BULLETINOFMARINESCIENCE.49(1-2): 137-147, 1991 GROWTH STAGES OF MOROTEUTHIS ROBUSTA (VERRILL, 1881) WITH THE RE-EV ALUATION OF THE GENUS Kotaro Tsuchiya and Takashi Okutani ABSTRACT Based on sequential growth stages of Moroteuthis robusta. M. japonica and M. pacifica are synonymous with M. robusta. and smaller stages are bridged to the Onykia "carribaea" species complex. Within the family Onychoteuthidae, the genus Onykia has in common with the genus Moroteuthis the absence of both visceral photophores and dorsal nuchal folds. Young Moroteuthis have a smooth mantle surface with a distinct iridescence, a small number of marginal suckers on the tentacular club and an indistinct cartilageous cap on the endocone. While, large Onykia develop rhomboidal fins, an inverted Y-shaped cartilageous ridge in the funnel groove, and a reduced number of marginal suckers on the club, all of which characterize Moroteuthis. Close examination of a series of O. "carribaea" specimens reveals that the species is not monospecific, but contains more than one species. It is thus suggested that the genus Onykia. therefore, appears to represent juvenile stages of the genus Moroteuthis. Moroteuthis robusta (Verrill, 1881) is a gigantic squid distributed in the North Pacific. However, its life cycle and growth stages have never been determined. Three smaller species of Moroteuthis were described from the North Pacific, namely, M. loennbergii Ishikawa and Wakiya, 1914, M. japonica (Taki, 1964) and M. pacifica Okutani, 1983, of which the latter two are apparently based on im- mature specimens. Within the family Onychoteuthidae, the genus Moroteuthis Verrill, 1881 and Onykia Lesueur, 1821 have common features that separate them from the other genera, such as, absence of crowded dorsal nuchal folds and visceral photophores, as well as the characters of the mantle surface texture, presence of marginal suckers on the club, and the shape of the gladius (Thiele, 1931; Filippova, 1972). Most species of the genus Onykia have been described from juveniles alone (Pfeffer, 1912). The only exception is O. rancureli Okutani, 1981. On the contrary, in the genus Moroteuthis, a very early juvenile specimen has been reported only for M. robsoni by Dubinina (1980), and information on the early growth stages of this genus is very scarce. The present study re-evaluates the generic characters of Onykia and Moroteu- this, and demonstrates the linkage of these two genera mainly through comparison of a growth series of M. robusta which is compared with early juveniles referable to so-called Onykia carribaea. MATERIALS EXAMINED Moroteuthis robustalOnykia carribaea from northwest Pacific: 3 unsexed (94, 135, 181 mm DML), 35°43.7'N 148"00.2'E, 0-100 m, 29 Apr. 1987, R/V KAIYO-MARU,midwater trawl. 1 unsexed (100 mm DML), 35°27.8'N 145°59.4'E 0-105 m, 24 Apr. 1987, R/V KAIYO-MARU,midwater trawl. 1 unsexed (60.7 mm DML), 32°30'N 158°30'E, 0-1,000 m, 29 May 1984, R/V KAIYO-MARU,midwater trawl. 2 unsexed (19.4, 42.8 mm DML), 35°59'N 142°31.8'E, surface, 12 May 1972, R/V SOYO-MARU, dip-netted. Reference Materials Moroteuthis ingens (Smith, 1881): I female (137 mm DML), 49°47'S I66°40'E, 136 m, 14 Jan. 1985, R/V SHINKo-MARu,jigging. 1 female (77.0 mm DML), 46°34'S 165°59'E, 155 mm, 3 Dec. 1984, R/V SHINKO-MARU,jigging. 137 138 BULLETINOFMARINESCIENCE,VOL.49, NO. 1-2, 1991 Figures 1-4. Moroteuthis robusta. Mantle texture. 1. 42.8 mm DML. 2. 60.7 mm DML. 3.100 mm DML. 4. 135 mm DML. [Scale bar: 10 mm.] Moroteuthis loennbergii Ishikawa and Wakiya, 1914: I female (350 mm DML), 30"N I35°E, 0-3392 m, 3 Aug. 1986, R/V KAlYO-MARU,midwater trawl. I male (307 mm DML), 31°37'N 128°13'E, 163 m, 18 July 1988, R/V TANsHu-MARu, bottom trawl. 1 female (102.1 mm DML), 29°N 135°E, surface, date unknown, 1968, P/V NOHMA,dip-netted, National Science Museum, Tokyo. Moroteuthis robsoni Adam, 1962: 3 unsexed (69.5,81,82 mm DML). 43°01'S 167°35'E, 27 Nov. 1984, R/V SHINKO-MARU. Moroteuthis sp.: 1 female (105.3 mm DML), 39°59'N 143°30'E, 18 July 1986, R/V OYASHIO-MARU, jigging. Onykia carribaea auctt.: Onykia sp.A: 1 un sexed (43.7 mm DML), 12°22'S 83°03'W, surface, 26 Aug. 1984, R/V SHINKo-MARU,dip-netted. Onykia sp.B: 1 un sexed (41.6 mm DML), 37°14.5'S 168°15.9'W, 25 Sept. 1956, R/V SHOYo-MARU,from stomach contents of Alepisaurus jerox. Onykia sp.C: I unsexed (40.0 mm DML), 14°56'S 81005'W, 28 July 1984, R/V SHINKo-MARU,long line, National Science Museum, Tokyo. Onykia sp.D: I unsexed (39.0 mm DML), 29°N 135°E, surface, 27 July 1969, PlY NOJIMA,dip-netted, National Science Museum, Tokyo. RESULTS Several M. robusta specimens of different sizes were compared with each other. The results exhibit quantitative and qualitative sequential morphological changes with growth. Mantle. -In specimens smaller than 42.8 mm DML, the mantle is ornamented with a distinct iridescent epidermis, under which numerous indistinct ridges are observed. The mantle ~mrfaceofthe 60.7 mm DML specimen is ornamented with not only fleshy ridges, but also a weak iridescent layer. The surface texture of the mantle is rugose with numerous fleshy ridges in specimens larger than 94 mm DML (Figs. 1-4). Fins. - The outline of fins are oval in the specimens smaller than 20 mm DML (Fig. 5). In the 42.8 mm specimen, the posterior angle of fins has become acute with the development of tail (Fig. 6). The fins of the 60.7 mm specimen are rhombic (Fig. 7), and those of the specimens larger than 94 mm are sagittate (Figs. 8-10). The fin length is about 50 to 60% ofDML in all specimens, while its width is largest (68.7% ofDML; 152.9% of fin length) at 60.7 mm DML, and smallest (49% ofDML; 84.2% affin length) at 181 mm. The fins are wider than long at smaller than 100 mm, while longer than wide over 135 mm DML. Cartilageous Ridge in the Funnel Groove. The specimens larger than 60.7 mm DML have a cartilageous, inverted Y-shaped ridge in the funnel groove (Figs. 12, 13). The similar ridge is also observed in the 42.8 mm specimen on the border TSUCHIYA AND OKUTANI: GROWTH STAGES OF MOROTEUTH/S ROBUSTA 139 Figures 5-10. Moroteuthis robusta. Ventral view. 5.19.4 mm DML. 6. 42.8 mm DML. 7. 60.7 mm DML. 8. 135 mm DML. 9. 181 mm DML. 10. 1615 mm DML after Sasaki (1929). [Scale bar: 20 mm.] 140 BULLETIN OF MARINE SCIENCE, VOL. 49, NO. 1-2,1991 \ \~ \1 "\'j \j 12 FiguresII-B. Moroteuthis robusta. Ventralviewof headshowinginvertedV-shapedridgein the funnelgroove.II. 42.8 mm DML. 12. 100 mm DML. 13. 181 mm DML. [Scalebar: 10 mm.] of the funnel retractor muscle (Fig. 11). In specimens smaller than 20 mm DML, the ridge has not developed. The ridge moves anteriorly with growth. Tentacular Club. - The club is short, compact and curved dorsally with a broad aboral keel and protective membranes in the specimens smaller than 42.8 mm DML (Figs. 14, 15). However, the club in the specimens exceeding 60.7 mm is elongate, straight and lanceolate, with a narrow aboral keel and narrow protective membranes (Figs. 16, 17). The carpus consists of 10 or 11 suckers and 8 to 10 fleshy pads. The carpal group is completely fi)rmed in specimens over 42.8 mm as a disc-like cluster or fixing apparatus. At 19.4 mm DML, at least 27 hooks are present on the manus (Fig. 14). The suckers distal to hooks are compressed. One of distal teeth of the inner ring is modified into an incomplete hook which has a long and narrow space under the cusp. The specimens larger than 42.8 mm DML have 30 to 32 hooks on the manus. All marginal suckers of the manus are present in the 19.4 mm specimen. At 42.8 mm DML, nine dorso-distal and eight ventro-proximal suckers are repre- sented only by vestigial pedicels. The specimens larger than 60.7 mm DML completely lack marginal suckers. However, the vestiges and some remnants of sucker pedicels are still present in the 60.7 mm specimen (Fig. 16). Gladius, - The cartilageous cap of the gladius endocone of a 42.8 mm specimen is only about 20% of DML, rather gelatinous and transparent with a brownish color (Figs. 19, 21). The specimens larger than 100 mm DML have an opaque and solid cartilageous cap, about 30% ofDML (Figs. 18,20). DISCUSSION Three other species of the genus Moroteuthis are reported from the North Pacific, namely, M. loennbergii Ishikawa and Wakiya, 1914, M.japonica (Taki, 1964) and M. pacifica Okutani, 1983. Moroteuthis loennbergii is easily separable by having smaller number of hooks on the club (26 to 28 is more than 30 in M. robusta) and by maturation at a smaller size. The penis elongate and protrudes from the funnel opening in a 307 TSUCHIYA AND OKUTANI: GROWTH STAGES OF MOROTEUTH1S ROBUSTA 141 Figures 14-17. Moroteuthis robusta. Left tentacular club. 14. 19.4 mm DML. 15.42.8 mm DML. 16.60.5 mm DML. 17. 135 mm DML. [Scale bar: 10 mm.] mm DML specimen. The inverted Y-shaped ridge in the funnel groove is evident even in a spent specimen (350 mm DML).