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. 2020 Oct 7:8:e9836.
doi: 10.7717/peerj.9836. eCollection 2020.

A taxonomic review of the genus Astrocladus (Echinodermata, Ophiuroidea, Euryalida, Gorgonocephalidae) from Japanese coastal waters

Masanori Okanishi  1 , Hisanori Kohtsuka  1 , Toshihiko Fujita  2
Affiliations
Free PMC article

A taxonomic review of the genus Astrocladus (Echinodermata, Ophiuroidea, Euryalida, Gorgonocephalidae) from Japanese coastal waters

Masanori Okanishi et al. PeerJ. .
Free PMC article

Abstract

Japanese species of the genus Astrocladus (Echinodermata, Ophiuroidea, Euryalida, Gorgonocephalidae) are reviewed. Astrocladus coniferus recently has two junior synonyms, A. dofleini Döderlein and A. pardalis Döderlein, however, status of these species has long been questioned. These species concepts have not been reviewed in recent years and no molecular phylogenetic analyses have been performed. Observations of the lectotype of A. coniferus, as well as the lectotype and four paralectotypes of A. dofleini and the holotype of A. pardalis have revealed that A. coniferus and A. pardalis are conspecific and morphologically distinguishable from A. dofleini. Astrocladus coniferus and A. dofleini are supported as distinct species by our molecular data. Additionally, we re-describe A. exiguus and A. annulatus, based on recently collected specimens and the holotype. We conclude that four species, A. annulatus, A. coniferus, A. dofleini, and A. exiguus are present in Japanese waters.

Keywords: Astrocladus coniferus; Astrocladus dofleini; Astrocladus pardalis; Basket star; Japan; Taxonomy.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1. Sampling sites of Astrocladus annulatus, A. coniferus, A. dofleini and A. exiguus.
Numerals indicate serial specimen number in Table 1.
Figure 2
Figure 2. Astrocladus coniferus, lectotype (ZSM 20000897).
(A) External view of lectotype bottle. (B) Original labels of the lectotype. (C) Dorsal view. (D) Ventral view. (E) Dorsal disc and proximal portion of arm. (F) Dorsal periphery of one radius of disc. (G) Ventral disc and proximal to middle portion of arm. (H) Ventral interradial disc. Abbreviations: G, genital slit; M, madreporite; T, large tubercle.
Figure 3
Figure 3. Astrocladus coniferus, lectotype (ZSM 20000897).
(A) Dorsal proximal portion of arm. (B) Dorsal middle portion of arm. (C) Ventral proximal portion of arm. (D) Ventral middle portion of arm. Arrowheads indicate rows of hooklets on dorsal and lateral side of the arms (A and B). Abbreviations: AS, arm spine; T, large tubercle.
Figure 4
Figure 4. Astrocladus coniferus, holotype of Astrophyton pardalis (ZSM 20000898) (A–F) and NSMT E-13118 (G and H).
(A) Dorsal view. (B) Original labels of the holotype. (C) Dorsal disc and proximal portion of arm. (D) Dorsal periphery of radial shield (E). Ventral disc. (F) Dorsal proximal portion of arm, partly enlarged. (G and H) Live specimens, dorsal (G) and ventral (H) views.
Figure 5
Figure 5. Astrocladus coniferus (NSMT E-13118). SEM photographs of ossicles.
(A–C) Hooklets on proximal (A), middle (B) and distal (C) portion of arm, arcs indicate reticular structure. (D) Hooket-bearing plate on proximal portion of arm. (E and F) Lateral arm plates on proximal portion of arm, internal (E) and external (F) views. (G and H) Arm spines from proximal portion of arm, inner most (G) and second inner most (H). (I and J) Lateral arm plates on middle portion of arm, distal (I) and internal (J) views. (K and L) Arm spines on middle portion of arms, inner most (K) and second inner most (L). Arrowheads indicate articulations for hooklets (D) and terminal projections (G, H, K and L). Orientations: dis, distal side; ex, external side; in, internal side; prox, proximal side. Abbreviations: B, border structure; MO, muscle opening; NO, nerve opening; P, perforation; ST, secondary tooth.
Figure 6
Figure 6. Astrocladus coniferus (NSMT E-13118). SEM photographs of ossicles.
(A and B) Lateral arm plates on distal portion of arm, external (A) and internal (B) views. (C) Hook-shaped arm spine on distal portion of arm. (D–G) Vertebrae from proximal (D and E) and middle (F and G) portion of arm, distal (D and G), ventral (E) and proximal (F) views. An arrowhead indicates articulation for hooklet (A). Orientations: d, dorsal side; dis, distal side; prox, proximal side; v, ventral side. Abbreviations: AAS, articulation for arm spine; B, border structure; LN, passage of lateral canal; NO, nerve opening; ST, secondary tooth.
Figure 7
Figure 7. Astrocladus coniferus (NSMT E-13118). SEM photographs of ossicles.
Vertebrae from middle (A and B) and distal (C–F) portion of arm, ventral (A and E), dorsal (B and F), proximal (C) and distal (D) views. Orientations: d, dorsal side; dis, distal side; prox, proximal side; v, ventral side. Abbreviations: DT, depression for tentacle; LC, passages of lateral canal; LN, passages of lateral nerve; T, tubercle.
Figure 8
Figure 8. Astrocladus dofleini, lectotype (ZSM 20000901/1).
(A) External view of lectotype bottle. (B) Original labels of the lectotype. (C) Dorsal disc and proximal portion of arm. (D) Dorsal proximal portion of arm, partly enlarged in upper right. (E) Interradial ventral disc. (F) Dorsal middle to distal portion of arm. (G) Ventral disc and proximal portion of arm. (H) Ventral middle to distal tips of arm. Abbreviation: G, genital slit.
Figure 9
Figure 9. Astrocladus dofleini (NSMT E-13124). SEM photographs of ossicles.
(A, B and D) Hooklets on proximal (A), middle (B) and distal (D) portion of arms, arcs indicate reticular structure. (C and E) Hooket-bearing plate on proximal (C) and distal (E) portion of arm. (F and I) Arm spines on proximal (F) and middle (I) portion of arms. (G, H, J and K) Lateral arm plates on proximal (G and H) and middle (J and K) portion of the arms, external (G and J) and internal (H and K) views. Arrowheads indicate articulations of hooklets (C, E and J) and terminal projections (F). Orientations: d, dorsal side; dis, distal side; ex, external side; in, internal side prox, proximal side; v, ventral side. Abbreviations: AAS, articulation for arm spine; B, border structure; MO, muscle opening; NO, nerve opening; ST, secondary tooth.
Figure 10
Figure 10. Astrocladus dofleini (NSMT E-13124). SEM photographs of ossicles.
(A) An arm spine from distal portion of arm. (B, C) Lateral arm plates on distal portion of arm, external (B) and internal (C) views. (D–H) Vertebrae from proximal portion of arm (H is branching vertebra), distal (D), proximal (E), dorsal (F) and ventral (G and H) views. Orientations: d, dorsal side; dis, distal side; prox, proximal side; v, ventral side. Arrowheads indicate articulations for hooklets. Abbreviations: B, boarder structure; DT, depression for tentacle; LC, passages of lateral canal; LN, passages of lateral nerve; MO, muscle opening; ST, secondary tooth; T, tubercle.
Figure 11
Figure 11. Astrocladus dofleini (NSMT E-13124). SEM photographs of ossicles.
(A–E) Vertebrae from middle portion of arm (C is branching vertebra), distal (A), ventral (B and C), dorsal (D) views, a part of (D) enlarged in (E). Vertebrae from distal portion of arm (F and G), distal (F) and proximal (G) views. Orientations: d, dorsal side; dis, distal side; prox, proximal side; v, ventral side. Arrowheads indicate tubercles on lateral furrow of vertebra. Abbreviations: DT, depression for tentacle; LC, passages of lateral canal; LN, passages of lateral nerve; T, tubercle.
Figure 12
Figure 12. Astrocladus dofleini (NSMT E-13124).
SEM photographs of vertebrae from distal portion of arm (C is branching vertebra), ventral (A and C) and dorsal (B) views. Orientations: dis, distal side; prox, proximal side. Abbreviation: DT, depression for tentacle.
Figure 13
Figure 13. Astrocladus exiguus (NSMT E-13126).
(A) Periphery of dorsal disc. (B) Central view of dorsal disc. (C) Ventral disc. (D) Interradial ventral disc. (E–G) Ventral surfaces of arms, proximal (E), middle (F) and distal (G) portion of arm. Dorsal surfaces of arms, proximal (H), middle (I) and distal (J) portion of arm. Arrowheads indicate rows of hooklets on dorsal and lateral side of the arms (I and J). Abbreviations: AS, arm spine; G, genital slit; M, madreporite; T, large tubercle. Photographs of this figure were focus-stacked using the software CombineZM v. 1.0.0 (https://www.softpedia.com/get/Multimedia/Graphic/Graphic-Editors/CombineZM.shtml).
Figure 14
Figure 14. Astrocladus exiguus (NSMT E-13126). SEM photographs of ossicles.
(A, C) Hooklets on proximal (A) and distal (C) portion of arms, arcs indicate reticular structure. (B and D) Hooket-bearing plate on proximal (B) and distal (D) portion of arm. (E–H) Lateral arm plates on proximal (E and F) and distal (G and H) portion of arms. (I) An arm spine on proximal portion of arm. Arrowheads indicate articulations for hooklets (B, D and H) and terminal projections (I). Orientations: d, dorsal side; dis, distal side; ex, internal side; in, internal side; prox, proximal side; v, ventral side. Abbreviations: AAS, articulation for arm spine; B, border structure; MO, muscle opening; NO, nerve opening; ST, secondary tooth.
Figure 15
Figure 15. Astrocladus exiguus (MO-2019-19). SEM photographs of ossicles.
(A) An arm spine on distal portion of arm. (B–F) Vertebrae from proximal portion of arm (E is branching vertebra), proximal (B), distal (C), ventral (D and E) and dorsal (F) views. (G and H) Vertebrae from distal portion of arm, proximal (G) and distal (H) views. Orientations: d, dorsal side; dis, distal side; prox, proximal side; v, ventral side. Abbreviations: DT, depression for tentacle; LC, passages of lateral canal; LN, passages of lateral nerve; ST, secondary tooth.
Figure 16
Figure 16. Astrocladus exiguus (NSMT E-13126). SEM photographs of ossicles.
(A–C) Vertebrae from distal portion of arm (B is branching vertebra), dorsal (A), ventral (B and C) views. (D) An conical external ossicle on proximal portion of arm, lateral view, an arc indicates a terminal projection. Orientations: ba, basal side; dis, distal side; ex, external side; prox, proximal side. Abbreviations: DT, depression for tentacle; LC, passages for lateral canals.
Figure 17
Figure 17. Astrocladus annulatus, holotype (UMUTZ-Ophi-26).
(A) Dorsal view. (B) Dorsal surface of periphery disc (C) Ventral view. (D) Jaws. (E) Interradial ventral disc. (F–H) Dorsal surface of arms, proximal (F), middle (G) and distal (H) portion of arm. (I and J) Ventral surface of arms, proximal (I) and distal (J) portion of arm. Arrowheads indicate rows of hooklets on dorsal and lateral side of the arms (B, G and H). Abbreviations: AS, arm spine; G, genital slit.
Figure 18
Figure 18. Maximum likelihood tree based on a partial sequence of mitochondrial COI gene (699 bp).
Support values for each node are shown by maximum likelihood bootstrap values (%) and Bayesian posterior probabilities. Numerals (1–5) in circles at nodes refer to the clade number discussed in the text. Bootstrap value less than 74% and Bayesian posterior probability value less than 0.97 and for each node were shown by as “–”.
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Grants and funding

This work was supported by a grant from the Research Institute of Marine Invertebrates, KAKENHI Grant Numbers 09041155, 125750008, 22570104, 25440226, 17K07549, and by the integrated research, “Geological, biological, and anthropological histories in relation to the Kuroshio Current” and “Spatiotemporal Analyses on Origins and Properties of the Biodiversity Hotspots in Japan”, conducted by the National Museum of Nature and Science. There was no additional external funding received for this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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