FISHERY BULLETIN: VOL 75, NO. 4 



stricted behind anus, tail exceedingly elongated in 

 juveniles and adults. Young with numerous dark 

 round spots. Skin of adults pierced by numerous 

 pores. 



Description — Body strongly compressed later- 

 ally, postanal portion of body narrowing into a 

 whiplike tail in juveniles and adults (posterior 

 vertebrae about four times as long as 14th ver- 

 tebra). Posterior region of body of larvae and pre- 

 juveniles narrow, but not exceedingly elongate 

 (posterior vertebrae shorter than 14th vertebra). 

 Seven pterygiophores before first neural spine, 

 one or two pterygiophores between first and sec- 

 ond neural spines. First pterygiophore closely 

 applies to back of skull, no predorsal bones. An- 

 terior five or six dorsal rays elongated in larvae 

 and prejuveniles to form a dorsal pennant; these 

 rays completely lost in adults. Pelvics long and 

 fanlike in young, absent in adults. Caudal well 

 developed, of 4-10 unbranched rays, parallel to 

 axis of tail. Caudal rays all borne on last ural 

 centrum, no ventral caudal lobe (Figure 1). 



Fin rays with a lateral row of small spines, these 

 weak or absent on posterior pelvic rays, middle 

 caudal rays, and pectoral rays. Each dorsal ray 

 anterior to elongated tail portion of body with a 

 single laterally directed stout spine on either side 

 of the base. 



Lateral line ending at caudal base, lateral-line 

 scales with a pair of spines. Body otherwise scale- 

 less at all sizes (D. polystictum ), or young covered 

 with scales, each with a pair of longitudinal spin- 

 ous ridges (D. lorum). Skin of adults with cartilag- 

 inous tubercles, and pierced by numerous pores 

 (Walters 1963). No enlarged tubercles on ventral 

 midline. 



FIGURE l.— Caudal skeleton of Desmodema polystictum, SIO 

 73-340. Camera lucida drawing at 25 x magnification. Only 

 bases of caudal rays shown. CR, caudal ray; Hy hypural; Ui, 

 first ural centrum; U2, second ural centrum and hypural. 



844 



Two nostrils in prejuveniles, the posterior just 

 before anterior margin of eye; posterior opening 

 obliterated in juveniles and adults. Nasal 

 epithelium without ridges or folds at all sizes. 

 Head bones cancellous and ridged. Mouth strongly 

 oblique. Teeth restricted to one to four in each 

 premaxilla and two enlarged, recurved fangs on 

 mandible, one on either side of symphysis. Gill 

 rakers (2-3) + (9-10) usually 3+ 9, fleshy, distally 

 expanded and leaflike. Rakers of upper limb with a 

 few teeth. Pseudobranch well developed. Gas 

 bladder present in smalljuveniles (to about30 mm 

 SV), rudimentary or absent in large juveniles and 

 adults. 



Very young silvery, prejuveniles silvery with 

 profuse dark spotting, adults without spots. 



Growth changes. — Although we have no mate- 

 rial smaller than 18.9 mm SV, it appears that 

 development from a silvery or transparent form 

 with a triangular outline with the head deepest, 

 into the polka-dotted, deep bodied prejuvenile is 

 gradual. The transition from prejuvenile to 

 juvenile is probably rapid and can fairly be termed 

 a metamorphosis. There is a large-size gap in our 

 material of D. polystictum (91-260 mm SV), but 

 our material of D. lorum includes the appropriate 

 size classes. The difference between the pre- 

 juvenile and the final body form can be seen in 

 Figure 5. The two specimens are almost identical 

 in snout-vent length. However, the upper speci- 

 men is essentially a miniature adult. The major 

 differences are in the change in the ventral profile, 

 elongation of the tail, increase in eye size, eruption 

 of lower jaw teeth, and loss of the spots, pelvic fins, 

 and posterior nostril. Juveniles, including our 

 largest (173 mm SV) have an elongate opening not 

 yet covered over by the skin at the position of the 

 pelvic fins, indicating that loss of the pelvics may 

 be rapid, and from the base. 



Walters (1963) indicated that juveniles of D. 

 polystictum are scaled, but that adults are scale- 

 less, and have cartilaginous tubercles and a sub- 

 dermal canal system connected to the surface by 

 numerous pores. In our material of D. lorum an 

 18.5-mm SV silvery individual lacks both scales 

 and tubercles. An individual 36 mm SV is scaled, 

 but lacks tubercles, and in another (36.5 mm SV), 

 tubercles are present ventrally, and on the sides 

 behind the head. Our largest polka-dotted pre- 

 juvenile is 95 mm SV. The upper sides are scaled; 

 the remainder of the body is covered with tuber- 

 cles and the subcutaneous canal system. is well 



