ABOUSSOUAN AND LEIS: BALISTOIDEI 



451 



tom-associated in shallow to moderate depths, but many tria- 

 canthodids live in deep (>500 m) water. Most species have a 

 pelagic, often oceanic, juvenile stage, and a few are pelagic 

 throughout their lives. 



Development 



Development of balistoid fishes is not well known. Previous 

 reviews of the early development of the group are by Breder 

 and Clark (1947), Tortonese (1956). and Martin and Drewry 

 (1978). The early development of aracanids is entirely unknown, 

 and. overall information is available for only 30 species. Often 

 the information available for a species is scanty. Complete (i.e., 

 egg to juvenile) information is available for only four or five 

 species (Table 1 16). This narrow data base makes generaliza- 

 tions about development somewhat suspect. However, we as- 

 sume that the few taxa for which information is available are 

 representative. 



Few generalizations can be made about development of balis- 

 toid fishes, but this is not surprising in view of the diversity of 

 the adults. A reference to development in juveniles, which usu- 

 ally differ little from adults, is given at the end of each section. 

 We make no attempt to review the literature on juvenile de- 

 velopment. 



Eggs (Table //6A — Balistoid fishes are oviparous. Pelagic and 

 demersal eggs are known: the chorion is usually smooth, but 

 may have limited sculpturing; oil droplets are usually present; 

 eggs range in size from small (0.5 mm) to large (2.0 mm) and 

 are approximately spherical; incubation times range from one 

 to four days; development at hatching vanes widely; the peri- 

 vitelline space is narrow; the yolk is unsegmented; and consid- 

 erable pigment may develop on the embryo. Parental care of 

 eggs ranges from non-existent (pelagic eggs) to considerable (Ba- 

 listidae). 



Larvae— AW balistoid larvae are pelagic. Development is gen- 

 erally direct (i.e., no specialized ontogenetic stages between lar- 

 vae and juveniles), with few larval specializations, and is com- 

 pleted at a small size (Figs. 244-25 1 ). There is often an apparently 

 unspecialized pelagic juvenile stage which may grow to a sig- 

 nificant fraction of the adult size. Larvae tend to be deep-bodied, 

 and many are also wide-bodied. The head is large and the gut 

 coiled and massive. The mouth is small. The head is usually 

 rounded, at least in preflexion larvae. The head and body of 

 young ostraciid larvae are enclosed in an inflated dermal sac 

 which has numerous vesicles (or tubercles) embedded in its 

 outer surface. Except in ostraciids, the specialized adult scales 

 pass through an unspecialized spinule stage. The caudal fin is 

 usually the last fin to form. The reduction in structures, notably 

 fins, which characterizes the balistoid fishes is not a case of 

 development followed by loss— these structures never develop. 

 The specialized dentition develops during the larval stage di- 

 rectly, without any intervening generalized or larval teeth. Me- 

 ristic characters are summarized in Table 1 15 (see Tyler. 1980 

 for further information). The number of vertebrae and caudal 

 fin rays is low. pelvic fins are reduced or lacking, anal fins lack 

 spines, and dorsal spines, if present, are few (Table 1 1 5). Larvae 

 are generally moderately to heavily pigmented. 



The few larval morphological specializations which do occur 

 are either developments of the often very specialized scales (or 

 their precursors) of the adults or delicate skin flaps, filaments 

 and tendrils. These are discussed under the appropriate family 

 section. There are no specialized ontogenetic stages between 

 larvae and juveniles. 



A shorthand notation will be used to designate the sequence 

 of fin formation. By formation, we mean ossification of the first 

 element, with the exception of the caudal fin where completion 

 of flexion is meant. However, except for some monacanthids 



