Overview
Brief Summary
Historical importance
Ecology
Local Distribution and Habitats
Biogeographical Distribution
Life History
Behaviour
Cyclicity
Evolution & Systematics
Systematics or Phylogenetics
Morphology and Physiology
External Morphology
Anatomy
Conservation
Threats
Wikipedia
References & More Information
Bibliographies | External Morphology
Mantle Characteristics
The most distinguishing feature of cowries is their extendible mantle which is able to cover the entire shell (see video below). It can be smooth, some have tubercles and others such as C. tigris possess branching papillae (Walls 1987). The function of these are unknown, but they may be used as sensory appendages. The mantle is consipicuously patterned and slightly transparent, mottled with brown and beige colouring. The colouring varies greatly between species (Walls 1987). When disturbed, the mantle can also secrete an acid as a method of chemical defense (Edmunds 1968).
Shell
The beautiful glossy shell of cowries have historically been exploited for human use as souvenirs and even currency (Harms 1986). Growth of the shell is unique from that of other Gastropods and during growth the lip involutes towards the body and produces a long restricted aperture (Besley et al. 1998). Once this occurs, shell growth can only occur via expansion by reabsorption internally of the shell and deposition by the mantle externally.
Below are details of a study conducted on Heron Island in September 2011, looking at the shell pigmentation of C. tigris.
Comparison of shell pigmentation and size in Cypraea tigris
CHANTELLE E. REID - University of Queensland
Introduction
The tiger cowry Cypraea tigris is one of the largest and most common species of cowries (Burgess 1986). Their shiny smooth shells can be completely enclosed and protected by extensions of the mantle, which is a unique feature amongst Molluscs (Walls 1987). During growth the mantle deposits pigment along the extending margin of the shell (Lindsay 1982). It is still generally unknown what mechanisms control and contribute to the patterns of pigment distribution of the shell. Studies on other species of Gastropods have found that cell division in the mantle epithelium cause the patterns to divaricate (Lindsay 1982). The aim of our study is to better understand these processes by firstly analysing the patterns of pigment distribtution on the shell. We discuss possible mechanisms that may determine pigment colour and investigate whether or not pigmentation increases with size.
Materials and Methods
Individuals were collected from the reef crest on the southern side of Heron Island (23° 27’ S, 151° 55’ E). These were kept in aquaria for four days at Heron Island research station for observation before being returned. The distribution and percentage of pigments on the shell of 4 individuals was measured. The entire shell area of each individual was photographed for analyses. These photos were uploaded and ImageJ was able to calculate the total area of brown pigmentation in comparison to the white background. Length and area of each specimen was noted to assist with these calculations.
Results
Using ImageJ to calculate the total area of the shell covered in pigmentation, it was found that percentage of pigmentation correlated negatively with total area of the shell (Figure 1). The results of linear regression yielded a slope of -2.0237 and an R2 value of 0.81789, which indicates that pigmentation decreased as shell size increased.
Figure 1. Linear regression of percentage shell pigmentation y = -2.0237x + 96.115, (R² = 0.81789) against total shell area.
Discussion
There is immense diversity in shell shape, size and patterning amongst Gastropods and cowries possess a particularly unique and beautiful shell (Walls 1987). Considering the patterns of distribution in proportion to the shell might help better understand the mechanisms underlying its creation. Our results show that as shell size increases, the percentage of pigmentation decreases (Figure 1). This may be due to a reduction of pigment deposition in mature cowries, when shell growth ceases once the lip completely involutes. Once maturity is reached growth ceases completely, apart from repairs to the surface (Frank 1969). Further expansion only occurs through reabsorption of the shell internally and deposition by the mantle externally (Besley et al. 1998). This may explain the increase shell area and decrease the amount of pigmentation. A study by Kozminsky & Lezin (2007) on the Gastropod Littorina obusata found that the character of pigment distribution remained constant throughout life, but the ratio and intensity of colour changed.
Below are the four individuals that were use for this experiment. The shell patterning and pigmentation between the same species alone is extremely variable. One particular individuals had spots that were particularly streaked, which may be due to pressure from predation or other factors, which increased the growth rate of the shell.
Studies have not looked at the mechanism by which the cowrie is able to develop colour formation and pigmentation on the shell. It is particularly interesting how the colouring of the mantle appears to match the position of pigments laid down on the shell. Unfortunately this was difficult to determine and this is more of a preliminary study to observe the general pattern and distribution of the shell pigments. Further research could look more closely at the mechanisms that are attributed to formation of coloration on the shell and how it is inherited. This would help to better understand how the mantle lays down the pigment in such diverse yet distinct shell patterns.
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