Ditty et al.: A redescription of Chaetodipterus faber larvae 



271 



2.5 mm, respectively. Differences between Ryder's 

 and our study do not support identification of 

 Ryder's larvae <4.0 mm as Atlantic spadefish even 

 if we allow for specimen shrinkage (also noted by 

 Johnson, 1978) and for slower development times 

 due to cooler waters of Chesapeake Bay during the 

 summer when Atlantic spadefish spawn. 



Johnson (1984) characterized the sequence of fin 

 completion in larval Atlantic spadefish as pattern A: 

 dorsal and anal soft rays - spinous dorsal - pelvics 

 - pectorals. We cleared and stained seven larvae and 

 found the sequence of fin completion more closely 

 resembles Johnson's (1984) pattern F with all ele- 

 ments of the pelvic fin present before dorsal and 

 anal soft rays. This difference in fin completion pat- 

 tern, however, may be due to differences in how we 

 and Johnson interpreted spine formation and fin 

 completion. We counted rays when first segmented 

 and spines when present; Johnson may have 

 counted pterygiophores. Pattern F is found in Hapa- 

 logenys, Monodactylidae, and Pempherididae 

 (Johnson, 1984). 



Larvae of Atlantic spadefish are characterized by 

 early development of specialized spinous scales or 

 "prescales" (at about 5.5 mm, this study) that even- 

 tually transform into adult ctenoid scales. Spinous 

 larval scales are present to about 15.0 mm (Johnson, 

 1984). Ctenoid scales are well developed by 18.0 mm 

 (Hildebrand and Cable, 1938). 



Developmental morphology and head spination of 

 Atlantic spadefish is generally similar to that of 

 Pacific spadefish ( Martinez-Pecero et al., 1990). Both 

 species are deep-bodied (usually 55-60% SL) and 

 preanal length is about 60% SL. Pigmentation and 

 standard length at which fins develop also are simi- 

 lar; a full complement of rays is present in all fins 

 by 8.0-9.0 mm in both species (Hildebrand and 

 Cable, 1938; Martinez-Pecero et al., 1990; this 

 study). However, consolidation of pigment into lat- 

 eral bands, resorption of the supraoccipital crest, 

 and the beginning of transition to the juvenile stage 

 occur earlier in Pacific spadefish than in Atlantic 

 spadefish. Larvae of ephippids from the Indo-Pacific 

 region differ from Chaetodipterus from the western 

 Atlantic and Pacific Oceans in extent of head 

 spination (Leis and Trnski, 1989; Martinez-Pecero 

 et al., 1990; this study). Larvae of Platax from the 

 Indo-Pacific have a median supraoccipital crest with 

 a serrate leading edge (Leis and Trnski, 1989) but 

 do not have the circumorbital series of spinous 

 ridges, nor spines on the jugal, tabular, pterotic, or 

 supracleithral bones found in Chaetodipterus 

 (Martinez-Pecero et al., 1990; this study). Head 

 spination in Ephippus larvae from the Indo-Pacific 

 is similar to that of Chaetodipterus and these two 



genera are probably more closely related than either 

 is to Platax. Other species-specific head spination 

 found in Chaetodipterus larvae from the western 

 Atlantic and Pacific Oceans, and in Ephippus orbis, 

 Platax batavianus, and three Platax species from 

 the Indo-Pacific region include a posttemporal spine 

 which may be reduced to a ridge in some species, a 

 supraorbital ridge that varies in size among species, 

 and one or two subopercular spines (Leis and Trnski, 

 1989; Martinez-Pecero et al., 1990; this study). 



Early larvae of Atlantic spadefish could be con- 

 fused with priacanthids, lobotids, some carangids 

 and stromateoids, the wreckfish — Polyprion amer- 

 icanus, and Menticirrhus spp. because of similari- 

 ties in head spination or in body pigmentation. 

 Priacanthids have an elongate, serrate, median 

 supraoccipital crest that extends posteriorly over the 

 mid- and hindbrain; serrations along the lower jaw 

 and frontal bone; and the angle preopercular spine 

 is elongate and serrate as is the pelvic spine. Trip- 

 letail, Lobotes surinamensis, have a vaulted, serrate 

 supraoccipital crest in early larvae, the pelvics are 

 inserted behind the pectoral fins, and have fewer 

 anal fin elements than Atlantic spadefish (Atlantic 

 spadefish: A. Ill, 17-18, tripletail: A. Ill, 11-12). In 

 carangids, the two anteriormost anal spines are 

 separated from the third by a distinct gap and most 

 species have a low, median supraoccipital crest that 

 has serrations along the dorsal edge; other carangids 

 lack a supraoccipital crest entirely. Some carangids 

 also have a precocious dorsal fin with anterior 

 spines or rays elongate, or with serrations along the 

 angle preopercular spine. Some stromateoids (e.g. 

 Ariommus spp., Nomeus gronovii) resemble Atlan- 

 tic spadefish in early body pigmentation, body 

 shape, and by having precocious pelvics, but 

 stromateoids lack a median supraoccipital crest, a 

 large preopercular angle spine, and all but 

 Hyperoglyphe have >30 myomeres. Polyprion 

 americanus larvae have a small, peak-like median 

 supraoccipital crest, but with serrations along the 

 leading edge, and lack a serrate pterotic ridge and 

 spines on the tabular bone (Johnson, 1984). 

 Wreckfish also have 27 myomeres, fewer dorsal (22- 

 24) and anal fin (11-13) elements, and the mouth 

 is larger than in Atlantic spadefish. Larval Atlantic 

 spadefish differ from early larvae of Menticirrhus 

 spp. by lack of both preopercular spines and the 

 median supraoccipital crest in the latter. 



We recently examined specimens reported by 

 Dawson (1971) as larval black driftfish, Hypero- 

 glyphe bythites. These specimens had a supra- 

 occipital crest, pterotic ridge, spine on the inter- 

 opercle, other head spination, and a pigmentation 

 pattern identical to Atlantic spadefish. Vertebral, 



