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| Xyloplax princealberti Payne, Tilic, Boschen-Rose, Gannon, Stiller, Hiley, Grupe, Mah & Rouse, 2023 |
Abstract
Xyloplax is a genus of three species of sea stars previously found only on sunken wood in the deep ocean. Their circular and petaloid bodies, which lend them their common name “sea daisy”, and their presumed exclusive diet of wood make them an unusual and rare element of deep-sea ecosystems. We describe here the fourth species of Xyloplax from the eastern Pacific Ocean, Xyloplax princealberti n. sp., which ranges from offshore Canada to the Gulf of California (Mexico) and Costa Rica. Though sampled geographically close to another described species of Xyloplax from the northeastern Pacific, X. janetae, this new species is unique morphologically and according to available DNA data. The short abactinal spines are the most obvious feature that distinguishes X. princealberti n. sp. from other Xyloplax. The minimum distance for mitochondrial cytochrome c oxidase subunit I from Xyloplax princealberti n. sp. to the only other available Xyloplax, X. janetae, was 13.5%. We also describe Ridgeia vestimentiferan tubeworm bushes from active hydrothermal vents as a new Xyloplax habitat, the first record of a non-wood substrate, and a new reproductive strategy, simultaneous hermaphroditism, for this genus. We generated the first mitochondrial genome for a member of Xyloplax and analyzed it with other available asteroid data using nucleotide-coding or amino acid (for protein-coding genes) plus nucleotide coding (for rRNA genes). The nucleotide-coding results place Xylopax as part of the clade Velatida, consistent with a previous phylogenomic analysis that included Xyloplax princealberti n. sp. (as Xyloplax sp.), though the placement of Velatida within Asteroidea differed. The amino acid plus nucleotide coding recovered Velatida to be a grade with X. princealberti n. sp. as sister group to all other Asteroidea.
Keywords: deep sea; asteroid; hydrothermal vent
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| Collection sites and representative individuals of Xyloplax princealberti n. sp. (A) Recovered wood block from Juan de Fuca Ridge, offshore Canada, showing a specimen on the surface (indicated with white arrow). Inset shows an animal in situ on the wood surface. (B) Ridgeia vestimentiferan bush sampled at the Juan de Fuca Ridge, offshore Canada. (C) Wood found with seven specimens of Xyloplax princealberti n. sp. at 2421 m on the Alarcón Rise, Gulf of California, Mexico. (D) Wood deployment at 1845 m at Jaco Scar, offshore Costa Rica. (E) Specimens in abactinal view collected from wood deployment in the Juan de Fuca Ridge, offshore Canada. (F) Specimens in abactinal view collected from wood in the Gulf of California, Mexico. (G) Two specimens in abactinal view from Jaco Scar, offshore Costa Rica. (H) Two specimens in actinal view from Jaco Scar, offshore Costa Rica. |
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| Images of Xyloplax princealberti n. sp. from the wood deployment in Juan de Fuca Ridge, offshore Canada. (A) Live specimen (from lot SIO-BIC E6809), abactinal view. * indicates hydropore. (B) Live specimen (lot SIO-BIC E6809), actinal view. (C) Closeup of the abactinal view of a live specimen (lot SIO-BIC E6809), showing adambulacral spines and short abactinal spinelets. * indicates hydropore. (D) Closeup of the actinal view of a live specimen (lot SIO-BIC E6809), showing tube feet and adambulacral spines. (E) Preserved holotype (SIO-BIC E11463), abactinal view. (F) Preserved holotype (SIO-BIC E11463), actinal view. (G) Preserved holotype (SIO-BIC E11463), closeup ambulacral area showing 7 tube feet and abactinal spinelets, abactinal view. |
VELATIDA
XYLOPLACIDAE Baker, Rowe & Clark, 1986
Xyloplax Baker, Rowe & Clark, 1986
Xyloplax princealberti n. sp.
Diagnosis: Xyloplax with rounded abactinal spine bases, spines uniformly short. Two to three adambulacral spines per plate; more than 100 total spines around margin. Tube feet rounded, bulbous, up to ten per segment. Terminal plates badge-shaped. Mouth, gut, and anus absent. “Viviparous”, simultaneous hermaphrodite.
Etymology: This species honors His Serene Highness Prince Albert II of Monaco for his efforts to protect the marine environment through the Prince Albert II of Monaco Foundation.
Cheyenne Y. Payne, Ekin Tilic, Rachel E. Boschen-Rose, Amanda Gannon, Josefin Stiller, Avery S. Hiley, Benjamin M. Grupe, Christopher L. Mah and Greg W. Rouse. 2023. Xyloplax princealberti (Asteroidea, Echinodermata): A New Species that is not always associated with Wood Falls. Diversity. 15(12), 1212. DOI: 10.3390/d15121212
(This article belongs to the Special Issue Diversity and Biogeography of Sea Stars (Echinodermata, Asteroidea))