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R.D. MOOI AND AC. GILL 



Fig. 16 Type 1 epaxial musculature in Pseudanthias taeniatus 

 (USNM 279782, 44.8 mm SL). A separate slip of the epaxial 

 inserts on to the first to fourth dorsal-fin pterygiophore, and 

 epaxial insertions occur as far posteriorly as the eighth 

 pterygiophore. Abbreviations and other methods of presentation 

 as in Figs 1,3. Scale bar = 5 mm. 



tions, an argument could be made for homology with a Type 

 2 morphology found among the perciforms, and implied 

 relationships should be investigated. Optimizing epaxial char- 

 acter distribution on existing phylogenies of the tetraodonti- 

 forms (Winterbottom, 1974b; Leis, 1984) implies that the 

 Type 2 morphology is the primitive condition for the order. 

 Unfortunately, the character does not provide additional 

 evidence for intrarelationships because the remaining extant 

 families of tetraodontiforms do not possess a spinous dorsal 

 fin. 



Even among taxa that do not exhibit epaxial insertions on 

 to the distal portions of the proximal-middle pterygiophores 

 or on to the distal radials, we did observe some possibly 

 significant variation in other muscle morphology. As noted 

 above, most (if not all) acanthomorphs have epaxial muscle 

 insertions on to the proximal ends or along the shafts of the 

 dorsal-fin pterygiophores. In most pleuronectiforms the 

 epaxial muscle inserts via bundles of muscle fibres that pass 

 underneath the depressores dorsales. Psettodes, usually con- 

 sidered the sister group of other pleuronectiforms, has the 

 epaxial muscles overlying most of the length of the pterygio- 

 phores, with very short connections extending under the 

 depressors to the pterygiophore shafts just ventral to the 

 spine articulations. These connections only occur on the first 

 12 pterygiophores. Psettodes is the only genus with dorsal-fin 

 spines; all other flatfishes have epaxial insertions on to a 

 higher number of pterygiophores, although most of the 

 examined taxa have dorsal fins extending over the head. The 

 extent to which the epaxials overlie the pterygiophores in 

 remaining flatfishes varies considerably and might be of 

 interest for determining relationships. The few examined 

 bothids, paralichthyids and samarines have the epaxials cov- 

 ering about half the length of the pterygiophores before short 

 fibres attach to these bones. In available achirids the arrange- 

 ment is similar to that described for bothids for the most 

 posterior insertions, but anteriorly there are separate, elon- 

 gate muscle slips that insert high on to the pterygiophore 

 shafts just ventral to the ray articulations (Fig. 18). The 

 cynoglossids, considered close relatives of the achirids (Chap- 

 leau, 1993), have an epaxial morphology more similar to that 

 of Psettodes in the one species examined. Poecilopsetta 

 (Poecilopsettinae) has epaxial muscles that lie only as far 

 dorsally as the proximal tips of the dorsal-fin pterygiophores, 

 a condition that appears derived among pleuronectiforms and 

 could provide evidence for relationship if observed in other 

 taxa. Additional taxa need to be surveyed and character 

 definitions must be clarified before epaxial morphology can 



contribute to an hypothesis of pleuronectiform phylogeny, 

 but such an investigation appears worthy of pursuit. 



A similar, though less extensive, series of epaxial insertions 

 under the depressors is found in Urophycis of the Gadidae 

 (Fig. 19). Gadoids have not been thoroughly surveyed, but 

 variation in epaxial muscle morphology, which is relatively 

 simple to observe, might be useful for defining broad groups 

 among gadoids, and paracanthopterygians in general. The 

 occurrence of a Type 1 epaxial morphology among batra- 

 choidids also suggests that a further survey of paracanthop- 

 terygians could contribute to the understanding of 

 relationships within this taxon. 



Of course, epaxial muscle morphology is not informative in 

 all cases. For example, the Callionymoidei have a highly 

 modified Type 2 condition consisting of a complex series of 

 epaxial insertions on to the pterygiophores and modified 

 neural spines. This will not help determine whether the 

 Callionymoidei and Gobiesocidae are sister taxa, as hypoth- 

 esized by Gosline (1970) and Winterbottom (1993: 409), 

 because the latter taxon does not have a spine-bearing dorsal 

 fin. It would be reasonable to suggest that any epaxial muscle 

 associated with the fin would also have disappeared or have 

 become reduced. Like any other feature, epaxial morphology 

 can undergo secondary loss or autapomorphic modification. 



The homology of the three epaxial muscle morphotypes 

 identified remains uncertain. It is unlikely that they form a 

 nested set of character states. That a single morphotype can 

 be independently derived from a Type condition is illus- 

 trated by the independent development of Type 2 in some 

 labrids, and similarly in the Acanthoclininae, a derived taxon 

 within the Plesiopidae which otherwise exhibit Type (Table 

 1). The occurrence of a Type 1 morphology in some paracan- 

 thopterygians, usually considered unrelated to perciforms, 

 also indicates non-homology of the character state as recog- 

 nized here. These examples suggest that the morphologies 

 themselves require better definition. With more sophisticated 

 inquiry through ontogenetic or neurological studies, it is 

 possible that these cases of non-homology can be dismissed as 

 inappropriately recognized character state equivalence. In 

 the apparently unique morphology of the Mullidae, Type 3, 

 the pterygiophore insertions involve both epaxial and supra- 

 carinalis fibres (Fig. 11). The muscle is essentially separate 

 from the main epaxial muscle body over its entire length, a 

 condition very different from that found in the Type 1 or 2 

 morphologies. It appears that the Type 3 musculature is 

 directly derived from the supracarinalis muscles, rather than 

 from the epaxial muscles. This also seems likely in the 

 pinguipedid trachinoid Parapercis, where the muscle bundle 

 inserting on to the dorsal-fin pterygiophores is continuous 

 with the supracarinalis anterior and posterior. The condition 

 in mullids and Parapercis could provide evidence that, in at 

 least these taxa, the sheet of muscle inserting on to dorsal-fin 

 pterygiophores is actually derived from the supracarinalis, 

 and only secondarily shares muscle fibres from the epaxialis. 

 These problems of homology and ontogeny of the muscle are 

 beyond the scope of this paper. 



Despite these concerns, we are confident that epaxial 

 morphology is useful for exploring the relationships of acan- 

 thomorph taxa. Of course, this one character complex must 

 be taken in the context of other characters before any 

 definitive statements can be made regarding, for example, 

 percoid/scorpaenoid relationships, or before making gener- 

 alizations concerning the integrity of such groups as the 

 trachinoids. However, one important concept that the inves- 



