The marine snail Cymbula oculus (Born, 1778), formerly of the genus Patella, is commonly known as the goat’s eye limpet. Did you know that marine snails have teeth? They possess a tongue-like organ, known as the radula (Koch 1949; Branch 1971; Steneck & Watling 1982), which is used for feeding on the rocky substratum. The radula consists of many transverse rows of teeth.
How to recognise a goat’s eye limpet
The goat’s eye limpet is a rocky intertidal species, occupying the mid-shore zone. The shape of the limpets’ shell is ovate and flattened, and the colour is dull brown (Branch et al. 2010). The colour of the foot is brown (Koch 1949; Branch 1971, 1981; Branch et al. 2010). At a taxonomic level, this limpet is more easily identifiable by its radula.
Getting around
Limpets are known to settle high up on shore, due to upward migration (Branch 1971, 1975). This upward migration is a result of desiccation stress.
Distribution
The goat’s eye limpet is endemic to the South African shoreline (Ridgway et al. 1998; Branch et al. 2010). This species is found throughout the eulittoral zone (intertidal or mid-shore area) along the east coast and extends as far as St Helena Bay in the west coast (Koch 1949; Branch 1971).
Habitat
The goat’s eye limpet is found in the mid-shore zone of the rocky, intertidal ecosystem. They display random to aggregated distributions, no territorial behaviour, poorly defined home scars (the same spot on a rock that some species of limpet return to) and temporary homing (Branch 1976).
Food
This marine snail is a generalist grazer (Branch 1971; Branch et al. 2010). It feeds on a variety of seaweed (macroalgae). Limpets use their radula to scrape food off the surface of rocks.
SEX and LIFE CYCLES
Sex:
Cymbula oculus is a protandrous hermaphrodite. This means that they are born male and after 1–3 years change their sex to become female (Branch & Odendaal 2003; Branch et al. 2010).
THE BIG PICTURE
Friends and Foes
The flat worm (Notoplana patellarum) is usually found underneath the foot of this limpet (Koch 1949; Branch 1971; Branch et al. 2010). The relationship between the limpet and flat worm is commensal, where the flat worm feeds on the limpets’ faeces and algal fragments (Branch 1975). Limpets are preyed on by birds, starfish, crayfish, crabs, whelks and fish (Branch 1981).
Smart Strategies
The structure of the tongue-like radula allows this limpet and other species of the Order Patellogastropoda to graze more efficiently (Steneck & Watling 1982; Maneveldt et al. 2006). This radula type allows for greater excavation of food sources from the substratum on which they feed. Their teeth are biominerally hardened (Jones et al. 1935).
Poorer world without me
Being a generalised grazer (feeding on a wide variety of food items), this limpet has a major influence on community structure in the rocky shore environment (Branch 1971, 1975, 1981; Maneveldt et al. 2009). This grazing behavior allows this limpet to control the diversity and abundance of macroalgae on the shore.
People & I
This limpet species is overexploited in the former Transkei (Eastern Cape) region, where they are harvested for food (Branch & Odendaal 2003; Branch et al. 2010).
Conservation status and what the future holds
Branch & Odendaal (2003) conducted a study in two Marine Protected Areas (MPAs) and four exploited sites. They found that limpets inside MPAs were larger, had greater densities and biomass when compared with harvested/ exploited sites. This study emphasised the importance of protection. Had it not been for the populations in the MPAs, the assessment of the effects of exploited populations may not have been possible.
Relatives
Patellogastropods, or true limpets, dominate South African rocky shores due to a high species richness and diversity (Branch 1976, 1981). There are eighteen species of patellid limpets in southern Africa, seven of which are endemic to South Africa, while most are able to co-exist (Branch 1976; Ridgway et al. 1998; Branch et al. 2010; Mmonwa 2014).
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
Order: Patellogastropoda
Superfamily: Patelloidea
Family: Patellidae
Genus: Cymbula
Species: Cymbula oculus (Born, 1778)
References and further reading
- Branch, G.M .1971. The ecology of Patella Linnaeus from the Cape Peninsula, South Africa. I. Zonation, movements and feeding. African Zoology 6: 1–38.
- Branch, G.M. 1975. Mechanisms reducing intraspecific competition in Patella spp.: Migration, differentiation and territorial behavior. Journal of Animal Ecology 44: 575–600.
- Branch, G.M. 1976 Interspecific competition experienced by South African Patella species. Journal of Animal Ecology 45: 507–529.
- Branch, G.M. 1981. The biology of limpets: physical factors, energy flow, and ecological interactions. Oceanography and Marine Biology Annual Review 19: 235–380.
- Branch, G. & Odendaal, F. 2003. The effects of marine protected areas on the population dynamics of Cymbula oculus, relative to wave action. Biological Conservation 114:255–269.
- Branch, G.M., Griffiths, C.L., Branch, M.L. & Beckley, L.E. 2010. Two oceans: A guide to the marine life of southern Africa. Struik Publishers, Cape Town, South Africa.
- Jones, E.I., McCance, R.A. & Shackleton, L.R.B. 1935. The role of iron and silica in the structure of the radular teeth of certain marine molluscs. Journal of Experimental Biology 12(1): 59–64.
- Koch, H.J. 1949. A review of the South African representatives of the genus Patella Linnaeus. Annals of the Natal Museum 11: 487–517.
- Maneveldt, G.W., Wilby, D., Potgieter, M. & Hendricks, M.G.J. 2006. The role of encrusting coralline algae in the diets of selected intertidal herbivores. Journal of Applied Phycology 18: 619–627.
- Maneveldt, G.W., Eager, R.C. & Bassier, A. 2009. Effects of long-term exclusion of the limpet Cymbula oculus (Born) on the distribution of intertidal organisms on a rocky shore. African Journal of Marine Science 31(2), 171–179.
- Mmonwa, K.L. 2014. Molecular phylogeny, phylogeography and evolutionary adaptation of foraging behaviour amongst sympatric patellid limpets along the southern African shoreline. Doctoral dissertation, Rhodes University.
- Ridgway, S.A., Reid, D.G., Taylor, J.D., Branch, G.M. & Hodgson, A.N. 1998. A cladistic phylogeny of the family Patellidae (Mollusca: Gastropoda). Philosophical Transactions of the Royal Society of London, Series B 353: 1645–1671.
- Steneck, R.S. & Watling, L. I982. Feeding capabilities and limitations of herbivorous molluscs: a functional group approach. Marine Biology. 68: 299–319.
Author: Bahia Groenewald
SANBI Marine Programme (MSIP)
May 2015