The Octopodous Mollusca of New Zealan—III. The Giant Octopus, Macroctopus maorum (Hutton)–in Youth, Adolescence and Maturity.

By W. B. Benham, K.B.E., F.R.S.

list that several other species are more or less “slender” and the. hectocotylus which in O. maorum has an index of 6·2-8% of the arm length, can be paralleled by other species; thus O. pallida, where it is described as “large and powerful” its index is 9-12%, in O. dopleini 6·2% but is pointed. As will be seen in the following account this organ in the present species is long and cylindrical when the groove is closed, in the adult, but has a different shape in the young.

In regard to the funnel lock, the “small ridges” are in reality small semicircular flaps, small certainly in proportion to the great size of the animal, but definite outwardly directed flaps rather than “ridges”.

There is no doubt that (3) the great size of the gill marks this species off from others; none of which attain to this number of lamellae.

Whether one is justified in establishing a new sub-genus on a combination of these features I doubt, but as I have not the large experience of the group that Robson has I am disinclined to go to the extent of denying the validity of his view.

Stages of Growth.

The juveniles are Nos. 60–62; the adolescents 63–67, and the adults 54 and 55.

Dates of capture.—The smallest, i.e. youngest, individual (No 60) was caught in November 1941; the next size, (61) in January 1942, and No. 62, a little larger, in March 1942. The series 63–67, adole scents, in September 1942 and the four adults (Nos. 54 and 55) were-taken in August and September respectively in 1939.

These dates are rather suggestive, though of course it is impossible to state definitely the rate of growth. But it is reasonable to suppose that the life history occupies about one year; for we don't as yet know at what date the eggs are deposited, though judging from the condition of the ovary in the two adults, where it is enormous, and that in the males spermatophores are already in Needham's sac, we are justified in supposing that the eggs will be fertilised and deposited in October. We know that the animals are still active in January when they enter the harbour, and that in February they are cast ashore in a dying condition.

Juvenile Stage

The youngest specimen of this species was living in one of the tanks at the Station. I thought it was a new species owing to its small size and distinctive colouration. Of it I took notes as to colouration; that was in 1941; early in the following year three more specimens were sent to me. But these four were all males and being desirous of obtaining females communicated with Mr. Adams, with the result that in late September of 1942, I received five more individuals, captured by Captain Black, of the s.s. “Hananui,” by whose good services the aquarium at Portobello, and we zoologists, are often provided with rare or interesting animals brought up in his dredge.

The living individual attracted my attention at once owing to the characteristic colour pattern, as well as the noticeably enlarged suckers on certain of the arms. The body is an oval with rounded posterior, its breadth rather more than half its length. The colour of the dorsal surface is a rich chocolate brown, with numerous pale spots, which have a bluish fluorescence, scattered over the surface. These give a somewhat greenish, tint marbled with dark brown; the colour fades towards the sides and the ventral surface is a pale cream, with a few spots.

When preserved in formaline the chocolate colour persists but the bluish spots are now yellowish.

The head is marked off from the body as well as from the arm base by a “neck,” being constricted in front and behind, though the depth of this depends on the degree of contraction. The colour of the head is paler than the body, but running across it from eye to eye is a dark brown band, a very striking feature when alive. From the middle of this transverse band there passes forwards a dark-streak to the median region of web; here it divides and sends a branch to each of the four dorsal arms. All these dark areas are plentifully bespattered with spots, which in the preserved state are yellow and slightly prominent. (Fig. 1, Plate 22.)

The outer surface of the other four arms is pale, as is the inner surface of all the arms.

The surface of the mantle in those preserved in formaline is rough, being covered with small rounded papillae, irregularly scattered; in some individuals they are more closely placed, in others more widely; on the head, on the web and back of the arms, the papillae are oval or even linear and of a bright yellow colour.

The eyes are invisible and the animal appears to be blind, but on cutting away the eyelid the eyeball is brought into view. In all these specimens, adolescent as well as adult, the same is true, the eye is withdrawn under the lids. And perhaps this strong contraction may account for certain inconsistencies in the Interocular width as recorded in the Indices at a latter page. Above each eye is a rosette-or circular clump of rounded papillae, with a large one centrally, representing the usual ocular cirrhus.

The series of suckers commences as a ring of eight small ones round the mouth. Then come three or more separate, and after that the usual duplicate-alternate condition. On the two dorsal arms the suckers of the 13th and 14th pairs are relatively enormous; those on the two dorso-laterals are also large, on the ventro-lateral and ventral they are successively smaller. These enlarged suckers are at the level of the attachment of the web to the arms (Fig. 2, Plate 22).

Adolescent.

Of the five captured in 1942, two are coloured chestnut brown like the young ones, one male and one female; but three are a pale grey, one male and two females. All five are much larger than the original lot. The sexual organs of the brown and grey specimens are identical. Apart from this difference in colour which at first suggested a difference of species, these five all agree with the former lots in general characters, especially in the indices.

Since the colour has no relation to the sex; it occured to me that perhaps it was related to the environment, to difference in the character of the bottom, or some other part of the environment. But I am informed by Captain Black that all five were caught in the same locality on September 21, “about 12 miles N.E. of Otago Heads, at a depth of 22–25 fathoms; the bottom was shell with a fair amount of weed.” There seems nothing, then, in the environment to explain the colouration: The fact that both sexes exhibit both colours nullifies the idea that sex has any influence. But may it be that when fully sexually mature the colour changes from brown to grey?

These five are twice to thrice the size of the former four. In my notes of the latter I find that the body measures from 60–75 mm. and the arms in the largest of the original four bring the total to about 16 inches. But these larger ones have a body up to 190 mm. and arms of 860 mm., so that the total length is more than three feet. No. 67 is almost adult, but is included here.

The two larger brown individuals present the same general colour pattern as the juvenile, though owing to the somewhat darker colour of the head the interoeular band is not so conspicuous nor are

the lines leading to the arms, they would indeed escape remark were it not for the condition noted in the young ones.

Eyen in the grey animals, which are nearly sexually mature, the characteristic interocular pigment band is quite recognisable though not so distinct as in the very young, further, whereas in the young ones the head is very definitely constricted off from the body and preocular region, these constrictions are less pronounced in these larger ones.

The shape of these adolescents is rather more like Robson's figure (1928, p. 259) as it is a longish oval.

The Adult State.

This large species of Octopus frequents the waters of the coast of Otago (as well as elsewhere off New Zealand) and scores of individuals enter the Otago Harbour during the month of January (our summer) and are washed up on the beaches during February. Why this occurs I don't know. In March of the present year I visited Anderson's Bay on three occasions, namely, on the 1st, 14th and 31st, when I examined some dozen or more individuals which had been left stranded by the receding tide. I hoped to find some evidence that might indicate the cause of this phenomenon. But on opening the mantle cavity no such evidence was found, the animals were in excellent condition, and the genital sacs were filled with sexual cells.

Professor Marples tells me that he has seen them actively swimming ashore; so perhaps they commit suicide through unrequited love!

I obtained two pairs—that is, two males and two females, (Nos. 54, 55) in a fresh condition from the Portobello Fisheries Research Station. They had been taken in 15–17 fathoms, at a spot some 3–4 miles N.E. of the Otago Heads. One pair was taken in August 1939, the second pair in September. I also took the opportunity of examining a specimen in the zoological laboratory (56).

My notes on externals were made while the animals were fresh; after they had been preserved in formaline I noted any differences in colour wrought by this reagent.

The form of the body differs from Robson's figure (1928, p. 259) which he describes as being “extremely narrow” and “slender” so- that I was at first -inclined to suppose that these belonged to some other species. But the measurements and the dissection convinced me that they were indeed O. maorum.

Robson himself states in his Monograph (p. 4 and elsewhere) that variations in body shape may occur, depending on the circumstance of death or preservation. For example, in his account of O cyanea (p. 95) it is stated as being “rounded pyriform,” or “it may be bursiform,” or again “elongate oblong.” Hence it is clear that the shape “can only be used for the discrimination of species with very great caution” (p. 25).

The general form or these specimens when fresh one would describe as broadly oval or as more or less “globular.” But in this fresh condition the body is so soft that when lying on the dissecting board the sides bulge outwards so as to assume a globular form.

The Gill is unusually massive, being broad and long and formed of 14 lamellae in most of the animals examined. But the number varies from 12 to 14 and even 15 in 54 female. In the juveniles all have 14; in one adolescent (64) only 13; in one adult female there are 12 in one gill and 14 in the other; and in one adult male only 12 in each gill, but the terminal lamellae are very small, so as to be possibly overlooked.

This high number, 14, is met with only in O. maorum according to Robson's list, and it was this fact that suggested to me that these small, brown fellows were really the young of the large grey ones. That and the agreement that I found in the Indices.

Visceral Organs.

Of the Alimentary tract, which was dissected-out in two of the young and one adult, the only point worth noting is the ink sac.

The ink sac, as in O vulgaris, extends back as far as the point at which the hepatic ducts issue from the liver; it lies just below the visceral membrane covering this organ, but its duct rises through this and is free for its entire length.

I extracted and examined the radula and made drawings of two radulae and found them to agree with Robson's figure (1918, p. 259).

The Renal sac is triangular (Fig. 8, Plate 23), the apex lying near the penis or “ejector” of the male duct, and in the adult pushed forward along the right side of this organ. The base is near the hinder end of the body towards the left side. When its ventral wall is opened the usual venae cavae are exposed, with the venous (renal) appendages springing therefrom in the typical manner.

The Male Organs (Figs. 9 and 10, Plate 24)

* In the two immature individuals which were dissected the testicular sac lies immediately in front of the intestinal caecum; in a mature specimen it has moved backwards so as to lie in its more usual position at or near the hinder end of the visceral cavity. Both in the immature as well as the mature state the group of closely coiled ducts, which Marchand speaks of as the “packet,” lies against the anterior border of the testicular sac (Fig. 9, Plate 24). It will be noted that Needham's sac lies transversely, its end being on the left side of the group of ducts. In the fully mature animal this is filled with a brown fluid, and when opened showed two or more spermatophores. The unravelled condition of the male organs is seen in Fig. 10, Plate 24.

The “Ejector,” formerly and usually termed. the “.Penis.”— The free portion of this organ is very short—that is, the portion which projects beyond the thin visceral wall. The form and size and even-position of the diverticulum is not constant; In one instance it is much like Robson's figure (1928, p. 26) that is, the base of the penis is “corrugated” or traversed by a few rounded prominences but he does not show the diverticulum, which is partly concealed by this corrugated base; it is a thin-walled oval sac lying rather dorsally. On opening the “penis” itself I was surprised to see that the distal vas deferens projects freely into the chamber, its free end being directed forward for a distance nearly half way along the chamber (Figs. 11a and b).

In another adult individual the diverticulum is not a simple oval sac, though it seems so till the organ is turned aside so as to bring the dorsal surface into view, when this oval sac is seen to be the end of an S-shaped sac which opens as before into the hinder end of the ejector. In this instance the chamber is almost filled with a brown semi-fluid granular material containing spermatophore, one end of which issues from the upturned distal vas deferens which is directed forwards.

In another adult grey animal (No. 66) the tip of the distal vas deferens enters the main chamber but is directed backwards and opens into the diverticulum, which is a simple sac lying dorsal of the posterior end. of the “ejector,” scarcely visible from the ventral view. No doubt this unusual position of the duct is due to contraction, on death (Fig. 12, Plate 24).

Note on the Misuse of the word “Penis.”

It is rather surprising that Marchand in his account of the male apparatus (1907) in which he substitutes new terms for most of those previously employed, such as “prostate,” “seminal veiscle” formerly used by analogy with mammalian apparatus, he should have omitted to draw attention to the fact that the term “penis” in octopods is a misuse of the word. For in these animals, as everyone must know, it has no power of.” intromission” into the terminal region of the female apparatus; which is the prime function for the organ in vertebrates; it is not even protrusible, nor eversible; it serves merely to expel the spermatophores as they arrive in its chamber from Needham 's sac or pouch. The contraction of its muscular wall serves to expel these extraordinary structures. Now, in insects the terminal part of the male apparatus is termed the “ductus ejaculatorins.” But to spea of this organ as an “ejaculator” would be to imply that it emitted a sound, an “ejaculation” of some kind. So I suggest the term “ejector,” for it shares with the penis of vertebrates the function of ejecting sperms. We zoologists have inherited in many instances the terminology for these organs in the invertebrates which were employed by the earlier students of zoology, who were usually medical men, and so the terms used by the human anatomists were conferred on organs from some resemblance or analogy to vertebrate structures. In most instances these wrongly applied terms have been replaced, but we zoologists are rather conservative in matters of terminology. Why the organ formerly called in Octopods “prostate,” is even now so called in most text books, when it has neither the relation nor the function of this organ in mammals, is difficult to understand. An example is found in the anatomy of earthworms where the greenish-yellow covering of the intestine has been referred to as “hepatic tissue.” It has nothing to do with the process of digestion. We know now that its cells have an excretory function.

The Female Organs (Fig. 13, Plate 24).

The ovipore at the end of the “vagina” lies far forwards in the same position as the male pore. In the mature animal the ovary or “ovarian sac” fills the posterior part of the body cavity. The proximal region of the oviduct is short and leads into the spherical oviducal gland which lies close to the ovarian sac. Thence the distal

Indices.

In the case of Robsonella australis there is a uniformity in size and actual measurements of the various external features (Benham, 1942) but in the present species, having both small and large, young and old specimens, there is naturally a considerable range in actual dimensions; and to meet this difficulty in identifying species Robson introduced his scheme of “Indices” whereby the proportions are recorded as percentages of some standard. These proportions for the three stages agree closely in spite of wide differences in actual dimensions of the parts.

In accordance with Robson's usage I append the Indices first for these nine individuals, four small and five medium sizes, and on a later page those for four mature ones. The meaning of the capital letters at the head of the columns of the figures, is as follows:

• A. Length of body to level of eyes.

• B. Breadth of body as % of length.

• C. Supra-ocular breadth as % of length.

• E. Length of longest arm as % of total leugth—i.e., body plus this arm.

• F. Number of lamellae in gill.

• G. Diameter of largest sucker, as % of body length.

• J. Web, depth of deepest sector as % of longest arm.

• K. Length of ligula as % of the hectocotylised arm.