these have scalloped margins and eire supported by rod- 

 like structures. The parietal crests in scorpaenids 

 typically have a serrate margin and have a single 

 strengthening rod at the posterior terminus. 



In Sebastes the paired parietal spines on top of the 

 head develop in larvae 6.0 to 7.0 mm in length, and by 

 the midlarval period each projects backward from a ser- 

 rated parietal ridge. Later in the larval period, a smaller 

 nuchal spine usually develops adjacent and posterior to 

 each parietal spine. In Sebastolobus and Scorpaenodes, 

 the nuchal spines form soon after the parietals and rapid- 

 ly become larger and more prominent than the parietals. 

 This difference in size of the nuchals relative to the 

 parietals is especially useful in separating larvae of 

 Sebastes from those of Sebastolobus. 



Spines also form on a number of head bones in addi- 

 tion to the parietals, e.g., the pterotics, frontals, nasals, 

 and circumorbitals (Moser 1972). Head spination is best 

 developed on postflexion larvae and is a primary charac- 

 ter in the key to postflexion larvae. Although they begin 

 to form on late preflexion larvae, head spines are seldom 

 differentiated enough to be used for identifying leirvae to 

 genus before flexion is completed. 



As in other families, meristic characters are essential 

 in identifying larvae of scorpionfish to genus and species. 

 The most fundamental meristic character is the number 

 of myomeres, since it is the earliest to appear and is 

 equivalent to the number of vertebrae that will develop. 

 The temperate or boreal genera {Sebastes, Sebas- 

 tolobus, Helicolenus) have higher counts than the 

 tropical-subtropical genera {Scorpaena, Scorpaenodes, 

 Pontinus, Trachyscorpia, Ectreposebastes) as sum- 

 marized in Table 2. 



Characters of the fins, including numbers of spines and 

 rays, relative size, shape, and pigmentation are in- 

 dispensable in identifying scorpaenid larvae. The pec- 

 torals are the first to appear and are usually the first in 

 which ossified rays are formed, followed by ossification of 

 principal caudal rays, rays and spines in the pelvics, dor- 



sal and anal fins, and finally procurrent caudal rays. Os- 

 sified rays begin to form in the pectoral fins prior to 

 notochord flexion; they form sequentially from the dor- 

 sal to the ventral margin. The 15 principal caudal rays 

 and pelvic rays (I, 5) form during flexion, whereas the 

 dorsal, anal, and procurrent caudal rays begin to ossify 

 during late flexion and early postflexion stages. The com- 

 plete complement of pectoral rays forms within a 3-mm 

 size range whereas the pelvic, dorsal, and anal fins form 

 within a 2-mm size range; only the formation of procur- 

 rent caudal rays is extended over a greater range of 

 length. 



The number of pectoral rays is not particularly useful 

 in distinguishing among most genera of scorpaenids. 

 Most genera dealt with in this report have 16 to 20 rays. 

 The only striking exceptions are one species of Sebas- 

 tolobus with 21 to 24 rays and Trachyscorpia with about 

 22 to 23 rays. 



The size, shape, and pigment pattern of the pectoral 

 fins are useful in distinguishing among genera and 

 species of scorpaenids (see key to genera for postflexion 

 larvae). Especially useful is the depth of the fin base, 

 which is narrowest in Sebastes, widest in Ec- 

 treposebastes, and of intermediate depths in the other 

 five genera. Values for this previously unutilized charac- 

 ter are summarized by species and stage of development 

 in Table 3. 



There is a marked range in the proportional size of the 

 pectoral fin among the genera included in this study. 

 Larvae of Ectreposebastes have huge fan-shaped pec- 

 torals which extend posteriad to the base of the caudal 

 fin; they increase in relative length during development 

 to a maximum of one-half the body length (Table 3). The 

 fan-shaped pectorals in Scorpaenodes are only slightly 

 smaller than in Ectreposebastes, attaining a maximum 

 of 45"^ of the body length. The pectorals in Sebastolobus 

 and Pontinus are moderately large but differ strikingly in 

 shape, being fan-shaped in the former and aliform in the 

 latter. In Scorpaena they are fem-shaped and moderate in 



Table 2. Meristics for scorpaenids included in this guide. 



