Crustacean Research

Descriptions and ecological notes of free-swimming forms of cymothoid isopods (Crustacea: Peracarida) collected in two coastal waters of Japan

Nobuhiro Saito, Takeo Yamauchi, Hiroyuki Ariyama, Osamu Hoshino

Article type: Article
2014 Volume 43 Pages 1-16
Published: December 15, 2014
Released on J-STAGE: May 15, 2017

DOIhttps://doi.org/10.18353/crustacea.43.0_1

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The objective of the study is to clarify the knowledge of free-swimming forms of cymothoid isopods, ectoparasites of fishes, collected in two coastal waters of Japan. The sampling was carried out in two ways, light-trap samplings at night in Osaka Bay, Pacific coast of central Honshu and direct observations and collections in the daytime in the coastal water of Izu-Ohshima Island, Sagami Sea. A total of 326 cymothoids was collected from both localities and they were identified as three morphotypes of mancae, unidentified early juvenile, and juveniles of three genera: Nerocila Leach, 1818, Anilocra Leach, 1818 and Mothocya Hope, 1851. Morphological characters of them were described in detail, and problems in the identification were discussed. The body shapes and the serrations on inner margins of the dactyli of pereopods are the most important characters to divide mancae. In addition, the seasonal occurrence and the swimming behavior of them are also reported.

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Prolonged maturation time in female Caprella acanthogaster (Crustacea, Amphipoda) at low temperature under laboratory conditions

Takashi Hosono

Article type: Article
2014 Volume 43 Pages 17-23
Published: December 15, 2014
Released on J-STAGE: May 15, 2017

DOIhttps://doi.org/10.18353/crustacea.43.0_17

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Caprellids are epifaunal crustaceans, widely distributed in marine environments. The life histories of many temperate caprellids have been described, but the growth pattern of a boreal species has not previously been observed. To fill this gap, a boreal species, Caprella acanthogaster, was reared at 5℃ under laboratory conditions and observed it from hatching to maturation and oviposition. Males were recognizable from instar IV and females from instar V. Female maturation was observed at instar VIII (115 days) and instar IX (126 days), whereas males did not mature morphologically in this study. The females matured at instar IX and oviposited subsequent to molting. These periods from hatching to maturation and oviposition are the longest known among previously reared female caprellids. Caprellids are known to mature rapidly in temperate regions. However, female C. acanthogaster required 4 months to mature at 5℃ while males need an even longer but unknown period. These observations at a low temperature fill a gap in the current information on caprellid life histories.

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[title in Japanese]

Article type: Appendix
2014 Volume 43 Pages 24-
Published: December 15, 2014
Released on J-STAGE: May 15, 2017

DOIhttps://doi.org/10.18353/crustacea.43.0_24

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Developmental morphological changes in protrusions in Artemia intestinal circular muscles

Masaki Ueno, Taketoshi Kimura

Article type: Article
2014 Volume 43 Pages 25-30
Published: December 15, 2014
Released on J-STAGE: May 15, 2017

DOIhttps://doi.org/10.18353/crustacea.43.0_25

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This study describes the electron microscopic features of protrusions on the intestinal circular muscle surface of Artemia nauplius larvae and adults. The distribution, thickness, and form of the protrusions changed with the growth and those of the adults were thicker, forming a bundle of fine protrusions. The budding form of the protrusion from the circular muscle surface was observed, and junctions were detected both at the parts in contact among the protrusions and the connection between the protrusion and the circular muscle cell. These results suggest that the network of protrusions allows communication among circular muscle cells.

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Acorn-foraging activity and feeding behaviour by two species of freshwater crabs (Brachyura: Potamidae) from Okinawa Island, Ryukyu Islands, Japan

Takeshi Sasaki, Tohru Naruse

Article type: Article
2014 Volume 43 Pages 31-40
Published: December 15, 2014
Released on J-STAGE: May 15, 2017

DOIhttps://doi.org/10.18353/crustacea.43.0_31

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Acorn foraging activity and feeding behaviour by two species of potamid freshwater crabs (Geothelphusa grandiovata and Candidiopotamon okinawense) were studied at Yanbaru forest, northern Okinawa Island, Ryukyu Islands, Japan. Adult females of the two species were observed to inhabit burrows that were filled with acorns of Castanopsis sieboldii and Quercus miyagii. The burrows with the crabs as well as gathered acorns were distributed relatively close to a stream (0.8-5 m) at slopes of the forest. Acorns were either eaten with a part of the lower part or seed coat remaining, or vertically broken up and only the inside consumed. Feeding experiments under laboratory conditions indicated that the acorns eaten by G. grandiovata had the same feeding scars as the ones found around crabs burrows, suggesting that the crabs were indeed feeding on acorns. There were 1-24 uneaten acorn(s) observed from all burrows with gathered acorns. Some of the uneaten acorns were even germinated at both around opening of and in the burrow. The accumulation of acorns by the crabs thus inadvertently helps the dispersal of C. sieboldii and Q. miyagii along the slopes of valleys, where the seeds cannot easily lodge and germinate.

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Effect of cheliped loss due to autotomy on shell selection behavior in the hermit crab Pagurus middendorffii

Kento Matsuo, Chiaki I. Yasuda, Satoshi Wada

Article type: Article
2014 Volume 43 Pages 41-46
Published: December 15, 2014
Released on J-STAGE: May 15, 2017

DOIhttps://doi.org/10.18353/crustacea.43.0_41

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Major cheliped is used in shell selection in the hermit crab Pagurus middendorffii. This study examined how loss of the major cheliped due to autotomy affected shell selection behavior and whether shell-size preference was affected. Crabs after autotomy changed shells less frequently than intact crabs. However, there was not a significant difference in shellsize preference between autotomized crabs and intact crabs. Since autotomy occurs during fleeing from a predatory attack in the field, subsequent reduction of frequency of changing shells might suppress the risk of predation for crabs.

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