Reproduction
  black dot
Research study 1
 

photograph of a moon snail Euspira lewisii pushing its egg collar to the sand surfaceSexes are separate in moon snails Euspira lewisii and sperm transfer is direct via a penis.  Later, the fertilised eggs are enclosed one to a capsule and extruded from the female in a mucousy mixture that is combined with sand (Left drawing below).  The unusual shape of the egg collar results from the extruded mixture being moulded between the propodium and the drawings showing a female moon snail pushing its egg collar to the sand surfaceshell before it sets into its final sand/jelly state (middle drawing below).  The extrusion and moulding take place under the sand, commence at the start of flood tide, and take 10-14h. 

After the initial moulding is finished, the female works over the egg-collar surface one more time adding a protective sheath of sand and mucus (Right drawing below).and, at the same time, pushing the collar upwards to the sand surface (drawing on Right).   Development within the capsule to a swimming veliger larva takes a week or so, and it is possible that the capsular fluid is utilised as food.  Simultaneous with the emergence of the larvae from their capsules, the sand-mucus matrix of the collar disintegrates and the larvae now swim freely in the ocean. 

 

drawing showing egg mass of a moon snail being moulded by the female drawing of moon snail with cross-sectional view of its egg collar indicating how the collar gets its distinctive shape drawing showing a female moon snail applying a jelly coat to its egg collar as it pushes it to the sand surface
 

photo/drawings of the composition of a moon snail's egg collarMoon snails Euspira lewisii on the east side of Vancouver Island, British Columbia have egg collars that are 2-3mm in thickness. The colour of the egg collar depends upon the type of sand and other inclusions contained within it. Each egg/embryo rests in a jelly matrix within an egg capsule. Moon snail veligers range in shell length from 150-200um. Giglioli 1955 J Fish Res Bd Can 12: 287.

NOTE lit. “front foot” G.

  black dot
Research study 2
 

graph comparing relative masses of shells of male and female moon snails Euspira lewisiiphotograph of moon snail Euspira lewisii pulling into its shellStudies on moon snails Euspira lewisi collected at Departure Bay, British Columbia indicate that sex ratios of small specimens (<50g live mass) are close to 1:1, but those of large specimens (270-350g) are heavily biased to females (85% female:15%  male).  The research additionally shows a sexual dimorphism in shell size, with a male of 300g live mass having a shell about 18% heavier than that of an equivalent-sized female (see graph).  The explanation for this is not known.  Bernard 1986 The Nautilus 82: 1.


Moon snail Euspira lewisii pulling into its shell 1X

  black dot
Research study 3
  photographs of the veliger larvae of a moon snail Euspira lewisii courtesy Pedersen & Page 2000 Veliger 43: 58photograph of a veliger larvae of a moon snail Euspira lewisii courtesy Pedersen & Page 2000 Veliger 43: 58A veliger larva of Euspira lewisii spends 4-5wk in the plankton (at 20-22oC) feeding on phytoplankton.  Towards the end of its pelagic existence the larva’s foot, shell, and tentacles begin to enlarge, and the velum bifurcates into 4 large lobes (photo on Right).   The function of the lobes is not known, but may be involved in selection of a settling site or increased feeding surface or, with the increasing mass of adult features being carried at this late stage of pelagic life, may increase locomotion and/or aid in the larva’s buoyancy.  Pedersen & Page 2000 Veliger 43: 58.
  black dot
Research study 4
 

photograph of a juvenile moon snail Euspira lewisii with a close view of an ostracod that it has drilled courtesy Pedersen & Page 2000 Veliger 43: 58

Within 3-5d after settling and metamorphosing, the tiny juvenile moon snail Euspira lewisii is busy drilling and eating small clams and ostracods. Note in the inset photo that the juvenile already is drilling a countersunk hole in its ostracod prey. Page & Pedersen 1998 Invert Biol 117: 208; photo from Pedersen & Page 2000 Veliger 43: 58.

  black dot
Research study 5
 

photographs of velar lobes and papulae on veliger larva of a moon snail Euspira lewisiiLike veliger larvae of other gastropods, those of moon snails Euspira lewisii can withdraw quickly and completely into their shells when disturbed or when danger threatens.  Even the extra-large lobes described for older larvae of this species in Research Study 3 above can be accommodated within the shell, and the question arises as to how this is accomplished.  By injecting fluoroscein dye into the hemocoelic spaces of anaesthetised larva and then monitoring what happens on retraction, a researcher at the University of Victoria, British Columbia finds that the dyed fluid is expelled in 4 streams originating from distinctive papillae located on the tips of the 4 large velar lobes.  Scanning electron microscopy of the release sites suggest that the skin, notably thin in these regions, actually ruptures then seals again during and after defensive withdrawals.  At this time the author is uncertain how reinflation of the velar hemal compartment occurs but, as reinflation may take several minutes, some sort of para-cellular route may be involved.  The mechanism is of major evolutionary importance in that it has allowed selection for allometric growth of the velum to occur in reponse to feeding and locomotory needs, but without compromise to the larva’s defensive capability.  Interestingly, an adult moon snail also releases fluid from hemal spaces in its voluminous foot during its withdrawal into the shell, but this occurs via pores or slits that are permanent morphological structures.  Page 2007 Proc R Soc B 274 (1628): 2989.

NOTE  a description of this can be found at LEARNABOUT: MOON: LOCOMOTION

  black dot
Research study 6
 

graph showing growth of veliger larvae of moon snails Euspira lewisiiphotographs showing increase in larval radula length and ctenidial number during period of delay of metamorphosisMost or perhaps all veliger larvae can delay metamorphosis for a time, and a question addressed by the above research group at University of Victoria is whether they continue to feed and grow after becoming competent to settle.  To test this the researchers rear larvae of moon snails Euspira lewisii through competency and beyond, but without a settlement inducer.  Results show that the larvae do, indeed, continue to grow during the period of delayed metamorphosis, not just in length of shell but also in length of prototroch (ciliated band for swimming and feeding) and number of ctenidial filaments and radular cusps.  These last structures are not used by the larvae but are required for post-metamorphic juvenile life.  Note in the graph that larval shell length increases 4-fold from hatching to metamorphic competency, with further enlargement during delay of metamorphosis.  Length of prototroch actually scales allometrically (slope of 2.0) from hatching to time of metamorphic competency, but significantly less than this in the period of delayed metamorphosis (1.3).  Note in the photographs that radula length and number of ctenidial filaments within the larva almost double in length during this time.  The authors comment that such changes in morphological complexity of the larva may potentially have strong functional and ecological consequences for the post-larval stages.  Lesoway & Page 2008 Mar Biol 153: 723.

NOTE  also included in the study are the west-coast opisthobranch Haminoea vesicula and 2 Australian species, results for which are not included here

  black dot
  RETURN TO TOP