The Journal of Veterinary Medical Science Wildlife Science Title: the Functional-morphological Adaptive Strategy of Digestive Organs of Decapodiform Authors Names and Affiliations: Ayano Omura Running Head: Digestive Organs in Decapodiformes Cephalopods

19 The digestive organs in decapodiform cephalopod species morphologically vary by 20 individual lifestyle. We examined the following six species of adult decapodiformes 21 cephalopods representing different habitats: Todarodes pacificus, Loligo bleekeri, Loligo 22 edulis, Watasenia scintillans (pelagic), Sepia lycidas, and Euprymna morsei (benthic). L. 23 bleekeri and L. edulis possess a bursiform caecal sac connected to the caecum. Pelagic species 24 have a single digestive gland smaller than in benthic species. T. pacificus has an oval digestive 25 gland larger than that of L. bleekeri and L. edulis, which possess withered-looking and smaller 26 digestive glands. In contrast, the digestive glands in benthic species are paired. S. lycidas and 27 E. morsei have well-developed and larger digestive glands than those of the pelagic species. 28 Well-developed digestive duct appendages are found in benthic species. In qualification of the 29 mass of digestive organs, pelagic species have smaller stomachs, digestive glands and 30 digestive ducts' appendages than benthic species. Because pelagic species need to swim, they 31 may possess smaller stomachs and larger caecums for more rapid digestion. A smaller 32 digestive gland may have the advantage of reducing the body weight in pelagic species for 33 rapid swimming. In contrast, benthic species burrow into sand. Because benthic species 34 require a longer time for digestion than pelagic species, they compact more food in their 35 stomachs and absorb nutrients via more organs such as the digestive grand and digestive duct 36 appendages in addition to caecum.