FISHERY BULLETIN: VOL. 70, NO. 3 



and achieves its adult shape over a span of about 

 1.0 mm (7.7-8.5 mm) . Similar variation is found 

 in the mandibular, palatine, and hyoid arches and 

 in the axial and appendicular skeletons. An- 

 other less obvious generalization from Table 3 

 is that functionally related contiguous elements 

 tend to achieve their adult form at about the 

 same larval stage, regardless of when they un- 

 derwent initial ossification. For example, the 

 first six bones listed in the table are the major 

 elements of the roof, sides, and floor of the brain 

 case. Although they undergo initial ossification 

 in a gradual sequence, all achieve their adult 

 form in larvae 7.9 to 9.2 mm long. The bones 

 of the opercular series (opercular, preopercular, 

 subopercular, interopercular) begin to ossify in 

 successive stages, but all achieve adult form at 

 about the same stage. The pectoral girdle pro- 

 vides two excellent examples of this tendency in 

 the cleithrum-supracleithrum-postemporal ser- 

 ies and the scapula-proximal radial-coracoid 

 series. Finally, there is no correlation between 

 sequence of ossification and the origin (endo- 

 chondral or dermal) of a bony element. Thus, 

 of the first six elements of the neurocranium 

 mentioned above, half are endochondral and half 

 are dermal in origin. Here, the early appear- 

 ance of these elements appears to be related to 

 function and not to the kind of bone formed. 

 Analysis of the sequence of ossification of 

 branchial elements is difficult since ossification 

 is so gradual that one cannot choose a larval 

 stage at which a given element achieves its basic 

 adult form. Accordingly, only the larval size 

 at which an element begins to ossify is listed 

 in Table 4. As in other teleosts examined by me, 

 the first bony structures to ossify in the larvae 

 are the pharyngobranchial teeth. In S. mac- 

 donaldi, the tooth patches of the third pair of 

 pharyngobranchial elements appear in the smal- 

 lest planktonic larvae and enlarge throughout 

 the larval period. In larvae of the Myctophidae 

 it is the tooth patches of the fourth pharyngo- 

 branchials which ossify first (Moser and Ahl- 

 strom, 1970). Aside from this, the sequence 

 of ossification is similar in Sebastes and Mycto- 

 phidae. The ceratobranchials are the first ele- 

 ments of the arches to ossify. These are fol- 

 lowed by the epibranchials and hypobranchials, 



generally in an anterior to posterior sequence, 

 beginning with those of the first arch. The first 

 gill rakers to form are those on the first pairs 

 of ceratobranchials and epibranchials and, grad- 

 ually, they appear on more posterior arches. 

 Within each arch, ossification proceeds outward 

 from the angle of the arch. The full comple- 

 ment of rakers on the first arch is not achieved 

 during the larval period. 



Head spines present a special problem since 

 some of the spines formed during the larval pe- 

 riod are not found in adults. The terminology 

 of Phillips (1957) is used in the discussion that 

 follows. The first spines to form on the neuro- 

 cranium are on the pterotic bones (Table 5). 

 Interestingly, these spines begin to ossify before 

 the bones themselves, and ossification of the 

 bones spreads outward from the base of each 

 spine. The spines are at first acute, but broaden 

 during the larval period to produce a pterotic 

 shelf in the largest larvae. The spine and shelf 

 become reduced in pelagic juveniles and are ab- 

 sent in demersal juveniles and in adults. The 

 two other pairs of spines which develop early 

 in the larval period are the parietals and postoc- 

 ulars. The paired parietal spines develop as the 

 terminal points of a pair of serrated parietal 

 ridges and attain their maximum relative length 

 (20-23^; of the head length) in larvae 8.0 to 

 10.0 mm long. The ridges and their spines be- 

 come reduced during later larval stages but re- 

 main in juveniles and adults. The postoculars 

 develop from lateral shelves of the frontal bones 

 that project over the eyes. Initially the spines 

 are positioned directly above the eyes but grad- 

 ually shift posteriad to their adult position. Pre- 

 ocular, supraocular, and tympanic spines do not 

 form during the larval period; they are begin- 

 ning to form in a pelagic juvenile 22.6 mm long 

 and are well formed in the largest pelagic ju- 

 veniles. 



Other prominent cranial spines which develop 

 later in the larval period are the suborbitals, 

 nuchals, and nasals (Table 5). The suborbital 

 spines form in two series: one series of ven- 

 trally directed spines develops on the ventral 

 margin of each lacrimal (first circumorbital) 

 bone and another series of laterally directed 

 spines forms directly below the orbit. This lat- 



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