Research Article |
Corresponding author: Alexandra Hiller ( alexandrahiller40@gmail.com ) Academic editor: Ingo S. Wehrtmann
© 2019 Bernd Werding, Alexandra Hiller.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Werding B, Hiller A (2019) A new species of Polyonyx (Crustacea, Anomura, Porcellanidae) inhabiting polychaete-worm tubes (Annelida, Chaetopteridae) in the Indo-West Pacific. ZooKeys 818: 25-34. https://doi.org/10.3897/zookeys.818.30587
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Polyonyx socialis sp. n. from the South China Sea of Vietnam is described. The new species was collected in a previous study that compared the vertebrate and invertebrate symbiont communities living in the tubes of two syntopic species of the polychaete genus Chaetopterus. Polyonyx socialis sp. n. inhabits the tubes of the smaller polychaete species as a heterosexual pair, and frequently shares the cavity of the host’s tube with a larger porcellanid, P. heok, also present as a male-female pair, and with a species of trinchesiid nudibranch. Less frequently, the new species shares its host with a heterosexual pair of a larger species of pinnotherid crab. Polyonyx socialis sp. n. belongs to the P. sinensis group, a world-wide distributed morphological line within the heterogeneous genus Polyonyx. Most species in this group are obligate commensals of chaetopterid polychaetes. The crabs have a transversally cylindrical habitus, which enables them to move laterally along the worm tubes with ease. Polyonyx socialis sp. n. is a relatively small species that lives attached to the inner walls of the polychaete tube. The small size and flattened chelipeds and walking legs of the new species confers it an advantage to cohabiting the same worm tube with larger decapod species occupying most of the tube’s cavity.
adaptation, Chaetopterus , commensalism, polychaete-inhabiting
The porcellanid genus Polyonyx Stimpson is a diverse and heterogeneous taxon containing more than 30 species worldwide, most of which distributed in the Indo-West Pacific (IWP) (
The largest of
The Polyonyx biunguiculatus group contains six species, four distributed in the Central Pacific (
In a recent study of symbionts of two syntopic species of chaetopterid polychaetes in the South China Sea of Vietnam,
Material of Polyonyx socialis sp. n. was provided by T Britayev (Severtzov Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow, Russian Federation) and D Martin (Department of Marine Ecology, Centre d’Estudis Avançats de Blanes, Blanes, Catalunya, Spain), and has been deposited in the Naturmuseum Senckenberg (
Holotype: female,
Carapace (Fig.
Third thoracic sternite (Fig.
Telson composed of seven plates (Fig.
Basal article of antennular peduncle unarmed. First antennal article broadly in contact with lower orbital margin, movable articles smooth, second elongate; flagellum long, reaching to tip of chelae.
Third maxilliped (Fig.
Polyonyx socialis sp. n., male paratype,
Chelipeds (Figs
Walking legs (Figs
Males with pair of pleopods on second abdominal segment.
The overall coloration of Polyonyx socialis sp. n. (Fig.
Polyonyx socialis sp. n. inhabits the tubes of a Chaetopterus sp. worm as heterosexual pairs, and shares its host with other symbionts, either a male-female pair of the porcellanid P. heok and the aeolid nudibranch Phestilla sp., or a male-female pair of the pinnotherid crab Tetrias sp. The hosts were collected between 6 and 20 m depth.
The specific name socialis, from the Latin, meaning social, refers to the sociable behaviour of the new species, as it tolerates and is tolerated by other symbionts inhabiting the same polychaete host.
The new species is morphologically similar and probably systematically close to P. utinomii Miyake, 1943 and P. boucheti Osawa, 2007, both of which also live in Chaetopterus tubes (
Currently known only from the Vietnamese coast of the South China Sea.
Polyonyx socialis sp. n. inhabits as a heterosexual pair the tubes of one of two syntopic species of Chaetopterus, which according to
The extremely broadened chelipeds and walking legs of P. socialis sp. n. are distinctive characters within Polyonyx, even when comparing the species with the morphologically closest P. boucheti and P. utinomii, and to all other tube-dwelling species of the genus. These characters are most likely adaptations to living tightly attached to the walls of the worm tube without being perceived as an obstacle for the larger crabs inhabiting the same tube. The new species is therefore morphologically adapted to cohabiting with a heterosexual pair of a congeneric larger crab, what is quite exceptional. The West Atlantic representative of the P. sinensis group, P. gibbesi Haig, 1956 inhabits the polychaete host Chaetopterus variopedatus (
Polyonyx socialis sp. n. and P. heok comprise the first pair of porcellanid crabs observed to share the same host.
We thank T Britayev and D Martin for sending us the porcellanid material collected in Vietnam, and for providing us with collection data and the photograph of the described crab species. We thank M Robert for inking our drawings, and I Wehrtmann (Universidad de Costa Rica, San José) and E Macpherson (Centro de Estudios Avanzados de Blanes, Girona, Spain) for their valuable contributions to this paper.