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Parahesione pulvinata P. apiculata Jimi, Gonzalez, Rouse & Britayev, in Jimi, Nakajima, Sato, Gonzalez, Woo, Rouse & Britayev, 2023. DOI: 10.7717/peerj.16346 |
Abstract
Two new species of Hesionidae, Parahesione pulvinata sp. nov. and Parahesione apiculata sp. nov. are described based on materials collected at tidal flats in Okinawa (Japan) from burrows of the ghost shrimps Neocallichirus jousseaumei and Glypturus armatus. The two new species are characterized by having eight enlarged cirri, dorsal cirrophores with dorsal foliose lobe and biramous parapodia, and by lacking median antenna. Parahesione apiculata sp. nov. has digitate lobes on the posterior margin of the dorsal foliose lobe (absent in P. pulvinata sp. nov.). The two new species were never found outside the ghost shrimp burrows, suggesting they are obligate symbionts. Phylogenetic analyses based on four concatenated genes suggest that the symbiotic lifestyle has evolved several times in Hesionidae.
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| Observations of Parahesione pulvinata sp. nov. and its hosts in situ. (A) Sampling at the sandy tidal flat of Uehara; (B) host and the new species; (C) detail of the host Neocallichirus jousseaumei; (D) another host with its symbiont (tube); (E) dorsal view of the new species of a living specimen (NSMT-Pol H-893); (F) dorsal view of a preserved specimen (NSMT-Pol H-893). |
Parahesione pulvinata Jimi, Gonzalez, Rouse and Britayev sp. nov.
[New Japanese name: ana-yadori-otohime]
Diagnosis. Parahesione with dorsal foliose lobe, without dorso-lateral digitate extension, and eight tentacular anterior cirri.
Etymology. The specific name “pulvinata”, derived from the Latin pulvinus (meaning cushion, pillow), referring to the shape of dorsal cirrophores. The specific name is an adjective in the nominative case.
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| Parahesione apiculata sp. nov. and hosts in situ (A) Sampling location at the Nanjo sandy tidal flat; (B) living specimen of the symbiont; (C) living specimen of the Glypturus armatus (host); (D) dorsal view of a living specimen, lacking posterior most segments (same individual with Fig. 6B, NSMT-Pol P-899). |
Parahesione apiculata Jimi, Gonzalez, Rouse and Britayev sp. nov.
[New Japanese name: toge-ana-yadori-otohime]
Diagnosis. Parahesione with dorsal foliose lobe, dorso-lateral digitate extension, and eight tentacular anterior cirri.
Etymology. The specific name “apiculata”, derives from the Latin apiculatus (meaning short pointed) and referring to the digitate extension on dorso-lateral margin of dorsal foliose lobe, is as an adjective in the nominative case.
Conclusions:
The genus Parahesione, belonging to Hesionidae, is a rare group of symbiotic polychaetes living in ghost shrimp burrows with two different sets of tentacular cirri; in one species there are only six whereas in the other there are eight. Interestingly, the prostomium have different shape being trapezoidal in those species with six pairs of tentacular cirri, and rectangular for those having eight pairs of tentacular cirri. Further, the dorsal parapodial modifications involving a foliose dorsal projection has been only reported in those species with eight pairs of tentacular cirri, whereas it has not been recorded in the only species having six pairs of tentacular cirri. We have discovered two new Parahesione species associated with ghost shrimps from the northwest Pacific. Both species are characterized by a flattened body, expanded foliose bases of cirrophores, and a bright red color. We consider these features as adaptations to thrive in the burrow hypoxic conditions. Reconstruction of the phylogenetic tree using four genes revealed their close relationship with non-symbiotic species of the sister clade Amphiduropsis-Amphiduros, suggested the independent establishment of symbiosis in various clades of the family Hesionidae.
Naoto Jimi, Hiroki Nakajima, Taigi Sato, Brett C. Gonzalez, Sau Pinn Woo, Greg W. Rouse and Temir Britayev. 2023. Two New Species of Parahesione (Annelida: Hesionidae) associated with Ghost Shrimps (Crustacea: Decapoda) and their phylogenetic relationships. PeerJ. 11:e16346. DOI: 10.7717/peerj.16346
