Habitat and Geographical Distribution

Haliotis occurs on exposed rocky coasts throughout New Zealand. It is common in the Wellington, Kaikoura and Stewart Island areas, where it grows to its largest size and produces the finest shell. On sheltered coasts, such as the coast around Auckland, H. iris is seldom seen (Powell, 1946), while only small shells are found in the Taranaki and Hawke's Bay districts. H. iris, however, varies to a considerable extent within small areas. This is demonstrated by specimens from the short stretch of coastline from Wellington Heads to Cape Terawhiti (see map). The shells are roughly classified into hard and soft shell. Soft shell comes from areas characterised by a sandy or muddy bottom with the seaweed often page 4covered with a brown slime, and holothurians, such as Stichopus, are commonly seen. This type of shell breaks in the hand and is useless commercially. "Hard shell" areas always have clean rock or shingle bottoms and although the shell may sometimes be thin it is very strong and difficult to break in the hand. From a map it can be seen that of the thirteen places from which collections were made, five gave soft shell and these are intercepted by the clear beds.

H. iris is found from just below low-tide level to a depth of approximately 30 feet. It may, however, occur at lower depths as other species of Haliotis have been found as deep as 33 fathoms, e.g. H. dalli was dredged from 33 fathoms near Charles Island, Galapagos (Bartsch, 1940). The small H. iris (1.0cm–9.0cm) are found from 1–2 feet below low-tide level and they are attached to the underside of boulders or resting on the upper surface of smaller stones beneath a boulder. The animals are never exposed to view but are always to be found out of the direct light either on the lower face of an overhanging ledge or beneath a rock. They are not attached to stones small enough to be moved by wave action unless these stones are sheltered from the direct force of the waves. The majority of small specimens occur in large shallow pools containing numerous stones and boulders and well protected from direct wave action by fringing, rocky reefs or large boulders. In some places, for example Te Kaminaru Bay, the small paua population is still extremely dense, over 300 being collected by one person in 1½ hours from 3 pools. These pools were all less than 6 feet in longest diameter. To the west of Island Bay the writer collected approximately 60 specimens from a pool about 4 feet long and 3 feet wide containing 2 large boulders and numerous small stones (about 8 inches in largest diameter).

Thus is can be seen that H. australis is in quite a small proportion to H. iris in the collections made. The habitat of H. australis appeared to be the same as that of H. iris. No living H. virginea were found although a few shells were observed on the beach at Stewart Island.

Behaviour

H. iris is a nocturnal animal. During the day it is always found away from direct light attached underneath ledges or on boulders. The small specimens are usually found on boulders or stones while the larger specimens in deeper water are generally attached to rock walls or overhanging ledges of rock. At no time during the day was a specimen seen moving unless it had been disturbed. When disturbed they cling tenaciously to the surface of the rock. Occasionally an animal would move from the exposed surface of a boulder that had been disturbed to the lower surface. This movement away from the light, however, occurred fairly frequently in the case of disturbed H. australis. Some specimens were attached to a broken piece of concrete and one had attached itself to a strip of rusty tin. This seems to point to the fact that they will attach to almost anything as long as it gives firm support and is out of direct light. It seems probable that where such a large number of specimens occurs in a small pool as described previously they must move out of such a pool during the night to feed, as often there is little or no algal growth on the rocks to which they are attached.

In one pool the writer observed a Haliotis (approximately 10cm in length) which on successive visits over a period of 3 months was still situated in the same place on the same rock. In addition, on 3 occasions on the removal of an animal from a rock there was left a definite mark on the rock where the animal had been attached. In one case a large surface of the rock was covered by small white tube worms except where a Haliotis had been removed and there remained a smooth surface of rock in the exact shape of the shell. From the above facts it is highly probable that H. iris has a homing instinct in its nocturnal movements. This view is supported by observations of the aquarium specimens. Graham (1941) expresses the opinion that Haliotis undergoes a winter migration to deeper water at Seal Point, Otago. This is a popularly held opinion. On the other hand a commercial fisherman in Island Bay, Wellington, who fishes for Haliotis throughout the year maintains that they do not migrate in the winter but can always be obtained at the same levels.

H. australis when found in any numbers was always intermingled with H. iris and never seen in groups of more than 2 or 3 as is often the case wim H. iris. It was more active than H. iris if disturbed and invariably quickly found its way back to the pool if placed out of the water on a nearby rock. On one occasion 4 small H. iris about 2.3cm in length were placed with a H. australis of the same size in an upturned billy lid. In about half an hour the H. australis had crept over the edge of the lid at least 3 times while all the H. iris remained completely immobile. H. iris specimens show a tendency to leave a pool if disturbed. In three cases specimens were noticed in the same positions on successive visits over a varying period ranging from a few weeks to about 3 months but in every case when lifted for measuring and disturbed they disappeared very quickly from that pool. H. iris if turned on to its back will right itself in the same manner as described by Crofts (1929).

Behaviour in Aquarium

A number of H. iris were kept in two small tanks for varying lengths of time. On February 21, 1946, four specimens ranging from 1.3cm–2.6cm were placed in each tank. One tank was aerated by sending a steady stream of air bubbles through the water for about 16 hours every day but the other was left undisturbed except for the removal and measurement of the specimens once a fortnight. The animals fed on algal growth present on the sides and floor of the tank. During the daytime the animals were invariably stationary, attached to the under side of a stone or the side of the tank near a corner although twice an animal page 6was found moving and eating in the daytime. A specimen would be in the same place during the day but would be seen moving about the tank at night. If a light were turned on immediately above them they would continue moving and feeding for ten minutes or more.

Although Haliotis is said to require very high aeration (Stephenson, 1924) the specimens in the aerated tank did not live as long as those in the non-aerated tank. Foot movements appeared to be exactly the same as those described by Lissmann (1945). Specimens often moved out of the water and when put back did not live more than a day. A possible explanation of this behaviour was that there was a change in the salinity of the water.

Shell

Growth of the Shell.

Graphs for two areas (Te Kaminaru and Island Bay) covering a total of 825 shells were made in order to find growth peaks. There was a difference of approximately one mm in shells from these two areas and this may be due to earlier settling time for larvae in one of the areas. The Te Kaminaru shells were lmm shorter in longest diameter at each age peak, but for all practical purposes the two areas can be counted as one and when graphed in this manner produce four definite peaks as shown in text figure 1.

Text-figure 1

These four peaks came approximately 1cm apart, the first being at 1.9cm mark, the second 2.9cm, the third 3.8cm, and the fourth at 4.7cm. The peaks after the highest at the 4.7cm mark are indistinct but appear to become closer together.

Crofts (1929) considers specimens from 30 to 40mm in spring and summer are probably two years old and that growth gets progressively slower after the first few months. In this she disagrees with Stephenson (1924) who considers specimens from 20 to 40mm in summer as one year old. If the distance between troughs on the present graph is taken as indicating a year's growth, then H. iris agrees with H. tuberculata (Crofts, 1929) in being approximately 3cm in length when 2 years old. Because of this agreement in age and length of shell with the figures given by Crofts and also on account of the quite distinct peaks (approxi-page 8mately 1cm apart) in the present specimens, it seems reasonable to consider that the distance between one trough and another represents a year's growth. Shells that are 1.9 to 2.9cm, and 2.9 to 3.8cm in length are in their second and third years of growth respectively.

Plate 2, Fig. 3 shows an example of a small shell 4.7cm in longest diameter with well defined intervals of growth showing on the outside of the shell. These demarcations are approximately 1cm apart and would appear to lend further support to the hypothesis that 1cm growth (at least over the first three years) represents a year's time interval.

It would appear from Text Fig. 1 that growth becomes progressively slower after the 4.7 peak. These intervals on the graph decrease from 1cm to approximately 0.5cm until the shells are 8cm in length. However, the peaks of shells greater than 4.7cm in length could not be determined accurately from this graph because as difference in growth each year becomes less, the number of shells necessary to give a definite peak is increased and sufficient quantities were not available within this size range to give a clear indication. Figures for the graph in Text Fig. 1 cover a range of shell from 1 to 8cm in length. All these shells were collected in the littoral area and the graph shows that the greatest number of shells inhabiting this area fall in the size range between 4.5 and 5.5cm in length.

Crofts (1929) collected H. tuberculata as small as 2mm in length. No specimens as small as this were found in the littoral zone in the parts of Cook Strait area covered by the present paper. Crofts (1929) reports that the smallest specimens are found at very low tides and this may also be the case with H. iris. The smallest H. iris shell found by the writer was 1cm in length and this was considered to be under one year in age, Text Fig. 1.

The estimated age of shells with a size range between 1 and 5cm was calculated from the growth peaks as stated above and the occasionally well defined intervals of growth visible on the external surface of some small shells. An attempt was made to calculate the age of shells from 5 to 17cm in length by means of the number of conchiolin growth lines laid down in the shell. These growth lines are usually well defined as shown in Fig. 4. Approximately 300 shells sectioned through the longitudinal axis were examined. The lines on each shell were counted from the nucleus to the lower edge of the columella plate and again from the nucleus to the anterior margin of the shell. The former count generally gave two more lines than the latter. It was seen that shells with a size range between 4 and 5cm in length show no distinct growth lines. A definite growth line first appears in shells between 5 and 6cm in length and in this group four out of eight shells had no lines showing at all. The average number of growth lines for each centimetre group increases as the size of the shell increases. There is, however, no regular increase between the averages, for example, the average number of lines for shells from 9 to 10cm in length is 5.0; 10 to 11cm is 9.0 and 11 to 12cm is 9.9. In addition, there is a great range in the number of growth lines within any centimetre group, e.g. in the 11 to 12cm group 1 shell has only five lines while another within the same group possesses 27 lines.

It was noticed on many occasions that the growth lines were laid down in pairs. This gave rise to the idea that the growth between one line and another may represent six months' time interval. The nacreous material between the pairs is greater than between the two lines of a pair and it was thought that this greater deposition of nacre alternating with a lesser period possibly represented summer and winter seasons of growth.

The occurrence of pairs of lines is not, however, a constant feature and from examination of the data it seems unlikely that a shell 14 to 15cm in length could be 13 years old. This would be the case if half the average number of page break

Fig. 1.—H. iris shell, photographed through the axis in order to calculate the constant angle of the shell.

Fig. 2.—Photograph of ground section of shell through the longitudinal axis and nucleus to show the conchiolin lines. A, growth lines. B, nucleus.

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Fig. 3.—Photograph to show the well defined intervals of growth visible on the external surface of some small shells. 1, 2, 3, 4, external demarcations of growth.

Fig. 4.—Photograph to show encasement of conical caecum by the shell. A, caecum encasement.

Fig. 5.—Photograph of posterior region of a diseased shell to show the gross distortion ol the shell and the numerous openings of worm tubes. A, gross distortions of the shell. B, openings of worm tubes.

Fig. 6.—Photograph of the feeding tracks of two small Haliotis iris. A, tracks of H. iris, approximately 3cm in lengths. B, tracks of H. iris, approximately 2cm in length.

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Fig. 7.—T.S. through a diseased shell to show tubercles and distortion of the conchiolin growth lines. A, tubercles. B, distortion of growth lines. C, position of insertion of shell muscle.

Fig. 8.—A polished specimen of H. iris to show the appearance of conchiolin growth lines on the outside of the shell. 1, 2, 3, growth lines.

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Fig. 9.—L.S. of diseased shell to show cavity from which one annelid worm was removed. Several small pearl-like formations also appear. A, cavity from which worm was removed. B, small pearl-like formations.

page 9 lines shown in Table I is taken, plus 4 for the four years' growth which occurs prior to the formation of conchiolin. From Text Fig. 1 it was concluded that in the first few years a shell grows approximately 1cm a year. It would be unusual if this growth rate did not decrease over a number of years. Yet a shell 14cm in length which is 13 years old would necessitate a growth of about 1cm a year for 13 years.

On the other hand the majority of the shells had the lines appearing singly and sometimes in groups of three as in Fig. 8. Therefore, it seems more probable that each growth line represents a year's growth. In this case a shell 14 to 15cm in length could be considered approximately 22 years old, i.e., the average number of growth lines plus 4. It must be remembered that the average for a group such as the 14 to 15cm group was obtained from a wide range in the number of growth lines. If a specific instance within a group is taken the age would be calculated from the number of lines actually present and not from the average for the group. For example, some old polished shells and pieces of shell have been examined with over 36 lines visible. This would mean that in some cases a shell was over forty years old. In contrast, however, some fairly large shells on the Table show very few growth lines, e.g., in the 12 to 13cm group two shells have only five lines. Therefore, their estimated age would be 9 years. This age is well below the estimated average age for the group and is open to the same objection as raised above where it was pointed out that a shell is not likely to continue growing at the same rate over a large number of years. As the rate of growth does not exceed 1cm a year the first 4 years it does not seem feasible to consider a shell 12 to 13cm in length as only 9 years old.

The only conclusion which can be drawn at present regarding the conchiolin growth lines is that these lines are put down regularly by the animal in response to some physiological need. It is not possible to state whether these lines are annual or biannual (i.e., twice yearly), or indeed give any indication of the growth-size ratio without further work being carried out.

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.

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.

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Determination of Logarithmic Spiral

The large shell of H. iris has a very small apical spire and an extremely large last whorl which is very depressed with a relatively enormous aperture.

Crofts (1929) suggests that the flattened shell of Haliotis has been evolved from a shell with a taller spiral because of the habit of squeezing into confined spaces between rocks. The shell of Haliotis grows in the form of a logarithmic spiral. The form of a single curve following a logarithmic spiral is given by the expression where r is the radius of the shell from centre to circumference; θ is the angle of revolution which the spiral has described and α is the angle between the tangent of the curve and the radius vector of this curve, which remains constant. This is known as the constant angle of the curve and has been determined in many species of Haliotis. D'Arcy Thompson (1942) states that in Haliotis the constant angle (α) varies from about 70 degrees to 75 degrees while in the majority of gastropods it lies between 80 degrees to 85 degrees or even more.

To determine the constant angle of H. iris a photograph was taken through the axis of a shell 9.9cm in largest diameter. The curve made by the line of holes in the shell was taken as the logarithmic spiral. Plate I shows a photograph and a diagram can be drawn from it. The following expression of the formula given above was used in the actual determination of the angle.

The result obtained gives α = 53 degrees 46′ which as far as the writer can ascertain is smaller than any other value of α obtained for a Haliotis. This means then, other things being equal, that H. iris has fewer whorls per unit height of shell than other species of Haliotis.

Moore (1936) found that the value of α in Purpura lapillus varied during the lifetime of the shell. The value of α calculated from a H. iris specimen 3.72cm in largest diameter was considerably higher in degree than in the case of the specimen 9.9cm in largest diameter. Therefore it appears probable that the value of α decreases as the shell grows.

Species	Longest Diameter in Cms	Constant Angle of Spiral (α)
H. australis	7.75	72 degrees 6′
H. iris	3.72	60 degrees 53′
H. iris	9.9	53 degrees 46′

The constant angle of the spiral of H. australis in the above table shows a large increase over the values given for H. iris and is higher than some other species of Haliotis, e.g. H. tuberculata where α = 69 degrees 48′ (Moore, 1936).

Crofts (1929) states that the shell of H. tuberculata is so flattened that the animal is unable to retract completely into the shell. From the value of the constant angle in H. iris given above it follows that the shell of H. iris is lower in relative height; but in contrast to H. tuberculata, H. iris can retract completely within the shell when disturbed.

Pathological Shells

From over a thousand Haliotis examined in a period of two years no specimen was observed with macroscopic disease of the soft parts, although a number had the dorsal region in various positions affected by contact with a diseased shell. Crofts (1929) states that she found no record of parasites occurring in Haliotis and in her examination of approximately four hundred specimens found only page 12two diseased. On the other hand, in H. iris the crab Elamena producta has been found on a large number of occasions apparently living in association with the New Zealand species. On removal of the shell from H. iris the crab is seen to be situated between the foot and the. mantle. Crofts found H. tuberculata shells frequently damaged by parasites, namely boring bivalves such as Lithodomus and various Pholadidea, but she does not mention tube worms. In the case of H. iris the shell is often heavily infested with these worms. Shells up to about 10cm in length are relatively clean on the surface and dark brown in colour. Above this size, however, out of a count of approximately 1,000 large shells all carried a heavy calcareous incrustation formed by algae covering the shell and in every case harbouring various species of annelid worm. Up to a hundred worms could be removed from one shell. These worms burrow through the periostracum of the shell and enter the nacreous portion ruining the shell for commercial use.

The most common worm found in the shell is Polydora sp. a member of the Spionidae. This is apparently P. monilaris. Polydora contains well known shell boring tube worms and has been described as causing a great destruction of oyster shells (Haswell, 1885). In some H. iris heavily infested with Polydora the calcareous crust of the shell will lift off in large pieces exposing a network of intertwining worms and their tubes. It is not known for certain how the worms burrow in the shell but it is probably by chemical means as the shell is much too hard for any mechanical means. The next most common worm found in the shell is the Terebellid Polycirrus. This dark brown worm has tubes very similar to those formed by Polydora. The tubes are not formed by many small particles adhering together but appear as thin chitin-like envelopes surrounding the worms. Nereis species are commonly found on H. iris shells although they probably do not destroy the shell as much as either Polydora or Polycirrus. The Nereis were identified as Nereis kerguelensis. Others were present. A number of Serpulids were found and one was identified as Hydroides.

In the shell shown in Plate 4 (Figure 9) the whole posterior dorsal region was completely deformed by worms. A large specimen of Thelepus was situated in the deep indentation shown in the photograph. Although the shell in this instance may have been slightly crushed to allow entry of the worms in the first place the major destruction of the shell appeared to be due to the worms. On the ventral side of the shell the indentation was covered by nacreous material except anteriorly along the edge of the muscle attachment where a great many small round protuberances on the shell were actually embedded in the muscle itself. In addition, some of these rounded projections had become detached from the shell and were lying in the muscle. It seems that the deformation made by the worm infestation caused the shell to proliferate these small round bodies which are not nacreous but rather resemble the periostracum structure of the shell. In section they show concentric rings. Although Polydora was seen on deformed shells it could not be said to cause the deformation as many shells perfectly normal on the inner surface had numbers of Polydora living on the outer surface. Only Thelepus and Nereis were found in direct connection with malformed shells. Plate 2 (Figure 5) shows a broken shell which was picked up from the beach near Island Bay. The whole outer surface of this shell is covered with worm holes and the severe distortion of the shell is without doubt due to heavy infestation of worms.

Plate 2 (Figure 4) shows a shell with a peculiar growth almost entirely enclosing the conical caecum of the visceral hump which contains a core of liver surrounded by gonad. This portion of the shell encasing the liver caecum appears to be made of nacreous layers in a way similar to the rest of the shell although it has not the lustre of the inner surface of a normal shell. In a normal shell the nacreous layers are put down at the posterior region of the shell by the mantle page 13covering the visceral hump but the major part of the caecum which extends forwards passes under a sheet of mantle stretching from the edge of the muscle attachment to the edge of the mantle plate, forming as it were a pocket in which the caecum is lodged. Thus the anterior part of the caecum has no contact with the shell either dorsally or ventrally. There is a distinct line of demarcation between the portion of shell laid down by the mantle of the posterior region of the visceral hump and that laid down by the mantle covering the anterior prolongation of the liver caecum.

In Fig. 4, however, there is no marked distinction on the inner surface of the shell showing where the mantle on the visceral hump ceases deposition of nacre and deposition of nacre by the mantle of the caecum pocket begins. In this case, therefore, it appears that for some reason the conical caecum has not been enclosed in the mantle pocket but has lain in direct contact with the shell and begun to secrete shell layers. Apparently the whole surface of the lobe has taken on a secretory function as shell has been formed enclosing the whole caecum. The ventral side of this cone of shell may have been formed as protection but it is not known whether the usual ventral covering of the visceral mass was present or not. Out of many thousands of specimens, Mr Taylor of Island Bay has found not more than 12 specimens of H. iris showing this peculiar formation of the shell. In some cases the cone of shell was not as complete as that shown in Fig. 4.

In one case in which the writer was able to see the animal that had been removed from the shell the caecum was twisted dorsally and was not covered by mantle except ventrally. The whole caecum had secreted shell dorsally but not ventrally where it was covered by the ventral portion of the mantle.

The most common type of diseased shell found was that depicted in Fig. 7. This formation of protuberances or tubercles on the inner surface of the shell was found frequently in some areas. In a section of the shell as shown in Fig. 7 these tubercles can be seen to have a core surrounded by numerous layers of nacreous material alternating with the dark conchiolin lines. This abnormal growth of the shell was probably due to irritation caused by sand particles becoming lodged between the mantle and the shell or, in some cases such as in Fig. 5, to the irritation caused by worms boring in the shell. Boutan (1923) succeeded in producing pearls in Haliotis by introducing foreign bodies in a suitable manner. Pearls have been found in H. iris in close proximity with such malformations as described above. These pearls were similar in structure to those tubercles seen in section but were always very small. Small shells are not often found with any tubercle formation on the shell and it is characteristic of this abnormal formation that it always occurs near or posterior to the muscle attachment region of the shell. Perhaps this is because only in this region does the animal find it impossible to rid itself of foreign bodies which have penetrated beneath the mantle. In the few small shells that were found with the tubercles just beginning to form the shell had a rough irregular inner surface apparently due to particles of sand which had been covered over by a dark conchiolin layer.

About 200 "frosted" shells were examined. These shells completely lacked the bright lustre of the inner surface of a normal shell. All the examples seen were large shells up to 17cm in longest diameter. The frosted appearance was due to some abnormality of the nacreous material laid down. Often this nacreous layer was flecked by conchiolin unlike a normal shell where the conchiolin layers are laid down in a fairly regular pattern. In addition, the shells were thick, the "frosted" nacreous layer being much thicker than a normal nacreous layer. The shell mentioned previously with the encased caecum (Fig. 4) is an example of a "frosted" shell. These shells are of no use commercially because they will not take a polish.

Food and Method of Feeding

H. iris feeds on a large variety of seaweeds. In some fifty specimens examined for gut contents the following seaweeds were identified: Xiphophora chondrophylla var. maxima, Caulerpa sedoides, Pterocladia lucida, Halopteris bordacea, Gigartina sp. and Ulva sp. Most of the animals examined were collected from Chaffer's Passage and The Runaround and they all had crop contents composed almost exclusively of brown seaweeds. Thus it can be said that in these animals which ranged from 10 to 16cm in length, brown seaweeds formed the predominating food. Crofts (1929) states for H. tuberculata that "mature animals show a preference for the delicate Algae, particularly red seaweeds such as Delesseria and Griffithsia, but will eat Chondrus as well as coarser weeds ". From examination of the gut content of H. iris the reverse condition appears to be the case. In small specimens the predominant food consists of small red seaweeds. In one instance a few specimens taken from a large pool just below low water mark, i.e. where the small paua between 1–8cm are found, the green seaweed Ulva was most noticeable but all the crops examined contained principally varieties of red seaweeds. A preference for red seaweed is undoubtedly shown by the New Zealand species but not by the larger specimens, as in H. tuberculata. The areas where the best shell grows generally contain a large amount of Xiphophora chondrophylla var. maxima and sometimes a great deal of Ulva.

Specimens held in aquaria were found to eat blue-green algae and diatoms which were present on the side of the tank. The diatom was Cocconeis sp. or a species very close to it. On a number of occasions Ulva was given to the aquarium specimens when there was very little algal growth on the sides of the tanks, but on only one occasion was a specimen observed eating it. The feeding of small H. iris on the sides and floor of the tanks was observed on many occasions. Each feeding movement of the radula resulted in two minute areas on the side of the tank being cleared of Algae, as can be seen in Fig. 6. As far as could be ascertained the scraping off of the Algae was accomplished by the two lateral sets of teeth in the radula as described by Crofts (1929). Six or seven feeding movements would be taken transversely with the posterior region of the foot hardly moving at all, then the whole animal would move forward sufficiently to be in a position to clean the next area in front. This method results in the feeding tracks having a branched appearance. In Fig. 6 the feeding tracks of two small specimens are shown. The larger set of "tracks" was made by an animal approximately 3cm in length and the smaller (lower left corner) by a specimen approximately 2cm in length. The latter did not make such regular tracks.

The size of the particles of seaweed found in the gut varied with the size of the animal. The largest specimens (13–17cm in length) contained food particles averaging 5mm in length and 1.5mm in width. They may, however, reach up to 10mm in length. The shape of the particles is fairly uniform, generally pointed at both ends and slightly curved towards one side.

Proportion of Male and Female Specimens

Counts of male and female specimens of H. iris taken from Karori Light, The Runaround and Sinclair Head were as follows:

Stephenson (1924) examined 127 specimens of H. tuberculata and found the proportion of males to females was 50 to 71. This gives a ratio of 0.7.

It is possible that the difference in relative proportions of males to females shown in the above figures was due to the different season at which they were taken. Stephenson (1924) obtained his specimens during the summer while the writer's figures are taken from specimens collected in the winter. Until a count can be taken in the summer from the Wellington areas no satisfactory comparison can be made between the two sets of figures.