OBSERVATIONS ON A LIVING SPECIMEN OF OCTOPUS HUMMELINCKI
Full text of "The Nautilus"
THE NAUTIUS Vol. 66 JANUARY, 1953 No. 3
OBSERVATIONS ON A LIVING SPECIMEN OF OCTOPUS HUMMELINCKI ADAM By gilbert L. VOSS
Marine Laboratory, University of Miami
Adam (1937) described Octopus hummelincki from preserved specimens collected from the island of Bonaire, in the Dutch West Indies, and since that date several other papers have appeared describing in detail the morphology of this species. In none of these papers, however, are there any observations or comments upon living specimens. On July 26, 1952 a specimen of this species was collected by Donald R. Moore at Long Reef in the Florida Keys while on a class collecting trip with the author. In view of the rather unusual characters displayed by this specimen it was considered that these observations should be added to the literature along with the author's conclusions.
The specimen, a male with a mantle length of 30 mm., was discovered at the entrance to a hole beneath a slab of coral in about three feet of water. Immediately upon capture he was handed to the author who had an opportunity to observe closely his sculpture, coloration, movements and habitat.
The sculpture, when living, is so different from that of the preserved animal that it would scarcely be recognizable as the same species. Outstretched in the palm of the author's hand each individual cirrus, amounting to about 50 or 60 in number, was fully distended into a wide, flat blade or band about 8 to 10 mm. in length ending distally in an arborescent crest. The eyes were raised boldly above the head and accentuated by the prominent supraocular cirri. The arms, when at rest, were held curled back over themselves with the sucker discs fully distended, adding to the irregular outline of the body. In general the entire surface is very rugose, especially on the dorsal portion of the body and arms. When swimming the cirri disappear, the rugosity of the skin itself smooths out, the arms point forward and adhere tightly together and the whole body is streamlined. Although the funnel is of normal size, this species appears to be a very active swimmer, much more so than the other oetopi such as 0. vulgaris and 0. briareus.
The color and color patterns seem to be rather distinctive although coloration is so variable in the octopods that in general it is not used as a diagnostic character. At rest or crawling the basic color was a rich reddish yellow-brown upon which were superimposed mottlings of light golden yellow. At intervals this pattern changed to a lighter brown with granular mottlings of grayish white. When swimming the mottlings disappeared and the color was a uniform light brown.
In the water, which was stirred by wave action, the animal appeared to be covered by a dense growth of marine algae waving with the motion of the water. This effect was heightened by the reef being completely covered with a heavy growth of attached Sargassum or Gulf weed and scattered clumps of Dictyota having the same general color and appearance of the cirri. Unfortunately the field data of the other specimens of this species now in the literature fail to give any mention of the prevailing algal growth. However, both Sargassum and Dictyota are commonly found on old coral reef formations in Florida and the West Indies and it would be interesting to know if it were prevalent in the collecting areas from which this species has been taken. A small collection of eight specimens of 0. hummelincki from Cay Sal Bank were taken from reefs having dense algal growth and a single specimen from Bimini, Bahamas, also was found surrounded by Sargassum. The striking coloration and general appearance of this species of octopus closely resembles that of the well-known Sargassum fish Histrio histrio as was noted by all of the observers present.
It is the opinion of the author that 0. hummelincki is re-
stricted to those reefs of coral origin now overgrown with Sargassum, Dictyota, and other genera of the brown algae and is peculiarly adapted among the octopoda to this floral habitat, similar to the close associations found in the drifting Sargassum complex, a field of study of great interest to marine biologists due to the adaptations found within it. The first color pattern noted corresponds in a striking degree to the colors exhibited by the surrounding algae and the granular grayish-white mottlings of the second phase imitated the white calcareous sedimentation found in small areas throughout the reef.
The specimen when preserved in 5 percent formalin immediately contracted the cirri into minute, filiform structures hardly noticeable except over the eyes, and the body changed in color to a mottled reddish-brown. In every way the specimen, preserved, resembled the other specimens described in the literature or in the possession of the author.
A few remarks on the ocellus of this species seems pertinent. Adam, Rees and Pickford variously described the ocellus of the specimens examined by them as consisting of a somewhat circu lar patch of brown or dark slate gray separated from a dark reddish-brown, brown, or gray center by a thin pale, black, or dark ring. Voss (1949) described the ocellus of the only other known Florida specimen as "a grayish-black ring surrounding a dark gray disc." These descriptions are extremely confusing and, in the light of examinations, made by the author of about ten specimens from the Bahamas and Florida, are erroneous.
Actually the ocellus consists of a reddish-brown irregular splotch within which is a narrow to broad band forming a more or less circular ring which both in life and in freshly preserved
animals is colored a most intense purplish-blue. In life this
may fluctuate from a pale blue to the deep color mentioned, apparently at the will of the animal. Specimens more than two years in preservative still retain this color. Any assumptions as to the use or value of this organ is dangerous, but the author cannot but point out that in an animal with such a high degree of mimicry it may well function as a means of recognition.
References
Adam, W. 1936. Notes sur les cephalopodes. VI. TJne nouvelle espece d 'octopus (Octopus hummelincki) des Indies Orientales
Neerlan daises. Bull. Mus. R. Hist. Nat. Belgique, 12: 1-3. 1937. Cephalopodes des lies Bonaire et Curacao.
Capita Zoologica, 8: 1-29. Rees, W. J. 1950. Notes on Cephalopoda from the Caribbean.
Proe. Malacolog. Soc. London, 28 (2, 3) : 9-114.
PiCKFORD, G. E. 1945. Le poulpe americain : A study of the littoral Octopoda of the western Atlantic. Trans. Conn. Acad. Arts Sci., 36: 701-811.
1946. A review of the littoral Octopoda from central and western Atlantic stations in the collections of the British Museum. Ann. Mag. Nat. Hist. (11), 13: 412-429.
1950. The Octopoda of the Oxford University Cayman Expedition. Proc. Malacolog. Soc. London, 28 (4, 5) : 139- 144.
Voss, G. L. 1949. Notes on a specimen of Octopus hummelincki Adam from the Florida Keys. Rev. Soc. Malacologica,