MOSER and AHLSTROM: DEVELOPMENT OF SCOPEWPSIS MULTIPUNCT ATI'S 



with Notoscopelus and Lampichthys, since the 

 three genera are the only myctophids with hor- 

 izontal POL photophore>5 on the posterior lateral 

 surface of the body, Scopelopsis and Notoscop- 

 elus have either two or three such photophores 

 in a horizontal line below the lateral line, while 

 in Lampichthys the two horizontal photophores 

 form a right angle with a third POL that is 

 placed midway between the two upper POL's and 

 the ventral series. Other characters of the lar- 

 vae substantiate the close relationship of these 

 three genera. The larvae are similar in shape 

 of the eye, head, and body. Scopelopsis and 

 Lampichthys have extremely similar pigment 

 patterns and differ only in the number and size 

 of the melanophores in each area (Figures 1-3, 

 5). Notoscopelus differs only slightly from the 

 other two, in its lack of a melanophore in the 

 ventral midline below the pectoral fin and in 

 having a prominent series of melanophores along 

 the lateral line (Figure 6). 



Characters of the adults affirm the close re- 

 lationship of the three genera. Scopelopsis and 

 the several species of Notoscopelus have the high- 

 est numbers of dorsal fin rays, 21-23 and 22-27 

 respectively, in the family. The Dn light organ 

 at the anterodorsal margin of the orbit is com- 

 posed of two contiguous structures in Scopelopsis 

 and Notoscopelus; it consists of a small photo- 

 phore, with a margin of black pigment, dorsal to 

 a larger opaque mass of tissue that lacks mar- 

 ginal pigment. In Lampichthys a mass of black 

 tissue lies below the opaque luminous tissue, 

 which extends posteriad over the entire dorsal 

 surface of the orbit. Scopelopsis is covered en- 

 tirely by small secondary photophores, as is the 

 body of Lampichthys. Such photophores are ab- 

 sent from the head of Lampichthys; however, 

 the four or five prominent cheek photophores of 

 Lampichthys are comparable to those of Scopel- 

 opsis. A single opaque patch of luminous tissue 

 lies below each pectoral fin base in Scopelopsis. 

 In Lampichthys, a luminous patch is present in 

 exactly the same position; however, several ad- 

 ditional patches are present on the lateral sur- 

 faces of the body. In Notoscopelus, luminous 

 patches are much more extensive, although the 

 prominent patch below the base of each pectoral 

 fin is present in all species of the genus. 



The sequential development of the Br2, Vn, 

 PLO, and PO5 is unique to the genera in group B 

 {Ceratoscopelus, Lepidophanes, Bolinichthys) ; 

 this, along with the small size of the photophores, 

 and their early appearance, points to close rela- 

 tionship of the three genera. The larvae of some 

 species of Bolinichthys are an exception, since 

 they develop only the Br2. Other characters of 

 the larvae, such as a similarity in body shape 

 and a general paucity of pigment, also suggest 

 the close relationship of the three genera (Fig- 

 ures 7, 8, 9). Paxton (1972) has pointed 

 out a number of osteological characters of the 

 adults that link the three genera, and the simi- 

 larity in the arrangement of luminous patches 

 among species of the three genera is well estab- 

 lished in the literature. 



The larvae of Lampadena and Lampanyctodes 

 (group C above) develop the Br2, PLO, and PO5. 

 The PLO photophores become conspicuously de- 

 veloped on small larvae of Lampadena soon after 

 the formation of the Bra pair; the PO5 pair 

 appear shortly thereafter (Figure 10). The 

 Vn pair is later-forming and may be preceded 

 by the POi pair, or the two pairs may form 

 simultaneously. The sequence of development 

 of early-forming photophores on Lampanyctodes 

 hectoris has not been fully established. The Br2, 

 PLO, and PO5 pairs were well developed on the 

 .smallest larva (9.2 mm) available for study 

 ( Figure 11). A 14.5-mm transforming specimen 

 of Lampanyctodes had 13 pairs of photophores 

 developed, including the Vn and PO pairs. Even 

 so, the only genera with this combination of three 

 early-forming photophores are Lampadena and 

 Lampanyctodes. Also, the larvae of the two gen- 

 era are similar in body shape and in pigmenta- 

 tion. 



The larvae of Gymnoscopelus (group D above) 

 form the Br2, PO5, and POi early (Figure 12), 

 Later in the protracted larval period, the VOi 

 and then PO2 appear. In some species (e.g., G. 

 aphya) the larvae reach a length of 28 mm and 

 are the largest of all myctophid larvae, Diaphus 

 and Lobianchia also develop the Br2, PO5, and 

 POi early in the larval period and are included 

 in group D. This, however, is virtually the only 

 larval character that the two genera share with 

 Gymnoscopelus. They develop photophores grad- 



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