un développementembryonnaire unique et présence d’une zonemarginale adhésive. 4. On considère les Maricola comme group-frère plus primitif 1. A phylogenetic hypothesis for the triclads is presented and de la paire de taxa Terricola + Paludicola, et les Paludicola the characters on which it is based are discussed. le le dérivé des Tricladida. Sont comme représentant groupe plus formed the Bothrio- 2. The sister group of the Tricladida is by discutés les caractères venant à l’appui de ces hypothèses (Fig. planida, and together the two taxa share a sistergroup relation- 1, caractères 14—16 et respectivement 20—22). ship with the Proseriata. 5. Au sein des Paludicola, les Planariidae et les Dendrocoelii- 3. The monophyletic status of the suborder Tricladida is sup- dae représentent ensemble le groupe-frère des Dugesiidae (Fig. ported by several derived features (Fig. 1., characters 9—12), in- 1, caractère 24). cluding a uniqueembryological developmentand the presence of 6. A l’appui du statut monophylétique des Maricola et des a marginal adhesive zone. Terricola on mentionne un caractère, et respectivement trois 4. It is postulated that the Maricola is the primitive sister caractères apomorphes (Fig. 1, caractère 13, et respectivement the that group of the Terricola and Paludicola together and the 17—19). advanced within the Tri- Paludicola represents the most group 7. Sont discutés les cas contradictoires ou insuffisamment cladida. Characters supporting these hypotheses are discussed clairs de distributions de caractères; ceci permet d’aboutir à (Fig. 1, characters 14-16, and 20-22, respectively). l’arbre phylogénétique le mieux en accord avec les données 5. Within the Paludicola the Planariidae and the Dendrocoeli- prises en considération. the the dae together are sister group of Dugesiidae (Fig. 1, character 24). 6. The monophyletic status of the Maricola and the Terricola is supported by one and three apomorphic characters, respec- I. Introduction tively (Fig. 1, characters 13, and 17—19). 7. Cases of conflicting or not sufficiently resolved character At present, phylogenetic research on the flatworms distributions are discussed and are evaluated in order to arrive (Platyhelminthes) is in a state of flux. This is wit- at a phylogenetic tree providing the best fit to the data set con- nessed studies with the sidered. by dealing relationships among the orders within the Platyhelminthes (cf. Ehlers, 1985) and by studies which tackle sub- of the such for Ball Résumé groups phylum, as, example, (1974a) on the Dugesiidae, Tajika (1982a) on the Coelogynoporidae, and Brooks et al. (1985a, b) on 1. On présente une hypothèse phylogénétique pour les tri- the clades, et on discute les caractères sur lequels celle-ci est fondée. parasitic flatworms. 2. Le groupe-frère de Tricladida et celui des Bothrioplanida; The present paper deals with the phylogenetic ces deux taxa ensemble ont comme groupe-frère les Proseriata. relationships of the triclads or planarians, repre- 3. Plusieurs caractères dérivés (Fig. 1, caractères 9—12) vien- senting a group of flatworms which has been sub- nent à l’appui du statut monophylétique du sous-ordre Tricladi- a wide of jected to range studies, involving mor- Downloaded from Brill.com10/10/2021 06:38:47AM via free access 4 R. Sluys - Phylogenetie relationships of the triclads Fig. 1. Phylogenetic hypothesis for the Tricladida. Numbers refer to postulated derived characters: 1, serial arrangement of testes and vitellaria; 2, backwards directed tubiform and plicate pharynx; 3, elongate body shape; 4, loss of lamellated rhabdites; 5, tricladoid intestine;6, crossing-over of pharynx muscles; 7, parthenogeneticreproduction; 8, four pairs of longitudinalnerve cords; 9, embryolo- cerebral female serial of adhesive Haftpapillen gy; 10, position gonads; 11, arrangement many nephridiopores; 12, marginal zone; 13, in annular zone; 14, loss of Haftpapillen; 15, resorptive vesicles; 16, reduction number of longitudinalnerve cords; 17, creeping sole; 18, pharynx musculature; 19, diploneurannervoussystem; 20, four subepidermalmuscle layers; 21, spermatophore; 22, probursal con- dendrocoelid anterior adhesive dition; 23, dugesiideye; 24, common oviduct opening into atrium; 25, pharyngealmusculature; 26, organ (for further explanation, see text). in the phology, physiology, karyology, ecology and re- perienced difficulties analyzing phylogeny generation. The Tricladida, which is best consi- and historical biogeography of the freshwater dered a suborder according to Ehlers' (1985) planarians of the family Dugesiidae because of the scheme, subsumes three subgroups or infraorders, lack of a well-substantiated hypothesis on the af- viz. thePaludicola, Terricola, and Maricola. To the finities between the Maricola, Terricola, and Palu- Paludicola belong the well-known freshwater tri- dicola. clads, whereas the Terricola and Maricolarepresent In this paper I review the phylogenetic status of the land- and marine Al- planarians, respectively. the Tricladida and put forward an hypothesis on though in the majority of cases there is no prob- the phylogenetic relationships between the three in- in whether triclad fraorders. The aim of this lem recognizing a particular study is to present a belongs to the Paludicola, Terricola, or Maricola, phylogenetic tree based on the strongest possible these infraorders always have been poorly defined evidence available at present and to discuss the from a phylogenetic point of view. Further research characters involved. This will enable, and hopefully the has been the fact on planarians hampered by stimulate, workers in this field to test a specific the between the that phylogenetic relationships hypothesis against future investigations. In a study three infraorders at such this were virtually unknown, or as one, hypothesized apomorphic or least highly problematical, as has been pointed out plesiomorphic characters are always based on only Ball For by (1981). example, Ball (1974a) ex- a sample of all the taxa involved, and it is only Downloaded from Brill.com10/10/2021 06:38:47AM via free access - 5 Bijdragen tot de Dierkunde, 59 (1) 1989 effort that be able check to assess more the relation- through a joint we may to came possible precisely of features between these Ax and whether the derived or primitive status ship taxa. (1961) Karling first workers conclude that the applies to all species and species groups for which (1974) were the to hold triclads the sister of the Proseria- they are supposed to true. represented group the Seri- ta, both groups constituting monophylum ata. According to Karling (1974) autapomorphic II. Material and methods characters for the Seriata are (a) the serial, longitu- vitellaria fol- dinal arrangement of testes and (yolk directedtubiformand The characters used were selected by a combination licles), (b) the posteriorly pli- of literature search and specimen examination. cate pharynx, and (c) the elongate body shape (Fig. which infor- characters There are only a few publications give 1, 1, 2, 3). of characters relevant the of the various mation on possible suites to Recently, phyletic status of taxa within the Seriata has been re- various aspects of the phylogenetic relationships proseriate concluded the Tricladida, viz. Steinbock (1925), Meixner examined by Sopott-Ehlers (1985). She that of the viz. the Bothrio- (1928), Kenk (1930), Karling (1974), Ball (1981), one proseriate taxa, with the and Sopott-Ehlers (1985). Other information was planida, shares a sistergroup relationship instead of related the obtained from primary literature sources. Tricladida being closely to I have been able to examine the majority of the other members of the Proseriata. According to species of marinetriclads but from theother two in- Sopott-Ehlers all proseriate taxa, excepting the characterized ab- fraorders 1 studied only various representatives. Bothrioplanida, are by secondary rhabditesof the lamellated which fea- The species of freshwater and land planarians sence of type, is considered be for the which were studied by specimen examination will ture to an autapomorphy Bothrio- be mentionedin the relevant sections discussing the taxon Proseriata(Fig. 1, character 4). The Proseriata because distribution of particular character states. planida does not belong to the the characteristics of The methodology applied in the present study the former lacks apomorphic Proseriata and has neither the derived features concerns the phylogenetic technique developed by the Hennig (1966). The theory and practical applica- of any of the proseriate subtaxa (Ehlers 1985: 172). tion of phylogenetic systematics have been amply The Bothrioplanida and the Tricladida, on the the tricladoid which discussed in recent literatureand it suffices to refer other hand, share (a) intestine and to the to Wiley (1981), Saether(1983), Hennig (1984), runs laterally pharynx (Sopott-Ehlers, 1985), Ax (1984). Relative degree of apomorphy and (b) the crossing-over of muscle layers at the tip of plesiomorphy of characters was determinedby out- the pharynx (Steinbock, 1925), and (c) the absence which has been of epidermal collar-receptors (Sopott-Ehlers, group
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