Giganturidae: Development and Relationships 

 R. K. Johnson 



THE Giganturidae contains two highly-specialized bathy- 

 pelagic species placed in two monotypic genera; Gigantura 

 chum Brauer, 1901 and Rosaura mdica (Brauer, 1901). Adults 

 now placed in Rosaura were formerly recognized as Bathyleptus 

 Walters, 1961. Morphological specializations of giganturids are 

 sufficiently divergent and numerous that the group has usually 

 been accorded subordinal or ordinal status somewhere within 

 the group now recognized as basal neoteleosts (Stomiiformes + 

 "Aulopiformes" + "Myctophiformes," see Rosen, 1973; John- 

 son, 1982; Fink and Weitzman, 1982). 



Giganturids are oceanic and deep mesopelagic or bathypelagic 

 as juveniles and adults. Most hauls successful for juveniles and 

 adults have been at depths in excess of 500 m (with closing net 

 captures as deep as 2,000-2,500 m). There is no evidence for 

 diel vertical migration. G. chum is tropical, R. indica tropical- 

 subtropical (sensu Johnson, 1982; 185). Giganturids are un- 

 known from the Southern Ocean, Pacific Subarctic, temperate 

 North Atlantic (including Mediterranean), and only a single 

 specimen (G. chum') is known from the eastern tropical Pacific. 



Giganturids are relatively large-bodied with adults of Rosaura 

 achieving more than 220 mm SL, adults of Gigantura more 

 than 1 70 mm SL. Giganturids are well-known swallowers with 

 greatly expandable pouchlike stomachs. Most identifiable gut 

 contents have been fishes, often single large fish ingested whole 

 (e.g., Regan, 1925). Transformed giganturids are distinguished 

 from most or all other teleosts by the following combination of 

 characters; (A) eyes tubular, directed straight forward, in parallel 

 with main axis of body; (B) gape of mouth extends far behind 

 eye; teeth fang-like, unbarbed, recurved, depressible; teeth bi- 

 serial on each jaw, a medial row of enlarged canines and a lateral, 

 more irregular row of smaller canines; anteriormost canine in 

 each jaw recurving anteriad; (C) bases of pectoral fins nearly 

 horizontal, above the gill openings; pectoral fins with a very 

 high fin-ray count, 37 to 43 in Rosaura. 30-33 in Gigantura; 

 (D) caudal forked, middle rays of lower lobe lengthened enor- 

 mously; in one 120.3 mm SL specimen of G. chuni the fila- 

 mentous extension of the lower caudal lobe adds 243 mm to 

 the length of the fish; (E) skin loose, scaleless, with a thick layer 

 of mesenchymal jelly adding substantially to an overall char- 

 acteristic flabbiness; (F) stomach a thickwalled blind pouch, 

 giving rise to the intestine ventrally, near midline; intestine 

 passing laterad and dorsad, to right, continuing along dorsal 

 contour of stomach until finally turning ventrad behind poste- 

 rior terminus of stomach and ending at anal papilla; (G) lack 

 of pelvic fins, dorsal adipose fin, branchiostegal rays, gill rakers; 

 loss of most of gill arch elements on arches I-III, but with strong, 

 recurved teeth on 3rd pharyngobranchial (pb) and 4th pb tooth- 

 plate; loss of numerous other skeletal elements (cf Regan, 1 925; 

 Walters, 1961, 1964; Rosen, 1973); and (H) considerable con- 

 solidation of caudal fin skeleton with two presumably com- 

 pound hypurals (Rosen, 1973). 



Development 



Eggs of giganturids are unknown. Larvae are known for both 

 species but only the larva of Rosaura (a single 8.4 mm specimen. 



Fig. 105) has been illustrated (Tucker, 1954). For both species 

 larvae have commonly been taken in the upper 100 m. The 

 distributional ranges of larvae and adults are coextensive and 

 there is no evidence for seasonality in reproductive effort (with 

 only ca 400 known larval specimens, the data are far from 

 complete). The sexes are separate and according to Clarke and 

 Wagner (1976) the females may reach twice the size of males, 

 although available data are sparse. Osteological examination 

 has been confined to adults except for those elements visible 

 and described in Tucker's (1954) astonishingly detailed decrip- 

 tion of the holotype of Rosaura rotunda. Development is direct 

 but transformation is abrupt with the change from larval to 

 adult morphology occurring over the approximate size range of 

 30-40 mm SL in Gigantura and 40-60 mm SL in Rosaura. 

 Transformation series are now known for both species (only 8 

 transforming specimens of Gigantura are known, for Rosaura 

 the count stands at 34) but these results remain unpublished. 

 The interim account below is thus based on work in progress. 



Gross aspect (Fig. 105). — "Rosaura" larvae are short, deep, glo- 

 bose, translucent and virtually colorless. The forehead is steep, 

 the eyes small, round and directed laterad. The snout is pointed. 

 The body is deepest at a vertical through the center of the 

 opercle. The pectoral insertion is nearly vertical. A dorsal adi- 

 pose and distinct partly-stalked 5-rayed pelvic fins are present. 

 Large, readily visible, rather platelike branchiostegal rays are 

 present. Raptorial jaw teeth are present in the smallest known 

 larvae (4 mm SL). Teeth on the jaws are biserial with an inner 

 series of prominent canines and an outer series of shorter more 

 broadbased teeth on the premaxillaries and dentaries. There are 

 2-4 recurved smaller fangs on the basihyal. The maxillary is 

 included in the gape but is edentulous. The abdominal body 

 wall is nearly transparent and balloonlike, enclosing an expan- 

 sive gut cavity. The body form remains essentially unchanged 

 over a period of larval growth extending to ca 30 mm SL (Gi- 

 gantura) and to ca 35 mm SL {Rosaura). when transformation 

 begins. Changes during transformation are striking, as described 

 below. At all stages— larvae, transforming specimens, and ju- 

 veniles and adults— the species can be distinguished on the basis 

 of relative depth of the caudal peduncle. The value of this char- 

 acter varies ontogenetically but the relative peduncle depth is 

 always greater in Gigantura. 



Meristic characters.— Courtis of fin rays do not differ between 

 larvae and adults except that semi-stalked pelvic fins (5 rayed) 

 are universally present in larvae and early transforming speci- 

 mens but are completely lost during transformation. Values for 

 anal-fin ray counts (8 to 10 in G. chuni. II to 14 in i?. indica) 

 and pectoral-fin ray counts (30 to 33 in G. chuni. 36 to 42 in 

 R. indica) separate the two species without overlap. Dorsal-fin 

 ray counts ( 1 6 to 19) have the same range in both species. The 

 caudal is the first fin to form; it is asymmetric with 10 -t- 6(7) 

 principle caudal rays and (3)4(5) procurrent caudal rays above 

 and below. Next to form, in order, are the dorsal + anal fins, 

 pelvic fins, and pectoral fins (the dorsalmost pectoral rays begin 



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