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| Astrolirus patricki
Zhang, Zhou, Xiao & Wang, 2020
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Abstract
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. |
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| 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. |
Systematics
Order Brisingida Fisher, 1928
Family Brisingidae G.O. Sars, 1875
Genus Astrolirus Fisher, 1917
Diagnosis to Genus. Intercostal integument covered by thin plates; the first pair of adambulacral plates do not touch by their interradial faces, but are separated by a pair of marginal plates; first pair of marginal plates unit closely with a large interradial plate in the interradial faces.
Astrolirus patricki sp. nov.
Diagnosis. Arms 7, robust. Intercostal integument densely covered by irregular, abutting plates. No syzygy between proximal arm plates. The first pair of adambulacral plates separated by a pair of marginal plates. A large interradial plate above the first marginal plates, visible from the abactinal side, covered by scattered spinelets. Mouth spines and proximal adambulacral spines robust, densely distributed. Suboral spines 3–4; subambulacral spines 1–2, proximal ones truncate, capitate. One lateral spine to each adambulacral plate, starting from about the 8th. A pair of gonads to each arm.
Etymology. The name is originated from the character “Patrick Star” in the famous cartoon “SpongeBob Squarepants”, who always spends time with his best friend “SpongeBob”, a benthic sponge. Since all specimens of the new species were observed in situ living on sponges (Fig. 1), it was name by Patrick to reflect this curious relationship.
Conclusions:
The new species Astrolirus patricki sp. nov. reported in this study represents the second known species in the genus, which is distinguished from its congener by the form and organization of costae and intercostal plates as well as numbers of spines and arms. Morphological description and molecular data delimitate the new species and provide reference for future taxonomic and phylogenetic study of related species. The current phylogenetic analysis on order Brisingida indicates an intermediate position of A. patricki sp. nov. between Brisinga and Hymenodiscus, but more samples and multi-gene analysis are needed in the future to clarify the actual systematic and phylogenetic relationships among these genera.
Ruiyan Zhang, Yadong Zhou, Ning Xiao and Chunsheng Wang. 2020. A New Sponge-associated Starfish, Astrolirus patricki sp. nov. (Asteroidea: Brisingida: Brisingidae), from the northwestern Pacific Seamounts. PeerJ. 8:e9071. DOI: 10.7717/peerj.9071
