subtitle for learnabout section of A SNAIL'S ODYSSEY
  Feeding & growth
 

Littorines and their relatives feed on various plant matter, including diatoms, algal sporlings, microalgae and macroalgae, lichens, and detritus.  The following articles are arranged by genera. Batillaria spp., Epitonium spp., Lacuna spp., and Trichotropis spp. are considered in this section, while LITTORINA spp. are considered in another section.

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Batillaria spp.

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Research study 1
 

photograph of mud snails Batillaria attramentariaThe mud-snail Batillaria attramentaria is an herbivorous, detritus-eating species that is common in mud-flats from mid- to high-intertidal heights.  During low-tide periods it burrows through the surface sediments and often buries itself head-first, or fashions a smooth-sided pit, perhaps as protection from desiccation.  Swinbanks & Murray 1981 Sedimentology 28: 201.

NOTE  several batillariids, including zonalis, are now grouped into the single species attramentaria

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Epitonium spp.

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Research study 1
 

Wenteltraps Epitonium tinctum and E. indianorum eat tentacles of sea anemones.  The former species seems to specialise on Anthopleura spp. and the latter on Urticina spp., but neither does this exclusively.  The proboscis is quite long and reaches out to enclose the tentacle end within the buccal cavity.  The radula then snips off the end portion.  Bites can also be made along the length of the tentacle.  Wenteltraps secrete a purple substance from the hypobranchial gland that is shown in preparations of frog sciatic nerves to have toxicity.  Y-apparatus choice tests show highly significant distance selection by Epitonium tinctum for Anthopleura elegantissima (84% prefer the anemone-side of the Y-apparatus to 16% for the empty side) and A. photograph of wenteltrap shell Epitonium tinctum courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washingtonxanthogrammica (88% vs. 12%), both of which are in the snail’s intertidal distributional range, but also for Urticina lofotensis (78 vs. 22) and Epiactis prolifera(80 vs. 20), neither of which are likely to be encountered by Epitonium in the field.  Seawater passing over plumose anemones Metridium senile seems to be actively avoided (12 vs. 88), and the snails are indifferent to the corallimorpharian Corynactis californica (60 vs. 40).  Smith 1977 Veliger 19: 331; other observations from Salo 1977 Veliger 20: 168. Photograph courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC.


A wenteltrap shell Epitonium tinctum sits on,
and perhaps feeds on, several aggregating
anemones Anthopleura elegantissima

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Lacuna spp.

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Research study 1
 

photograph of lacunid snail Lacuna porrecta courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, WashingtonSpecies of lacunid snails Lacuna in San Juan Islands, Washington feed on epiphytic algae, such as that growing on kelp and eelgrass.  As in other grazing gastropods, rows of cusps are worn and shed anteriorly while constantly being produced in the radula sac posteriorly.  Radula production is therefore in dynamic equilibrium.  An individual will replace its entire radula several times over its lifetime depending upon the length of the radula and its rate of wear.  Researchers at Friday Harbor Laboratories, Washington use a method of cold-shocking the whole animal to mark the radula in situ, enabling estimates to be made of radula replacement rates on later dissection.  Results for Lacuna vincta and L. variegata reveal similar replacement rates of 2.9 and 3.0 cusp rows . d-1, respectively.  However, owing in part to differences in total lengths of radulae within each species (47-94 cusp rows in L. vincta and 53-99 in L. variegata), replacement rates for the entire radula differ significantly, from an average of 3.5wk in vincta to 3wk in variegataPadilla et al. 1996 J Moll Stud 62: 275. Photograph courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC.

NOTE  the method involves immersing a snail in seawater of -1oC for 48h.  This disrupts cusp formation, leaving an easily observed mark on later dissection

NOTE  the results given here are combined data for males and females, as no significant differences are found between them

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Research study 2
 

photographs of radulae of a lacunid snail Lacuna variegata showing morphological differences in the radula induced phenotypically by feeding on different algal foods, courtesy Padilla 1998 Veliger 41: 202As noted above the radulae of Lacuna variegata and L. vincta in San Juan Islands, Washington are replaced at a rate of about 3 cusp rows . d-1, with complete replacement of a radula taking 3-4wk.  If snails are allowed to graze for 8wk on epiphytes growing on kelp and eelgrass, a remarkable transformation in cusp morphology occurs.  The snails on kelp develop more pointed cusps (upper photo on Left), while the ones on eelgrass develop more blunt cusps (lower photo on Left). Although only changes in radula form in L. variegata are illustrated here, similar results are found for L. vincta. The change is abrupt and no intermediate morphologies are found.  The interesting thing is that the new cusp morphology is, of course, produced at the posterior end of the radula, and is physically distant from the cusps in use at the time.  The authors remark that radula morphology in gastropods is commonly used as a species identifier, and so a demonstration that this morphology is actually plastic and may vary with the type photograph of lacunid snails Lacuna vincta feeding on the float of a bull kelp Nereocystis luetkeana, courtesty N. Elder and Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washingtonof food is certain to create questions about its usefulness as a taxonomic tool.  This is the first demonstration that the form of a radula cusp in a snail is phenotypically plastic and that changes are inducible in the adult state. Whether an induced morphology is more functionally effective for a particular alga is not known, nor is the proximal cause of the change known. Padilla 1998 Veliger 41: 201. Photograph courtesy N. Elder & Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC.

NOTE  this could be a type of proprio-receptive signal from mechanical differences in rasping, or a chemical signal originating from the food after consumption

When eating the pneumatocyst of a bull kelp
Nereocystis luetkena, these Lacuna vincta
scratch at the epithelial layer, consuming
it and perhaps any epiphytes growing on it

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Research study 3
 

photograph of snails Lacuna vincta on some sea lettuce Ulvagraph showing feeding preferences of snails Lacuna vincta for 3 species of west-coast kelps, including Sargassum muticumIf you wonder how long it takes for an indigenous west-coast herbivorous snail, like Lacuna vincta, to adapt to an introduced seaweed, like Sargassum muticum, the answer is quite quickly if it is edible, and several decades to acquire a preference for it. Researchers at Friday Harbor Laboratories, Washington determine that since its introduction to the Puget Sound area in the 1940s, this alga has not only become a favoured food for Lacuna, but in laboratory choice tests it is preferred as food over 2 other shallow-water native kelp species Saccharina subsimplex and Agarum fimbriatum (see histogram). Other preference tests using agar gels containing homogenised algal tissues, show that Lacuna prefers the flavour of S. muticum rather than other possible features such as morphology or texture. Field assessments at 5 sites in Puget Sound additionally reveal that Lacuna is about 10-fold more abundant on S. muticum than on these same 2 native kelp species. Britton-Simmons et al. 2011 Hydrobiologia 661: 187. Photograph courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC.

NOTE this is a highly successful invasive species, having spread since its introduction north to Alaska and south to Baja California

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Trichotropis spp.

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Research study 1
 

graph showing relationship between density of the snail Trichotropis cancellata and that of the tubeworms that it parasitiseshistogram showing frequency of parasitism by snails Trichotropis cancellata and its host tubewormsThis fairly distant relative of littorines has unusual feeding habits in that it both suspension-feeds from the plankton and parasitises tube-dwelling polychaete worms for their own filtrate yields.  A researcher from Muhlenberg College, Pennsylvania who has contributed greatly to our knowledge of Trichotropis cancellata’s feeding behaviour provides information on its distribution and that of congeneric relatives in areas of Washington, British Columbia, and throughout Alaska, along with details of host tubeworm species that it parasitises in these areas.  Results show that T. cancellata is relatively common and evenly distributed along the northwest coast.  Its host worms include all of the larger tubeworm species found in the area, and local distributions and densities of the snail may be skewed to distributions and densities of its host species (see graph on Left showing a weak but significant correlation).  During the period of sampling (Jun-Jul for most locations) the frequency of snails parasitising ranges from 50-90% (see histogram).  Tubeworm abundances throughout Trichotropis’ range do not appear to be limiting, save perhaps for some areas in southwest Alaska where, in place of absent tubeworm hosts, a holothurian Eupentacta quinquesemita is used.  Interestingly, one congenor, T. conica, is confirmed by the author as a kelptoparasite on tubeworms, while another, the more narrowly distributed T. insignis, only suspension-feeds.  Iyengar 2008 J Moll Stud 74: 55.

NOTE  a behaviour known as kleptoparasitism;  more on this topic can be found at LEARN ABOUT TUBEWORMS: FOODS & FEEDING: SUSPENSION-FEEDING: THEFT OF FOOD BY SNAILS

NOTE  these are T. conica, sympatric with T. cancellata on Vancouver Island and throughout Alaska, and T. insignis, found only in selected areas of southwest Alaska where it is sympatric with the both of the other species

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