Published Papers - Ikeda Yuzuru

Evolutionary history influences the microbiomes of a female symbiotic reproductive organ in cephalopods

Nidhi Vijayan, Sarah J. McAnulty, Gustavo Sanchez, Jeffrey Jolly, Yuzuru Ikeda, Michele K. Nishiguchi, Elodie Réveillac, Camino Gestal, Blake L. Spady, Diana H. Li, Benjamin P. Burford, Allison H. Kerwin, Spencer V. Nyholm

Applied and Environmental Microbiology ( American Society for Microbiology )  90 ( 3 )   2024.02 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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ABSTRACT Many female squids and cuttlefishes have a symbiotic reproductive organ called the accessory nidamental gland (ANG) that hosts a bacterial consortium involved with egg defense against pathogens and fouling organisms. While the ANG is found in multiple cephalopod families, little is known about the global microbial diversity of these ANG bacterial symbionts. We used 16S rRNA gene community analysis to characterize the ANG microbiome from different cephalopod species and assess the relationship between host and symbiont phylogenies. The ANG microbiome of 11 species of cephalopods from four families (superorder: Decapodiformes) that span seven geographic locations was characterized. Bacteria of class Alphaproteobacteria, Gammaproteobacteria , and Flavobacteriia were found in all species, yet analysis of amplicon sequence variants by multiple distance metrics revealed a significant difference between ANG microbiomes of cephalopod families (weighted/unweighted UniFrac, Bray–Curtis, P = 0.001). Despite being collected from widely disparate geographic locations, members of the family Sepiolidae (bobtail squid) shared many bacterial taxa including (~50%) Opitutae (Verrucomicrobia) and Ruegeria (Alphaproteobacteria) species. Furthermore, we tested for phylosymbiosis and found a positive correlation between host phylogenetic distance and bacterial community dissimilarity (Mantel test r = 0.7). These data suggest that closely related sepiolids select for distinct symbionts from similar bacterial taxa. Overall, the ANGs of different cephalopod species harbor distinct microbiomes and thus offer a diverse symbiont community to explore antimicrobial activity and other functional roles in host fitness. IMPORTANCE Many aquatic organisms recruit microbial symbionts from the environment that provide a variety of functions, including defense from pathogens. Some female cephalopods (squids, bobtail squids, and cuttlefish) have a reproductive organ called the accessory nidamental gland (ANG) that contains a bacterial consortium that protects eggs from pathogens. Despite the wide distribution of these cephalopods, whether they share similar microbiomes is unknown. Here, we studied the microbial diversity of the ANG in 11 species of cephalopods distributed over a broad geographic range and representing 15–120 million years of host divergence. The ANG microbiomes shared some bacterial taxa, but each cephalopod species had unique symbiotic members. Additionally, analysis of host–symbiont phylogenies suggests that the evolutionary histories of the partners have been important in shaping the ANG microbiome. This study advances our knowledge of cephalopod–bacteria relationships and provides a foundation to explore defensive symbionts in other systems.

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Relationship between seasonal seagrass growth and egg case dynamics of the oval squid (Sepioteuthis lessoniana Férussac in Lesson, 1832) in the coastal waters of the Ryukyu Archipelago

Sho Kimoto, Ritsuki Kawabata, Yuzuru Ikeda

Regional Studies in Marine Science ( Elsevier BV )  67   103190 - 103190   2023.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Allometry for Eyes and Optic Lobes in Oval Squid (Sepioteuthis lessoniana) with Special Reference to Their Ontogenetic Asymmetry

Yuma Sakurai, Yuzuru Ikeda

Symmetry ( MDPI AG )  14 ( 4 ) 644 - 644   2022.03 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Eyes develop in relation to body size and brain area for visual processing in some vertebrates. Meanwhile, it is well known that many animals exhibit left–right asymmetry in both morphology and behavior, namely, lateralization. However, it remains unclear whether the eyes and visual processing brain areas synchronously develop for their asymmetry. Oval squid (Sepioteuthis lessoniana) exhibits lateralization of optic lobe volume and left or right eye usage toward specific targets during their ontogeny. We address the question of how left–right asymmetry of the eyes and optic lobes exhibit an allometric pattern. To examine this question, we estimated the left and right volumes of eyes and optic lobes using microcomputed tomography. We found that, for the optic lobe volume, the right enlargement that appeared at ages 45 and 80 days then shifted to the left at age 120 days. In contrast, the volume of eyes did not show any left–right asymmetries from hatching to age 120 days. We also found that the volume of the eyes and optic lobes showed a slower increase than that of the whole-body size. Within these two visually related organs, the eyes grew faster than the optic lobes until age 120 days. These results are discussed in the context of the survival strategy of oval squid that form schools, two months post-hatching.

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Visual and brain lateralization during the posthatching phase in squid under solitary and group conditions

Yuma Sakurai, Yuzuru Ikeda

Animal Behaviour ( Elsevier BV )  183   13 - 28   2022.01 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Evaluation of Visual and Tactile Perception by Plain-Body Octopus (<i>Callistoctopus aspilosomatis</i>) of Prey-Like Objects.

Kawashima S, Ikeda Y

Zoological science ( Zoological Science )  38 ( 6 ) 495 - 505   2021.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Morphology of the suckers for hunting behavior in broadclub cuttlefish (Sepia latimanus)

Omura A.

Ecological Research ( Ecological Research )  37 ( 1 ) 156 - 162   2021.11 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Plain-body Octopus's (<i>Callistoctopus aspilosomatis</i>) Learning About Objects via Both Visual and Tactile Sensory Inputs: a Pilot Study

Kawashima, S; Yasumuro, H; Ikeda, Y

ZOOLOGICAL SCIENCE ( Zoological Science )  38 ( 5 ) 383 - 396   2021.10 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Although various recognizing abilities have been revealed for octopuses, they predominantly deal with only a few species. Therefore, cognition diversity among other octopus species that have been overlooked needs to be investigated. We investigated whether plain-body octopus can learn a symbolic stimulus, for the reason that this octopus is abundant around Okinawa Island with a complex coral community landscape. Attention was paid to whether an octopus can learn a stimulus based solely on visual information without previous experience of learning it tactilely as well as visually. Furthermore, we examined whether different sensory inputs affect learning in octopuses. First, we tested whether octopuses can be conditioned to three different stimuli (object, picture, and video of a white cross). Octopuses that were presented an object or a picture could learn to touch them. However, octopuses that were presented a video could not learn to touch the stimulus. Second, we showed a video to octopuses that had already learned about an object or a picture to investigate whether the octopuses, having experienced a target using visual and tactile senses, can recognize a video of the target based solely on visual information. Octopuses could learn to touch the video. When a conditioned stimulus and a novel stimulus were simultaneously presented on a computer screen, an octopus that had learned an object more often selected the conditioned stimulus when compared with an octopus that had experienced only a picture. These findings suggest that octopuses use multisensory information to recognize a specific object.

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Plain-body octopus's (Callistoctopus aspilosomatis) learning about objects via both visual and tactile sensory inputs: A pilot study.

Sumire Kawashima, Haruhiko Yasumuro, Yuzuru Ikeda

Zoological Science   38 ( 5 ) 383 - 396   2021.07 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Sociality and communication of cephalopods

Yuzuru Ikeda

Aquabiology   43 ( 2 ) 154 - 158   2021.04

Type of publication: Research paper (scientific journal)

Ontogenetic trajectories of septal spacing in modern cuttlefishes are phylogenetically dependent

Noba K.

Lethaia ( Lethaia )  53 ( 4 ) 563 - 573   2020.10 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Tropical Octopus <i>Abdopus aculeatus</i> Can Learn to Recognize Real and Virtual Symbolic Objects.

Kawashima S, Takei K, Yoshikawa S, Yasumuro H, Ikeda Y

The Biological bulletin ( Biological Bulletin )  238 ( 1 ) 12 - 24   2020.02 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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The diverse morphology of decapodiform cephalopods: A summer lecture

Ayano Omura, Yuzuru Ikeda

Contemporary Mathematics and Science Education   1 ( 1 ) ep20005   2020 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

Survival of squid, Aka-ika, Sepioteuthis sp. 1, hatched from egg cases exposed to stressful conditions during the early-middle embryonic stage of development

Akira Amida, Hisaya Washitake, Takuma Kimura, Tetsuya Umino, Yuzuru Ikeda

Aquaculture Science   67 ( 3 ) 241 - 248   2020 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

Development of a contrast-enhanced micro computed tomography protocol for the oval squid (Sepioteuthis lessoniana) brain.

Sakurai Y, Ikeda Y

Microscopy research and technique ( Microscopy Research and Technique )  82 ( 11 ) 1941 - 1952   2019.11 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Preliminary report of specific behaviours of juvenile greater blue-ringed octopus Hapalochlaena lunulata (Quoy and Gaimard, 1832)

Kawashima Sumire, Amida Akira, Ikeda Yuzuru

MOLLUSCAN RESEARCH ( Molluscan Research )  39 ( 4 ) 291 - 295   2019.07 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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タコにおける視覚・触覚にもとづく行動:タコは世界をクロスモーダルに知覚しているのか?

川島 菫, 池田 譲

動物心理学研究 ( 日本動物心理学会 )  69 ( 2 ) 91 - 99   2019 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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<p>Octopuses, a member of molluscan class, possess well-developed nervous system such as lens eyes that is anatomically similar to our own, and the relative proportion of brain to body is equivalent to vertebrates. Octopuses are also characterized with their muscular highly sensitive sensory receptors, namely, suckers on their arms. Due to these biological uniqueness, octopuses have been a target for psychological studies and were reported their advanced abilities for learning and memory, which are achieved via visual and tactile perceptions. All of these findings have come from experiments that tested single sensory perception (i.e., visual or tactile). On the other hand, it is known in vertebrates that they can integrate multiple sensory information, by which they can vividly image their environments. In this review, we will briefly introduce our knowledge for biology of octopuses with special reference to their cognition, and we will shed light on an idea for cross-modal perception in octopuses, which is based on our on-going projects for visual and tactile learning, and manipulation of arms in tropical octopuses inhabiting the coastal waters of the Ryukyu Archipelago.</p>

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胚発生期にストレス条件に置かれたアオリイカ類アカイカ型の生残

網田 全, 和志武 尚弥, 木村 琢磨, 海野 徹也, 池田 譲

水産増殖 ( 日本水産増殖学会 )  67 ( 3 ) 241 - 248   2019 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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<p>琉球列島近海の水深50-100 m に海上保安庁が設置した流速計に，アオリイカ類アカイカ型の卵塊が異なる3 つの年に産み付けられた。これら卵塊のうちの1 つは，採集直後の25時間程度，海水を含まないビニールパックに容れて冷蔵庫（8℃）に保存された。その後，この卵塊を閉鎖型循環水槽にて飼育したところ，正常発生を経て高率で孵化が見られ，孵化個体は4 か月間にわたり生残した。 一方，琉球列島近海の水深15-20 m に設置した人工産卵礁に産み付けられた孵化直近のアオリイカ類アカイカ型卵塊を採集し，前記の卵塊と同様の条件で飼育したところ，高率で孵化し，一部は性成熟に達した。これら2 つの卵塊由来の孵化個体の生残，成長を比較したところ，両者に違いは見られなかった。本研究はアオリイカ類アカイカ型の卵および孵化個体の初めての長期飼育記録であり，本種の卵嚢がストレス時に胚を防衛する機能を有することを示すものである。</p>

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Activity rhythms of the shallow-water octopuses Octopus laqueus and Abdopus aculeatus with special reference to its relation to light and tidal cycles

Yuzuru Ikeda, Ryoko Yanagisawa

Biological Rhythm Research ( Taylor and Francis Ltd. )  49 ( 4 ) 566 - 580   2018.07 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Patterns of activity and inactivity were experimentally measured for two shallow-water octopuses, Octopus laqueus (n = 8) and Abdopus aculeatus (n = 4), inhabiting the Ryukyu Archipelago. Octopuses that were collected from the coastal waters of Okinawa Island were held in experimental tanks under controlled light conditions (L, light D, dark 12L:12D, LD conditions 12D:12D, DD conditions). Behaviors of these two species were continuously recorded for 9 to 10 days. Under LD conditions, O. laqueus were active for 7 to 14 min during daytime and 298 to 339 min at night, and under DD conditions, for 97 to 140 min during daytime and 71 to 169 min at night. A. aculeatus were active for 49 to 99 min during daytime and 138 to 185 min at night under LD conditions, whereas under DD conditions, they were active for 36 to 56 min during daytime and 55 to 154 min at night. Continuous duration for activity cycles was 39 ± 7.6 h under LD conditions and 42 ± 2.6 h under DD conditions in O. laqueus, and 38 ± 7.4 h under LD conditions and 42 ± 2.8 h under DD conditions in A. aculeatus. Ratios for active duration to inactive duration did not differ between LD condition and DD condition both in O. laqueus and A. aculeatus.

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Environmental enrichment affects the ontogeny of learning, memory, and depth perception of the pharaoh cuttlefish Sepia pharaonis.

Yasumuro H, Ikeda Y

Zoology (Jena, Germany) ( Elsevier GmbH )  128   27 - 37   2018.06 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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We investigated the effects of environmental enrichment on the cognitive abilities of pharaoh cuttlefish, Sepia pharaonis, which were reared from day seven in four different environments: isolated, poor, standard, and enriched. First, we used “prawn-in-the-tube” to test whether environmental enrichment affects the ontogeny of learning and memory of S. pharaonis. The results showed that cuttlefish could usually learn the task regardless of their age and environment. At early age (74 – 81 d), cuttlefish from the isolated environment memorized the task for 24 h. However, at later age (104 – 171 d), the isolated cuttlefish were unable to remember the task. In addition, cuttlefish from the poor environment could not memorize the task at all ages examined. Cuttlefish from the standard environment could memorize the task in later ages (134 – 171 d). In contrast, cuttlefish from the enriched environment could memorize the task at all ages examined. Second, we examined the effect of environmental enrichment on the ontogeny of depth perception of S. pharaonis by observing their hunting behavior. Distance from the prey during hunting was always greater in isolated cuttlefish than those from the other three environments. In addition, hunting success and number of prey captured were always lowest in the isolated cuttlefish for all ages. In contrast, hunting success was always the highest in cuttlefish from the enriched environment. These variations in behavior among cuttlefish raised in different environments suggest that the visual/tactic input derived from social and physical factors of the surrounding environment could promote maturation of learning, memory, and depth perception in S. pharaonis.

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Visual Stimuli for the Induction of Hunting Behavior in Cuttlefish Sepia pharaonis.

Shinzato S, Yasumuro H, Ikeda Y

The Biological bulletin ( Biological Bulletin )  234 ( 2 ) 106 - 115   2018.04 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Erratum to: Structure of the seminal receptacle and sperm storage in the Japanese pygmy squid: Structure of the seminal receptacle of pygmy squids (Journal of Zoology, (2010), 282, 3, (151-156), 10.1111/j.1469-7998.2010.00733.x)

N. Sato, T. Kasugai, Y. Ikeda, H. Munehara

Journal of Zoology ( Blackwell Publishing Ltd )  282 ( 3 ) 151 - 156   2018.02 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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To examine the mechanism of sperm storage in Idiosepius paradoxus, here we describe aspects of the mating behavior of I. paradoxus and the morphology of the spermatozoa and the seminal receptacle after copulation. The seminal receptacle is located in the ventral portion of the buccal membrane surrounding the buccal mass, and opens inside the buccal membrane. It branches into approximately six sacs, similar in appearance to a bunch of bananas, and its wall consists of cuboidal ciliated epithelial cells (with oval nuclei) surrounded by a connective tissue. Multiple vacuoles are distributed in the bottom region of each sac. These histological and morphological characteristics differ from previous reports for loliginid squids and cuttlefish. In all except one receptacle observed in this study, sperm were stored near the bottom of each sac, and each sperm was facing the sac bottom. We observed spermatozoa in the entrance of the seminal receptacle in only one squid. These results suggest that spermatozoa were actively moving, and that sperm actively swam to the seminal receptacle. The volume of sperm in the seminal receptacles of the squid that had copulated eight times was the same as that in the squid that had copulated 29 times, which suggests that the seminal receptacle was filled after approximately eight copulation events. A squid that had copulated nine times retained a significant number of sperm in the seminal receptacle after spawning, suggesting that all of the sperm in the receptacle was not depleted after one spawning event. © 2010 The Authors. Journal of Zoology © 2010 The Zoological Society of London.

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Correction to: Unique arm-flapping behavior of the pharaoh cuttlefish, <i>Sepia pharaonis</i>: putative mimicry of a hermit crab.

Okamoto K, Yasumuro H, Mori A, Ikeda Y

Journal of ethology ( Journal of Ethology )  36 ( 2 ) 219 - 219   2018 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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The article, “Unique arm-flapping behavior of the pharaoh cuttlefish, Sepia pharaonis: putative mimicry of a hermit crab”, written by Kohei Okamoto, Haruhiko Yasumuro.

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A catalog of the chromatic, postural, and locomotor behaviors of the pharaoh cuttlefish (Sepia pharaonis) from Okinawa Island, Japan

Ryuta Nakajima, Yuzuru Ikeda

MARINE BIODIVERSITY ( SPRINGER HEIDELBERG )  47 ( 3 ) 735 - 753   2017.09 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Coleoid cephalopods such as cuttlefishes, squids, and octopods are able to produce a diverse array of visual expressions that are used for mimesis and inter- and intraspecific communication. They achieve this by intricately combining several neurally controlled behaviors, which include chromatic, textural, postural, and locomotor components. To understand this diverse range of body patterns, it is necessary to develop an accurate and extensive catalog of them, which can then be used as a tool for future behavioral monitoring and quantitative analyses, as well as for the identification of morphologically identical sub-species. In this study, a catalog of the chromatic, postural, and locomotor behaviors was produced for the pharaoh cuttlefish (Sepia pharaonis) from coastal waters of Okinawa Island, Japan. Data were collected from aquacultured animals using egg masses sampled from around the island and hatched in aquaria during 2010, 2011, 2012, and 2014. In total, 53 chromatic, four supplementary chromatic conditions, three textural, 11 postural, and nine locomotor components were identified and described in detail. Many of the described components are similar to previously described body patterns of Sepia officinalis. However, there are notable differences between the two species, which may indicate that they use body patterns in different ways for cryptic behavior and inter- and intraspecific communication.

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Unique arm-flapping behavior of the pharaoh cuttlefish, <i>Sepia pharaonis</i>: putative mimicry of a hermit crab.

Okamoto K, Yasumuro H, Mori A, Ikeda Y

Journal of ethology ( SPRINGER JAPAN KK )  35 ( 3 ) 307 - 311   2017 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Cephalopods are able to control their arms sophisticatedly and use them for various behaviors, such as camouflage, startling predators and hunting prey. Here, we report a previously undescribed arm-flapping behavior of the pharaoh cuttlefish, Sepia pharaonis, observed in captivity. S. pharaonis raised the first pair of arms and wrinkled the parts near the distal end, where the skin color was darkened. Additionally, S. pharaonis spread the second and third pairs of arms and bent them as if they were jointed, and flapped the distal ends. S. pharaonis showed this behavior in two different situations: after being introduced into a large space, and during hunting. We discuss the putative functions of this behavior, including possible mimicry of a hermit crab, considering the situations in which the behavior was observed.

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Salt soluble without jelly-like component from the oviducal gland induces chorionic expansion in the ova of the Japanese common squid Todarodes pacificus

Kohsuke Adachi, Mao Yabumoto, Haekyun Yoo, Katsuji Morioka, Yuzuru Ikeda, Yukio Ueta, Yasunori Sakurai

INVERTEBRATE REPRODUCTION & DEVELOPMENT ( TAYLOR & FRANCIS LTD )  60 ( 4 ) 281 - 289   2016.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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In vitro fertilization of squid requires the jelly substance found in the female oviducal gland; yet, the active component of this substance that facilitates fertilization remains unknown. Here, we used biochemical methods to separate the jelly substance of Todarodes pacificus (Oegopsida) and Sepioteuthis lessoniana (Myopsida family) into four fractions; specifically, two water soluble fractions (Molecular weight&gt;10,000 and&lt;10,000), one salt soluble fraction, and one insoluble fraction. The salt soluble fraction of T. pacificus induced chorionic expansion (perivitelline space formation), which precedes the normal embryonic development of ova. In contrast, the salt soluble fraction of S. lessoniana elicited insufficient expansion of the ova, only producing embryos with high abnormality rates. These results suggest that the salt soluble component(s) (not the jelly-like substances) in the oviducal gland induce chorionic expansion and hatching in Oegopsida, and that these components may be similar in Myopsida.

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Environmental Enrichment Accelerates the Ontogeny of Cryptic Behavior in Pharaoh Cuttlefish (Sepia pharaonis).

Yasumuro H, Ikeda Y

Zoological science ( ZOOLOGICAL SOC JAPAN )  33 ( 3 ) 255 - 65   2016.06 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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We examined effect of environmental enrichment on cuttlefish, the most neutrally advanced invertebrate, to compare species variation of genetic and environmental influences. Cuttlefish were reared from seven to 117 days in one of three environments, namely, "poor" (artificial bottom without objects), "standard" (sandy bottom), and "enriched" (sandy bottom with objects). In Experiment 1, we explored whether enrichment affects the exhibition of crypsis in the cuttlefish. The cuttlefish in the standard and enriched environments spent most of their time at the bottom, exhibiting the mottled or disruptive pattern starting at 27 days of age. On the contrary, those in the poor environment exhibited uniform pattern starting at 87 days of age. Additionally, they repeatedly attempted to dig from 27 to 87 days of age, and moved around by hovering from 77 to 117 days of age. In Experiment 2, we exposed the cuttlefish to six novel substrates every other month after 53 days of age to verify whether enrichment actually affected the maturation of cryptic ability. Cuttlefish from the poor environment tended not to dig into white sandy bottom at 53-55 days of age. Additionally, they did not clearly exhibit appropriate body patterns in response to the six substrates compared to those from the other two environments at 81-83 days of age. However, at 113-115 days of age, most cuttlefish from the three environments exhibited similar cryptic behaviors in response to novel substrates. We conclude that physical enrichment promotes crypsis and accelerates the maturation of this ability in cuttlefish.

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Effects of Visual Cues of a Moving Model Predator on Body Patterns in Cuttlefish Sepia pharaonis.

Okamoto K, Mori A, Ikeda Y

Zoological science ( ZOOLOGICAL SOC JAPAN )  32 ( 4 ) 336 - 44   2015.08 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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We examined the effects of predator-prey distance (PPD) and trajectory of the predator on the body patterns that the pharaoh cuttlefish, Sepia pharaonis, shows in response to a predator. A model predator moving in three different trajectories was presented to the cuttlefish: T1, approached the cuttlefish but bypassed above; T2, approached directly toward the cuttlefish; T3, bypassed the cuttlefish both vertically and horizontally. We divided the body patterns that the cuttlefish expressed into seven categories, i.e., "uniform light", "disruptive", "center circle", "dark square", "vertical stripe", "all dark"and "eyespots". In T1, the number of individuals that showed "dark square"increased as the model approached the cuttlefish, whereas the number of individuals that showed "disruptive" decreased. In T2, the number of individuals that showed "all dark"and "eyespots"increased as the model approached the cuttlefish. In T3, the number of individuals that showed "dark square" and "vertical stripe"increased as the model approached the cuttlefish, and it tended to decrease as the model receded from the cuttlefish. These results demonstrate that S. pharaonis changes its body patterns according to PPD and the trajectory of the predator, which would affect predation risk and/or predator perception.

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Cuttlefish can school in the field

Haruhiko Yasumuro, Shogo Nakatsuru, Yuzuru Ikeda

MARINE BIOLOGY ( SPRINGER HEIDELBERG )  162 ( 4 ) 763 - 771   2015.04 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Cuttlefish (Sepiidae) are usually solitary in nature, but we have found evidence that the broadclub cuttlefish (Sepia latimanus) forms schools. S. latimanus groups of various sizes were observed for 145 min in Okinawa, Japan. The groups were comprised of 2-9 members that were usually of similar body sizes. The groups continuously changed shape, forming either clusters or lines. The groups were regarded as schools and had characteristic structures such as synchronized and polarized swimming with similar distances apart from each other (similar to 4.0 mantle length), and swam in parallel (under 20A degrees or over 110A degrees in angle) to their nearest neighbours, regardless of the numbers of members in the group. Small members sometimes followed larger members within the school. These characteristics were similar to those observed in schools of Teuthoidea squid. Schools comprising large numbers of members frequently exhibited hunting behaviour for small crustaceans and fish. This is the first observation of schooling behaviour in wild Sepiidae.

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6. 頭足類学という可能性

池田 譲

日本水産学会誌 ( 公益社団法人 日本水産学会 )  81 ( 1 ) 139 - 139   2015

Type of publication: Research paper (research society, symposium materials, etc.)

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はじめに

池田 譲, 宮崎 多恵子

日本水産学会誌 ( 公益社団法人 日本水産学会 )  81 ( 1 ) 133 - 133   2015 [ Peer Review Accepted ]

Type of publication: Research paper (research society, symposium materials, etc.)

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Notes on an exhausted Japanese common squid, Todarodes pacificus (Cephalopoda: Ommastrephidae), with an unusually short arm

Kidokoro　Hideaki,Uji　Ryosuke

No.77 (2004/3) ( 琉球大学理学部 )  ( 77 ) 143 - 148   2009.08

Type of publication: Research paper (bulletin of university, research institution)

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A Japanese common squid, Todarodes pacificus with an unusually short left fourth arm was captured from the Sea of Japan on October 1996. This specimen was a mature male (mantle length 216 mm, body weight 186 g) ""Kawa-ika"" squid that seemed to be nearing the end of its reproductive life. About two-thirds of the left fourth arm of this individual was lost and the surface of the arm's tip was completely covered with skin. This short arm was either caused by i) malformation or ii) accidental loss of the tip, followed by regeneration. Arm regeneration is common in cephalopods, and the left fourth arm of the present specimen was very similar to the regenerating arms of other cephalopods. Therefore, the arm of the present specimen may be regenerating. Since T. pacificus is a terminal spawner, this specimen indicates that regeneration can still occur even during later phases of the life cycle. （管理者追加）リポジトリ登録情報を移行しました。確認のうえ、加除修正をしてください。

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Reproduction and life span of the oval squid Sepioteuthis lessoniana (Cephalopoda: Loliginidae): comparison between laboratory-cultured and wild-caught squid

Y. Ikeda, Y. Ueta, F. E. Anderson and G. Matsumoto

JMBA2-Biodiversity Records ( その他の出版社 )    2008.08 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Low genetic diversity of oval squid Sepioteuthis cf. lessoniana (Cephalopoda: Loliginidae), in Japanese waters inferred from a mitochondrial DND non-coding region

M. Aoki, H. Imai, T. Naruse, Y. Ikeda

Pacific Science ( その他の出版社 )  62   403 - 411   2008.03 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

Mirror image reactions in the oval squid Sepioteuthis lessoniana

Ikeda, Y. and G. Matsumoto

Fisheries Science ( その他の出版社 )  73   1401 - 1403   2007.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Egg brooding behavior and embryonic development of Octopus laqueus (Cephalopoda: Octopodidae).

Kaneko, N., Osima, Y., and Ikeda, Y.

Molluscan Research ( その他の出版社 )  26   113 - 117   2006.01 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

Rearing of squid hatchlings, Heterololigo bleekeri (Keferstein 1866) up to 2 months in a closed seawater system.

Ikeda Y., Sakurazawa I., Ito K., Sakurai Y., Matsumoto G.

Aquaculture Research ( その他の出版社 )  36   409 - 412   2005.01 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Transport of the oval squid Sepioteuthis lessoniana Feussac, 1831 in Lesson 1830-1831 (Cephalopoda: Loliginidae) for up to 24 hours and subsequent transfer to an aquarium

Ikeda.Y,et al

Fisheries Sci ( その他の出版社 )  ( 70 ) 21 - 27   2004.03

Type of publication: Research paper (other science council materials etc.)

Feeding, external digestion in Japanese pygmy squid, Idiosepius paradoxus (Cephalopoda：Idiosepiidae)

Kasugai.T,et al

J. Mollus. St. ( その他の出版社 )  70   231 - 236   2004.03 [ Peer Review Accepted ]

Type of publication: Research paper (other science council materials etc.)

Note on fertilizing capacity of spermatozoa stored in spermatangium: a possible extra sperm storage site in the Japanese common squid Todarodes pacificus

Ikeda.Y,Sakurai.Y

Suisanzoshoku ( その他の出版社 )  51   101 - 102   2004.01 [ Peer Review Accepted ]

Type of publication: Research paper (other science council materials etc.)

Notes on an exhausted Japanese common squid, Todarodes pacificus (Cephalopoda: Ommastrephidae), with an unusually short arm.

Ikeda Y., Uji R., Kidokoro H.

Bulletin of the Faculty of Science, University of the Rykyus ( その他の出版社 )  77   143 - 147   2004.01 [ Peer Review Accepted ]

Type of publication: Research paper (bulletin of university, research institution)

Does light intensity affect embryonic development of squid (Heterololigo bleekeri)?

Ikeda Y., Ito K., Matsumoto G.

Journal of Marine Biological Association of UK ( その他の出版社 )  84   1215 - 1219   2004.01 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)