Scopelarchidae: Development and Relationships 

 R. K. Johnson 



THE Scopelarchidae has traditionally been included with the 

 primarily oceanic Alepisauroidei (Marshall, 1955; Gosline 

 et al., 1966; Rosen, 1973; Johnson, 1974b, the most recent 

 complete revision). Johnson (1982) excludes the scopelarchids 

 from the alepisauroids, rejects putative sister-group relationship 

 with the Evermannellidae, and provisionally allies the scope- 

 larchids with the chlorophthalmoids. All scopelarchids are 

 oceanic and meso- or bathypelagic. The majority of known adult 

 specimens were taken in hauls to depths between 500 and 1 ,000 

 m. For most species there exists no evidence to suggest diel 

 migration, however, Merrett et al. ( 1 973:39-40) present limited 

 evidence for diel migration ("considerably dispersed vertically") 

 in Benthalhella infans. Scopelarchids are relativedly large-bod- 

 ied (to 302 mm SL; Iwami and Abe, 1980). All Scopelarchidae 

 are tubular-eyed predators (see Munk, 1966; Locket, 1970; 

 Muntz, 1976; Johnson, 1982) concentrating most frequently on 

 fish, not capable of engorgement of enormously large food par- 

 ticles (unlike evermannellids, Omosudis, Alepisaurus, Antop- 

 terus and at least some paralepidids). Luminous tissue occurs 

 in Benthalhella infans (Merren et al., 1973) and probably occurs 

 in Scopelarchoides kreffti (Johnson, 1 974b). The family contains 

 1 7 species arranged in four genera and occurs throughout the 

 world ocean except that no scopelarchid inhabits the Arctic 

 Ocean or the Mediterranean Sea. Among iniomous fishes, the 

 Scopelarchidae is distmguished by the following combmation 

 of characters: ( 1 ) basihyal short to elongate but well-ossified; (2) 

 lingual teeth strong, straight to strongly hooked, invariably pres- 

 ent over basihyal, present or absent over basibranchials; (3) body 

 and postorbital regions of head completely covered with cycloid 

 scales; (4) lateral line scales large, differing distinctively in exact 

 conformation between all species (Johnson, 1974b: Fig. 2); (5) 

 parietal bones, when present, small, widely separated by frontals 

 and supraoccipital; (6) coracoid broadly expanded; (7) two post- 

 cleithra, widely separated in vertical dimension; (8) unossified 

 gap (filled by tube-like structure of fibrous connective tissue) 

 between skull and first vertebral centrum (see Merrett et al., 

 1973:17); (9) posttemporal unforked; (10) no basisphenoid, or- 

 bitosphenoid, gill rakers, or free second ural centrum; (11) eyes 

 tubular, directed straight upward (except in 3 species where 

 directed dorsoanteriad); (12) larvae with 0, 1 or 3 peritoneal 

 pigment sections. The genera and species are distinguished by 

 gross morphological, meristic, morphometric, osteological, pig- 

 ment and larval characters (Tables 65 and 66). 



Development 



Eggs of scopelarchids are unknown. Larvae are known for all 

 species except Scopelarchoides kreffti and developmental series 

 have been illustrated and described (Rosen, 1973; Merrett et 

 al., 1973; Johnson, 1974b; Belyanina, 1981, 1982a;Moser, 1981). 

 Except for limited information on Benthalhella infans in Merrett 

 et al. ( 1 973), osteological description has been confined to adults. 

 Except in Benthalhella. development is direct, adult characters 

 are essentially acquired one by one, with completion of trans- 

 formation at 30 to more than 80 mm SL depending upon the 



species. Larvae of Benthalhella undergo very rapid (i.e., small 

 size increment) transformation after a prolonged period of growth 

 while retaining larval form (see below). Larvae of most species 

 are known from hauls within the top 100 m and the larvae of 

 a number of species have been taken in the top 50 m. Con- 

 trariwise the larvae of one species, Benthalhella dentata. have 

 not been taken in hauls shallower than 150 m and most were 

 taken in hauls to depths in excess of 500 m. Except possibly the 

 cases oi Benthalhella elongata and B. macropmna (see Johnson, 

 1974b:228), the distributional ranges of larvae and adults are 

 coextensive. There is no evidence (the data are quite incomplete) 

 for seasonality in reproductive effort. Scopelarchids are syn- 

 chronous hermaphrodites. 



The following paragraphs describe those characters most ev- 

 ident in the early life history of scopelarchids, including those 

 of value in distinguishing genera and species. 



Gross aspect (Fig. 127). — Larvae range from extremely elongate 

 and shallow (Benthalhella) to quite short and deep (some species 

 of Scopelarchus and Scopelarchoides). Small larvae are trans- 

 lucent, scaleless, colorless (except for pentoneal pigment sec- 

 tions, when present), with a characteristic "bowed down" an- 

 terior dorsal profile. The body is deepest at the pectoral girdle 

 and the trunk elongate. Anteriorly the hypaxial muscles do not 

 embrace the abdominal cavity walls which are therefore highly 

 translucent. Only the muscles of the pelvic girdle are visibly 

 evident. The abdominal cavity is triangular, deep anteriorly. 

 Peritoneal pigment appears early except in Benthalhella which 

 lacks peritoneal pigment until transformation. The gut is mid- 

 ventral. In larvae the anus is anterior (relative to distance be- 

 tween pelvic fin insertion and anal fin origin) to position in 

 adults, far anterior in some (Benthalhella). The head is very 



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