Sepiolina nipponensis (Berry, 1911)

Introduction

Sepiolina nipponensis is a peculiar sepiolid whose characteristics place it between the Heteroteuthinae and the Sepiolinae. The tentacular club with a normal keel is similar to that of the Sepiolinae while the silvery sides, ventral shield and large visceral photophore are similar to those of the Heteroteuthinae. A better understanding of the features and habits of this species should greatly aid our understanding of the evolution within the family.

Diagnosis

A heteroteuthin ...

• with mantle narrowly fused to head dorsally.
• without tentacular organ on tentacles.

Characteristics

1. Arms
   1. Arms I of males with glandular structures along dorsal and ventral margins over most of arm length.
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   Figure. Left - Oral view of left arms I-IV of S. nipponensis, mature male, 24 mm ML, Philippine waters. Drawing from Voss (1963). Right - Partial oral view of arms of a mature male, preserved, Japanese waters. Photograph by R. Young.

   2. Arms II and III, in males, with greatly enlarged suckers; suckers enlarged to a lesser extent on arms IV.
   3. Arms of females without obvious modifications.
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   Figure. Oral views of brachial crowns of S. nipponensis, Japanese waters . Left - Mature male. Right - Mature female. Drawings from Sasaki (1929).

2. Tentacles
   1. Keel extends full length of tentacular club (unlike other heterothins, a tentacular organ is lacking) however, the base of the keel is modified with a permanent fold.
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   Figure. Side view of the club of S. nipponensis. preserved. Arrow points to the base of the keel which is folded over like the tentacular organ of other heteroteuthins. Photograph by R. Young.

3. Head
1. Ocular pore present unlike most (all?) other heteroteuthins.


4. Funnel
   1. Funnel locking-apparatus with a deep, elongate anterior pit.
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   Figure. Funnel/mantle locking apparatus of S. nipponensis, Suruga Bay, Japan, 35°N,138°E, NMNH 816246, left = anterior. Top - Frontal view of funnel component. Bottom - Side-oblique view of the mantle component. Photographs by M. Vecchione.

5. Mantle
   1. Mantle fused to head dorsally; fusion narrower than head width.
   2. Ventral mantle shield extends almost entire length of mantle (see title photograph).
   3. Lateral mantle with broad, silver band.
      
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      Figure. Side (top) and ventral views of preserved S. nipponensis, 23 mm ML, female (top), 15 mm ML, male (bottom),Japanese waters, showing the extent of the ventral shield. Photograph by R. Young.

6. Fins
   1. Fins do not reach anterior or posterior margins of mantle.
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   Figure. Dorsal view of a mature male S. nipponensis, ca. 19 mm ML, Japanese waters. Drawing from Sasaki, 1929.

Distribution

Southern Japan, Philippines, southern Australia, upper slope (Nesis, 1982/87).

References

Nesis, K. N. 1982/87. Abridged key to the cephalopod mollusks of the world's ocean. 385+ii pp. Light and Food Industry Publishing House, Moscow. (In Russian.). Translated into English by B. S. Levitov, ed. by L. A. Burgess (1987), Cephalopods of the world. T. F. H. Publications, Neptune City, NJ, 351pp.

Sasaki, M. 1929. A Monograph of the Dibranchiate Cephalopods of the Japanese and Adjacent Waters. Journal of the College of Agriculture, Hokkaido Imperial University, 20(supplement):357 pages.