OKIYAMA: MYCTOPHIFORMES 



Table 58. Comparison of the Larval Characters Among Four Genera of the Ipnopidae. 



209 



' Details are mentioned in the text. 



zontal pigment bar across the head. Small preopercular spines 

 are known only in Neoscopelus whereas a long snout is peculiar 

 to Scopelengys. 



Chlorophthalmidae (Fig. ]09E-F).— Of Ihe three genera of this 

 benthic family, the cosmopolitan Chlorophthalmus is particu- 

 larly diverse and abundant. Extensive revision of this genus is 

 needed, since there are many undescribed species from the West- 

 em Pacific and the known species can be divided into two dis- 

 tinct groups, each warranting generic status (Doi and Okamura, 

 1983). 



Eggs are not known. Despite the abundance of adults, few 

 larvae have been reported. Complete developmental series are 

 available for only C. agassizi (Tamng. 1918). Known larvae of 

 other species such as C. mento, C. prondens and Chlorophthal- 

 mus spp. (Pertseva-Ostroumova and Rass, 1973; Miller et al., 

 1979; Okiyama, unpubl.) show close resemblance to C. agassizi 

 having the extremely short gut with large preanal interspace, a 

 similar pigment pattern composed of a single peritoneal pigment 

 section lying at the pectoral fin base and a melanophore at the 

 hypural complex, short fins and anteriorly placed dorsal and 

 pelvic fins (as in Aulopidae). There are possible specific differ- 

 ences in the size at appearance of the peritoneal pigment section 

 (ca. 7 mm in C. prondens vs 5-6.6 mm in C. mento) and in the 

 arrangement of the few small melanophores on the dorsal and 

 ventral margin of the tail near the notochord tip in early larvae. 

 Meristic characters are useful in discriminating the particular 

 species or species groups, although early developmental stages 

 are usually very difficult to identify to species. 



Larval osteology was studied in detail for C. agassizi (Rosen, 

 1971) but the sequence of fin formation is not clear except that 

 the pectoral fin develops early. Principal changes during the 

 gradual metamorphosis include the rotation of the eyes dorsally 

 which takes place at sizes less than 40 mm (Ahlstrom, 1972a). 



Unusual larvae with a pigmentation pattern similar to the 

 above described forms are found in ORl collections from the 

 Kuroshio area (Fig. 1 09 A). These are distinct in that the head 

 is markedly depressed, bowed with duckbilled appearance, and 

 a single peritoneal pigment section is large enough to cover the 

 dorsal half of the short gut. Their meristic characters (ca. 42 

 myomeres and ca. 1 7 pectoral rays) suggest a possible affinity 

 with Chlorophthalmus (sensu lato). These two larval types seem 

 to substantiate the suggested dichotomy of this genus. No in- 

 formation is available for larvae of the other two genera (Par- 

 asiidis and Bathysauropsis). 



Ipnopidae (Fig. 1 1 OA-E). — Four benthic genera compose this 

 family which has been variously classified (e.g.. Nielsen. 1966; 

 Sulak. 1977). Despite their deep-sea mode of existence, larval 

 stages of all genera have been mostly obtained from the surface 

 waters. Developing eggs are not known. Mature ovarian eggs 

 are known for all genera with virtually identical features such 

 as a spherical shape, diameter of about 1.0-1.2 mm, and the 

 presence of a single large oil globule (Nielsen, 1966; Sulak, 1977 

 and pers. comm.; Merrett, 1980). Although intergeneric differ- 

 ences of the early larval stages are remarkable (Table 58). they 

 share several conspicuous characters including the more or less 

 hung-down head profile and the elongated precocious pectoral 

 fins. At metamorphosis these become less prominent in asso- 

 ciation with the drastic change in the mouth size from moderate 

 to huge and the appearance of heavy body pigmentation. 



Two larvae (13.9, 10.6 mm) are known for Ipnops: the larger 

 specimen referred to /. agassizi was described in considerable 

 detail and illustrated (Okiyama, 1981). The smaller one may be 

 /. meadi in view of its higher anal ray count (ca. 13). A divided 

 pectoral fin with elongated upper rays is peculiar to this genus 

 (Table 58). Principal changes at metamorphosis include the de- 

 velopment of the unique eye plaque, a depressed head with 

 straight profile, and the disappearance of the peculiar feature of 

 the pectoral fins along with the loss of several rays. Metamor- 

 phosis may be rapid, but the smallest benthic juvenile of 40 

 mm still bears the immature eye plaque (Sulak, 1977). 



Bathytyphlops includes only two species, B. sewelli and S. 

 marionae (Merrett. 1980). A larva of this genus was first de- 

 scribed under the name Macristiella perlucens of uncertain af- 

 finity (Berry and Robins, 1967). The known "Macristiella" (19 

 specimens, 7-43 mm) are all referable to B. marionae except 

 for the 37 mm larva from the Indian Ocean and the smallest 

 specimen (Parin and Belyanina, 1972). The Indian Ocean spec- 

 imen may be identified as B. sewelli on the basis of the higher 

 anal ray count (18), a unique character for this species. 



Early stage larvae have little melanistic pigmentation, but 

 some bluish or violet coloration is present on the fins and var- 

 ious body parts in living specimens (Berry and Robins, 1967). 

 Preserved individuals sometimes retain this feature, usually on 

 the large pectoral or pelvic fins. Reduction of the relative size 

 of eyes, and the loss or replacement of the teeth as well as gill 

 rakers are among the major changes at metamorphosis, in ad- 

 dition to those common to the family. Otherwise, larval de- 

 velopment is rather direct and the relative position of the fins 

 and the anus changes little throughout ontogeny. The osteology 



