title for learn-about section on whelks & relatives in A SNAIL'S ODYSSEY
  Reproduction & development
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Egg production & encapsulated development

  Topics in this section include egg production & encapsulated development, considered here, and NURSE EGGS, HATCHLING ECOLOGY, DISPERSAL HETEROZYGOSITY & GLACIAL REFUGIA, and IMPOSEX, considered in other sections.
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Other genera

  The topic of egg production & encapsulated development is divided into a section on other genera considered here, and a section on NUCELLA spp., presented elsewhere. The studies below proceed alphabetically.
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Callianax (Olivella)

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Research study 1
 

photograph of olive shell Callianax biplicata leaving a track in the sandSexes are separate in olive shells Callianax (Olivella) biplicata and individuals mature at about 16mm shell length.  After copulation, females deposit single fertilised eggs in capsules (cases) that are attached to solid substrata, such as shell bits and small rocks.  A single female may deposit several thousand capsules over a period of a few weeks.  Although olive shells are reported by some authors to hatch from their capsules as veliger larvae, this may be a laboratory artifact, as other world species of Callianax spend their larval lives within their capsules and emerge as tiny juveniles.  The adults are thought to live for 10-12yr.  Edwards 1968 The Veliger 10: 297; Edwards 1969 Am Zool 9: 399; Stohler 1969 The Veliger 11: 259.


Olive shells Callianax biplicata can often be located at low
tide through signs of their subterranean burrowing 0.5X

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Cerithidea

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Research study 1
 

photograph of hornsnails Cerithidea californicahistogram of size-class frequencies of hornsnails Cerithidea californica in San Francisco Bay, CaliforniaA researcher from the University of California, Berkeley reports on reproduction and growth of the California hornsnail Cerithidea californica, apparently the only representative of Family Potamidae on the California coast.  The 4yr study also includes features of temperature, salinity, and desiccation tolerances, not included here.  The species inhabits marshy regions, such as in the San Francisco Bay area, where it encounters and is usually competitively recessive to introduced east-coast mud snails Ilyanassa obsoleta.  Densities in such areas can be large, reaching up to 200,000 individuals . m-2. Copulation in Cerithidea occurs in late spring/summer and eggs are deposited in cases in May.  Each egg case contains 50-160 eggs.  The eggs hatch in June to crawl-away juveniles.  This spring cohort can be seen on the shore in July, and by August the young snails have grown to about half adult size (see histograms).  The cohort of larger snails shown in the figure will die out during the following year, so life span is about 2yr.  Race 1981 The Veliger 24 (1): 18.

NOTE  the author remarks that Ilyanassa is known to eat the eggs and juveniles of Cerithidea

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Ceratostoma

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Research study 1
 

drawings of a leafy hornmouth whelk Ceratostoma foliatum courtesy D’Asaro 1991 Ophelia 35: 1. In San Juan Islands, Washington female leafy-hornmouth snails Ceratostoma foliatum deposit capsules in Feb-Mar, and the juveniles emerge after about 4mo at 11oC.  An average female deposits 40 egg cases during seasonal laying, each containing about 50 eggs.  Over a reproductive life span of 7yr, then, an average female will produce about 14,000 eggs.  An individual reaches a 6cm shell length after about 2.5yr, and an 8cm shell length after about 5yr.  Reproductive maturity is reached after 4yr, and total life span is about 11yr.  Spight et al. 1974 Mar Biol 24: 229. Drawings courtesy D’Asaro 1991 Ophelia 35: 1.

NOTE  this species appears not to produce any nurse eggs. These are the unfertilised eggs that in some species of whelks provide sustenance to the juveniles later in development within the capsules

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Fusitriton

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Research study 1
 

There is little information on egg-capsule morphology and development in Oregon tritons Fusitriton oregonensis.  An early observation in Baranoff Island, Alaska describes a mixed-sex  aggregation in shallow water at low tide, with some females being partially emerged photograph of whelk Fusitriton oregonensis laying egg capsules courtesy Howard 1962 Veliger 4: 160by the tide, but still depositing egg cases in the wave swash.  The cases are laid in a alt="photograph of whelk Fusitriton oregonensis laying egg capsules courtesy Howard 1962 Veliger 4: 160counterclockwise spiral. The author does not give information on rate of deposition, number of eggs per case, or other details.  Howard 1962 Veliger 4: 160. Photos courtesy author.

Oregon or hairy triton Fusitriton oregonensis with egg cases 1X

 
Research study 2
 

In San Juan Islands, Washington egg-case deposition by Oregon tritons Fusitriton oregonensis occurs during July following large and prolonged aggregations of sexes.  After deposition, the female apparently remains around the egg casesfor a time, a behaviour thought by the authors in some way photograph of head of an Oregon triton Fusitriton oregonensis, courtesy Ron Long, Simon Fraser University, Burnaby, British Columbiato prevent predators from eating the cases.  Determination of body-component indices indicates a distinct seasonal cycle of reproduction for females, with largest sizes of gonad and capsule-albumin glands occurring during aggregation, then declining as the eggs are manufactured and deposited.  The authors observe no similar body-component cycles in the males.  Stickle & Mrozek 1973 The Veliger 16: 195. Photograph courtesy Ron Long, Simon Fraser University, Burnaby, British Columbia.

NOTE  the authors provide no further information on this interesting behaviour, and it might be something that would repay further investigation

NOTE  these include shell mass, water content, relative sizes of gonad/digestive glands and capsule-albumin glands. These data are not presented here



Close view of head of Fusitriton oregonensis showing right
tentacle, right eye, proboscis with puckery mouth , and encrusted
shell above. The left tentacle and eye appear to be missing 2X

 
Research study 3
 

histogram comparing capsule-wall thickness in early and late developmental times for whelks Fusitriton oregonensishistogram comparing oxygen partial pressures in egg capsules at early and late developmental times for whelks Fusitriton oregonensisAll snail species that package their eggs within jelly masses or capsules have the potential problem of reduced oxygen supply to the developing embryos, especially as the embryos grow larger.  Several previous studies on gastropods have documented a thinning of capsule walls during development, possibly a hatching strategy, but also raising the question that the thinning may enhance diffusion of oxygen to the developing embryos.  This is investigated at Friday Harbor Laboratories, Washington using encased eggs of Fusitriton oregonensis. 

Results show that capsule-wall thickness decreases by 50% from early to late developmental stages (see histogram on Left) and, while oxygen consumption of the embryos increases by 6-fold during the same period, there is no significant decrease in oxygen partial pressures within the capsules (see histogram upper Right). The explanation rests in a significantly increased diffusibility of oxygen through the capsule wall from early to late developmental stages (see histogram lower Right). The author suggests that, as has been found for other species that encapsulate their embryos, thinning of the capsule wall may be caused by feeding by the embryos on the structural proteins comprising the inner capsular walls.  The study is the first of its kind to couple capsule thinning during development with increased need of the embryos for oxygen.  Brante 2006 Mar Biol 149: 269.

NOTE  “early’ refers to egg-to-late trochophore, while “late” refers to early veliger-to-shelled veliger. There are about 1800 embryos per capsule in F. oregonensis

NOTE  partial pressures of oxygen are measured with oxygen microelectrodes inserted within and without the capsule

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Kelletia

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Research study 1
 

The Californian whelk Kelletia kelletii grows to shell lengths of 15cm.  Copulation occurs in springtime with egg-capsule deposition in April-May.  A photograph of whelk Kelletia kelletii depositing egg capsules, courtesy Dr. Rosenthal, Californiafemale may have multiple depositions over a period of several weeks.  Capsule size depends on size of female and ranges from 7-12mm in height.  In the study reported here, each capsule contains 400-1000 eggs, but up to 2000 may be present in capsules in other populations.  Eggs are yellow in colour and range from 200-300µm in diameter.  In the laboratory at 14-17oC the eggs hatch in 30-34d.  Rosenthal 1970 The Veliger 12: 319.

NOTE the locations of these other populations are not specified in the study referred to, one cited in MacGinitie & MacGinitie 1968 Natural history of marine animals McGraw-Hill, NY.

NOTE does the author actually mean "hatch" or does this refer to emergence of the veliger larvae from the egg case? (a standardised terminology is needed)

Southern California whelk Kelletia kelletii depositing
capsules 0.8X (the snail is outlined in white for clarity)

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Research study 2
 

map showing collecting sites for elemental-chemical study of larvae of whelks Kelletia kelletiiAn increasingly popular method to determine natal origins of larvae in marine-invertebrate ecological studies is trace-element analysis.  The efficacy of the method is tested by a researcher at the University of California, Santa Barbara using field-collected encapsulated veliger larvae of the buccinid snail Kelletia kelletii, specifically, to determine the extent to which elemental compositions (specifically, magnesium, strontium, and barium) of statoliths and protochonchs vary spatially and temporally at different natal sources.  Results indicate that elemental compositions of larval statoliths and protoconchs can provide 80% and 89%, respectively, correct identification of site of formation, and thus have potential for use as tags of natal origin.  Zacherl 2005 Mar Ecol Progr Ser 290: 145; see also Zacherl et al. 2003 Geochiica et Cosmochimica Acta 67 (21): 4091 for an earlier background study.

NOTE  the method currently provides the only “tried and true” way to track marine larvae from their source to their recruitment site.  The method originated with, and has been used successfully over the past 2 decades for, identification of spawning grounds and juvenile habitats of fishes

NOTE  the veligers eventually break free of their cases (referred to here as “capsules”) and spend an unknown length of time swimming freely in the plankton

 

 

 

 

Map showing northern and central California distribution
of, and collection sites for, whelks Kelletia kelletii.
Sites north of Point Conception are characterised by
upwelling of colder, nutrient- and metal-rich, seawater

 
Research study 3
 

map showing collection sites for eggs of the whelk Kelletia kelletii in southern CaliforniaA later study by some of these same researchers on elemental signatures in statoliths of larval Kelletia kelletii from 2 source populations in southern California reveals significant effects of environmental conditions on elemental composition of the statoliths.  Most notable were differences in responses of Ba, Pb, Mg, Sr, Mn, and Zn to culture concentrations of these elements and to temperature.  As in previous studies, egg source has strong and significant effects on elemental signatures in statoliths in the larvae, and confirms the method as an effective means of tracking free-spawned larvae.  Lloyd et al. 2008 Mar Ecol Prog Ser 353: 115.

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Lirabuccinum

 
Research study 1
 

photograph of dire whelk Lirabuccinum dirumThe dire whelk Lirabuccinum dirum (Searlesia dira) is a scavenger/predator inhabiting intertidal and subtidal shores from Alaska to Monterey, California.  Females do not congregate to lay eggs.  Females deposit clutches of capsules (cases), up to 6-10 at a time, each of 4.0 x 3.2mm internal chamber size, and each containing an average of 7 fertilised eggs and 125-145 nurse eggs.  Development to a crawl-away juvenile takes several months and occurs when the capsule deteriorates. Unlike in Nucella capsules there is no handy plug-hole for egress of the juveniles.  Rivest 1983 J Exp Mar Biol Ecol 69: 217.

NOTE  more on this subject can be found in the section on NURSE EGGS

 
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