A Cladistic Reassessment

BULLETIN OF MARINE SCIENCE, 52(1): 516-540,1993 PLEURONECTIFORM RELATIONSHIPS: A CLADISTIC REASSESSMENT Franqois Chapleau ABSTRACT Flatfish monophyly, interrelationships and intrarelationships are examined. The order Pleuronectiformes is monophyletic on the basis ofthree synapomorphies: cranial asymmetry associated with ocular migration, advanced position of the dorsal fin over the cranium and presence of a recessus orbitalis. Characters used to postulate a relationship between percoids and flatfishes are found to be plesiomorphic and the sister group of flatfishes remains unknown. The monophyletic status of all suprageneric taxa of Pleuronectiformes is reexamined and a cladistic analysis is performed using a character state matrix of 39 polarized morphological (mainly osteological) characters, Eighteen equally parsimonious trees were generated. A consensus tree was constructed and discussed in detail. It is concluded that phylogenetic knowledge within flatfishes remains very incomplete. The monophyletic status of speciose taxa such as the Pleuronectinae and Paralichthyidae will have to be reassessed before any fruitful statement of relationships can be formulated. Hensley and Ahlstrom (1984) and Ahlstrom et al. (1984) provided the most recent synthesis on flatfish classification (Table 1), phylogeny (Fig. 1) and larval morphology. Hensley and Ahlstrom (1984) reexamined the homology of characters traditionally used to define higher flatfish taxa (i.e., suborders, families and subfamilies). They also introduced new characters and suggested the formation of a "bothoid group" made up of an array of dextral and sinistral flatfishes. The monophyletic status of all higher taxa within flatfishes was examined, but no attempts were made to build a cladogram depicting flatfish intrarelationships. This article reviews studies on flatfish phylogeny since the synthesis of Hensley and Ahlstrom (1984) and addresses the following issues: (1) Are flatfishes a monophyletic group? (2) In light of recent advances in percoid phylogeny, what can be said of Regan's (1910) and Norman's (1934) assertions that Psettodes, the most primitive flatfish, is an asymmetrical percoid that could almost be placed in the family Serranidae? (3) What is the monophyletic status of higher taxa (suborders, families and subfamilies) within the Pleuronectiformes and what do we know of their interrelationships? To visualize current knowledge on flatfish relationships, a cladistic analysis of familial and subfamilial relationships is performed using available ordered and polarized morphological characters. Except for the cladogram of Lauder and Liem (1983) based on a more limited data set, this cladistic analysis represents the first attempt to incorporate all available information to build a cladogram of intrarelationships within the Pleuronectiformes. MATERIALS AND METHODS The following taxa were used in the cladistic analysis (see below for justification): Psettodidae, Lepidoblepharon, Brachypleura, Citharoides, Citharus, Scophthalmidae, Paralichthyidae, Bothidae, Pleuronectinae, Poecilopsettinae, Rhombosoleinae, Samarinae, Achiridae, Soleidae, and Cynoglos- sidae. All polarized characters used in the analysis are listed in the appendix. The character matrix is presented in Table 2. Characters examined in Chapleau (1988a, 1988b) and Chapleau and Keast (I988) that depicted the intra- and interrelationships of the Soleidae, Archiridae and Cynoglossidae with the Pleuronectoidei are part of the analysis except for the 27 characters used to build the hypothesis of subfamilial 516 CHAPLEAU: PLEURONECfIFORM RELATIONSHIPS 517 Table I. Classification of the Pleuronectiformes according to Ahlstrom et al. (1984) Order Pleuronectiformes Suborder Psettodoidei Family Psettodidae Suborder Pleuronectoidei Family Citharidae Subfamily Brachypleurinae Subfamily Citharinae Family Scophthalmidae Family Paralichthyidae Family Bothidae Subfamily Taeniopsettinae Subfamily Bothinae Family Pleuronectidae Subfamily Pleuronectinae Subfamily Poecilopsettinae Subfamily Paralichthodinae Subfamily Samarinae Subfamily Rhombosoleinae Suborder Soleoidei Family Soleidae Subfamily Soleinae Subfamily Achirinae Family Cynoglossidae Subfamily Symphurinae Subfamily Cynoglossinae relationships within the cynoglossids (Chapleau, 1988a). Autapomorphies of taxa are not incorporated in the data matrix as they do not help in clarifying interrelationships. Morphological data from several studies were used to construct the character matrix. Sakamoto (1984) observed the distribution of 78 characters for 77 species of Pleuronectidae. Amaoka (1969) noted the distribution of 48 characters for 41 species belonging to the Psettodidae, Citharidae, Par- alichthyidae and Bothidae. In Amaoka (1969), the following regions of the body were examined: cranium, orbital bones (infraorbitals), branchial arches, urohyal, vertebrae and accessory bones, and the caudal skeleton and fin. Features of phylogenetic importance, with known character state distribution in the Pleuronectidae, Achiridae, Soleidae and Cynoglossidae and not found in Amaoka (1969), were examined in some cleared and stained specimens (see list of material in Chapleau, 1986). Osteological data on Brachypleura were extracted from Amaoka (1972). Additional osteological and morphological data were taken from Hubbs (1945) and Hensley and Ahlstrom (1984). The level of universality adopted in the present study is subfamilies and families. Only characters with the appropriate level of generality were included in the analysis. Because monophyly remains a problem at the familial and subfamiliallevel (see below), a set of conditions was defined to include a character in the analysis. The following types of characters were not included in the analysis: (I) Characters with an apomorphic state restricted to a few species and genera within a large taxonomic unit. These characters will eventually be useful in defining relationships at the genus and tribe levels but they do not add information on relationships at higher levels of universality. (2) Characters with two states (plesiomorphic and apomorphic) found in members of a family or subfamily but with one state found only in a few species. The more common (apomorphic or plesiomorphic) character state was attributed to the taxonomic unit. Exceptions to character state as- signments are all listed in the character list (see appendix). This criterion was necessary because some families and subfamilies included in the analysis are obviously nonmonophyletic and will have to be redefined in the future. (3) Characters for which the polarity could not be established without a reasonable doubt. This was the case for the position and degree of asymmetry of pelvic fin bases, the ordering and polarity of ocular asymmetry within the flatfishes, and the type of optic chiasma (see Hensley and Ahlstrom (1984) for discussion of these characters). The character state matrix was analyzed using Hennig86 (version 1.5). All trees of equal length were found (procedure ie) and a Nelson consensus tree (procedure nelsen) was obtained. Psettodes, the most plesiomorphic flatfish, was used as the primary outgroup to define interrelationships within the Pleu- 518 BULLETINOFMARINESCIENCE,VOL.52, NO.1, 1993 ~ ~ ~ .$ ~ .~ ~ ·1 .~ ~ ~ .~ ~ ~ ~ ~ ~ l'I.l J ~I ~ ·1 g. j ~ '§ ! g. ~ ~ ~ = ~ .$ 0 ~go 1 'S ~ ~ ~ ] J0 i J..... 'I 0 ~ !:l.t f,:Q C,) ~ !:l.t ~ ~ s: ! ~ rI.) ~ rI.) ~ a rI.) Figure 1. Hypothesis of interrelationships of pleuronectiform fishes presented in Hensley and Ahl- strom (1984). It is based on Norman (1934, 1966), Hubbs (1945) and Amaoka (1969). ronectoidei. Basal percoids (Johnson, 1980, 1984) and Beryciformes (Zehren, 1979; Keene and Tighe, 1984) were used as secondary outgroups. A hypothetical ancestor with plesiomorphic states for all characters was incorporated in the analysis. This consensus tree is discussed in detail. As already indicated, some taxa used in this analysis are, admittedly, not monophyletic and will have to be redefined in the future. However, because all the information on characters, their ordering and their polarity is presented, it is suggested that the hypothesis found in this study provides a good summary of our current knowledge of relationships. List of Materials. - The museum codes follow Leviton et al. (1985). Severa] X-rays were made from specimens preserved in alcoholic solutions. Some cleared and stained specimens were also examined. PSETTODIDAE.Psettodes ANSP 145394, cleared and stained (CS), 61 mm SL, 25°II'N 66°20'E. ANSP 145397, 5 spec., 112-154 mm SL, 13°24'S 48°42'E. ANSP 145396,132 mm SL, 13°24'30"S 48°39'30"E. ANSP 145399,6,109-170 mm SL, 15°08'N 94°54'E. ANSP 145395, 104 mm SL, 15°08'N 95°54'E. USNM 286356, 2, 111-132 mm SL, Ghana, Tema-Teshie Bay. CITHARIDAE.Citharus linguatula USNM 236123, 13, 100-1]9 mm SL, 05°30'30"N 09°44'30"W. Citharoides cf. macrolepidotus AMS 1.25801-016, 6, 85-156 mm SL, Australia, Queensland, just N of Townsville. Lepidoblepharon sp. AMS 1.20118-012, 6, 103-166 mm SL, Australia, New South Wales, E of Wooli. Brachypleura novaezeelandiae USNM 236122, 33, 74-94 mm SL, Philippines, purchased at Manila fish market. SCOPHTHALMIDAE.Scophthalmus aquosus ANSP 150131, I CS out of65, 75 mm SL, USA, New Jersey. ANSP 166257,6 X-rays, 70-93 mm SL, USA, New Jersey. Scophthalmus maeoticus ANSP 100071, 3 X-rays, 103-130 mm SL, Rumania, Black Sea at Sulina. Lepidorhombus boscii USNM 236124, CS, 113 mm SL, Mediterranean Sea, olfTunisia. Phrynorhombus unimaculatus ANSP 872932,

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