Zhang R et al. (2020), A new sponge-associated starfish, Astrolirus pa...

ECB-ART-49793

PeerJ 2020 Jan 01;8:e9071. doi: 10.7717/peerj.9071.

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A new sponge-associated starfish, Astrolirus patricki sp. nov. (Asteroidea: Brisingida: Brisingidae), from the northwestern Pacific seamounts.

Zhang R , Zhou Y , Xiao N , Wang C .

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Seamounts are important deep ocean entities that serve as reservoirs for varied types of habitats and fauna. During the Chinese cruises in the northwestern Pacific seamount areas, a new starfish species of order Brisingida, Astrolirus patricki, was found at 1,458-2,125 m depth. All specimens of the new species were observed in situ attaching on hexactinellid sponges, suggesting a possible close relationship between the two taxa. A. patricki sp. nov. is the second known species of the genus, characterized by the abutting plates in the intercostal integument, separated first pair of adambulacral plates and densely distributed proximal spines. Phylogenetic analyses were conducted for order Brisingida to incorporate the new species as well as Hymenodiscus cf. fragilis (Fisher, 1906), Freyella cf. attenuata Sladen, 1889 and two Brisinga spp., for which we present the molecular data for the first time. Phylogenetic trees suggest a close relationship between A. patricki sp. nov. with Brisinga species rather than with Hymenodiscus species, which is inconsistent with morphological taxonomy. This study highlights the distinct morphological and ecological characters of the new species and provides new data for future investigation on Brisingida phylogeny.

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	Figure 1. In situ photographs of Astrolirus patricki sp. nov.(A) Holotype RSIOAS044. (B) Paratype RSIOAS028. (C) Paratype RSIOAS003. (D) Paratype RSIOAS052. (E) Paratype MBM286625.
	Figure 2. Astrolirus patricki sp. nov., abactinal view.(A) Paratype RSIOAS028. (B) Paratype RSIOAS003. (C), (D), (H), holotype RSIOAS044, (C) Abactinal surface of disk and proximal part of arms, with red arrow pointing at the madreporite body, white arrow at the interradial plate and yellow arrows at the marginal plates. The red frame indicates the proximal region of arm connecting the disk and genital region, where pedicellariae do no form regular costae. (D) Abactinal surface of arm genital area with mosaic plating, red arrows show the costae bands. (E) Paratype RSIOAS003, abactinal surface of arm genital area, red arrows show the costae bands. (F) Paratype RSIOAS052, zoom in view of the abactinal disk, showing the multiple sharp spinelets on disk plates. (G) Paratype RSIOAS052, a piece of dissected skin from abactinal disk, shot from the inner side of the skin, showing the small round disk plates. (H) Abactinal surface at the middle of arm, black arrows indicate the pedicellariae bands.
	Figure 3. Astrolirus. patricki sp. nov. actinal view.(A–D), (G), holotype RSIOAS044. (A) Actinal surface of the disk. (B) oral plates and spines; (C) Interradial angle between arms, red arrow shows the first marginal plates, yellow arrow shows the second marginal plate. (D) Lateral view of the disk, showing the conjunction of plates in the interradii. Red arrows show the first marginal plates, yellow arrows show the first adambulacral plates, white arrow shoes the interradial plate. (E) Paratype RSIOAS003, lateral view of the disk, red arrows show the first marginal plates, yellow arrows show the first adambulacral plates, white arrow shoes the interradial plate. (F) Paratype RSIOAS052, adambulacral plates and spines at the middle of arm, yellow arrows show the subambulacral spines, white arrows show the furrow spines, red arrows show the lateral spines. (G) One of the paired gonads and digestive caeca in genital area.
	Figure 4. Astrolirus. patricki sp. nov. holotype RSIOAS044, mosaic image of abactinal arm.Yellow arrows show the subambulacral spines, white arrow shows the aboral furrow spine, black arrow shows the adoral furrow spine, red arrows show the lateral spines.
	Figure 5. Phylogenetic tree of order Brisingida including Astrolirus patricki sp. nov. and 4 new specimens based on a concatenated dataset of COI, 16S, H3, 12S and 18S genes.Topology follows the result of Bayes tree, bootstrap values and posterior probabilities are shown for each node. Nodes marked by black dots are support by both Maximum Likelihood Tree and Bayes Tree. The new species and new data reported in this study are colored red in the tree.

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