450 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



formation is: P.-D = A-C'. The long notochord tip persists for 

 a time following flexion. The vesicles of the dermal sac are said 

 to be the source of the small dermal ossifications (Welsh and 

 Breder, 1921). The dermal ossifications (=scales) develop di- 

 rectly into small, often embedded, spines. The dermal spines 

 seem to first appear on the belly, usually in the preflexion stage. 

 Depending on species, the spines may appear on the rest of the 

 body shortly thereafter, slowly and gradually, or not at all. Pig- 

 ment is mitially heavy over the gut, brain and yolk sac, and 

 usually spreads to cover much of the head and trunk before 

 flexion. Welsh and Breder (1921) and Munro (1945) report the 

 presence of a single opercular spine in preflexion larvae of 

 Sphoeroides maculalus and Torquigener pleurogramina, re- 

 spectively. None of the larvae examined for the present study 

 has such a spine, but these two species have not been examined. 



Diodontidae. — Diodontid eggs are pelagic, large, have multiple 

 oil droplets (Table 114) and hatch in 3 to 5 days. Larvae are 

 moderately to well developed at hatching, but development var- 

 ies between species and possibly between populations of the 

 same species: jaws range from totally unformed to formed and 

 apparently functional; eyes are partially to fully pigmented; the 

 gill opening is reduced to a pore; moderate to heavy pigment 

 (including yellow, red and orange) is present; much yolk re- 

 mains; and a well-developed, inflated, vesicular dermal sac en- 

 closes head and trunk (Fig. 242). Larvae are deep-bodied and 

 broader than deep (Fig. 243). At hatching or very shortly there- 

 after, diodontid larvae are extremely rotund with head and trunk 

 a single ball-like unit. The tail is small and becomes relatively 

 smaller still with age. It becomes nearly vestigial during flexion, 

 but thereafter starts to increase in size. Body shape changes little 

 during development. The fins form P.-D = A-C. The mouth 

 is large compared with other tetraodontiform larvae. Shortly 

 before flexion, lens-like thickenings form in the dermal sac, and 

 (depending on species) small swellings or elongate papillae form 

 over these. The large spines (=scales) subsequently form inside 

 these structures without an intermediate stage. In most species, 

 spines are present around the time flexion is completed, but in 

 Chilomyclerus antennatus and C. schoepfi (but not C. affinis or 

 C. orbicularis) there is a specialized pelagic stage which lacks 



' Sequence of ossification of first element in each fin, except that the 

 symbol for caudal fin (C) refers to completion of notochord flexion. Fin 

 preceding dash forms prior to fin following dash. 



spines and may have some of the elongate papillae enormously 

 enlarged (the genus Lyosphaera was described from such a stage). 

 The spines in the "Lyosphaera" stage form after settlement. 

 Nostrils of diodontids form in a conventional manner. Only 

 following development of a short tentacle with two openings do 

 the split nasal flaps of Dicotylichthys or the open reticulated 

 nasal cups of Ctiilomyclerus ajfinis form during the late juvenile 

 stage. Pigment is moderate to heavy and in preflexion larvae 

 much heavier dorsally than ventrally. Following flexion, there 

 is a tendency for the belly to become more heavily pigmented 

 than the dorsum. 



A/olidae. — Mo\id eggs are pelagic, large, have multiple oil drop- 

 lets (Table 114). and hatch in 7 to 8 days. Larvae are devel- 

 opmentally very advanced at hatching with: jaws formed; eyes 

 pigmented; gill opening reduced to a pore; a well-developed 

 vesicular dermal sac enclosing head and trunk; the cleithrum 

 and several pectoral fin rays ossified; a dorsal fin anlage; heavy 

 pigment; and an unknown amount of yolk (Fig. 242). The body 

 is deep (Fig. 243) and wide but not as wide as deep. At hatching 

 molid larvae are extremely rotund with head and trunk a single 

 ball-like unit. The compressed tail becomes progressively small- 

 er. With growth and body spine development the body even- 

 tually becomes more compressed and a ventral keel forms. The 

 fins form Pi-D = A-Clavus. The P, forms very early and be- 

 comes large. The tail of young larvae is normal, but soon begins 

 to atrophy, and a true caudal fin never forms. Notochord flexion 

 does not take place, so the clavus is not homologous with the 

 caudal fin. Shortly after hatching, the huge spines which char- 

 acterize molid larvae begin to form. These reach a maximum 

 size at about the time the clavus is formed. As the massive 

 spines decrease in size, small spines form elsewhere, particularly 

 on the ventral keel. Also, small ossifications within the skin 

 begin to form, and these eventually make up the carapace-like 

 skin covering. Mo/a and Mastwus pass through a fairly long 

 ontogenetic stage between larvae and juveniles which is char- 

 acterized by retention of reduced massive spines, a deep, com- 

 pressed body with a ventral keel and a shape quite unlike the 

 adult (the genus Molacanthus was described from such a stage). 

 Ranzania. in contrast, loses its spines relatively quickly and 

 directly assumes the adult shape. Larvae are heavily pigmented 

 over the gut and on the dorsal surfaces. 



Department of Ichthyology, The Australian Museum, P.O. 

 Box A285, Sydney, 2000, Australia. 



Balistoidei: Development 



A. Aboussouan and J. M. Leis 



THE tetraodontiform suborder Balistoidei (Sclerodermi) is a 

 small group of six families with about 175 recent species 

 of great morphological diversity (Tyler, 1968, 1980; Winter- 

 bottom, 1974a;Matsuura, 1979).Thesuborderisgenerallyagreed 

 to consist of the six families (Table 115) considered here (Tyler, 



1980). However, Winterbottom (1974a) has suggested that the 

 triacanthodids and triacanthids could be removed to a suborder 

 distinct from all other tetraodontiform fishes. The group is large- 

 ly tropical and marine, but some species range well into the 

 temperate zones, particularly in Australia. Most species are bot- 



