Substrate-dependent shell morphology in a deep-sea vetigastropod limpet
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Substrate-dependent shell morphology in a deep-sea vetigastropod limpet Chong Chen 1
&
Hiromi Kayama Watanabe 1
Received: 11 August 2020 / Revised: 6 October 2020 / Accepted: 25 October 2020 # Senckenberg Gesellschaft für Naturforschung 2020
Abstract Having a noncoiled, limpet-like shell is a characteristic shared by numerous gastropod molluscs, including many lineages outside the true limpets (Patellogastropoda) where it has evolved convergently. The shell shape of limpet-formed gastropods has often been used as a key taxonomic character, and although studies have shown that it can vary depending on the substrate morphology, these have mostly been examples from true limpets. Over a dozen origins of limpet-form are known in Vetigastropoda, and these limpets are still generally assumed to have rather stable shell forms that are useful for taxonomy and species identification. Here, we show that the vetigastropod limpet Lepetodrilus nux (Okutani, Fujikura & Sasaki, 1993) from a deep-sea hot vent in the Okinawa Trough develop distinct shell forms when living on different substrate types. Sequences of the barcoding region of the mitochondrial cytochrome c oxidase subunit I gene among the three forms only differed by 0.31–0.63% (K2P distance) in a 637 bp alignment, in line with the differences in shell morphology being intraspecific. The extent of shell form shift seen in this species is likely the largest reported for a vetigastropod limpet and provide further evidence that such plasticity is not phylogenetically constrained but is an intrinsic part of having a limpet-like shell. Keywords Gastropoda . Hydrothermal vent . Lepetodrilus . Mollusca . Okinawa Trough
Introduction Gastropod molluscs have independently evolved the limpet shell form at least 54 times (Vermeij 2016). The limpet form has been associated with variability in shell shape, with translocation experiments on both shallow and deep water true (patellogastropod) limpets showing changes in the shell profile during growth according to the substrate shape and type (Lindberg and Pearse 1990; Chen et al. 2019). Few cases of such shifts and phenotypic plasticity in the limpet form have been reported outside true limpets (e.g., Teske et al. 2007 for the heterobranch limpet of the genus Siphonaria Yipp, 1980 for the caenogastropod limpet Ergaea walshi (Reeve, 1859)),
Communicated by V. Urgorri * Chong Chen [email protected] 1
X-STAR, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2–15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan
but already suggest that this plasticity is not phylogenetically constrained to the true limpets and is instead widespread among limpet-shaped gastropods. Lepetodrilus is a genus of vetigastropod limpets (family Lepetodrilidae) found only in chemosynthesis-based ecosystems including hot vents, cold seeps, and organic falls in the deep sea (Sasaki et al. 2010). Lepetodrilus is known to combine a number of feeding mechanisms such as grazing, filterfeeding, and farming epibionts on the gil
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