Research Article |
Corresponding author: Jhoe Reyes ( jreyesp@cientifica.edu.pe ) Academic editor: Pavel Stoev
© 2024 Aoi Tsuyuki, Jhoe Reyes, Yuki Oya, Kevin C. Wakeman, Brian S. Leander, Niels W. L. Van Steenkiste.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Tsuyuki A, Reyes J, Oya Y, Wakeman KC, Leander BS, Van Steenkiste NWL (2024) Marine microturbellarians from Japan, with descriptions of two new species of Reinhardorhynchus (Platyhelminthes, Rhabdocoela, Koinocystididae). Zoosystematics and Evolution 100(3): 877-895. https://doi.org/10.3897/zse.100.120244
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Marine microturbellarians are an assemblage of meiofaunal flatworms abundant in sediments and on seaweeds around the world. The diversity and distribution of these animals in Japan are poorly understood. Here, we provide an overview of all recorded species in Japan and characterize two new species of the rhabdocoel genus Reinhardorhynchus based on morphological features and a molecular phylogeny inferred from 18S and 28S rDNA sequences. Reinhardorhynchus ryukyuensis sp. nov. can be distinguished from other species in the genus by the lack of an armed cirrus and by the presence of two larger opposing hooks and five smaller interconnected hooks in its male copulatory organ. Reinhardorhynchus sagamianus sp. nov. differs from its congeners because its male copulatory organ combines a bipartite cirrus armed with a belt of overlapping scale-like spines, an unarmed accessory cirrus, and two large distal accessory hooks. Our molecular phylogenetic analyses show that R. ryukyuensis sp. nov. and R. sagamianus sp. nov. form a clade with all the other species of Reinhardorhynchus for which DNA sequence data are available. Within this clade, R. sagamianus sp. nov. is in a clade that also includes R. riegeri and R. anamariae. The discovery of these new species highlights the importance of uncovering and documenting the hidden biodiversity along Japan’s coastal margin.
Distribution, flatworms, Japanese invertebrates, Kalyptorhynchia, marine meiofauna
Microturbellarians are microscopic and mostly free-living flatworms that are common in marine meiofaunal communities around the globe (
For Japan, only scattered records of marine and brackish water microturbellarians are known from the literature. The first marine microturbellarians described from Japan were prolecithophorans (
Here, we characterize two new species of Koinocystididae (Rhabdocoela) with morphological and molecular data. Their phylogenetic positions are determined based on analyses using 18S and 28S rDNA sequences. Additionally, we provide a concise overview of the marine and brackish microturbellarian diversity of Japan and highlight the importance of such research.
The specimens of Reinhardorhynchus ryukyuensis sp. nov. were collected by Niels Van Steenkiste and Kevin Wakeman at Onna, Okinawa, Japan (26°28'52.7"N, 127°50'18.8"E) in February 2019 from a coarse mixture of sand, coral fragments, and shell hash in seagrass meadows in a shallow intertidal bay. The specimens of Reinhardorhynchus sagamianus sp. nov. were collected by Aoi Tsuyuki and Yuki Oya at Sangashita beach, Hayama, Kanagawa (35°15'58.3"N, 139°34'19.64"E) in April and August 2023, from clean, coarse sandy sediments in the upper intertidal zone (Fig.
Records of marine microturbellarians in Japan. A. Map shows the documented occurrences of marine microturbellarians reported from Japan. The size and numbers within the pie chart represent the number of recorded species from a) the Okhotsk Sea coast of Hokkaido, b) the Sea of Japan coast of Hokkaido, c) the Pacific coast of Hokkaido, d) Mutsu Bay and the brackish water areas of Aomori, and e) the Pacific coast of Kanagawa. The small circles without numbers indicate single species from the Inland Sea, East China, and the Pacific coasts of Okinawa and Ishigaki Islands, respectively. B. Magnification of the area, including Okinawa, with a star designating the type locality of Reinhardorhynchus ryukyuensis n. sp. C. Magnification of the area, including Kanagawa, with a star designating the type locality of R. sagamianus sp. nov.
Measurements and descriptions were made based on squashed preparations. Measurements of the sclerotized structures such as hooks and spines, as well as for soft body tissues, are expressed in micrometers (μm) and were taken using ImageJ software (
Total genomic DNA was extracted using a DNeasy Blood & Tissue Kit (Qiagen) following the manufacturer’s instructions. For phylogenetic inference, fragments of the 18S rDNA and 28S rDNA were PCR amplified using the primers and thermocycling conditions in Table
Primers | Primer name | Sequence (5‘–3‘) | Application | Reference |
---|---|---|---|---|
R. ryukyuensis sp. nov. | ||||
18S rDNA | TimA | AMCTGGTTGATCCTGCCAG | Amplification and sequencing |
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18S rDNA | TimB | TGATCCATCTGCAGGTTCACCT | Amplification and sequencing |
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18S rDNA | 600F | GGTGCCAGCAGCCGCGGT | Sequencing |
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18S rDNA | 600R | ACCGCGGCTGCTGGCACC | Sequencing |
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18S rDNA | 1100F | CAGAGGTTCGAAGACGATC | Sequencing |
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18S rDNA | 1100R | GATCGTCTTCGAACCTCTG | Sequencing |
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18S rDNA | 18S7F | GCAATAACAGGTCTGTGATGC | Sequencing |
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18S rDNA | 18S7FK | GCATCACAGACCTGTTATTGC | Sequencing |
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28S rDNA | LSU5 | TAGGTCGACCCGCTGAAYTTA | Amplification and sequencing |
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28S rDNA | LSUD6-3B | GCTGTTCACATGGAACCCTTCTC | Amplification and sequencing |
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28S rDNA | L300F | CAAGTACCGTGAGGGAAAGTTG | Sequencing |
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28S rDNA | L300R | CAACTTTCCCTCACGGTACTTG | Sequencing |
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28S rDNA | L1200F | CCCGAAAGATGGTGAACTATG | Sequencing |
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28S rDNA | L1200R | GCATAGTTCACCATCTTTCGG | Sequencing |
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R. sagamianus sp. nov. | ||||
18S rDNA | hrms18S_F | ATCCTGCCAGTAGTCATATGC | Amplification and sequencing |
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18S rDNA | hrms18S_Fi1 | GCCGCGGTAATTCCAG | Sequencing |
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18S rDNA | hrms18S_R | CTACGGAAACCTTGTTACGAC | Sequencing |
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18S rDNA | hrms18S_Ri1 | CTTTAATATACGCTATTGGAGCTGG | Sequencing |
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18S rDNA | hrms18S_Ri2 | CTATTTAGTGGCTAGAGTCTCGTTCG | Amplification and sequencing |
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28S rDNA | LSU5 | TAGGTCGACCCGCTGAAYTTA | Amplification and sequencing |
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28S rDNA | Rd4.8a | ACCTATTCTCAAACTTTAAATGG | Sequencing |
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28S rDNA | rD5b | CCACAGCGCCAGTTCTGCTTAC | Sequencing |
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28S rDNA | LSUD6-3B | GCTGTTCACATGGAACCCTTCTC | Amplification and sequencing |
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Thermocycling conditions | ||||
R. ryukyuensis | ||||
18S rDNA | 95 °C for 3m, touch down in 9 cycles (94 °C for 30 s, 60 °C down to 56 °C for 30 s, 72 °C for 1 m 30 s), 31 cycles (94 °C for 30s, 55 °C for 30 s, 72 °C for 1 m 30 s), 72 °C for 5m | |||
28S rDNA | 95 °C for 3m, touch down in 9 cycles (94 °C for 30 s, 60 °C down to 56 °C for 30 s, 72 °C for 1 m 30 s), 31 cycles (94 °C for 30 s, 55 °C for 30 s, 72 °C for 1 m 30 s), 72 °C for 5m | |||
R. sagamianus | ||||
18S rDNA | 94 °C for 1 m, 35 cycles (94 °C for 30 s, 50 °C for 30 s, 72 °C for 2 m), 72 °C for 7 m | |||
28S rDNA | 94 °C for 1m, 35 cycles (94 °C for 30 s, 50 °C for 30 s, 72 °C for 1.5 m), 72 °C for 7 m |
List of species and respective GenBank accession numbers used for the molecular phylogenetic analyses in this study.
Species | 18S rDNA | 28S rDNA |
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Itaipusa divae | MW081596 | MW054455 |
Itaipusa biglandula | MW081601 | MW054460 |
Itaipusa karlingi | MW081598 | MW054457 |
Itaipusa novacaledonica | KJ887481 | KJ887528 |
Itaipusa sp. 1 | KJ887451 | KJ887557 |
Koinogladius sinensis YTP1 | MF443159 | MF443174 |
Koinogladius sinensis YTP2 | MF443160 | MF443175 |
Koinogladius sinensis YTP3 | MF443161 | MF443176 |
Mesorhynchus terminostylis | AY775741 | KJ887500 |
Reinhardorhynchus anamariae | MW081597 | MW054456 |
Reinhardorhynchus hexacornutus | MW054464 | MW054451 |
Reinhardorhynchus riegeri | MW081595 | MW054454 |
Reinhardorhynchus riegeri (CU1272) | OR490859 | OR490875 |
Reinhardorhynchus ryukyuensis sp. nov. | LC807766 | LC807768 |
Reinhardorhynchus ryukyuensis sp. nov. | – | LC807769 |
Reinhardorhynchus sagamianus sp. nov. | LC807767 | LC807770 |
Reinhardorhynchus tahitiensis A | MW054463 | MW054452 |
Reinhardorhynchus tahitiensis B | MW054462 | MW054453 |
Rhinolasius dillonicus | MW081602 | MW054461 |
Sekerana stolci | – | KJ887537 |
Utelga heinckei | MW081600 | MW054459 |
Utelga heinckei (QU4) | OR490861 | OR490876 |
Utelga heinckei (QU43) | OR490862 | – |
Utelga heinckei (QU44) | OR490863 | OR490877 |
Utelga pseudoheinckei | MW081599 | MW054458 |
Koinocystididae sp. 1 | KR339027 | – |
Outgroup | ||
Cystiplex axi | KJ887437 | KJ887549 |
Cystiplex sp. | KJ887469 | KJ887495 |
For phylogenetic analyses, a concatenated dataset (3,264 bp) comprising partial 18S rDNA (1,642 bp) and 28S rDNA (1,622 bp) was prepared using DNA sequences of 24 koinocystidids in addition to the sequences of two individuals of Reinhardorhynchus ryukyuensis sp. nov. and one individual of R. sagamianus sp. nov. (Table
a: apicomplexan; br: brain; bs: bursal stalk; bu: bursa; cg: common gonopore; cds: spines of the distal part of the spiny belt; ciu: unarmed accessory cirrus; cia: armed cirrus; cm: circular muscles; cms: spines of the middle part of the spiny belt; cps: spines of the proximal part of the spiny belt; ed: ejaculatory duct; fa: female atrium; fd: female duct; fg: female glands; h: hook; i: intestine; ilm: inner layer of longitudinal muscles; lh: larger hooks; ma: male genital atrium; oe: oesophagus; olm: outer layer of longitudinal muscles; om: oblique muscles; ov: ovary; pg: prostate glands; ph: pharynx; pp: penis papilla; pr: proboscis; s: spine; sh: smaller hook; scl: sclerotized layer; sv: seminal vesicle; t: testis; u: uterus; vi: vitellaria.
Rhabdocoela Ehrenberg, 1831
Kalyptorhynchia von Graff, 1905
Eukalyptorhynchia Meixner, 1928
Koinocystididae Meixner, 1924
Reinhardorhynchus Diez, Monnens, & Artois, 2021
Holotype: Japan •1; Okinawa Prefecture, Onna; 26°28'52.7"N, 127°50'18.8"E; Feb. 2019; coarse mixture of sand, coral fragments, and shell hash from an intertidal seagrass bed; Niels Van Steenkiste and Kevin Wakeman leg.; one individual worm in a single slide [Holotype: NSMT-Pl 6458];
Paratype: Japan •1; locality same as for holotype; Feb. 2019; Niels Van Steenkiste and Kevin Wakeman leg.; one individual worm in a single slide; [Paratype: NSMT-Pl 6459].
Japan, Okinawa Prefecture, Onna (26°28'52.7"N, 127°50'18.8"E).
Species of Reinhardorhynchus with conjuncta-duplex type male copulatory organ composed of a proximal globular part, a weakly sclerotized cylindrical middle part, and a distal penis papilla. Sclerotized structures of the copulatory organ consist of two large, separate hooks at the transition between the middle part and penis papilla and a distal girdle of two semi-elliptical plates bearing five smaller hooks. One larger hook with collared striated base, 29–31 μm long, pointing proximally; the other larger hook straight, with striated base, 29–34 μm long, pointing distally. The smaller distal hooks are 9–17 μm long. Female system with bipartite female duct, muscular bursal stalk, large bursa, and pouch of female glands.
General morphology.
Animals are 840–1060 μm long (x̄ = 935 μm; n = 4), transparent, and have two eyes (Fig.
Reinhardorhynchus ryukyuensis sp. nov. A, B. Micrograph and drawing of a live animal. C. Detail of the atrial organs in a live specimen. D. Male copulatory organ in a whole-mounted specimen fixed in lactophenol. E, F. Drawing and micrograph of the sclerotized parts of the male copulatory organ in the holo/paratype. G, H. Drawing and micrograph of the sclerotized parts of the male copulatory organ in the holo/paratype.
The globular pharynx (ph, Fig.
Male reproductive system.
Paired testes are located in front of the pharynx (t, Fig.
The male copulatory organ is provided with sclerotized structures consisting of two larger separate hooks and a girdle of five smaller interconnected hooks (lh1–lh2, sh1–sh5, Fig.
Female reproductive system.
The female structures are located caudal to the pharynx and include paired ovaries (ov, Fig.
Species epithet based on its occurrence on the Ryukyu Islands.
Okinawa Islands, Japan.
Holotype: Japan •1; Kanagawa Prefecture, Hayama, Sangashita beach; (35°15'58.3"N, 139°34'19.6"E); 21 April 2023; sandy substrates; Aoi Tsuyuki and Yuki Oya leg.; one individual worm in a single slide; [Holotype: NSMT-Pl 6460].
Paratype: Japan •1; locality same as for holotype; 30 Aug 2023; Yuki Oya leg.; genomic DNA extract from one individual stored at -20 °C; GenBank: LC807767 (18S rDNA; 1,654 bp), LC807770 (28S rDNA; 1,667 bp); [Paratype: NSMT-DNA 56985].
Japan, Kanagawa Prefecture, Hayama, Sangashita Beach (35°15'58.3"N, 139°34'19.6"E).
Species of Reinhardorhynchus with a copulatory organ encompassing an armed cirrus, an unarmed accessory cirrus, and two distal hooks. Bipartite armed cirrus consisting of two sacs lined with a continuous ±295.2-μm-long sclerotized belt of overlapping scale-like spines. Larger sac with more spaced-out, triangular, ±20.1 μm-long spines on the proximal end of the belt. Spines gradually decrease in size distally as the belt runs towards and folds into the smaller sac, increasing in size (±6.1 to ±22.2 μm long) towards the proximal tip of the smaller sac, and decreasing in size again from the proximal to the distal tip of the smaller sac. Unarmed accessory cirrus as an elongated sac. The larger distal hook is slightly curved, ±111.5 μm long and ±43.5 μm wide at its base; its base is provided with a slightly curved, ±42.3 μm-long projection with a blunt distal tip forming a ~90° angle with the axis of the hook. The smaller hook is funnel-shaped, ±58.9 μm long and ±46.6 μm wide at its base.
General morphology.
Live mature specimens are 1500–1800 µm long (n = 2), with two eyes (Fig.
Reinhardorhynchus sagamianus n. sp., NSMT-DNA 56985 (paratype) (A) and NSMT-Pl 6460 (holotype) (B–H). A, B. Micrograph and drawing of live animals. C. Detail of the male copulatory organ in a live animal. D, E. Drawing and micrograph of the belt of overlapping spines in the armed cirrus of the male copulatory organ in a whole mounted specimen fixed in Entellan New. F–H. Drawings and micrograph of the distal hooks associated with the male copulatory organ in a whole mounted specimen fixed in Entellan New.
Male reproductive system.
Paired testes anterior to the pharynx are on each side of the body (t, Fig.
Female reproductive system.
The vitellaria (vi; Fig.
The species epithet sagamianus refers to the type locality, which is located in Sagami Bay.
Kanawaga, Sangashita Beach, Japan.
The resulting ML and BI trees were congruent with each other in terms of topology, so only the ML tree is shown in Fig.
A total of 58 taxa of marine and brackish water microturbellarians that have been identified to species level have been recorded from the coastal areas of Japan, including the two new species of Reinhardorhynchus described in this study; four taxa were only identified up to genus level (Table
Species of free-living microturbellarians from marine (M) and brackish water (B) habitats in Japan and territories claimed by Japan, including their geographical distributions and reference literature.
Taxonomic idenitity | Locality in Japan | Prefecture in Japan | Reference | Distribution outside of Japan | ||
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Identitified species | ||||||
Macrostomorpha | Macrostomidae | Macrostomum flexum Ax, 2008 (B) | Jusan Lake | Aomori |
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– |
Macrostomum guttulatum Ax, 2008 (B) | Jusan Lake, Noheji River, Obuchi Pond | Aomori |
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– | ||
Macrostomum semicirculatum Ax, 2008 (B) | Takase River, Obuchi Pond, Takahoko Pond | Aomori |
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– | ||
Macrostomum uncinatum Ax, 2008 (B) | Takase River | Aomori |
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– | ||
Rhabdocoela | Koinocystididae | Reinhardorhynchus ryukyuensis sp. nov. (M) | Onna (26°28'52.7"N, 127°50'18.8"E) | Okinawa | This study | – |
Reinhardorhynchus sagamianus sp. nov. (M) | Hayama (35°1'58"N, 139°3'19.4"E) | Kanagawa | This study | – | ||
Utelga monodon Ax, 2008 (B) | Obuchi pond, Takase River | Aomori |
|
– | ||
Polycystididae | Palladia nigrescens (Evdonin, 1971) Evdonin, 1977 (B) | Kominato River, Obuchi Pond, Takase River | Aomori |
|
Posyet, Russia ( |
|
Phonorhynchoides japonicus Ax, 2008 (B) | Takase River | Aomori |
|
– | ||
Cheliplanidae | Cheliplana setosa Evdonin, 1971 (B) | Takase River | Aomori |
|
Posyet, Russia ( |
|
Cheliplana terminalis Brunet, 1968 (M) | Igei (26°27'17.9"N, 127°52'27.5"E) | Okinawa |
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Port Lincoln, Australia ( |
||
Freddius tricaudatus Takeda & Kajihara, 2018 (M) | Akkeshi (43°01'16"N, 144°50'13"E) | Hokkaido |
|
– | ||
Schizorhynchidae | Proschizorhynchella caudociliata Takeda & Kajihara, 2018 (M) | Mukawa (42°33'25"N, 141°55'42"E) | Hokkaido |
|
– | |
Proschizorhynchella magnoliae Takeda & Kajihara, 2018 (M) | Akkeshi (43°01'16"N, 144°50'13"E) | Hokkaido |
|
– | ||
Proschizorhynchella shibazakii Takeda & Kajihara, 2018 (M) | Oshoro (43°12'33"N, 140°51'31"E) | Hokkaido |
|
– | ||
Proschizorhynchella shuttlecock Takeda & Kajihara, 2018 (M) | Obira (44°03'03"N, 141°39'46"E), Soya (45°29'16"N, 141°58'05"E) | Hokkaido |
|
– | ||
Proschizorhynchella pacificus (Evdonin, 1969) (M) | Kunashiri | Hokkaido‡ |
|
– | ||
Rhabdocoela | Provorticidae | Pogaina japonica Ax, 2008 (B) | Takase River, Obuchi Pond, Noheji River, Takahoko Pond | Aomori |
|
– |
Pogaina scypha Ax, 2008 (B) | Obuchi Pond | Aomori |
|
– | ||
Trigonostomidae |
Trigonostomum vanmecheleni |
Otaru (43°13'31.2"N, 141°01'04.0"E) | Hokkaido |
|
Venice, Italy ( |
|
Ptychopera japonica Ax, 2008 (B) | Takase River, Obuchi Pond | Aomori |
|
British Columbia, Canada ( |
||
Promesostomidae | Promesostoma teshirogii Ax, 1992 (B) | Takase River, Jusan Lake, Takahoko Pond | Aomori | Ax (1992) | – | |
Prolecithophora | Plagiostomidae | Vorticeros lobatum Tozawa, 1918 (M) | Misaki | Kanagawa |
|
– |
Prolecithophora | Plagiostomidae | Vorticeros ijimai Tozawa, 1918 (M) | 1) Misaki; 2) Ushimado | 1)Kanagawa; 2)Okayama |
|
– |
Plagiostomum lobatum kurilense Kulinitch, 1979 (M) | Rishiri Island | Hokkaido |
|
– | ||
Pseudostomidae | ?Allostoma durum ( |
Misaki | Kanagawa |
|
Concarneau, France ( |
|
Cylindrostoma monotrochum (Graff, 1882) Westblad, 1955 (M) | Wakkanai, Rishiri Island (from Kelps) | Hokkaido |
|
Kınalıada, Turkey ( |
||
Enterostomula densissimabursa Omi, 2020 (B) | Shinji Lake, Nakaumi | Shimane |
|
– | ||
Multipeniatidae | Multipeniata kho Nasonov, 1927 (B) | Jusan Lake, Kominato River, Takahoko Pond, Takase River | Aomori |
|
Posyet, Russia ( |
|
Japanoplana insolita Ax, 1994 (B) | Kominato River, Takase River | Aomori |
|
– | ||
Proseriata | Monocelididae | Minona pelvivaginalis Tajika, 1982 (M) | Rumoi, Raigishi, Setana | Hokkaido |
|
– |
Tajikina juliae (Tajika, 1982) (M) | Onbetsu, Akkeshi | Hokkaido |
|
– | ||
Monocelis tenella japonica Tajika, 1982 (M) | Oshoro | Hokkaido |
|
– | ||
Monocelis colpotriplicis Tajika, 1982 (M) | Oshoro, Abuta, Shakubetsu, Akkeshi, Habomai, Abashiri, Saruru | Hokkaido |
|
– | ||
Minona dolichovesicula Tajika, 1982 (M) | Muroran, Habomai, Nemuro | Hokkaido |
|
– | ||
Duplominona filiformis Ax, 2008 (B) | Takase River | Aomori |
|
– | ||
Duplominona japonica Ax, 2008 (B) | Jusan Lake | Aomori |
|
– | ||
Archilina japonica Ax, 2008 (B) | Noheji River, Takase River | Aomori |
|
– | ||
Minona minuta Ax, 2008 (B) | Obuchi pond | Aomori |
|
– | ||
Nematoplanidae | Ezoplana oxygona Tajika, 1982 (M) | 1) Cape Erimo, Harutachi; 2) Yaeyama Islands | 1)Hokkaido; 2)Okinawa |
|
– | |
Ezoplana masacoae Tajika, 1982 (M) | 1) Raigishi, Kameda Peninnsula, Hidaka, Abashiri; 2) Joga-Shima Island; 3) Hateruma Island | 1)Hokkaido; 2)Kanagawa; 3)Okinawa |
|
– | ||
Coelogynoporidae | Ezona habomaiensis Tajika, 1980 (M) | Habomai | Hokkaido |
|
– | |
Coelogynopora coniuncta Tajika, 1978 (M) | Oshoro, Hakodate, Akkeshi | Hokkaido |
|
– | ||
Ezona pinnigera Tajika, 1980 (M) | Oshoro, Cape Aikappu, Raigishi, Habomai | Hokkaido |
|
– | ||
Invenusta paracnida (Karling, 1966) (M) | Akkeshi, Ishikari, Harutachi, Erimo, Habomai, Saruru | Hokkaido |
|
Alaska, USA ( |
||
Coelogynopora birostrata Tajika, 1978 (M) | Oshoro, Hakodate, Akkeshi, Okushiri Island | Hokkaido |
|
– | ||
Pseudovannuccia hirutai (Tajika, 1981) (M) | 1) Oshoro, Tomamae, Rebun Island, Rishiri Island, Muroran, Abuta, Akkeshi; 2) Ishigaki Island | 1)Hokkaido, 2)Okinawa |
|
– | ||
Proseriata | Coelogynoporidae | Vannuccia tripapillosa Tajika, 1977 (M) | Oshoro, Akkeshi, Rebun Island, Cape Erimo | Hokkaido |
|
– |
Coelogynopora alata Tajika, 1981 (M) | Okushiri Island, Muroran, Harutachi | Hokkaido |
|
– | ||
Otoplanidae | Archotoplana abutaensis Tajika, 1983 (M) | Abuta | Hokkaido |
|
– | |
Zygotoplana ezoensis Tajika, 1983 (M) | Ishikari | Hokkaido |
|
– | ||
Archotoplana yamadai Tajika, 1983 (M) | Ishikari | Hokkaido |
|
– | ||
Polyrhabdoplana perforata Tajika, 1983 (M) | Muroran | Hokkaido |
|
– | ||
Notocaryoplana geminofollicularis Tajika, 1983 (M) | Ishikari, Raigishi, Muroran, Samani, Akkeshi, Habomai, Abashiri, Sawaki | Hokkaido |
|
– | ||
Itaspiella macrostilifera Tajika, 1984 (M) | Muroran, Raigishi | Hokkaido |
|
– | ||
Nematoplanidae | Nematoplana ciliovesiculae Tajika, 1979 (M) | Raigishi | Hokkaido |
|
– | |
Nematoplana pullolineata Tajika, 1979 (M) | Toya | Hokkaido |
|
– | ||
Archimonocelididae | Tajikacelis itoi (Tajika, 1981) Curini-Galletti & Schockaert, 2021 (M) | Uchikabuto, Satokabuto (Oshoro) | Hokkaido |
|
– | |
Unidentified species | ||||||
Macrostomorpha | Macrostomidae | Bradburia sp.§ (M) | Kataya Port, Miura Peninnsula (35°08'31.24"N, 139°40'14.50"E) | Kanagawa |
|
|
Macrostomum sp. (M) | Hanami Beach, Noto Peninnsula (37°17'19.09"N, 137°0'00.76"E) | Ishikawa | Kobayashiw (2009) | |||
Rhabdocoela | Koinocystididae | Parautelga sp. (M) | Igei (26°27'17.9"N, 127°52'27.5"E) | Okinawa |
|
|
Schizorhynchidae | Carcharodorhynchus sp. (M) | Onna (26°29'05.1"N, 127°50'25.6"E) | Okinawa |
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Koinocystididae is one of the most species-rich groups of kalyptorhynch rhabdocoels. Its representatives are found globally in marine sediments and on seaweeds; however, some species also occur in freshwater habitats. Most koinocystidids have a large proboscis with a sphincter at the base of the cone and complex atrial organs with sclerotized structures and a copulatory bursa (
The new species of Reinhardorhynchus from Okinawa, R. ryukyuensis sp. nov., has a unique combination of features. Firstly, R. ryukyuensis sp. nov. has no armed cirrus in its male copulatory organ. However, the presence of a short, unarmed cirrus cannot be excluded, as the exact ending of the prostate glands and ejaculatory duct in the tip of the penis papilla could not be observed. In all other known species of Reinhardorhynchus, except for R. scoticus (Karling, 1954), the male copulatory organ possesses one (R. hexacornutus Jouk, Diez, Reygel & Artois, 2021, R. renei (Reygel, Willems & Artois, 2011)), two (R. riegeri (Karling, 1978), R. unicornis Diez, Aguirre, Reygel, & Artois, 2021, R. variodentatus (Karling, Mack-Fira, & Doerjes, 1972)) or three (R. pacificus Diez, Reygel & Artois, 2021) armed cirri provided with fields of spines, or a single cirrus armed with belts/rows of overlapping spines (R. anamariae Diez, Reygel & Artois, 2021, R. beatrizae Diez, Aguirre, Reygel & Artois, 2021, R. bispina (Karling, 1980), R. curvicirrus (Karling, 1980), R. evelinae (Marcus, 1954), R. riae Diez, Reygel & Artois, 2021, R. ruffinjonesi (Karling, 1978), R. soror Diez, Reygel & Artois, 2021, R. tahitiensis Jouk, Diez, Yurduseven, Reygel, & Artois, 2021) (
The new species of Reinhardorhynchus from Kanagawa, R. sagamianus sp. nov., is also unique among its congeners because it is the only species with the combination of a bipartite armed cirrus with a belt of spines, an unarmed accessory cirrus, and two distal accessory hooks associated with the male copulatory organ. Only three other species of Reinhardorhynchus, R. riegeri, R. unicornis, and R. variodentatus, possess two cirri and one (R. unicornis) or two (R. riegeri and R. variodentatus) accessory hooks in their male copulatory organ. However, in these three species, both the cirri are provided with spines. Eight other species of Reinhardorhynchus, R. anamariae, R. beatrizae, R. bispina, R. curvicirrus, R. riae, R. ruffinjonesi, R. soror, and R. tahitiensis, possess a single cirrus armed with belts or rows of spines and two distal hooks (
The interrelationships of the Koinocystididae have been extensively discussed by
Most of the species recorded in Japan have been accurately identified except for a prolecithophoran that most likely belongs to the species Allostoma durum (Fuhrmann, 1896) and four unidentified species of Macrostomorpha (Bradburia, Macrostomum) and Rhabdocoela (Carcharodorhynchus, Parautelga), respectively (Table
Macrostomorphs, rhabdocoels, prolecithophorans, and proseriates are the most commonly encountered microturbellarians in marine and brackish water environments around the world. It is, therefore, not surprising that all microturbellarians collected in Japan so far belong to these groups (Table
Only nine out of 58 species of marine or brackish water microturbellarians from Japan have also been collected in other parts of the world (Table
The scarcity of researchers focusing on various meiofaunal groups, such as microturbellarians, has been recognized as a significant challenge that needs urgent attention (
This work was funded by the Universidad Cientifica del Sur (JR), the Tula Foundation’s Hakai Institute (NWLVS and BSL), and the Natural Sciences and Engineering Research Council of Canada (NSERC 2019-03986 to BSL). We thank Dr. Yander Diez and Dr. Julian Smith III for critically reviewing previous versions of the manuscript.
Reinhardorhynchus sagamianus sp. nov – detail of the male copulatory organ in a live animal
Data type: mov
Reinhardorhynchus sagamianus sp. nov – detail of the male copulatory organ in a live animal
Data type: mov
Reinhardorhynchus sagamianus sp. nov – detail of the male copulatory organ in a live animal
Data type: mov