COHEN: ONTOGENY, SYSTEMATICS, PHYLOGENY 



11 



instances for which it is difficult to accept that ontogeny has 

 recapitulated phylogeny include the leptocephalus of eels, the 

 stalked eyes of assorted larval bathylagids, myctophids and Idi- 

 acanthus. the elongated guts of larval melanostomiatids, the 

 extensive armature of many spiny-rayed fishes during their lar- 

 val stages, and the produced fin rays found in many kinds of 

 larval fishes. Examples of all of these are illustrated and de- 

 scribed in this volume. With regard to proposition three in 

 particular, Ahlie often pointed out instances of fishes that were 

 easily distinguished as larvae but became more similar in ap- 

 pearance as adults; one example is Bathylagiis milleh and B. 

 pacificus; Myctophum aurolaternalum and other myctophid 

 species is another. Von Baer's propositions as applied to phy- 

 logeny are tidy and appealing but are completely operative only 

 under the rather special condition that major evolutionary 

 changes (except for paedomorphosis) are restricted to the adult 

 stage (Gould, 1977; Fink. 1982). 



For cladistic analysis, the polarization of characters through 

 direct observation of their transformation during ontogeny has 

 been discussed by Nelson (1978) and others as an alternative 

 to the often unsatisfactory indirect method of outgroup com- 

 parison. Such use of ontogeny, which depends on von Baer's 

 first three propositions, has been analyzed by Henning (1966), 

 who noted its uncertainty. As examples from fish ontogeny given 

 above indicate, ontogeny could replace or corroborate outgroup 

 comparison but only to the extent that the biogenetic law is 

 valid for a particular situation. Patterson's (1982) statement, 

 "that ontogeny is the decisive criterion in determining polarity," 

 would seem to be based on limited acquaintance with ELH 

 stages. 



Paedomorphosis refers to the presence in adults of larval char- 

 acters (De Beer, 1951) and has been variously considered as 



insignificant to very important in evolution. For fishes at least, 

 I think the latter is the case. As one example, small adult size 

 could be considered a particularly widely distributed neotenic 

 character. In his discussion of paedomorphosis and cladistics. 

 Fink (1982) remarked that it is difficult to identify this phe- 

 nomenon without paired taxa, but surely this is not always true. 

 Although the relationships of the curious little fish Schindleria 

 are unknown, it would be difficult to deny that it has many 

 neotenic characters (Watson, Stevens and Matarese, this vol- 

 ume). On a larger scale paedomorphosis may have been im- 

 portant in establishing novel phyletic lines as well as isolated 

 species or genera, and the study of ELH stages will be essential 

 in detecting these divergences. 



I end this essay by noting that the most important use of all 

 for information about fish ontogeny may be providing characters 

 for charting fish phylogeny rather than theories about phylogeny. 

 Distinguishing and identifying species for purposes of fish bi- 

 ology and management has been the chief use for what is called 

 larval fish taxonomy, and the large resulting literature is sum- 

 marized in this volume. Many of the same descriptive data are 

 of apparent value for purposes of grouping similar species or 

 other taxa for phyletic purposes. Published examples of syn- 

 thesis are far fewer than of descriptions, but accounts using each 

 of the three methodologies previously described are available, 

 either cited in this volume or presented here as original research. 

 ELH characters can meet many methodological constraints and 

 will be used increasingly by ichthyologists. To what advantage 

 remains to be seen, but the prognosis is good. 



Life Sciences Division, Los Angeles County Museum of 

 Natural History, 900 Exposition Boulevard, Los 

 Angeles, California 90007. 



Early Life History Stages of Fishes and Their Characters 

 A. W. Kendall, Jr., E. H. Ahlstrom and H. G. Moser 



Patterns of Teleost Early 

 Life History 



IN discovering that Atlantic cod lay free-floating planktonic 

 eggs which develop into pelagic larvae, G. O. Sars, in 1865 

 (see Hempel, 1979; Ahlstrom and Moser, 1981) had also come 

 upon an example of the widespread life history pattern of marine 

 fishes. Most marine fishes, regardless of systematic affinities, 

 demersal or pelagic habits, coastal or oceanic distribution, trop- 

 ical or boreal ranges, spawn pelagic eggs that are fertilized ex- 

 ternally and float individually near the surface of the sea (Fig. 

 5). These eggs range from about 0.6 to 4.0 mm in diameter 

 (mode about 1 mm) and generally are spherical. Within a species 

 there is little variation in egg characters such as size, number 

 and size of oil globules, and pigmentation and morphology of 

 the developing embryo. Development time is highly tempera- 

 ture dependent and also species-specific. The eggs hatch into 

 relatively undeveloped yolk-sac larvae which swim feebly and 



rely on their yolk for nourishment while their sensory, circu- 

 latory, muscular, and digestive systems develop to the point 

 that they can feed on plankton. Even these yolk-sac larvae have 

 characters (pigment patterns, body size and shape, myomere 

 number) that reflect their heritage. After the yolk is utilized, 

 they develop transient "larval" characters such as pigment pat- 

 terns and, in some, specialized head spines and fin structures 

 that are apparently adaptive for this phase of their life history. 

 During this period more characteristics of the adult (e.g., me- 

 ristic characters) gradually develop. At the end of the larval 

 stage, they may go through an abrupt transformation to the 

 juvenile stage, particularly if they move from a pelagic to de- 

 mersal habitat, or the transformation may be gradual. In some 

 fishes, there is a prolonged and specialized stage between the 

 larval and juvenile stages. These pelagic (often neustonic) forms 

 eventually transform into demersal juveniles. The juvenile stage 

 is characterized by specimens having the appearance of small 

 adults— all fin rays and scales are formed, the skeleton is almost 



