Care of Eggs by Octopus maorum
[Read by Title and Abstract before Otago Branch on May 1,1956; received by Editor, May 17, 1956.]
Care of eggs was strongly shown by a specimen of Octopus maorum Hutton in the Portobello Aquarium. During the 11 weeks between laying and hatching, the eggs were almost continuously guarded. The mother swept them with one or more tentacles. This presumably helped aerate them, and kept debris from aggregating on them. Predators on reaching the egg mass were perceived sometimes by tentacle touch, at others visually. They were rapidly grasped by the suckers and pushed away by the tentacles. Squirting water on the eggs by the siphon was only occasionally observed until the day of main hatching, when it was frequent.
Egg capsules were elongate-pyriform, stalked, and in clusters of usually 3 to 10, attached directly to the substratum. Young on hatching were 7 mm long, with only one colour of chromatophore (red-brown). Eggs and larvae are described and photographed. The adult is a typical Octopus maorum, with 13 gill filaments on each side. As the eggs resemble those Benham described for Paroctopus zealandicus n.sp., his type for this species has been re-examined. Reasons are given for regarding P. zealandicus as a synonym of O. maorum.
On entering the aquarium during the evening of October 26, 1955, I saw that the octopus was in the process of laying a great sheet of eggs on the glass of her tank. Subsequently she gave these eggs almost continuous attention. As care of eggs is unusual among marine animals, and as little has been recorded about the behaviour and habits of New Zealand octopuses, an account is here presented.
The octopus, a medium-sized specimen of O. maorum, was taken by the trawler “Foam” in a crayfish pot between Karitane and Palmerston (north of Otago Heads), and brought to the aquarium on September 10, 1955. After that, Mr. McArthur, who looks after the aquarium, assures me that she was not in a tank with another octopus. As the eggs proved fertile, this indicates that copulation occurred at least 45 days before egg-laying.
During most of the period concerned I was living at the marine station, and was thus enabled to observe the octopus a number of times daily, between 10 a.m. and 10 p.m., on most days. When I was absent, Mr. McArthur (caretaker of the aquarium) and Mr. Gadd (who relieved him in January) kindly made observations for me.
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
Photographs are all of living specimens, not anaesthetised. For all except Fig. 1, lighting was by a “Mecablitz” electronic flash of 1/500 sec. duration. This “stopped” most movements (e.g. in Figs. 2 and 6–9), but not the fastest swimming darts of newly hatched young, when they were magnified × 5 on the negative.
Gare-of-Eggs Behaviour by Female
The sheet of eggs, laid on and after October 26, is described in a later section and shown in Fig. 1.
For the 80 days from the beginning of laying until the day of main hatching, the octopus almost continuously brooded the eggs. During the first few days she usually
lay in the corner of the tank below them, extending 2 or 3 tentacles up over the egg sheet (Fig. 1). Later, she more frequently squatted directly over the eggs, holding the glass with some suckers and waving free tentacles across the egg sheet (Fig. 5). Usually two or more tentacles were continuously sweeping the eggs with slow, radial sweeps and an undulating movement along each tentacle. A passing tentacle swayed the suspended eggs vigorously sideways, an action caught in Fig. 2, where a tentacle is swinging to the right. This tentacle activity probably has an aerating function. It also tends to keep particles of debris and micro-organisms from aggregating on the eggs. The question arose as to whether or not it served as a defence against predators.
On October 30 I observed a large black sea slug (Scutus breviculus) crawling along the aquarium glass in the direction of the egg-sheet; so watched to see what would happen. The octopus, as usual, was sweeping the eggs with tentacles. As the Scutus came to the edge of the egg-sheet, a tentacle passed within a few mms of it. No change in the octopus's behaviour occurred, although the slug appeared to be within its range of vision. The Scutus then opened its mouth, swung its radula forwards, and engulfed an octopus egg. Before there was time for another egg to be eaten, the next sweep of the tentacle encountered the slug. Thereupon the tentacle threaded itself between the mantle and foot of the slug, first on one side and then on the other. A second tentacle joined the first, running itself round the front end of the slug. This change in the behaviour of the octopus was not as marked as its food response to crabs when not brooding, but was a marked deviation from the gentle undulating of separate tentacles over the egg-sheet. After about 10 minutes of being vigorously handled by the octopus tentacles, the slug changed its direction, first upwards and then away from the eggs without eating more of them. In Fig. 1 it is retreating from the right end of the egg-sheet.
Sea-slugs were observed to approach on several occasions, chiefly during the first few days. Sometimes a slug would eat several eggs—e.g., one engulfed, in 14 minutes, 6, 8, 2, 2 and a further 2 eggs, whilst one tentacle twisted round it. After that, however, the Scutus moved up and away from the eggs, still with a tentacle pushing it. Hence it is seen that the tentacle activity of the octopus, as well as presumably aerating and cleansing the eggs, may discover and reject predators.
The form of the rejection was most readily appreciated when I put my arm into the tank and handled some eggs. As soon as my hand was touched by a sweeping tentacle, it was gripped by several suckers and pushed gently away until clear of the egg-sheet.
On the morning and afternoon of January 4, I kept my arm almost continuously in the vicinity of the egg-sheet for two 2-hour periods (in order to clean an algal film from the glass between egg clusters, prior to taking the photograph of Fig. 5). Throughout this time the octopus was continually grasping my arm with suckers and pushing it from the egg-sheet. After about half an hour, she bit me; three more bites followed during the next two and a-half hours. They were not severe, only two drawing blood. Whereas she might have bitten more often if I had not tended to avoid her mouth after the first nip, this line of defence appeared merely a secondary and intermittent one, brought into play after prolonged stimulation.
On the morning of 31.10.55, the octopus tank while being cleaned was half-emptied of sea-water. This left more than half of the egg-sheet out of water till the tank refilled. While the eggs were exposed, the octopus remained immediately below. She regularly reared two tentacles out of the water and continued to sweep them over the egg-sheet—air-exposed as well as water-covered portions. Such abnormal activity as rearing its arms far out of water shows how strong the care-of-egg behaviour is in the female octopus.
The first time since egg laying that I saw the octopus away from the eggs was on November 30, five weeks after laying began. For some minutes she sat on the
bottom of the tank below them, without waving tentacles over them. From then till the day of main hatching (January 13) I observed the octopus away from the eggs five times altogether. On four of these I gently handled some of the egg clusters with my fingers. One time, although my hand was presumably within her visual range, no response occurred. On the other three occasions, she reacted after 3–12 seconds, returning to the egg-sheet, grasping me with suckers, and pushing my hand from the region of the eggs.
These and other observations indicate that reception of stimuli leading to predator rejection is sometimes tactile, via the scanning tentacles, and at others visual.
Mr. McArthur reported that the octopus, while brooding, fed when crabs were dropped on top of her, but as a whole probably ate less than before the eggs were laid. When he dropped a large piece of fish on her while over the eggs, she carried it to the far end of the tank and dropped it there. Crabs dropped in the far end of the tank were not promptly taken by the octopus in her usual manner prior to brooding; the egg-care behaviour pattern inhibiting the usual feeding response.
However, such crabs were liable to be found as empty remains the next morning, and it is improbable that they were eaten by other occupants of the tank (Scutus and starfish). This suggests that some feeding occurred at night, and that egg-care might not be as continuous during darkness as during daylight.
To check the latter point, the octopus was visited on the night of December 29–30 at 10.30 p.m., 1.30 a.m. and 4.30 a.m., and on the night of January 11–12 at 1 a.m. At each of these times when I turned the light on she was over the eggs, suggesting that she usually guarded them during the night as well as day.
In some octopus species, care of egg behaviour includes squirting water on to the egg mass from the siphon, either as well as or instead of manipulating them with the tentacles (Table 1). I watched for such behaviour in the present instance. It occurred scarcely at all until January 13, the day of main hatching, when there was a sudden marked change. On most of the numerous occasions when I observed her that day, the siphon was vigorously squirting the egg capsules, sometimes between one pair of tentacles and sometimes between another. The question arises, did this sudden change in behaviour pattern accelerate the hatching. Or did the mechanical stimulus of empty egg capsules, or some chemical they released, cause the change in the behaviour pattern?
After January 13 the majority of egg capsules still on the glass were empty. The next day the octopus was more often on than off the egg capsules, but when off did not respond when I twiddled some. During the next few days she left the remains of the egg sheet with increasing frequency, being more often off than on by January 19. Her death occurred (during a heat wave) on January 23. Hatching had ceased a few days before, only a number of empty egg capsures and a few with dead eggs remaining on the aquarium glass.
Egg Sheet and Eggs
Most of the egg sheet is shown, viewed through the aquarium glass on which it was laid, in Fig. 1. Individual eggs in their capsules are grouped in clusters, each cluster being cemented independently to the aquarium glass (Figs. 2, 3, 5). One cluster usually has from 3 to 10 eggs. The range in a sample of 28 clusters was from 1 to 19, with an average of 7 eggs per cluster. Each cluster is attached directly to the glass by a dab of cement. This at first is pale yellow, but after a few hours changes to light yellow-green and later to a dark yellow-green. This colour change drew attention to the fact that the egg sheet was not completely laid on October 26, but that further clusters were added intermittently during about a week. Fig. 1 shows the nearly complete egg sheet (except for a small portion of it on a glass
sheet at right angles) on October 30, 1955. A rough estimate of the total number of eggs is 7,000.
The egg-capsule surrounding each egg is transparent, stalked, and elongate-pyrifom in shape (Figs. 2, 3). The tip of the stalk, embedded in the cement, has a slight bulbous expansion (Text-fig. 5). Twenty egg capsules, formalin-fixed on November 25, ranged in length (including their stalks) from 9.8 to 11.8 mms, their average length being 10.8 mms. Widths ranged from 1.4 to 1.8 mms.
The egg inside each capsule is elongate-ovoid, 4–6 mms long, and at first semi-translucent with a pale yellowish tinge. By November 25 (nearly a month after laying) no macroscopic changes had occurred, although a minority of specimens fixed on this date microscopically showed rudiments of several organs on the side of the egg. By December 19, large dark brown paired eyes were visible in most, and tan chromatophores in some. Embryos showed slight general movement and hearts already beating. By December 29 (Fig. 3), one could readily see in the embryo, as well as eyes and chromatophores, the tentacles encircling the yolk sac at the bottom of the egg, brain, siphon, mantle, stellate ganglia and ink sac. By January 4 a few, and by January 5 nearly all of the embryos had turned upside down in their egg capsules, so that tentacles now pointed towards the stalk, mantle towards the lower end.
By January 4 (Fig. 5) only a few hundred eggs of the original egg-sheet remained. A few had been eaten by predators, a few removed for preservation or during cleaning, and a number had been dislodged by the tentacle activity of the female. Presumably in natural conditions the eggs are laid on rock. Seemingly the cement was here scarcely strong enough to stand 11 weeks of agitation when attached to a glass surface.
A few young hatched each day (mostly at night) from January 4 to January 12. Then suddenly, on January 13, 120 or more larvae hatched. After that the majority of egg capsules left on the glass were empty, and only a few further larvae were observed hatched in the tank. Seemingly hatching began gradually, reached a peak after nine days, and then almost ceased.
As eggs were laid over about a week, and as hatchings occurred over about 10 days, precise time from laying to hatching for one individual was not recorded. But the period from main laying (October 26) to main hatching (January 13) was 80 days. Otago Harbour sea temperatures during this period (surface temperatures measured daily at 9 a.m. from the end of the Marine Station wharf) ranged from 11.0° C%. to 19.4° C%., lying between 13° C%. and 17°C. during most of the period. Occasional recordings of the octopus tank temperature on warm days were about 0.5° C%. above the harbour (channel surface) at the same time.
This was directly observed in several specimens in dishes of sea-water in the laboratory (Fig. 4). Vigorous activity of the mantle bursts the egg capsule round a ring near its lower end. Soon after the siphon also emerges. Specimens in dishes, where the cement was no longer attached, took up to an hour or more to hatch; as the vigorous contractions of the exposed mantle moved the whole egg cluster round in the dish, instead of freeing the individual concerned. Specimens hatching directly from the egg-sheet in the aquarium probably did so much more rapidly. For I frequently observed the egg-sheet during the final few days, but saw only one young (an abnormal specimen) in the act of hatching.
The young on hatching tended to swim upwards and towards light. A specimen in the large aquarium tank would give several successive contractions of its mantle, with its siphon pointing towards the tentacles (Figs. 6 and 7). This would take it
Fig. 5.—Egg sheet on day when hatching began, showing usual brooding position of mother octopus, × 0.3.
Figs. 6–9.—Young octopuses on day of hatching, showing various swimming positions, × 8. Fig. 6—Siphon pointing towards head, mantle expanded. Fig. 7.—Mantle contracts, whereupon jet through siphon sends larva to left. Fig. 8—Pause. Spreading of tentacles increases surface area, slows sinking. Fig. 9.—Siphon directed away from teatacles reverses direction of swimming
obliquely upwards in the water, mantle end forward. Then mantle contractions ceased for some seconds, during which, the larva fairly rapidly sank. Sinking to some extent was slowed by spreading of the tentacles, a position partially shown in Fig. 8. But in the main tank, tentacles were more fully spread out during sinking than in this individual photographed in a small dish. Occasionally the siphon is turned towards the mantle (Fig. 9). The larva then darts in the opposite direction, tentacles forwards. Sudden mechanical stimulation causes more rapid darting in various directions. This is generally accompanied by expanding of some or all of the chromatophores, so that the usually largely transparent larva flushes to a rich red-brown.
Some larvae were kept for a few days in bowls of aerated sea water in the laboratory; from one to six specimens per 2-litre bowl, changed twice daily. Most swam actively, chiefly near the surface, for the greater part of the first two or three days. They then were chiefly on the bottom, largely inactive, and dying 4–8 days after hatching. Six placed in a jar of running sea-water in the aquarium fared no better A heat wave during this period submitted them to water temperatures they would not normally encounter in local seas. Hence the length of their planktonic phase remains undetermined.
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
These larvae seemed particularly sensitive to unaerated sea-water, and anaesthetised surprisingly rapidly in 1 part sea-water, 1 part 71/2% MgCl2. After 5 minutes in this their swimming usually ceased, and after another 10 the mantle commonly became distorted posteriorly.
The larvae on hatching have an overall length of about 7 mms (50 slightly anaesthetised specimens were measured, within two hours of hatching, on 13.1.56. Lengths ranged from 6.7 to 7.6 mms, with an average of 7.1 mms).
The general appearance and chromatophore pattern of newly hatched larvae are shown in Text-Figs. 1 and 2. These are based primarily on camera lucida drawings of living specimens briefly anaesthetised in MgCl2-sea-water. Some details have been checked from cleared preparations and serial sections However, fixation by formalin or Susa, despite anaesthetisation, caused significant shrinkage.
In the newly hatched larvae, eyes are large and strongly pigmented, the tentacles relatively short. Each tentacle has 7 or 8 suckers in an irregular zig-zag (Text-fig. 3). Tentacles are all of approximately equal length, the dorsal ones tending to be slighth longer than the ventral ones. The main nerve ganglia and large otocysts, visible by transparency, fill the posterior part of the head. Sections show a slender oesophagus running from the mouth through the dense mass of ganglia in the head, bending sharply ventrally and then dorsally to enter the visceral mass, and entering posteriorly an expanded, yolk-filled vesicle—presumably the future stomach. This is in connection with a smaller vesicle posteriorly. From the latter, sections show a narrow intestine running forward immediately ventral to the ink sac and its duct. The anus opens just inside the mantle, by the ink duct opening. At the sides of the mantle the two stellate ganglia are conspicuous, though radiating giant fibres to the mantle have not yet developed. The mantle is freely provided with blood vessels, capillaries being especially rich round the stellate ganglia. Gills and branchial hearts are conspicuous in live individuals, but sections are needed to follow details of auricles and ventricle.
The chromatophores, all of the same red-brown colour, show a distinct pattern in their distribution. Exact numbers vary from one individual to another; so typical numbers and ranges observed will be described. Along each tentacle runs a single row of usually 8, sometimes up to 11, chromatophores This row is usually straight, sometimes slightly wavy Occasionally one extra chromatophore is beside one in the row. The head dorsally shows 2–4 small chromatophores between the eyes and one small anterior and two large posterior ones around each eye. Overlying the ganglionic
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
Text-Figs. 1 and 2.—Dorsal and ventral views of newly hatched larvae of Octopus maorum, lightly anaesthetised, × 21. Superficial chromatophores shown as black dots; those on viscera, under mantle, as ovals. Organs visible by transparency lightly lined.
Text-fig. 3.—Inner face of tentacle, newly hatched larva, fixed material, × 21.
Text-fig. 4.—L.S. portion of mantle wall, showing knob, × 350.
Text-fig. 5.—Egg capsule fixed on November 11, × 31/3, showing expansion at tip of stalk.
|Species||Locality||Form of Egg-care||Ate During Brood-ing||Died Soon After Brooding||Egg length,* mms||Estimated Egg Number||Grouping of Eggs||Period, Laying to Hatching||Total length, mms, new larva||Reference|
|Octopus valgaris||English Channel, etc.||Squirts water often||f||2.5||150,000||Long strings of clusters||21–30 days||3||Rees|
|Octopus cyaneus||Sydney||Siphon squirting; prevented interference||“Practically refused all food.”||Died before embryos reached hatching||1,500–5,000||Long strips of dark brown mucus enclose egg capsules||More than 5 weeks||Le Souef and Allan, 1933|
|Octopus sp., greenish body, outsides of suckers tan||Sydney||Siphon squirting; also constant tentacle movement Repulsed other occupant||No||Yes||3||Hundreds of main stems, 3–4ins long, with numbers of cream egg capsules||At least 5–6 weeks||3–4||Le Souef and Allan, 1937|
|Polypus bimaculatus||S. California||Siphon squirting; crouched over eggs at all times||Refused food while crouching over eggs||Colourless clusters of eggs attached to central stalks||D.L.Fox|
|Paroctopus binaculatus||S. California||Chiefly tentacle manipulating, less frequent siphon squirting||No||12–16||600||Clusters attached to rock||4 months||8||MacGinitie and MacGinitie|
|Octopus apollyon||S. California||Chiefly siphon squirting; also tentacle manipulating||Small (half size of uncooked rice grain)||45,000||Long strands of pearly white eggs||More than 6 week||MacGinite and MacGinite|
|Probably Octopus spollyon (“Mephiste 1”)||California||Tentacle manipulating; siphon restless||Probably at night. During day fish pieces moved off eggs||Yes||Long festoons, eggs nearly transparent, axis brown||About 9 weeks||Fisher|
|Octopus spollyon (“Mephista II”)||California||1.4||Ricktts and Calvin|
|Octopus maroum||Portobello, New Zealand||Siphon squirting; occasional tentacle swinging||“Attached in pairs to the glass.”||80 days||(Benham)|
|Octopus maorum||Portobello, New Zealand||Tentacle manipulating. Almost no siphon squirting till day of main hatching||Probably at night||Yes||4–6||7,000||Clusters of usually 3–10 eggs cemented directly to substratum||Approximately 80 days||6.7–7.6||Batham|
[Footnote] * Length of egg within capsule, excluding capsule stalk.
mass dorsally are 4–5 pairs, while another large pair lies just posterior to these, under the mantle (shown partially filled in, Text-fig. 1). Along the dorsal junction of mantle with head is a row of from 2 to 7 small chromatophores—4 in Text-fig. 1. Apart from this the mantle dorsally lacks chromatophores except for a close cluster of 24–32, some dorsal, some ventral, on its posterior tip. But visible through the mantle dorsally by transparency are a large number of chromatophores (47–53) overlying the viscera. These are shown as open ovals, and not solid black, in Text-fig. 1.
Ventrally (Text-fig. 2) the head has 2 or sometimes 3 chromatophores lying behind the eyes. The siphon carries usually 2, sometimes 3, small ones just behind its opening. Along the ventral mantle margin lies a row of 6–8. A sparse sprinkling (3 in Text-fig. 2, ranging up to 8) lies scattered posteriorly to this row on the ventral mantle. Then, at the extreme posterior end of the mantle, the cluster of 24–32 chromatophores already mentioned is visible partly ventrally, partly dorsally.
Rees mentions the occurrence of numerous bristles on head, mantle and arms of newly hatched Octopus vulgaris (1951, p. 371). Octopus maorum larvae show small knobs abundant on tentacles, scattered on head and mantle (Text-fig. 4). These are barely raised above the ectoderm surface, and are all directed anteriorly.
Comparison With Other Species
From the literature, it seems that care of eggs is rather general among female octopuses. Robson (1929, p. 22) notes a number of such observations dating from those of Aristotle onwards. The more detailed data available to me concerned 6 species, and are summarised in Table I. In each case the eggs are frequently moved by the female. Sometimes the emphasis is on squirting of water by the siphon; at others, as in the present instance, on tentacle activity. For example, the MacGinities (1949, p. 399), familiar with brooding in two species, state that “the southern octopus (P. bimaculatus) does not shoot jets of water over the eggs nearly so frequently as does the northern octopus. Too, probably because the larger size of egg makes this more feasible, the southern octopus manipulates the egg more with the suckers.” In some instances it is possible that a personal element is significant in relative emphasis, or possibly different individuals vary within a species in this matter. For Fisher (1923), describing brooding in probably the same species of northern octopus (Octopus? apollyon), stresses tentacle combing of eggs rather than siphon squirting. And with the present species, Benham's brief report (Benham, 1936) describes another Octopus maorum. watching over eggs, “directing constant streams of water over them from the exhalent tube and occasionally sweeping them with her tentacles.” Such a description would have applied to the specimen I observed only at the very end of the brooding. Error in emphasis may have occurred in Benham's report in that it was almost certainly second-hand. Alternately, the future may show that different individuals within this species show real differences in behaviour in this respect.
There seems a general tendency for octopuses to eat little if at all while brooding. Actually, evidence here can easily be uncertain For if food placed in an octopus's tank has been partly eaten by the next morning, but other animals are present that possibly ate it, one lacks direct evidence about the octopus. In general, it seems that the normal direct food response to a live crab is inhibited, but that total starvation during brooding does not necessarily occur.
In various instances described the female dies soon after the eggs hatch. Whether or not this is usual in natural conditions is less sure Doubtless the prolonged food shortage and tentacle activity during brooding leaves a female octopus considerably weakened. But the fact that the present specimen of O. maorum was by no means full-sized suggests that brooding in the natural environment is not necessarily followed by death.
It is also clear from Table I that among different species egg masses vary greatly in form, and eggs in size and number. In view of the confusion reigning in octopus systematics, fuller consideration of the highly characteristic egg and egg clusters seems worth while. Actually the genus Paroctopus, for those species with large eggs (5 mms or more long, Pickford, 1945, p. 703), attached directly and not in strings, was thus erected but seems now to be falling into disuse. Octopus maorum, with eggs 4–6 mms long, in this respect falls marginally between Octopus and Paroctopus. It was on the basis of its eggs that Benham (1944) tentatively placed a female from Portobello Aquarium in a new. species, Paroctopus zealandicus; overlooking that such eggs had already been obtained here (but not figured) for Octopus maorum. While the nature of the eggs in this instance thus seems unsatisfactory as a generic distinction, it may well help characterise the various species.
In the examples in Table I for which figures are available, egg size and egg numbers show roughly an inverse relationship. Another point of interest is that length of embryonic life seems directly related to size of egg among different species, rather than to sea temperatures. Otago Harbour and the English Channel have closely similar temperature ranges. Sydney and California are warmer. Yet Octopus vulgaris takes about ⅓ the time to reach hatching that Octopus maorum, with its larger eggs, shows; and of two Californian species in one locality, O. apollyon with small eggs takes about half the great time of Paroctopus bimaculatus (four months).
Notes on Adult and on Paroctopus zealandicus Benham
As the systematics of New Zealand octopuses are not yet on a fully satisfactory basis, an account of the external features of the female here concerned is given.
Her general colour, when the chromatophores were moderately expanded, was usually a warm greyish red (in the region of y R 4/2 to y R 2/2, using Munsell Color Charts). The dorsal side of the mantle and outer surface of web and tentacles were on the average deeper than other regions, owing to greater concentration of chromatophores. The animal could flush to a very dark, dull red-brown or blanch to a dirty white. But no mottled colour pattern was shown, the chromatophores appearing to be all of a single red-brown colour. In this feature, the present species differs from the local midget octopus Robsonella, whose several colours of chromatophores enable the body to show mottled coloration. Along the outer surface of the tentacles of this and other specimens of Octopus maorum are irregular rows of small, whitish papillae, with a reduced concentration of chromatophores (Fig. 5). The mantle in typical state is mildly sculptured and usually ovoid in shape (Fig. 5).
The gills show 13 filaments in each demibranch. The arms are long and slender, their largest suckers lying from 16th to 21st from the mouth. The web is bilateral, the depth of sectors diminishing slightly dorso-ventrally. The eyes are small and placed close together.
The animal was measured when freshly dead, before it was fixed in formalin. In this flaccid, extended state, measurements of parts such as tentacles and web are doubtless considerably greater than after shringage in fixative. Following other authors, measurements are given in mms, but except for sucker diameter the last figure is not significant. The following measurements and indices are based on the plan of Robson (1929), followed by Benham (1943, p. 150) and Dell (1952, pp. 23 and 29). The letters refer to those defined by Benham (1943 and 1944) and used by Dell (1952).
Mantle length (A), 210 mms; mantle width, 129 mms; interocular width, 61 mms; total length, 1030 mms. Arm lengths: R1, 810 mms; R2, 890 mms; R3, 735 mms; R4, 713 mms; (L1, 700 mms); (L2.204 mms); L3, 620 mms; L4, 713 mms; (L1 and L2 both show signs of damage and regeneration). The arm formula (D) for the right side is 2134. Diameter of largest sucker, 21 mms. Median funnel length, 90 mms.
Inidces. Mantle index (B), 61; interocular index (C), 29; arm index (E) 86; sucker index (G), 10; web index (J), 24.
Web Depths. Sector A, 210 mms; sector B, 200 mms (right), 180 mms (left); sector C, 190 mms (right), 170 mms (left); sector D, 190 mms (right), 170 mms (left); sector E, 150 mms. Web formula is thus A. B. C. = D. E.
This octopus seems beyond all reasonable doubt to be a specimen of the common New Zealand large coastal octopus, Octopus (Macroctopus) maorum Hutton. It has the large number of gill filaments (13) characterising this species, and is of typical size, shape and appearance for a female. Arm formula, web formula and indices fall in the range shown by Dell (1952) for this species.
Eggs have not previously been figured for Octopus maorum. But the eggs laid by the present specimen resemble preserved eggs laid by an octopus in the Portobello Aquarium on 4.11.41. These were described by Benham who, because of their nature, tentatively described the female that laid them as a new species of the genus Par-octopus (Paroctopus zealandicus Benham 1944). I have re-examined the type and eggs of this specimen of Benham's in the Otago Museum. I find the adult has 12–13 pairs of gill filaments, and not 9, as described by Benham. Five egg capsules from Ben-ham's material were examined and measured. They were a little larger than those of the present octopus, ranging in length from 12.2 to 13.6 mms, in width from 1.6 to 1.8 mms. But in other respects they appear essentially similar. Likewise his adult does not differ significantly from the present specimens. In other words, Benham's Paroctopus zealandicus seems beyond reasonable doubt to be a synonym of Octopus maorum.
Dell (1952, p. 26) discusses similarities and differences between the New Zealand Octopus maorum and the widely distributed Octopus macropus. To his list of differences may be added that of egg size. Whereas eggs of Octopus maorum are 4–6 mms long, those of O. macropus are only 1.2–2 mms long (Robson 1929, p. 21)
This work was carried out while I was holding Nuffield and N.Z.U. Research Grants, which I gratefully acknowledge. I wish to thank Mr. D. McArthur and Mr. Gadd for looking after the octopus and for making observations when I was absent; also Mr. Edsell, of the trawler “Foam”, for kindly supplying the octopus. To Mr. R. K. Dell (Dominion Museum) I am indebted for helpful discussion of systematics and literature.
Benham, W. B., 1936. Marine Fish Hatchery and Biological Station, Portobello Report for year ended March, 1936, to New Zealand Marine Department, New Zealand Marine Department Annual Report for the year 1935–36.
—— 1944. The Octopodous Mollusca of New Zealand Part IV. Trans. N. Z. Roy. Soc. 73: 255–261.
Dell, R. K., 1952. The Recent Cephalopoda of New Zealand. Dominion Museum Bulletin, No. 16.
Fisher, W. K., 1923. Brooding Habits of a Cephalopod. Ann. Mag. Nat. Hist. 12: 147–9.
Fox, D. L., 1938. An illustrated note on the mating and egg-brooding habits of the two-spotted octopus Trans. San Diego Soc. Nat. Hist. IX, 7: 31–34.
Le Souef, A. S. and Allen, J., 1933. Habits of the Sydney Octopus (Octopus cyaneus) in captivity. Australian Zoologist, 7: 373–376.
—— 1937. Breeding Habits of a Female Octopus. Australian Zoologist, 9. 64–67.
MacGinitie, G. E. and MacGinitie, N., 1949. Natural History of Marine Animals. McGraw Hill.
Munsell Book of Color. Pocket Ed. Vols I and II. 1929–1942. Munsell Color Co. Inc. Baltimore.
Pickford, G. E., 1945. Le Poulpe Américain a study of the littoral Octopoda of the Western Atlantic Trans. Connecticut Acad. Arts Sciences, 36: 701–811.
Rees, W. J., 1950. The Distribution of Octopus vulgaris Lamarck in British Waters. Jour. Mar. Biol. Assoc. 29: 361–378.
—— 1952. Octopuses in the Channel. New Biology 12: 58–67.
—— 1954. The Macrotritopus Problem. Bull. Brit. Mus. (Nat. Hist.) Zoology II, 4. 67–100.
Ricketts, E. F. and Calvin, J., 1948. Between Pacific Tides. Stanford University Press.
Robson, G. C., 1929. A Monograph of the Recent Cephalopoda. Part I. Octopodinae. Brit. Mus. Nat. Hist.
E. J. Batham,Ph.D.,
Portobello Marine Biological Station,
Portobello, New Zealand.