title for learn-about section on whelks & relatives in A SNAIL'S ODYSSEY
  Foods, feeding, & growth
  Topics in this secion include use of shell spines in feeding, considered here, and
, and
HATCHLINGS AS PREDATORS considered in other sections.
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Use of shell spines in feeding

  Topics in this secion include use of shell spines in feeding, considered here, and RADULAR DRILLING, CALIFORNIA CONE SHELLS: CUSPS USED AS HARPOONS, DIETS, FACTORS IN DIET SELECTION, GROWTH, and HATCHLINGS AS PREDATORS considered in other sections.
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Research study 1

photograph of whelk Acanthinucella punctulata courtesy Gary McDonaldThe use of a shell spine as a stabilising device by whelks is proposed in an early review of its use by Acanthinucella species in the Gulf of California.  The author reports no indication of its use in feeding, and this is both confirmed and refuted by the results of other studies on Californian Acanthinucella species (see Research Studies below).  Paine 1966 Veliger 9: 117. Photograph courtesy Gary McDonald, Santa Cruz, California and CALPHOTOS.



Acanthinucella punctulata, not showing its shell spine.
The little striped object poking out is its right tentacle 2X

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Research study 2

drawings of whelk Acanthinucella punctulata holding and drilling a winkle preyFor example, a later study on feeding of Acanthinucella (Acanthina) punctulata on littorines Littorina scutulata and L. planaxis in Santa Cruz Island, California suggests that the prominent tooth does not play any special role during feeding; rather, the author suggests that it is the predator’s foot that holds the prey in place during drilling and eating. Menge 1974 Oecologia 17: 293.

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Research study 3

photographs of labial spines of leafy hornmouth whelk Ceratostoma foliatumThe leafy hornmouth shell Cetatostoma foliatum also has a prominant labial spine.  The spine becomes relatively larger with age and size of the snail, and is thought to become functional at shell lengths of 5-6cm.  But what is its function?  Ideas include that it may be employed as a stabilising device during feeding, such as being pressed against the substratum for firm purchase, or perhaps being inserted between the shell valves of barnacles during feeding.  Kent 1981 The Nautilus 95: 38.

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Research study 4

Although apparently not used by the whelk Acanthinucella punctulata when eating littorines, the spine does seem to be used in attacking barnacles.  This is described in a report on feeding of Acanthinucella at Hopkins Marine Station, Pacific Grove, California.  When attacking barnacles the whelk uses its spine as a hammer to open the scutal plates.  In such instances, the barnacle remains open as if paralysed, suggesting that a fast-acting toxin has also been applied.  As a test of this, if barnacles Chthamalus dalli are injected with crude extract of the snail’s accessory boring organ (ABO), most show temporary signs of paralytis, with about 25% of the test subjects dying after 24h.  Interestingly, if the labial spines are removed from whelks and the whelks given barnacles to eat, much more damage is inflicted on the barnacles.  In fact, 3 times more opercular plates are completely ripped off by spineless whelks than would occur in attacks by whelks with spines.  The author suggests that use of the spine in conjunction with ABO secretion allows a whelk access to a barnacle with much less energy expenditure than if it were to drill and/or rip off the opercular plates.  Sleder 1981 Veliger 24: 172.

NOTE  0.2ml of crude extract of ground ABO in seawater are injected into the barnacle’s mantle cavity when it opens to feed.  Identical injections of seawater into control barnacles results in mostly no effects and no deaths in 24h

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Research study 5

graph showing times required for a whelk Acanthinucella spirata to kill and eat various barnacles with shell spine removed and intactUse of a shell spine by whelks for penetrating barnacles is confirmed in a study on Acanthinucella spirata in Palos Verdes, California.  Here, barnacles Balanus glandula and photograph of whelk Acanthinucella spirata poised over a prey barnacle with its shell spine ready to strikeChthamalus fissus are the sole prey of A. spirata.  The author shows that the spine is used as a ram to pry open the opercular plates of its prey.  Barnacles attacked in this way can then be eaten without drilling.  The photograph on the Left shows the predator initiating an attack on B. glandula. The spine is positioned directly over the 4 opercular plates of the prey, then rammed rapidly down.  By raising its foot at the back, the whelk then levers the spine forward in a prying motion.  The sequence is repeated until the plates are pried apart.  The author reports that 100% of attacks by snails bearing a shell spine are conducted in photograph of whelk Acanthinucella spirata courtesy Kaustuv Roy, UC San Diegothis way.  Snails with their spines filed off  somehow sense that this mode is useless, and resort to drilling. 

graph showing time taken for spine regeneration in the whelk Acanthinucella spirataExperiments conducted with caged snails in the field show that Acanthinucella with intact spines have shorter handling times and feed at greater rates than snails with their spines experimentally removed, and that have to drill their prey (see graph upper Right).  If thrusts of intact spines are used, the whelks take almost twice as long to attack and eat Balanus as compared with Chthamalus, but if drilling is used, as by individuals with spines experimentally removed, then the reverse is the case. The author notes that a third attack method may be employed by snails lacking a spine, one involving possible injection of toxin, but the process is not visible to an observer because the foot and shell tend to hide the opercular plates from view. Perry 1985 Mar Biol 88: 51. Colour photo courtesy Kaustuv Roy.

NOTE   it takes about 4wk for a snail to regrow its spine after it is experimentally removed (see graph lower Right; temperature not specified)  Natural spine breakage is apparently quite common in the species. The author notes that about 40% of all attacks lead to breakage

NOTE   "sense" may not be the correct word to describe it, but the behaviour is an interesting one and probably deserves further research (along with the whole question of spine use in west-coast muricids)

Acanthinucella spirata with apertural spines

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  Research study 5.1

photograph of whelk Acanthina angelicaAnother whelk that uses its shell spine in this way to attack barnacles is Mexacanthina angelica. In habitats in the Gulf of California this snail feeds on barnacles, most notably volcano barnacles Tetraclita stalactifera and Chthamalus anisopoma. The whelk uses its spine as a wedge to force open the opercular plates or drills through the top (opercular) or side plates by use of its radula. Once an opening is created, the snail inserts its proboscis and consumes the prey. Which method is used relates to relative length of spine and to size of the barnacle prey. Wedging is quicker than drilling, especially in volcano barnacles, perhaps owing to the increasing thickness of the side plates from top to bottom (see photo below). During a wedging attack, a snail anchors with its foot and lunges downwards with its spine towards the junction of the opercular plates, sometimes repeatedly (up to 5 times per minute). Laboratory observations of long- and short-spined whelks attacking and eating small-, medium-, and large-sized volcano barnacles yeild the following main conclusions: 1) as prey size increases, whelks switch from wedging to drilling, and 2) small-spined snails switch at smaller prey size than long-spined ones. Wedging is used for 100% of small barnacles, 87% of medium-sized ones, and only 43% of large ones. Although the author notes that wedging is much quicker than drilling, no supportive data are provided; nor is there any discussion of the plate thickness of a volcano barnacle as an obstacle to drilling. Malusa 1985 The Veliger 28 (1): 1. Photograph of snail courtesy Guido & Philippe Poppe, Conchology, Inc., Philippiines.photographs of volcano barnacles Tetraclita spp.

NOTE adult Acanthina angelica are about 35mm in length. Spine lengths range in adults from 2-7mm. Large adults with long spines predominate in the high intertidal zone where large volcano barnacles are common, while short-spined snails are more prevalent in the low intertidal zone in association with small barnacle prey Chthamalus anisopoma

NOTE interestingly, spine length is controlled by size of prey. Thus, long-spined whelks given only small barnacles as prey over 3mo develop smaller spines, while short-spined whelks grow longer spines after 3mo on diets of large barnacles


A crevice with volcano barnacles Tetraclita sp. Inset: ventral
view of shell illustrating thicknesses of the basal parts of the
plate. The vacuolated structure aids in thermal protection (inset 1X)

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Research study 6

dendrogram showing phylogenetic lineages of spines in whelksThere are about 16 species of west-coast ocenebrinids (Mexico to Alaska), 6 of which in the genera Ceratostoma, Mexacanthina (proposed new genus), and Acanthinucella possess labral spines. As noted in the previous Research Studies, labral spines aid in feeding on hard-shelled prey, such as breaking or forcing open opercular plates of prey barnacles, wedging open valves of prey clams, and prying open opercula of prey gastropods. Recent molecular analysis of these species by researchers at the University of California indicate 3 independent lineages corresponding to the genera just listed (see dendrogram, extinct species not included). Each type of spine differs in its place of origin on the shell, whether external or internal in relation to the aperture and whether it originates from a groove or a cord/ridge. In Ceratostoma foliatum, for example, the spine is external to the aperture and arises from a ridge (see photograph below and in spine of whelk Ceratostoma foliatum showing its origin on the shellResearch Study 3 above). Marko & Vermeij 1999 Mol Phylog Evol 13 (2): 275.

NOTE two terms most commonly used to describe the spine are labial and labral, the former referring to “lip”; the latter, to “lip/edge”. The spine does sit on the lip or edge of the aperture,
so either term is good.
The term “tooth” is also used,
as in the present study, but
“spine” seems more appropriate

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