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An unusual habitat for bivalves: rediscovery of the enigmatic commensal clam Sagamiscintilla thalassemicola (Habe, 1962) (Bivalvia: Galeommatoidea) from spoon worm’s spoon


Sagamiscintilla thalassemicola (Bivalvia: Galeommatoidea: Galeommatidae sensu lato) is a white-robed commensal clam that lives on the body surface of spoon worms (Annelida: Echiura). This species was described based on specimens collected from the spoon worm Anelassorhynchus mucosus (Thalassematidae) in Amakusa, Kyushu, Japan, in 1962, but there has been no reliable record since the first description. Thus, some researchers suspected that this species may have become extinct. In this study, we rediscovered this species from the spoon-shaped proboscis of the echiuran Anelassorhynchus sp. in Shikoku and Kyushu Islands, Japan. Although the original description did not mention the details of its host use pattern, we found that this species lives almost exclusively within the proboscis gutter of the host, where it is almost hidden from the outside. Such a cryptic habitat is probably the reason why this species has remained undiscovered for over 50 years. Living hidden in the host probosces probably provides an anti-predation benefit for S. thalassemicola. The host echiurans create ciliary water currents on the proboscis gutter to transfer food particles into the mouth, and the bivalves can utilize this water currents for respiration and filter feeding. Sagamiscinitlla thalassemicola is distinctive among ectocommensal galeommatoideans in having a mantle that fully covers the shell valves. It may be a morphological adaptation to protect the shell valves from sand and other hard particles transferred through the proboscis gutter of the host.

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  • Anker A, Murina GV, Lira C, Vera Caripe JA, Palmer AR, Jeng MS (2005) Macrofauna associated with echiuran burrows: a review with new observations of the innkeeper worm, Ochetostoma erythrogrammon Leuckart and Rüppel, in Venezuela. Zool Stud 44:157–190

    Google Scholar 

  • Boss KJ (1965) Symbiotic erycinacean bivalves. Malacologia 3:183–195

    Google Scholar 

  • Chuang SH (1962) Feeding mechanism of the echiuroid, Ochetostoma erythrogrammon Leuckart & Rueppell, 1828. Biol Bull 123:80–85

    Article  Google Scholar 

  • Coan EV, Valentich-Scott P (2012) Bivalve seashells of tropical west America: marine bivalves from Baja California to northern Peru. Santa Barbara Museum of Natural History Monographs 6: iii–xv + 1–1258, pls. 1–326

  • Goto R (2016a) A comprehensive molecular phylogeny of spoon worms (Echiura, Annelida): implications for morphological evolution, the origin of dwarf males, and habitat shifts. Mol Phylogenet Evol 99:247–260

    Article  PubMed  Google Scholar 

  • Goto R (2016b) The Echiura of Japan: diversity, classification, phylogeny and their associated fauna. In: Motokawa M, Kajihara H (eds) Species Diversity of Animals in Japan. Springer, Tokyo, pp 513–542

    Google Scholar 

  • Goto R, Kato M (2012) Geographic mosaic of mutually exclusive dominance of obligate commensals in the symbiotic communities associated with a burrowing echiuran worm. Mar Biol 159:319–330

    Article  Google Scholar 

  • Goto R, Hamamura Y, Kato M (2007) Obligate commensalism of Curvemysella paula (Bivalvia: Galeommatoidea) with hermit crabs. Mar Biol 151:1615–1622

    Article  Google Scholar 

  • Goto R, Hamamura Y, Kato M (2011) Morphological and ecological adaptation of Basterotia bivalves (Galeommatoidea: Sportellidae) to symbiotic association with burrowing echiuran worms. Zool Sci 28:225–234

    Article  PubMed  Google Scholar 

  • Goto R, Kawakita A, Ishikawa H, Hamamura Y, Kato M (2012) Molecular phylogeny of the bivalve superfamily Galeommatoidea (Heterodonta, Veneroida) reveals dynamic evolution of symbiotic lifestyle and interphylum host switching. BMC Evol Biol 12:172

    Article  PubMed  PubMed Central  Google Scholar 

  • Goto R, Okamoto T, Ishikawa H, Hamamura Y, Kato M (2013) Molecular phylogeny of echiuran worms (Phylum: Annelida) reveals evolutionary pattern of feeding mode and sexual dimorphism. PLoS ONE 8:e56809

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  • Goto R, Ishikawa H, Hamamura Y, Sato S, Kato M (2014) Evolution of symbiosis with Lingula (Brachiopoda) in the bivalve superfamily Galeommatoidea (Heterodonta), with description of a new species of Koreamya. J Mollus Stud 80:148–160

    Article  Google Scholar 

  • Goto R, Ishikawa H, Hamamura Y (2016a) The enigmatic bivalve genus Paramya (Myoidea: Myidae): symbiotic association of an East Asian species with spoon worms (Echiura) and its transfer to the family Basterotiidae (Galeommatoidea). J Mar Biol Ass UK 97:1447–1454

    Article  CAS  Google Scholar 

  • Goto R, Ishikawa H, Hamamura Y (2016b) Symbiotic association of the bivalve Tellimya fujitaniana (Galeommatoidea) with the heart urchin Echinocardium cordatum (Spatangoida) in the northwestern Pacific. Zool Sci 33:434–440

    Article  CAS  PubMed  Google Scholar 

  • Habe T (1962) Achasmea thalassemicola sp. nov., a new commensal bivalve found in an echiuroid, Thalassema mucosum Ikeda. Venus 22:117–119

    Google Scholar 

  • Habe T (1981) A catalogue of molluscs of Wakayama Prefecture, the province of Kii 1. Bivalvia, Scaphopoda and Cephalopoda. Seto Mar Biol Lab Spec Publ Ser 7:1–303

    Google Scholar 

  • Huber M (2015) Compendium of Bivalves 2. A full-color guide to the remaining seven families. A systematic listing of 8500 bivalve species and 10500 synonyms. ConchBooks, Harxheim

  • Ikeda I (1904) The Gephyrea of Japan. J Coll Sci Imp Univ Tokyo 20:1–87

    Google Scholar 

  • Itani G, Kato M, Shirayama Y (2002) Behaviour of the shrimp ectosymbionts, Peregrinamor ohshimai (Mollusca: Bivalvia) and Phyllodurus sp. (Crustacea: isopoda) through host ecdyses. J Mar Biol Ass UK 82:69–78

    Article  Google Scholar 

  • Kato M (1998) Morphological and ecological adaptations in montacutid bivalves endo- and ecto-symbiotic with holothurians. Can J Zool 76:1403–1410

    Article  Google Scholar 

  • Kato M, Itani G (1995) Commensalism of a bivalve, Peregrinamor ohshimai, with a thalassinidean burrowing shrimp, Upogebia major. J Mar Biol Ass UK 75:941–947

    Article  Google Scholar 

  • Li J, Ó Foighil D, Middelfart P (2012) The evolutionary ecology of biotic association in a megadiverse bivalve superfamily: sponsorship required for permanent residency in sediment. PLoS ONE 8:e42121

    Article  CAS  Google Scholar 

  • Li J, Ó Foighil D, Strong EE (2016) Commensal associations and benthic habitats shape macroevolution of the bivalve clade Galeommatoidea. Pro R Soc B 20161006:283

    Google Scholar 

  • Lützen J, Nielsen C (2005) Galeommatid bivalves from Phuket, Thailand. Zool J Linnean Soc 144:261–308

    Article  Google Scholar 

  • Mikkelsen PM, Bieler R (1989) Biology and comparative anatomy of Divariscintilla yoyo and D. troglodytes, two new species of Galeommatidae (Bivalvia) from stomatopod burrows in eastern Florida. Malacologia 31:175–195

    Google Scholar 

  • Mikkelsen PM, Bieler R (1992) Biology and comparative anatomy of three new species of commensal Galeommatidae, with a possible case of mating behavior in bivalves. Malacologia 34:1–24

    Google Scholar 

  • Morton B (1972) Some aspects of the functional morphology and biology of Pseudopythina subsinuata (Bivalvia: Leptonacea) commensal on stomatopod crustaceans. J Zool (Lond) 166:79–96

    Article  Google Scholar 

  • Morton B (1973) The biology and functional morphology of Galeomma (Paralepida) takii (Bivalvia: Leptonacea). J Zool (Lond) 169:133–150

    Article  Google Scholar 

  • Morton B (1981) The biology and functional morphology Chlamydoconcha orcutii with a discussion on the taxonomic status of the Chlamydoconchacea (Mollusca: Bivalvia). J Zool (Lond) 195:81–121

    Article  Google Scholar 

  • Morton B, Scott PH (1989) Hong Kong Galeommatacea (Mollusca: Bivalvia) and their hosts, with descriptions of new species. Asian Mar Biol 6:129–160

    Google Scholar 

  • Paulay G (2003) Marine Bivalvia (Mollusca) of Guam. Micronesica 35–36:218–243

    Google Scholar 

  • Sato S, Owada M, Haga T, Hong J-S, Lützen J, Yamashita H (2011) Genus-specific commensalism of the galeommatoid bivalve Koreamya arcuata (A. Adams, 1856) associated with lingulid brachiopods. Mollus Res 31:95–105

    Google Scholar 

  • Wada K, Nishihira M, Furota T, Nojima S, Yamanishi R, Nishikawa T, Goshima S, Suzuki T, Kato M, Shimamura K, Fukuda H (1996) Present status of estuarine locales and benthic invertebrates occurring in estuarine environment in Japan. WWF Jpn Sci Rep 3:1–182

    Google Scholar 

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We are grateful to Takuma Haga (National Museum of Natural and Science, Tokyo, Japan) for providing us the echiuran specimen collected in Minami Satsuma.


This study was partially supported by grants to RG from the Japan Society for the Promotion of Science (JSPS) Research Fellowship for Young Scientists (no. 12J07151), JSPS Postdoctoral Fellowship for Research Abroad (no. 27-186), and JSPS KAKENHI (no. 17H06795).

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Correspondence to Ryutaro Goto.

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All applicable international, national, and/or institutional guidelines for the care and use of animals were followed by the authors.

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All necessary permits for sampling and observational field studies have been obtained by the authors from the competent authorities and are mentioned in the acknowledgements, if applicable.

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Communicated by G. Steiner

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Goto, R., Ishikawa, H. An unusual habitat for bivalves: rediscovery of the enigmatic commensal clam Sagamiscintilla thalassemicola (Habe, 1962) (Bivalvia: Galeommatoidea) from spoon worm’s spoon. Mar Biodiv 49, 1553–1558 (2019).

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  • Adaptation
  • Anelassorhynchus
  • Commensalism
  • Echiura
  • Ectocommensal
  • Symbiosis