Journal Molluscan Studies Advance Access originally published online on February 23, 2006
Journal of Molluscan Studies 2006 72(2):199-205; doi:10.1093/mollus/eyi068
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LABORATORY OBSERVATIONS ON THE EARLY LIFE STAGES OF THE DIAMOND SQUID THYSANOTEUTHIS RHOMBUS
1Hyogo Tajima Fisheries Technology Institute, 1126-5 Sakae, Kasumi, Kami, Hyogo 669-6541, Japan; 2Shimane Prefectural Fisheries Experimental Station, 25-1 Setogashima, Hamada, Shimane 697-0051, Japan; 3Tottori Prefectual Fisheries Research Center, Ishiwaki, Yurihama, Tohaku, Tottori 689-0602, Japan; and 4Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori, Amamiya-machi, Aoba, Sendai, Miyagi 981-8555, Japan
Correspondence: K. Miyahara; e-mail: kazutaka_miyahara{at}pref.hyogo.jp
The early life stages of the diamond squid Thysanoteuthis rhombus from early embryogenesis to post-hatching (07 days old) were observed through laboratory incubation using egg masses collected in the southern Sea of Japan. The egg diameter and mantle length increased during embryonic development through hatching. Mantle-length growth was linear over time, and the growth rate was significantly higher at 25°C than at 20°C. The inner yolk was located on the dorsal side of the mantle cavity and increased in volume through hatching. Immediately after they hatched, the hatchlings remained on the bottom of culture plates with their ventral sides facing up, but 23 days after hatching they began to swim with their dorsal sides facing up. Feeding experiments were conducted, but none of the hatchlings fed. Statolith growth increments were shown to form daily. Ontogenetic changes that occur from fertilization through post-hatching are discussed.
(Received 8 June 2005; accepted 2 November 2005)