SHORT BIGEYE IX WESTERN NORTH ATLANTIC 



121 



discussions, as the precise size at whicli a char- 

 acter developed could not be determined. Com- 

 plete segmentation and complete branching 

 indicate at least one segmentation line or one 

 branch in each ray (which segments or branches) 

 of the fin. 



Caudal fin. — Development of the hypural com- 

 plex began at about 3.5 mm. The turned-up 

 urostyle was still obvious at 6.6 mm. and devel- 

 opment of the hypural was complete before 8.2 

 mm. Ossification was first noted in a 4.0-mm. 

 individual. 



In the development of the caudal fin, a finfold 

 was present in the smallest larva (2.2 mm.; see 

 fig. 8), and rays apparently were forming, although 

 no ossification of rays was noted in stained speci- 

 mens until a size of 3.5 mm. Ossification pro- 

 ceeded anteriorly, and the full complement of 16 

 principal rays was evident in a stained 4.4-mm. 

 larva. Segmentation, beginning with the inner- 

 most rays, had begun by at least 4.4 mm., and 

 was completed by at least 8.2 mm. Branching 

 had begun at 10.2 mm., and was complete at 

 16.8 mm. Four dorsal and four ventral ossified 

 secondary rays were present for the first time at 

 8.2 mm. Lai^e adults showed, by gross micro- 

 scopic examination, all secondary rays to be 

 segmented. 



All 121 caudal fins so examined had 14 branched 

 principal soft-rays and two unbranched principal 

 soft-rays (the most-dorsal and-ventral principal 

 rays of the fin). The principal rays are divided 

 equally between the two caudal lobes. 



Pectoral fins. — A pectoral-fin membrane (fold) 

 with forming rays was present in the smallest 

 larva (2.2 mm.; see fig. 8). Ossification, shown 

 by staining, began ventrally at about 3.5 mm. 

 There were 13 rays in the pectoral fin of a 4.4- 

 mm. larva, 15 in one of a 4.8-mm. larva, and 17 

 were seen in a 5.3-mm. individual. Segmentation 

 had begun by at least 6.6 mm., starting with the 

 uppermost rays, and was complete by about 8.2 

 mm. Neither the size at which branching began, 

 nor the sequence, could be determined, but it 

 was complete by 8.2 mm. In large individuals 

 the most-dorsal and two most-ventral rays are 

 unbranched. 



The variation in immber of pectoral rays of the 

 full complement is shown in table 3. In addition, 

 three other individuals had 17 left pectoral rays 

 (the right rays were not counted). Large series 



Table 3. — Variation in pectoral fin-ray counts for 138 pairs 

 of fins in Pseudopriacanthus altus 



IThe upper number in each block is the count obtained for that combination, 

 and the number in parentheses below is the approximate percentaee of 

 that count in the total sample] 



Total 



of specimens contained individuals with both the 

 17-17 and 18-18 counts, as well as ones with unhke 

 combinations. Some juvenile and adult fish had 

 17 or 19 rays, but the usual count was 18, while 

 the predominant count for prejuveniles was 17, 

 with two specimens having 16. 



Dorsal fin. — -A finfold was present posteriorly 

 at 2.6 mm., and there was a complete fold in a 

 2.7-mm. specimen. No ossified rays were found 

 in stained specimens until 3.5 mm.; and ossifica- 

 tion proceeded posteriorly. A full complement 

 of ossified rays, distinguishable as pro-spines and 

 pro-soft-rays, was present in a 4.4-mm. stained 

 specimen. Segmentation of pro-soft-rays began 

 at about 6.6 mm., starting with the posteriorinost 

 rays, and was complete by at least 8.2 mm. No 

 soft-rays were branched at 15.0 mm., but some 

 posterior ones were branched at 16.8 mm., and 

 branching was apparently complete at 20 mm., 

 and certainly at 34.0 mm. 



The full complement of dorsal spines, 10 (X), 

 found in all 233 prejuvenile, juvenile, and adult 

 specimens so examined, was present by 8.2 mm. 

 (the earliest prejuvenile of the study), when seg- 

 mentation of the soft-rays was complete. Varia- 

 tion in the nunibor of fully developed soft-rays is 

 simunai'ized in table 4. 



Table 4. — Variation in dorsal and anal fin-ray counts for 

 233 .'specimens of Pseudopriacaiithiis altus 



[The upper number in each block is the count obtained for that combination, 

 and the number in parentheses below is the approximate percentage of 

 that count in the total sample) 



COMBINATIONS OF FIN-RAY COUNTS (DORSAL; ANAL) 



a 

 m 

 S 

 P 



z 



