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Summary | |
This species of Zafra (genus) sea snail belongs to the family Columbellidae, a diverse group comprising of small, active epibenthic marine snails (deMaintenon1999) that accounts for around four hundred extant species of small to medium sized shell (Beechey and Willan 2007) marine gastropod species. They are distributed globally, but most common in the south-west pacific, and temperate Australia. Columbellids are most prevalent epifaunally in shallow tropical habitats, but their diversity is also represented in infaunal, deep ocean, and high latitude marine environments (deMaintenon1999). Unlike some more popular Columbellids such as Strombina and Mitrella little is known about the Zafra genus. They are recognised to be found within shallow tropical water including the coasts of Papua New Guinea along, the eastern coast of Queensland and New South Wales (Australia). This Zafra specimen was found in at Amity Point, North Stradbroke Island, Moreton Bay, Queensland.
Their small size and distribution relies on specific environmental conditions and it is likely that future discoveries will see the genus increase from its current count of 79 species.
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Physical Description |
Defining Characters | |
Defining characteristics of this Zafra specimen:
- Aperture teeth, inner (5) and outer (7) lip denticles.
- Spire consists of 3 ½ whorls, winding in a clockwise direction from the protoconch, which consists of 2½ whorls.
- Narrow aperture with little to no columellar folds/callus.
- Siphonal canal does not extend, is short.
- Axial ribs (15 at base) present from the spire down to the base followed by spiral cords at the anterior by way of the siphonal fasciole.
- Separation between axial ribs and basal nodes is coexpressed with white and brown patterned colouration of shell.
- Axial ribs form bulbs below the suture, referred to as nodes.
- Size: Length from protoconch (apex) to anterior siphonal canal is 5mm.
See figures 1-4 for general terms and specimen.
Defining characteristics of columbellidae snail family may be found at seashellsofnsw.org.au by Des Beechey (2007).
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Shell Description | |
Shell Size
In columbellidae gastropods size shows significant variance among genera, among sub-genera within each and more remarkably, among species within each sub-genus. (Budd and Johnson 1991). This species can grow up to 5 mm, this is most likely the upper limit if its size; its shell possess more whorls than most other species of Zafra columbellids and it developed a number of denticles. This is most likely a mature adult as it has developed a number of whorls along its teleconch and there a protrusions of several teeth within the inner and outer lips of the aperture, all indicators of maturity.
Shell Shape
Columbellids have been shown to have a linear relationship between height and width, consequently their growth is never allometric. The relative shape of this Zafra sp. is consistent, imposing a constraint on shape change (Budd and Johnson 1991), so this species will maintain its superficial shape as it grows towards maturity. Among columbellids and Zafra the shell’s shape and sculpture independently or mutually, nonetheless a constant feature is spiral cords on the base (fig. 8).
Shell Colour and sculpture
The colouration of some species of columbellids have resulted in their name “dove shell” snails which resemble the appearance of doves. In many gastropods the genes encoding for colouration and sculpture of the shell are coexpressed resulting in colour patches or spot occurring at specific sites of the axial ribs, as is the case for this Zafra species (fig. 7). Shell colour, and to a lesser extent the sculpture, may vary within the same species depending on the site of their larval settlement. Environmental conditions and diet can influence the shell greatly, this is commonly attributed to the vast biogeographical distribution of these animals. Gastropods’ genes encode instruction for the biofabrication of a diversity of shell forms, the sculpture within genus and even species may not be conserved depending their settlement. Example of this can be seen with Zafra altispira and Zafra obesula which have similar sizes yet vastly different shapes. Sell surface varies among columbellids however when considering the Zafra genus there is homogeneity among the observed species. In gastropods the periostracal tissue layer synthesises the outer organic layer of the shell. The shell layers (smooth inner nacreous, prismatic middle and sculpted periostracal outer) are secreted from the mantle zones by the animal, these tissues are unique to the shell tissue forming the protoconch (fig. 5 & 6).
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Aperture Description | |
Shell Mouth
Homologous within the Buccinidae, Nassariidae and Turridea, Columbellids shells share the features of highly evolved gastropods, particularly the presence of a siphonal canal. Columbellids have a short siphonal canal at the end of the aperture (Beechey and Willan 2007). This is clearly seen in this Zafra species (fig. 9 & 10).
Outer lip sinus: there is a sinus, or gap, in the top of the outer lip. In the Columbellidae it is usually shallow compared to other taxa. It is almost non-existent in this species of Zafra, adding to its phylogenetic grouping in this family.
Outer lip dentition: there are usually aperture teeth (denticles) inside the outer lip, although some species have just a single indistinct bulge. The strength of the denticles varies from species to species, and with growth stage of the shell. In some species the denticles are only developed in the most mature specimens, therefore only being seen in a small percentage of shells (Beechey and Willan 2007).
Inner (columellar) lip dentition: the inner lip of the aperture is without plaits, providing a point of separation from Marginellidae, Mitridae, and Volutidae. There are often weak denticles on the inner lip, aligned on an axial ridge just inside the edge of the callus, but these also tend to be restricted to mature shells (Beechey and Willan 2007). The aperture dentition present within this Zafra species occurs on both the outer (7) and inner lips (5).
The specimen featured possesses the above characters that group it within the the genus Zafra. A notable feature that separates it from all other currently recognised species is the number of whorls along its spire (fig. 7). Excluding the protoconch whorls, the teleconch has 3 and a half whorls which carry a distinct colour pattern. Its shape and general features are homogeneous with other Zafra species however these defining features separate it from others in the genus. Study of the animal within the shell would provide more information about the specimen.
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| Figure 10 |
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Ecology | |
Currently to date there have been very few studies published on the anatomy, natural history or ecology of the columbellidae family within Australian waters. Work has been carried out in other parts of the world to provide us with knowledge of the biology of these very common gastropods, particularly in the West Atlantic and Caribbean (Wilson et al., 1994). As form tends to follow function, the traits and biology among this family is general conserved, bar local specialised species, which can be used to generalise Zafra population around Australia and adjacent island.
Diet
Columbellids are unusual in that they eat both plant and animal material. Mitrella and some species Anachis are said to be carnivores (cite this). Many species of the Mitrella and Anachis genus scale to a similar size as this Zafra species and inhabit very similar biogeographic distribution. Zafra sp. is most likely carnivorous but as with many columbellids is a facultative herbivore, likely unable to fully digest the plant matter (deMaintenon 1999).
The majority of neogastropods are basally carnivorous however few taxa such as the columbellids include herbivorous species. The herbivorous gut typically possesses a gastric shield and small sorting areas which isn’t usually present in the neogastropods. They usually have u-shaped stomachs, without a gastric shield and sorting area, and the hindgut is short and straight (deMaintenon 1999).
In several species of columbellids, plant matter comprises a measurable portion of their diet, this indicates that in this gastropod family herbivory is facultative (deMaintenon 1999). Carnivorous columbellids show morphological differences to their herbivorous counterparts, this is seen within the radular and stomach. The extent to which columbellids, like Zafra species, are able to digest and utilise plant matter in unknown (deMaintenon 1999) because digestive enzymes haven’t been identified within any species. These snails may also ingest some plant material without being particularly capable of digesting it. Whether they are aware of this or not is yet to be understood.
Most of the herbivorous columbellid species are members of the Columbellinae subfamily, so it is likely that Zafra species are purely carnivorous, predating microscopic organisms, small meiofaunal crustacean and polychaete worms, however herbivory is suggested to have evolved multiple times in gastropods (deMaintenon 1999) they could very well be feeding on plant tissue.
Predators /Competition
Molluscs are also well known for predating on other molluscs. Gastropods show the same cannibal characteristics by praying on other gastropods that are smaller than them. Snails of the genus Zafra are likely targets for other gastropods in general which may play a role in competition among other columbellids who occupy a very similar biogeographical distribution. It is likely that very little distance is covered by these animals during their lifetime, compared to larger benthic adults so their positioning during settlement is important.
During the snails’ veliger larval life stage it needs to acquire enough food from phytoplankton, diatoms and so on that timing of reproduction is important. The planktotrophic larvae will not reach competency unless it attains enough food to develop it. Competition among larvae would be a very probable scenario and this can have compounding effects if the eventual settlement site is not ideal. It’s also likely that chemosensory responses that many gastropods possess is required to settle at spatially suitable sites.
Population
Little research have been conducted to estimate populations of columbellids, particularly the genus Zafra. Their size in particular would make it difficult to quantify their existence. Estimates of tens of thousands of species of gastropods are predicted to still be unidentified, this reasons to the inability to truly account for the true number of species and individuals present at any given time.
The geographical distribution of these snails is vast however they have a specific set of environmental conditions to which they inhabit (see Biogeograohical Distribution).
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Life History and Behaviour |
Reproduction and Larval Development | |
Life history and behaviour of gastropods in the Zafra genus have not been recorded specifically to date. Few studies have documented the larval development of the family columbellidae. Columbellids, like nearly all adult prosobranch gastropods, usually retain the protoconch (fig. 7). The protoconch is produced during the embryonic development of the gastropod and through their planktotrophic larval life stage (Oliverio 1995). Planktotrophic larvae keep this larval shell, when they mature, separate from the shell that is secreted post metamorphosis, which is different in its composition and sculpture.
Zafra gastropods have a biphasic life cycle, as is common among most marine phyla, referred to as the pelagobenthic life cycle. Benthic adults, who reside on the sea floor, are gonochorus (separate sexes) and represent the reproductive phase of the pelagobenthic life cycle. They reproduce, most likely via internal fertilization, to produce the planktonic embryos which are protected within corneous capsules. Free swimming planktonic larvae hatch from capsuled egg. This entails the pelagic phase, the planktonic larvae develop into a secondary larval form, the planktonic veliger larvae. During the process of embryonic and larval development the protoconch is developed, then when the larvae have reached larval competency (maturation of sensory systems) they transition into the benthic phase. As the larvae are planktotrophic, they will have to feed on phytoplankton and tiny zooplankton to reach competency . The pelagic phase transitions abruptly into the benthic phase via the process of larval settlement and metamorphosis. Settlement and metamorphosis is likely to be accompanied by a change in a habitat, diet, ecology, behaviour etc…
Achieving larval competency prepares the larva to receive and respond to environmental inputs to sensory cells. In Zafra species, also the case for most pelagobenthic organisms with planktotrophic larvae, this would most likely include phototaxis, geotaxis and chemotaxis sensory responses to ensure the best chance of survival. Competency is dependent on the food availability therefore timing of spawning is important. Planktotrophic gastropod larvae may take weeks, even months to reach competency after hatching. The pelagic nature of larval dispersal can result in huge variations in dispersal capability among species. The larvae of some species might travel for weeks in the plankton before competency, thousands of kilometres away, while the larvae of other species might settle within metres from their parents (Fortunato 2004). Growth and maturation takes place on the benthos until the snail is reproductive.
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Behaviour | |
The behaviour of this genus has never been documented in the wild. Diet of several columbellids indicate that they are likely faculative herbivores, often showing the presence of algae within their gut. In most cases this algae and other plant matter are not digested. Radular structure is fairly similar amongst columbellids even between several Zafra species indicating their disposition to feed on the benthos and hard substrates. Zafra species require comparatively shallow warm tropical waters. No species has been seen to occupy fresh waters.
Other members of the Columbellidae family have been recorded for feeding and behaviour.
- Kantor, Y. I., & Medinskaya, A. I. (1991). Morphology and feeding of Mitrella burchardi (Gastropoda: Columbellidae). Asian Marine Biology, 8, 25-33.
- John D. Taylor & David G. Reid (1984) The abundance and trophic
classification of molluscs upon coral reefs in the Sudanese Red Sea, Journal of Natural History,
18:2, 175-209.
- Russini, V., Fassio, G., Modica, M. V., deMaintenon, M. J., & Oliverio, M. (2017). An assessment of the genus Columbella Lamarck, 1799 (Gastropoda: Columbellidae) from eastern Atlantic. Zoosystema, 39(2), 197-213.
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Anatomy and Physiology | |
No studies have been conducted to date showing the anatomy or Physiology of Zafra species. Related genera from the Columbelidae family have been conducted:
- Guralnick, R., & de Maintenon, M. J. (1997). Formation and homology of radular teeth; a case study using columbellid gastropods (Neogastropoda: Columbellidae). Journal of Molluscan Studies, 63(1), 65-77.
- Kantor, Y. I., & Medinskaya, A. I. (1991). Morphology and feeding of Mitrella burchardi (Gastropoda: Columbellidae). Asian Marine Biology, 8, 25-33.
See references for more.
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Biogeographic Distribution |
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Specimen location | |
This specific Zafra speimen was found on an Automated Reef Monitoring Systems (ARMS) settlement plate hung upside down from the end of the jetty in front of Amity Point Caravan Park on 20th November 2018, so have had almost 4 months of summer conditions to accumulate a benthic community from settled larvae. This jetty, accessed via Claytons Road, is used by recreational fishers and swimmers, but is not used as a dock for boats. This jetty is a fixed structure, so the ARMS will fluctuate in depth below the sea surface according to tide cycles.
Amity Point isn't an uncommon place for Columbellids to settle and metamorphose into their benthic state. Some Zafra species have been found around this biogeographic location, seen in fig. 16, however it is less common for species with the shell morphology such as this specimen, see Shell Description. It's suggested that this Zafra specimen was transported from from ship ballast.
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Evolution and Systematics | |
Phylogeny.
Detailed classification of the Zafra sp. is as follows:
- Domain: Eukarya
- Supergroup: Opisthokonta
- Kingdom: Animalia
- Phylum: Mollusca
- Class: Gastropoda
- Subclass: Orthogastropoda
- Superorder: Caenogastropoda
- Order: Neogastropoda
- Superfamily: Buccinoidea
- Family: Columbellidae
- Genus: Zafra (A. Adams, 1860)
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Conservation and Threats | |
Little is known about the many genera of columbellids, even less is known about the genus Zafra. There may be potentially essential ecosystem functions that they may provide.
Figure 12 & 14 show that Zafra species live within habitats of specific environmental conditions. Of the 2,581 previously recorded individuals the salinity and temperature levels are greatly skewed. Changes in the warming of the ocean may sea the distribution of these snails expand as occupy a small environmental niche. The plasticity of Zafra snails has not been subject to research. Further research into population dynamics and function of this genus and its species may provide insight however this is difficult due to their size and access to them.
Like many other marine invertebrates, Zafra sp. is likely to be affected by habitat disturbance via human activity from pollution and sediment destruction.
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References | |
Beechey, D. L. and R. C. Willan (2007). "Establishment of the East Asian dove snail Mitrella bicincta (Gould, 1860)(Mollusca: Gastropoda: Columbellidae) in Australia." Molluscan Research 27(2): 51-59.
Budd, A. F. and K. G. Johnson (1991). "Size-related evolutionary patterns among species and subgenera in the Strombina group (Gastropoda: Columbellidae)." Journal of Paleontology 65(3): 417-434.
deMaintenon, M. J. (1999). "Phylogenetic analysis of the Columbellidae (Mollusca: Neogastropoda) and the evolution of herbivory from carnivory." Invertebrate Biology: 258-288.
Fortunato, H. (2004). "Reproductive strategies in gastropods across the Panama seaway." Invertebrate reproduction & development 46(2-3): 139-148.
Leal, J. H. and B. Matthews (2013). Gastropods.
Oliverio, M. (1995). "Larval development and allozyme variation in the East Atlantic Columbella
(Gastropoda, Prosobranchia, Columbellidae)." Scientia marina 59(1): 77-86.
Wilson, Barry & Wilson, Carina et al. (1994). Australian marine shells. Part two : prosobranch gastropods (neogastropods). Odyssey Publishing, Kallaroo, W.A
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