Plankton and Benthos Research
Online ISSN : 1882-627X
Print ISSN : 1880-8247
ISSN-L : 1880-8247
15 巻, 4 号
選択された号の論文の7件中1~7を表示しています
Original Papers
  • Takahiro Sugiyama, Naoto Jimi, Ryutaro Goto
    2020 年 15 巻 4 号 p. 289-295
    発行日: 2020/11/18
    公開日: 2020/11/12
    ジャーナル フリー

    The Polynoidae, commonly known as “scale-worms” due to the scale-like elytra on the dorsal surface, contains many species living in symbioses with other invertebrates. Most of these symbionts are host-specific, but some have a wide range of hosts. The genus Asterophilia includes two species living in shallow subtropical to tropical waters in the Pacific Ocean as ectosymbionts of asteroids and, more rarely, crinoids. Here, we recorded Asterophilia culcitae from asteroid hosts (Culcita novaeguineae, Linckia laevigata, L. guildingi, and Leiaster leachi) and, for the first time, from holothurian hosts [Stichopus chloronotus, Holothuria atra, H. (Stauropora) pervicax, and Bohadschia argus] along warm Japanese Pacific coasts. The cytochrome c oxidase subunit I sequences of the specimens from holothurians did not differ significantly from those on asteroid hosts, proving that A. culcitae has a wide host range across three different echinoderm classes: asteroids, holothurians, and crinoids. The general body color of A. culcitae was constantly reddish (female) or whitish (male), regardless of the host body color, although a previous study suggested that it differs in accordance with the host body color. However, we found that one individual from a holothurian host showed a different color pattern: A. culcitae typically shows three whitish or yellowish elytral mounds that have been suggested to mimic the tube foot of the asteroid hosts, whereas one individual from S. chloronotus had reddish brown translucent mounds, which we suggest might be cryptic on its holothurian host.

  • Michael Ford, Nicholas Bezio, Allen Collins
    2020 年 15 巻 4 号 p. 296-305
    発行日: 2020/11/18
    公開日: 2020/11/12
    ジャーナル フリー

    On April 10, 2015, three individuals of an undescribed species of ctenophore were observed moving just above the seafloor in the Arecibo Amphitheater inside the Guajataca Canyon, north-northwest of Puerto Rico at a depth of approximately 3,900 m. The ctenophore is distinctive; having two prominent tentacle arms, a body that is rectangular when observed laterally along the tentacular plane, and rounded when observed laterally along the stomodeal plane. The tentacle arms each give rise to an extensible tentacle bearing short tentilla of uniform length and distribution. One ctenophore appeared to be anchored to the seafloor by its two long flexible tentacles, as well as by two filaments exiting its oral end. The overall form of the ctenophore suggests classification within the problematic, non-monophyletic order Cydippida, but the robust tentacle arms are more reminiscent of benthic species of Platyctenida, particularly those of families Lyroctenidae and Ctenoplanidae. Whereas most platyctenid ctenophores do not possess ctene rows in their adult forms, features that are possessed by the new species described herein, species of Ctenoplanidae retain comb rows as adults and are capable of limited swimming. The species described herein is easily distinguishable from all other known species of Ctenophora and may trace its origin to a lineage diverging near the origin of Platyctenida.

  • Takehiro Matsumoto, Hiroaki Arakawa, Takaya Murakami, Seiji Yanai
    2020 年 15 巻 4 号 p. 306-316
    発行日: 2020/11/18
    公開日: 2020/11/12
    ジャーナル フリー

    Two semi-terrestrial crab species, Chiromantes haematocheir and Chiromantes dehaani, are closely related and have a sympatric distribution. The ecological characteristics of these species, including habitat and behavior during the adult stage, have been investigated. However, the larval stage remains poorly understood because it is difficult to identify larvae morphologically. Our study objectives are to clarify the settlement patterns involved in recruitment of the two species of megalopae using genetic analysis and the effects of ecological factors on settlement, including 1) seasonal changes, 2) spatial variations (dominated by conspecific or heterospecific adults), and 3) tidal effects. The Chiromantes megalopae were collected in the lower reach of the Sai River during spring and neap tides from August to November 2017. Megalopa larvae were collected from three areas: one dominated by C. haematocheir adults, one dominated by C. dehaani adults, and a revetment area. Both species of megalopae showed seasonal and spatial variations in settlement, which also differed with tidal fluctuations. Chiromantes dehaani megalopae settled from mid-August to early October and C. haematocheir megalopae settled from early September to early November. Chiromantes haematocheir megalopae preferentially settled in the area dominated by conspecific adults over the area dominated by C. dehaani and the revetment area, while no difference in the settlement of C. dehaani megalopae was observed among areas. Chiromantes haematocheir megalopae returned on the spring tide; however, C. dehaani megalopae showed no tidal pattern.

  • Krishan D. Karunarathne, M.D.S.T. de Croos
    2020 年 15 巻 4 号 p. 317-326
    発行日: 2020/11/18
    公開日: 2020/11/12
    ジャーナル フリー
    電子付録

    A new species of box jellyfish, Carybdea wayamba sp. nov. is described here based on forty specimens collected from the south and northeast coasts of Sri Lanka, with the type location being Bonavista Reef, Galle Bay. This species is classified in the genus Carybdea due to the possession of a typical heart-shaped rhopaliar niche ostia with only one upper scale and epaulette-shaped gastric phacellae in the four corners of the stomach. This new species can be distinguished from other valid members of the genus Carybdea by the combination of the structure of the two velarial canal roots per octant with one broadly bi-forked velarial canal with narrow, lateral lobations on each root, and other morphological characters such as having typical knee-shaped pedalial canal bends without any appendages, and epaulette-shaped gastric phacellae with single-rooted, brush-shaped, multiple (three to five) short-stemmed, dendritically branched (both short and long branches) gastric filaments. This is the first novel cubomedusa described from Sri Lankan waters; and the first Carybdea species described with material from the North Indian Ocean.

  • Sho Toshino
    2020 年 15 巻 4 号 p. 327-333
    発行日: 2020/11/18
    公開日: 2020/11/12
    ジャーナル フリー

    The order Coronatae is a unique group, with the following characters distinguishing them from other scyphozoans: a coronal furrow, a coronate pedalium, and oocytes that develop without accessory pigments. Coronatae polyps are enclosed in chitinous tubes and produce multiple ephyrae via polydisk strobilation. So far, eleven described species of Coronatae have been reported in Japanese waters: Atolla wyvillei, Atolla vanhoeffeni, Atolla russelli, Atorella vanhoeffeni, Atorella japonica, Nausithoe punctata, Palephyra pelagica, Periphylla periphylla, Periphyllopsis braueri, Stephanoscyphistoma corniformis and Nausithoe racemosa. The present study reports detailed observations of the morphology of one species newly recorded in Japan: Linuche draco. Development from ephyra to mature medusa was observed and recorded. Additional investigations are needed to understand the diversity of the order Coronatae in Japan.

Notes
  • Norihito Takahashi
    2020 年 15 巻 4 号 p. 334-336
    発行日: 2020/11/18
    公開日: 2020/11/12
    ジャーナル フリー

    A new Japanese record of the Holarctic clam shrimp Lynceus brachyurus is presented with key morphological characteristics and habitat information. The rostrum, clasper, telson, and lamina abdominalis of this insular record are similar to those of the common form of L. brachyurus in continental populations, and our specimens fall within the previously reported species variability.

  • Hiroshi Kajihara, Atsushi Yamaguchi
    2020 年 15 巻 4 号 p. 337-341
    発行日: 2020/11/18
    公開日: 2020/11/12
    ジャーナル フリー

    The three currently recognized species comprising the pelagic polystiliferous hoplonemertean genus Protopelagonemertes Brinkmann, 1917 are supposedly distinguishable chiefly with respect to the number of proboscis nerves: 29 (varying from 22 to 30) in P. hubrechti (Brinkmann, 1917); 19–21 (varying from 19 to 22) in P. beebei Coe, 1936; and 36 in P. joculatori Van der Spoel, 1988. A single specimen collected off the Pacific coast of Hokkaido, Japan, herein identified as P. beebei, was found to possess 19–23 primary proboscis nerves. In addition to the primary proboscis nerves, the material also possessed 12–16 secondary proboscis nerves, which are discernible from the primary nerves in that they coexist with putative glial cells. Although secondary proboscis nerves have been identified in some other species in the Pelagica, they have not previously been described for any members of the Protopelagonemertes. Our findings thus prompted us to question the validity of morphological species delimitation within this genus, given that the distinction between primary and secondary proboscis nerves has previously not been taken into consideration. Close examination of the specimen in the living state revealed that it is characterized by a pair of cephalic furrows, a structure commonly found in benthic representatives of the phylum, but herein confirmed for the first time among the Pelagica. A 658-bp partial sequence of the mitochondrial cytochrome c oxidase subunit I gene from the newly examined specimen was found to be identical to sequences derived from two other specimens previously collected in Sagami Bay, thereby indicating that P. beebei may occur commonly in Japanese meso- to bathypelagic waters.

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