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Summary |
Classification | |
Mollusca
Gastropoda
Caenogastropoda
Littorinimorpha
Naticoidea
Naticidae
Conuber sordidus
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Background and Synonyms | |
Conuber sordidus, or the Leaden sand snail, was first described by W. J. Swainson in 1821 under the name Natica sordida. They are a part of the Naticidae family, a cosmopolitan family that describes predatory marine molluscs (Hülsken 2008). The species lives for 5 years on average and lives in sandy intertidal areas (Beechey, 2017).
Synonyms include:
Polinices sordidus Swainson, 1821
Natica sordida Swainson, 1821
Natica plumbea Lamarck, 1822
Natica microstoma Quoy & Gaimard, 1833
Natica leucophaea Reeve, 1855
Natica strangei Reeve, 1855
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Physical Description | |
The shell of Conuber sordidus is 40mm in diameter on average (Grove 2017). It can be cream to dark grey in colour with a purplish brown aperture. It is pyriform in shape, with an enlarged body whorl and aperture (Hülsken 2008, Swainson, 1821). The umbilicus of C. sordidus is relatively small in comparison to other gastropods, while the spire is elevated (Swainson, 1821). The outer lip of the aperture is not sculpted unlike in other species of Gastropod. Features of the shell can be seen in figure 1. Originally, the shell similarity of Conuber sordidus to the genus Polinices caused it to be categorised as Polinices sordidus. However, a phylogenetic study by Huelsken et al. in 2012 showed that the species fit within the genus Conuber due to the characteristic egg collars they produce, which are described under ‘Life History and Behaviour’ in this webpage.
The species has a large foot that is characteristic of the Naticidae, of which there are two parts; the mesopodium and the propodium. The foot expands up over the shell, with the mesopodium covering the posterior part of the shell including the apex, and the propodium covering the anterior part of the body whorl (see figure 2). The operculum is dark brown to orange in colour. Opercula of Conuber can be either calcareous or corneous (Beechey 2017).
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| Figure 1 |
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| Figure 2 |
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Ecology | |
The Naticidae are burrowing marine snails that live in muddy and sandy intertidal zones. The ecology of all Naticidae species is thought to be very similar (Huelsken, Tapken, Dalhmann et al. 2012). C. sordidus stays burrowed during high tide, emerging during low tide to find food (Ying, Ahsanullah & Batley 1993). They are restricted to sediments that are relatively coarse as fine sand grain is too tightly packed for them to burrow (Kabat 1990).
Species within Naticidae are predatory snails known to feed on other gastropods and in some cases, bivalves. However, the range of prey eaten by C. sordidus has been found to also include crustaceans such as soldier and hermit crabs (Huelsken et al. 2012). Currently, this is the only Naticid species that has been confirmed to prey on species with an external skeleton (Huelsken et al. 2012). A study by Bishop et al. showed that in both preference and non-preference tests, C. sordidus ate a ratio of approximately 67-73% small (30.1-40.0mm shell height) to 27-33% medium (50.1-60.0mm shell height) sized molluscs (of the species P. ebeninus), but did not eat larger sized molluscs (70.1-80.0mm shell height) even in the absence of other prey. This shows that there is likely a limitation to the size of prey that C. sordidus is able to capture or consume.
The main feeding mode used by C. sordidus involves drilling into the shell or exoskeleton of captured prey. They detect their prey using a structure called the osphradium (Kabat 1990). This organ allows the snail to use chemoreception, although it has been thought that mechanoreception is another method this species could use to detect prey (Hülsken 2008, Kabat 1990). Prey are held in the large foot of the snail and mucus is used to aid in capture (Huelsken 2008). The accessory boring organ (ABO) and the radula are used in succession to drill a hole in the the prey (Kabat 1990). The boring organ secretes acid-enzymes which helps to break down the prey’s exterior (Kabat 1990). The size of the hole drilled has been found to be positively correlated with the size of the predator (Kabat 1990). Once the hole is complete, C. sordidus is able to consume the prey tissue (Beechey 2017, Kabbat 1990).
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Adult C. sordidus burrowing in sandy sediment.
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Life History and Behaviour |
Reproduction | |
C. sordidus, like all Naticidae, are gonochoristic (have separate sexes) and reproduce sexually via copulation (Kingsley-Smith et al. 2003). Females will retain sperm in their reproductive tract which will then be used to fertilise eggs which are laid in an egg collar (Booth 1995). The egg collar consists of a gelatinous matrix in which embryos are contained, which after being laid fills with water and expands to become a horseshoe or ‘collar’ shape, which is where they get their name (Booth 1995). These egg collars are only found in Naticidae and usually have sand grain incorporated into the transparent membrane surrounding the matrix (Huelsken, Tapken, Dalhmann et al. 2012). However, Conuber species are unique in excluding sand grain, resulting in completely transparent egg collars (Huelsken, Tapken, Dalhmann et al. 2012). The gelatinous matrix structure of the egg collars is made of mucus produced by the snail's foot, which is mixed with the eggs within the mantle cavity of the snail (Kingsley-Smith et al. 2003).
According to a study by Booth in 1995 the average C. sordidus egg collar is approximately 95.7% water, has a radius of 18mm and weighs 107g. The embryos of C. sordidus are distributed throughout the matrix of the collar, however approximately 65% will be within 3mm of the surface (Booth 1995). Due to the large size of these egg collars and the limited distance of oxygen diffusion through the matrix, C. sordidus embryos must be capable of tolerating long periods without oxygen availability (Booth 1995). As well as allowing for a large egg mass, their tolerance to anoxic conditions allows C. sordidus embryos to hatch asynchronously, over a period of 4-17 days (Booth 1995). It is believed that the evolutionary advantage to this longer period of hatching is that it results in a greater dispersal distance of the mature larvae (Booth 1995).
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Larva and Development | |
C. sordidus have veliger larvae, and although the details of the larvae in this species have not been studied, a general description of the veliger larvae found within Naticidae can give an idea of what may occur in this species.
Of the species that have been studied within Naticidae, there are few observed differences in the larval stage (Hülsken 2008). Naticidae larvae are planktonic, and use a ciliated velum to swim through the water column. Naticidae larvae have a velum, a structure associated with the veliger life stage, which is either bi- or quadi-lobed (Hülsken 2008, Pederson 1997). After emerging from the egg collar, larvae have already developed a protoconch 0.1 – 1mm in size (Hülsken 2008, Pederson 1997). Also already present in the larval stage is the foot, which is known as the larval retractor muscle (Pederson 1997). Attached to this muscle is the operculum (Hülsken 2008, Pederson 1997). Eyespots and statocysts are present in early veliger larvae as well (Pederson 1997). Once mature, larvae become pediveligers which are able to dig into the substrate to test is suitability. Larvae that have found suitable substrate will metamorphose (Hülsken 2008).
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Anatomy and Physiology |
External Anatomy | |
The foot of C. sordidus is a vital
aspect of the snail’s anatomy as it is used in general locomotion, burrowing
and prey capture. Movement of the foot operates using a water-filled vascular
system (Russel-Hunter 1968). Water is taken into pores in the foot allowing it
to expand, and contract by releasing water (Russel-Hunter 1968). Unlike other
gastropods which have a hemal system in their foot, the size of the fully
expanded C. sordidus foot is not constricted by the volume that can be
retracted into the shell (Russel-Hunter 1968). As such, a study by
Russel-Hunter in 1968 has shown that the fully expanded foot of some Naticidae
species can weigh up to 3.5 times more than the contracted foot.
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Locomotion of C. sordidus by method of retrograde waves, as described by Miller, 1972.
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Internal Anatomy | |
C. sordidus has a narrow proboscis located below the tentacles and above the propodium which is able to expand and contract to access food (Golding, Ponder & Byrne 2009). Two accessory retractor muscles surround the oesophagus and control the expansion and contraction of the proboscis (Golding, Ponder & Byrne 2009). These muscles are attached at the base and anterior ends of the proboscis (Golding, Ponder & Byrne 2009). When the muscles contract, the proboscis becomes introverted in a pleurembolic manner – meaning that the proboscis is pulled inside the buccal cavity posterior end first (Golding, Ponder & Byrne 2009). Located within the proboscis wall is the anterior aorta, which is surrounded by aortic muscle (Golding, Ponder & Byrne 2009). Both the aortic muscle and the accessory retractor muscles connect to the foot of the snail (Golding, Ponder & Byrne 2009). A sheath of circular muscle surrounds the oesophagus and aorta (Golding, Ponder & Byrne 2009). This sheath as well as the accessory retractor muscles are unique to the family Naticidae (Golding, Ponder & Byrne 2009). The accessory boring organ is located ventrally on the end of the proboscis (Golding, Ponder & Byrne 2009). Figures 3 and 4 show the anatomy of the proboscis and buccal cavity.
A brief dissection of a C. sordidus specimen was done during this study. Detail on the general anatomy of this species could not be found so all features described in the dissection were compared to the general anatomy of Caenogastropoda. The snout (or proboscis) was located ventrally to the two head tentacles. The ocular peduncle is fused to the tentacles and contains a simple eye (Fox 2007). Attempts to remove the radula from the buccal cavity were not successful. The gill axes is located on the dorsal side of the body whorl and has afferent and efferent branchial vessels on its right and left side (figure 5) (Fox 2007). To the right of the gill axes is the rectum which is dark and tubular. The hypobranchial gland which is used in mucus secretion is attached to the right of the rectum (figure 6) (Fox 2007). Ventral to the gill axes are the intestines which curve around several of the lower whorls. The digestive cecae are located in the topmost whorls of the snail. Along with the stomach,the digestive cecae make up the mid-gut and are where the majority of enzyme breakdown occurs (Fox 2007).
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| Figure 3 |
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| Figure 4 |
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| Figure 5 |
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| Figure 6 |
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Biogeographic Distribution | |
Conuber sordidus is a relatively common marine invertebrate along sandy and muddy substrates in the east and south coasts of Australia, where it is endemic (figure 7). The specimens collected for this study were found on North Stradbroke Island, in Queensland, Australia.
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| Figure 7 |
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Evolution and Systematics | |
The phylum Mollusca is the second largest phylum and has a highly diverse range of body plans and features. General key features of this phyla include an open circulatory system, a mantle, a radula, fully developed anterior ganglia and bilateral symmetry. C. sordidus falls under the most diverse class within this phylum, the Gastropoda, which has approximately 80,000 species, roughly 30,000 of which are marine (Wanetta 2012). This Class has the unique feature of torsion – where the visceral mass of an individual rotates 180 degrees counter clockwise during development.
Within the Gastropoda, C. sordidus are part of the paraphyletic group Littorinimorpha (Beesley 1998). Under Littorinimorpha, C. sordidus are part of the superfamily Naticoidea which are characterised by shell boring predation (Beesley 1998). The evolutionary history of boring predation in the Naticidae family has showed little variation in the general mechanisms used, however there have been changes in prey preference over time (Kabat 1990). The earliest records of boring predation by molluscs were seen in the Triassic however it has not been confirmed to have been from Naticid species (Kabat 1990). This type of predation was then lost during the Jurassic period before reappearing in the Cretaceous period where there was a large diversification of marine species, called the ‘Mesozoic marine revolution’ (Kabat 1990). At this point in time, boring predation was definitely being done by Naticids, with an equal ratio of gastropod to bivalve prey (Kabat 1990). In the Eocene period, the first signs of confamilial predation of Naticids was seen, and higher rates of mollusc predation were found (Kabat 1990). The prey preference of Naticids has fluctuated over time, showing no real trend (Kabat 1990).
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Conservation and Threats | |
Conuber sordidus is not currently threatened, and can be found fairly commonly throughout its native distribution.
A study by Ying et al. in 1993 looked at the potential use of C. sordidus in detecting environmental changes to coastal habitats. As they are a burrowing species, their intimate relationship with the sediment in the environments they live in could cause them to accumulate contaminants found in those sediments (Ying, Ahsanullah & Batley 1993). The study found that snails accumulated lead and manganese and could be useful indicators of pollution of these two metals, which could help in the conservation of the intertidal habitats that they live in (Ying, Ahsanullah & Batley 1993).
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References | |
Beechey, D. (2017). Family Naticidae. Retrieved from http://seashellsofnsw.org.au/Naticidae/Pages/Naticidae_Intro.htm
Beesley, P. L., Ross, G. J. B. & Wells, A (eds) (1998). Mollusca the southern synthesis. Melbourne: CSIRO Publishing.
Bishop, M. J., Cole, M. R., Taylor, S. L., Wilkie, E. M., Kelaher, B. P. (2008). Size-specific predation by dominant consumers maintains a ‘trophic cul-de-sac’. Marine Ecology Progress Series, 354, 75-83, doi: 10.3354/meps07219
Booth, D. (1995). Oxygen availability and embryonic development in sand snail (Polinices sordidus) egg masses. Journal of Experimental Biology, 198, 241-247.
Bouchet, P. (2011). Conuber sordidum (Swainson, 1821). Retrieved from: http://www.marinespecies.org/aphia.php?p=taxdetails&id=585300
Fox, R. (2007). Invertebrate Anatomy Online: Bellyma japonica. Retrieved from: http://lanwebs.lander.edu/faculty/rsfox/invertebrates/bellamya.html
Golding, R. E., Ponder, W., F., & Byrne, M. (2009). The evolutionary and biomechanical implications of snout and proboscis morphology in Caenogastropoda (Mollusca: Gastropoda). Journal of Natural History, 43(43-44), 2723-2763, doi: 10.1080/00222930903219954
Grove, S. & de Little, R. (2017). A guide to the seashells and other marine molluscs of Tasmania. Retrieved from: http://www.molluscsoftasmania.net/Species%20pages/Conuber%20sordidum.html
Huelsken, T., Tapken, D., Dahlmann, T., Wagele, H., Riginos, C., Hollmann, M. (2012). Systematics and phylogenetic species delimination within Polinices s.I. (Caenogastropoda: Naticidae) based on molecular data and shell morphology. Organisms Diversity & Evolution, 12(4), 349-375, doi: 10.1007/s13127-012-0111-5
Hülsken, T. (2008). Phylogenetic relationship and species identification within the Naticidae Guilding, 1834 (Gastropoda: Caenogastropoda). (Doctoral Dissertation, Ruhr University Bochum). Retrieved from: http://www-brs.ub.ruhr-uni-bochum.de/netahtml/HSS/Diss/HuelskenThomas/diss.pdf
Miller, S. E. L. (1972). Adaptive design of locomotion and foot form in prosobranch gastropods. Proquest Dissertations and Theses, 225
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Pederson, R. V. K. (1997). Morphogenesis of planktotrophic veligers of naticidean gastropods. Proquest Dissertations and Theses, 132.
Kabat, A. R. (1990). Predatory ecology of Naticid gastropods with a review of shell boring predation. Malacologia, 32(1), 155-193.
Kingsley-Smith, P. R., Richardson, C. A., Seed, R. (2003). Size-related and seasonal patterns of egg collar production in Polinices pulchellus (Gastropoda: Naticidae) Risso 1826. Journal of Experimental Marine Biology and Ecology, 295(2), 191-206, doi: 10.1016/S0022-0981(03)00300-9
Russel-Hunter, W. D., Russel-Hunter, M. (1968). Pedal Expansion in the Naticid Snails. I. Introduction and weighing experiments. Biological bulletin, 135(3), 548-562, doi: 10.2307/1539717
Swainson, W. J. (1821). Zoological Illustrations, Or Original Figures and Descriptions of New, Rare Or Interesting Animals: Selected Chiefly from the Classes of Ornithology, Entomology and Conchology and Arranged on the Principles of Cuvier and Other Modern Zoologists. Retrieved from: https://books.google.com.au/books?id=yaI-AAAAcAAJ&pg=PT51&lpg=PT51&dq=THis+shell+is+both+undescribed+and+apparently+unfigured;+the+spire+is+more+elevated+than+usual&source=bl&ots=_Y28zSps1u&sig=i2MlgZ4fTp78WGRGF20c1pxAtig&hl=en&sa=X&ved=0ahUKEwiS5qH0z5nUAhWKmpQKHbcYAYcQ6AEIJzAA#v=onepage&q=THis%20shell%20is%20both%20undescribed%20and%20apparently%20unfigured%3B%20the%20spire%20is%20more%20elevated%20than%20usual&f=fals
Wanetta, V. (2012). Gastropods and their study. World Technologies.
Ying, W., Ahsanulla, M. & Batley, G. E. (1993). Accumulation and regulation of heavy metals by the intertidal snail Polinices sordidus. Marine Biology, 116(3), 417-422, doi: 10.1007/BF00350058
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