PIETSCH; OSTEOLOGY AND RELATIONSHIPS OF TETRABRACHIUM 



material unavailable for comparison includes the 

 lophioid genus Sladenia Regan, seven of the nine 

 ogcocephalidid genera, and a number of rare and 

 highly derived ceratioid genera), as well as rep- 

 resentative taxa of the Batrachoidiformes (3 of 

 the 12 nominal genera), the only group bearing 

 evidence of sister-group relationship with the 

 Lophiiformes (Regan 1912; Gregory 1933; Rosen 

 and Patterson 1967) (see Appendix). 



Antennarius, used here as the representative 

 taxa of the Antennariidae, is recognized as the 

 least derived genus of the family based on a 

 comparative anatomical study of some eight nom- 

 inal antennariid genera (Pietsch in prep., see 

 Appendix). Except for synapomorphies that estab- 

 lish monophyly for Antennarius, all known char- 

 acters of taxonomic importance found among the 

 eight genera are present in Antennarius in the 

 primitive state. For example, a mesopterygoid and 

 an epural are present in Antennarius but absent 

 in all other genera except Histrio; Histrio is 

 clearly derived relative to Antennarius in having 

 enlarged pelvic fins, a pectoral fin lobe that is 

 detached from the body along most of its length, 

 absence of skin spines, and a unique pelagic 

 habitat in sargassum weed. Similarly, each of the 

 remaining six antennariid genera possesses a 

 number of autapomorphic features that indicate 

 its derived nature relative to Antennarius. Al- 

 though these and other data support the least 

 derived position o{ Antennarius, this verification 

 is not basic to the subsequent discussion of rela- 

 tionships since the synapomorphic features used 

 to establish the sister groups proposed below are 

 synapomorphic for all eight antennariid genera. 



Tetrahrachiutn is most closely related cladistic- 

 ally to Antennarius, and is here classified on this 

 basis as a sister- family, the Tetrabrachiidae (first 

 proposed by Whitley 1935), of the Antennariidae 

 (Figure 41). This hypothesis of relationship is 

 supported by three synapomorphies: 



Posteromedial process of vomer emerging 

 from ventral surface as a laterally com- 

 pressed, keellike structure, its ventral mar- 

 gin (as seen in lateral view) strongly convex 

 (this character state is present in Tetrabrach- 

 ium and in all antennariid taxa examined; 

 in the batrachoidids and other lophiiforms 

 examined the posteromedial process is flush 

 with the ventral surface of the vomer, its 

 ventral margin straight to slightly concave); 



2) Postmaxillary process of premaxilla spat- 

 ulate (this character state is present in 

 Tetrabrachium and in all antennariid taxa 

 examined; in the batrachoidids and other 

 lophiiforms examined the postmaxillary pro- 

 cess of the premaxilla is connected to the 

 toothed portion of this element by bone, rep- 

 resented by a narrow, tapering structure, 

 or absent); 



3) Opercle similarly reduced in size (in Tetra- 

 brachium and all antennariid taxa examined 

 the width of the opercle is approximately 

 ^25% the length of the suspensorium; in the 

 batrachoidids and other lophiiforms exam- 

 ined this distance is >40%). 



Although the classification of taxa presented 

 here is based on recency of common descent, the 

 amount and nature of evolutionary change be- 

 tween the Antennariidae and the Tetrabrachiidae 

 is an important part of their evolutionary his- 

 tories. That the Tetrabrachiidae has entered a 

 "new adaptive zone" relative to the Antennariidae 

 is evidenced morphologically by a number of 

 unique, derived features: eyes small, close set, 

 protruding from the dorsal surface of the head; 

 mouth small, superior, lower lip fringed with 

 small cutaneous papillae; illicial apparatus re- 

 duced; pectoral fin double, the ventral portion 

 membranously attached to the side of the body; 

 and pectoral fin lobe membranously attached to 

 the rays of the pelvic fin. The webbing between 

 the pectoral fin and the body, and between the 

 pectoral and pelvic fins is apparently used to 

 remove soft-bottom substrate (fine sand or mud) 

 from beneath by scooping material away in a 

 lateral direction and simultaneously throwing 

 material up and over to cover the animal; the 

 fringed lip allows for intake of water while helping 

 to prevent particles from entering the pharyngeal 

 cavity. These and other characters listed above 

 reflect a life style similar to that of a uranoscopid 

 or synanceiid, lying for long periods of time buried 

 up to the eyes in sand or mud, a mode of existence 

 unlike that of any other antennarioid. 



The results of this study further show that the 

 Antennariidae and Tetrabrachiidae together form 

 the primitive sister group of the Lophichthyidae 

 and that these three taxa together form the 

 primitive sister group of the Brachionichthyidae 

 (Figure 41). The monophyly of a group including 

 the Antennariidae, Tetrabrachiidae, and Loph- 

 ichthyidae is supported by a single synapomorphy: 



413 



