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Studies on the Paua, Haliotis iris Martyn in the Wellington district, 1945-46

Shell Perforations

Shell Perforations

Boutan (1886) states that the shell of Haliotis commences as in Fissurella and Pleurotomari a without slit or perforations and Crofts (1929) found a distinct protoconch in her smallest specimens. In the smallest specimens examined by the writer for H. iris, H. virginea and H. australis the protoconch was plainly visible and approximately the same size (1.5mm long) in all three species. As soon as growth begins perforations are formed and the difference in number of perforations for approximately the same length of shell is considerable in the three species.

Number of Specimens Long. Diam. of Shell Total Number Perforations Open Perforations
H. iris 1 1.10cm 15 4
H. virginea 1 .95cm 17 4
H. australis 1 1.20cm 21 5
H. iris 1 2.10cm 21 5
H. virginea 1 2.10cm 25 5
H. australis 1 2.20cm 32 6

Only single specimens were obtained in the size range shown above. The difference in number of perforations per unit length between the three species is due to the distinctive nature of the logarithmic spiral in each species, i.e., it follows that the constant angle of the logarithmic spiral in H. virginea will fall probably between that of the other two species.

There is a close correlation between the number of perforations present in tho shell and the length of the shell. This can most easily be ascertained in the page 10smaller shells. It is very difficult to obtain an accurate count of perforations in the older shells because of the heavy encrustation of coralline algae, tube worms, etc. In a count of fifty shells taken from different areas ranging from one to seven centimetres in longest diameter the number of perforations increased regularly with the length except in one case. The average number of open perforations was five but ranged in number from 4 to 7. Suter (1913) states that open perforations in H. iris range from five to seven. In a count of approximately 340 shells ranging between 12 and 16cm the following estimate of shell perforations was obtained.

Table showing the number of shell perforations found over a population of H. iris.

It can be said that the range for open perforations for this species is from 0 to 7 while the average is from 3 to 5 rather than between 5 and 7 as stated by Suter (1913).

Crofts (1929) found in a count of 194 specimens of H. tuberculata of marketable size that 101 had 6 perforations and she states that the number of perforations in H. californica vary from 5 to 9 in young animals and from 2 to 3 in the adult. These latter figures resemble those given for H. iris in having fewer perforations in older shells. Crofts found only one shell imperforate and this had closed holes in the older part of the shell.

Pelseneer (1920) has described abnormalities of the shell in Haliotis as instances of continuous and discontinuous variation and cited the variations in the number of perforations in H. tuberculata and H. californica.