Nutrition & growth
 
photograph of a northern abalone Haliotis kamtschatkana eating a piece of kelp

Abalones, top shells, and turban shells are herbivorous.  As juveniles they subsist on diatom and bacterial scums, while as adults they eat seaweeds. 

 

 

Northern or pinto abalone Haliotis kamtschatkana
eating a bit of kelp. The abalone's posterior end is
at 4 o'clock in the photo and the kelp is the black bit
trailing off to the right at the 2-o'clock position 0.33X

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  Feeding & digestion
  The topic of feeding & digestion is considered here, while FOOD PREFERENCES and SHELL & GROWTH are considered in other sections. Abalones are considered first, followed by trochid snails.
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Haliotis spp.

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Research study 1
 

drawing of an abalone showing location of mouth

An abalone’s foot is highly prehensile, especially at the front or propodial region, and is used to grab and hold bits of algae for eating.  In this manner the abalone can reach out to grab algal bits floating by in the current, and reach up for kelp fronds overhead. An algal bit is gripped by a pair of jaws within the buccal cavity and rasped by the radula. Drawing modified from Crofts 1929 HALIOTIS  Publ XXIX Liverpool Mar Biol Comm Memoirs, Univ Press Liverpool, 174 pp.

 

NOTE  lit. “in front of foot” G.

photograph of a black abalone Haliotis cracherodii showing its prehensile foot
Black abalone Haliotis cracherodii showng its prehensile foot 0.4X
 

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Research study 2

 

drawing of the gut system of an abaloneFeeding in abalones as in all gastropods involves use of a radula, a ribbon bearing rows of teeth or cusps, common to all gastropods.  The ribbon of cusps is produced in a sac extending back from the lower part of the gullet. Cusps are worn off at the front of the radula and replaced by production of new ones. When feeding, the front part of the radula is extended slightly out of the mouth and rasped upwards against the food, which is held against a pair of immovable jaws.  Four to 6 tooth rows may be in contact with the food at any given time. The cusps scrape algal tissue into the buccal cavity, from which it is moved into the esophagus.  The medially located cusps are the scraping ones (central and drawing of the radular cusps of an abalonelateral rows in the figure on Right), while the finely structured cusps on the sides (marginal rows) appear to function more as sieves to prevent overly large food bits from entering the gullet.  Drawings modified from Crofts 1929 HALIOTIS  Publ XXIX Liverpool Mar Biol Comm Memoirs, Univ Press Liverpool, 174 pp.

NOTE  lit. “scraper” L. The drawing on the Right shows 3 rows of cusps on the left side of an abalone radula (and part of a 4th row), plus the central row, out of several hundred rows in total. The anterior end of the radula is at the top

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Research study 3
 

A nutritional study at the Scripps Institution of Oceanography on juvenile red abalone Haliotis rufescens provides considerable data on digestive-enzyme production in individuals feeding on kelp and 2 artificial compounded diets.  The authors present detailed information on 2 carbohydrases (including cellulase), 3 proteases, and a lipase, and semiquantitative data on several other digestive enzymes.  Two main digestive regions are identified: the mouth-intestine characterised by high activity of lipase and amino-peptidase, and the the digestive gland-stomach characterised by high activities of cellulase and lysozyme, and chymotrypsin and protease.  Although only one natural diet (a favoured one for red abalone: Macrocystis pyrifera) is included in the study, comparison of enzyme production and activity on this diet with those on 2 artificial diets shows, not surprisingly, that H. rufescens abalone Haliotis rufescens courtesy Kevin Lee, Fullertoncan adjust its enzyme levels to maximize acquisition of dietary protein and carbohydrates.  The authors note an increase in number of gut bacteria in individuals fed carbohydrate- and protein-enriched artificial diets, but do not quantify this.  Garcia-Esquivel & Felbeck 2006 Aquaculture 261: 615. Photograph courtesy Kevin Lee, Fullerton, California

NOTE  the diet-comparison part of the study is principally aquaculture oriented and, as such, falls outside of the intended scope of the ODYSSEY.  However, the kelp-diet part provides much useful information on "natural" digestive capabilities in abalone, and so is included here

NOTE  the compounded diets contain 17-22% kelp meal.  This, along with added corn starch, leads to diets with 48-64% carbohydrate, but with different levels of protein enrichment.  Both artificial diets promote better growth than the natural kelp diet


Juvenile red abalone Haliotis rufescens 2X

 

 

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Chlorostoma spp.

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Research study 1
 

Chlorostoma funebralis locates and judges the quality of algal foods through chemotactile means, using its cephalic tentacles, osphradium, foot, and mouth.  drawing of the mouth and anterior gut system of a black turban snail Chlorostoma funebralisThe mouth is somewhat extensible and can be partially wrapped around food.  There is a pair of jaws to help hold the food while the radula rasps off chunks for transport through the buccal cavity into the opening of the esophagus.  As it grows, photograph of a snail Calliostoma ligatum from below showing foot musculaturethe radula slides over paired radular cartilages (odontophores), but remains firmly attached, much like a fingernail on a human finger. Strong muscles attach to the radular cartilage, and move it and the attached radula in its feeding motion. Upward movement of the radula scrapes the cusps over the alga food and moves the scraped bits into the esophagus opening. The food is processed in a large digestive gland and wastes are discharged from the anus located in the right side of the mantle cavity.  MacDonald & Maine 1964 Veliger 6(Suppl.): 50.

Shown here is the related snail Calliostoma ligatum
rasping algae from the side of an aquarium tank 1.5X

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Research study 1.1
 

A researcher from Boise Junior College, Idaho categorises 7 west-coast trochid snails into 3 groupings based on structure of the radula.  At the time of the study the 7 species were classified as Tegula, but the recent restructuring of the genus shows an intermixturing of species in the 3 groups as follows:

drawings of radulae of trochid snails Chlorostoma funebralis and Tegula gallina drawings of radulae of trochid snails Promartynia pulligo and Chlorostoma montereyiGroup 1: Chlorostoma funebralis, Tegula (?) gallina
Group 2: T. (?) eiseni
Group 3: C. brunnea, C. montereyi, C. aurotincta, Promartynia pulligo

Two representatives of each of Group 1 and 3 are feature here, so that the reader can gain some measure of extent to which the groups differ in radula structure.

So, does radula morphology not accord with genus in these trochids, or is some other force at work here?  Fritchman 1965 The Veliger 8 (1): 11.

 

The basic radula pattern in these trochids is a single central
cusp flanked by 5 lateral cusps with heavy blades. The difference
between these Groups 1 and 3 may mainly relate to the degree and pattern
of serrations on the 5th lateral cusps; otherwise, they look much the same

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photograph of a snail Calliostoma annulatum taken from a video

CLICK HERE to see a video of a trochid snail Calliostoma annulatum exploring a part of its aquarium tank. Note the lively "attitude" of the snail as it searches, with mantle and cephalic tentacles waving, and the anterior part of foot and surrounding part of mouth roled into contact-sensory devices.

NOTE the video replays automatically

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photograph of a snail from below showing mouth taken from a video

CLICK HERE to see a video of an unidentified snail feeding on aquarium glass. The radula is colorless in this species, but its rounded form is visible.

NOTE the video replays automatically

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Research study 2
 
photograph of a cluster of black turban snails Chlorostoma funebralisIn the process of removing radulae of Chlorostoma (Tegula) funebralis for study, researchers in Berkeley, California observe that the previous models of radula action as a flat, toothed ribbon drawn over the end of the odontophores (radular cartilages) does not fully depict the actual complexity of the action.  In their view the radula is best visualised as a cylinder with its anterior end splayed out on either side over the odontophore cartilages.  This, in effect, produes a food groove between the central rows of cusps.  The diagram shows a Chlorostoma radula in its most protacted position (i.e., ready for the rasping action) with actual contact of the radula with the substratum being at the point where the radula is folded over. As the radula is retracted during the rasp, the crease moves anteriorly so that successively more anterior rows of teeth fold inward until the whole lot disappears into the mouth. The action is then repeated. Morris & Hickman 1981 Veliger 24: 85. drawing of a radula of a black turban snail Chlorostoma funebralis showing how it rolls back on itself during feeding
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Research study 3
 
 

Feeding tracks created by the radulae of photograph of radular scratchings from a black turban snail Chlorostoma funebralis on the surface of a kelpgastropod herbivores can readily be preserved on “artificial” substrata, such as beeswax, for comparison with tracks on natural substrata.  Observation of tracks of Chlorostoma (Tegula) funebralis using this technique, for example, reveals a surprisingly variable application of the radula, from light brush marks to deep incisions, and these variations are reflected in how different substrata are scraped.  Different cusps contact the algal tissue in different places depending upon textural and hardness differences in the alga being eaten.  The photograph on the Right shows scratchings on the surface of a kelp (Laminaria sp.) created by the radula of Chlorostoma (yellow scale bar = 400um). Hickman & Morris 1985 Veliger 27: 357.

Chlorostoma (Tegula) funebralis with limpets on its shell, possibly Lottia asmi. 1.5X

photograph of a black turban snail Chlorostoma funebralis bearing a limpet Lottia asmi on its shell
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Research study 4
 
photograph of radular scratchings on algae on the interior surface of an aquarium A radula feeding-track made by a Chlorostoma sp. on the inside of an aquarium glass. Although not perfect, note the economy of motion exhibited in the track. The back-and-forth action follows the track from the previous traverse closely, but rarely overlaps it, with quite effective removal of the algal coating. The snail has had to work around a sea anemone Urticina sp., whose red basal disc and white tentacles are visible 1X
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