48 



ONTOGENY AND SYSTEMATICS OF FISHES -AHLSTROM SYMPOSIUM 



(Fig. 18C) as compared to that oi Pleuronichthys coenosus (Fig. 

 18E, F). Here, the hexagons are not only smaller, but the area 

 within the facets does not appear porous. SEM was used for this 

 species and its congeners for egg description by Sumida et al. 

 (1979). It is interesting to note that these authors discussed the 

 similarity in chorion structure of Plenronichthys spp. with that 

 oi Synodus lucioceps. While there were slight differences in sizes 

 of the polygons, the superficial similarity of chorion structure 

 on these phylogenetically distant genera supports a functional 

 role (Robertson, 1981) and independent derivation. In this in- 

 stance, however, SEM was valuable for understanding and in- 

 terpreting the differences between species and genera subse- 

 quently observed under the light microscope (Sumida et al., 

 1979). Similarly, Keevin et al. (1980) used chorion ornamen- 

 tation to distinguish among genera of killifishes. 



Other ornamentations include more random ridges (Para- 

 callionymus costatus. Fig. 19C, and Mugil cephalus. Fig. 19D), 

 filaments of varied length, diameter, and base morphology (Ath- 

 erinopsis califormensis and Athehnops affinis. Fig. 19A, B; see 

 also Hubbs and Kampa, 1946), tufts (Scomberesox saurus. Fig. 

 20B), spines (Oxyporhamphus microptents. Fig. 20A), and pits 

 and pores (Lactoria diaphana. Fig. 20C, D). In thecallionymids, 

 the small eggs of species of Callionynms have hexagonal sculp- 

 turing similar to that oi Pleuronichthys (Fig. 18E). In Paracal- 

 lionymus costatus (Fig. 19C), however, random ridges similar 

 to those in Mugil cephalus are apparent. 



Since chorion microstruclure is formed by follicle cells during 

 oogenesis (Sponaugle and Wourms, 1979; Stehr, 1979), patterns 

 may also be discerned in ovarian eggs. The pelagic eggs of mac- 



rourids are poorly known but have been described for selected 

 species by Sanzo ( 1 933a), Robertson ( 1 98 1 ), and Grigor'ev and 

 Serebryakov (1981). For Pacific species of Coryphaenoides. pe- 

 lagic eggs remain poorly known but apparently have hexagonal 

 patterns as in other members of the genus; this, is clearly shown 

 in ovarian eggs near the maximum size observed by Stein and 

 Pearcy (1982; Fig. 19E, F). Thus SEM of developing ovarian 

 eggs may be used to discern differences which then aid in iden- 

 tification of eggs from plankton samples. 



For larval stages, SEM has been used for the description of 

 development of several surface structures, such as the olfactory 

 organ (Elston et al., 1981) and lateral line neuromasts (Dobbs, 

 1974). For taxonomic studies, differentiation of fine-scale mor- 

 phological differences, such as dentition or fine-scale spine ser- 

 ration, may be useful. Its most valuable use may therefore be 

 for later larval development, since pigmentation and other char- 

 acteristics in early larvae are better seen with conventional 

 methods (Fig. 20E, F). 



To conclude, SEM may serve as an adj uct to traditional meth- 

 ods in the description of fine structure in fish eggs and larvae. 

 For high magnification, high resolution visualization of surface 

 morphology, it remains the most effective tool available. Under 

 lower magnifications, it may allow one to clearly visualize struc- 

 tures which are difficult to interpret using standard microscop- 

 ical methods (Fig. 1 8A, B). 



Oregon State University , Marine Science Center, Newport, 

 Oregon 97365. 



Developmental Osteology 

 J. R. Dunn 



ONE legacy left by Elbert H. Ahlstrom was an appreciation 

 of the value of developmental osteology of teleosts as a 

 taxonomic aid and as an indicator of phylogenetic affinities. 

 Although numerous studies have been made on the growth of 

 various bones in teleosts, such descriptions have not been widely 

 used in assessing relationships of fishes. I have recently re- 

 viewed, in some depth, the application of developmental os- 

 teology in taxonomic and systematic studies of teleosl larvae 

 (Dunn, 1983b). Here I present a brief overview of some skeletal 

 structures in teleosts whose ontogeny offers potential utility in 

 inferring phylogenetic affinities. It is hoped that this precis will 

 encourage ichthyologists to examine the development of bones 

 in the course of their systematic studies. 



Ontogenetic Changes in Skeletal 

 Structures 



Cranial and associated bones— CTaniaX osteology has, of course, 

 been the foundation of systematic studies of adult fishes, but 

 the development of cranial bones has been little used in phy- 

 logenetic studies. Numerous descriptions of the ontogeny of 



cranial bones exist in the literature (e.g., Bhargava, 1958; Bert- 

 mar, 1959; Kadam, 1961; Weisel, 1967; Moser and Ahlstrom, 

 l970;Mook, l977;Leiby, 1979b; Yuschak, 1982). Additionally, 

 the sequence of ossification of head bones has been described 

 for a variety of taxa (e.g., Moser, 1972; Aprieto, 1974; Leiby, 

 1979a; Dunn, 1983a; Kendall and Vinter, 1984). The devel- 

 opment of certain cranial structures has also been shown to be 

 of taxonomic value (Fritzsche and Johnson, 1980), yet com- 

 parative studies of the developmental osteology of the skull of 

 related groups of teleosts seem rare (e.g., Norman. 1926b; De 

 Beer, 1937). 



Available evidence suggests that the sequence of ossification 

 of the skull of teleosts is a conservative (i.e., relatively constant 

 among different phyletic groups) process (De Beer, 1 937; Mook, 

 1977). Among the bones which ossify first are those in areas of 

 high stress, such as feeding (jaw bones) and respiration (bran- 

 chial region), as noted by De Beer ( 1 937), Weisel ( 1 967), Moser 

 and Ahlstrom (1970), Mook (1977), Yuschak (1982). 



Examples of ontogenetic changes in skull bones which suggest 

 that these structures might offer insight into phylogenetic affin- 



