Brooding in a Bathypelagic Octopusl RICHARD EDWARD YOUNG2 ABSTRACT: A mature female and 12 larvae of the octopus Bolitaena microcotyla were captured at bathypelagic depths off Hawaii. The female appears to have been brooding the larvae in a large chamber formed by the oral arms and web. This finding supports the likelihood that the brooding habit is universal in pelagic incir­ rate octopods. VERY LITTLE IS KNOWN about the reproductive usual position. They arch forward and converge habits of oceanic cephalopods, particularly those near their tips. All of the arms except the two inhabiting the deep sea. Recently a specimen of ventral ones are connected by a deep web which the poorly known octopus Bolitaena microcotyla is characteristic of this species. The web is Hoyle, 1886, was captured off Oahu, Hawaii. longest between the dorsal arms where it reaches The specimen was taken at depths between 830 about 60 percent of the arm length, becomes and 975 m in an opening-closing mid-water progressively shorter between arms I and II, trawl (modified Tucker Trawl). Off Hawaii arms II and III, and arms III and IV although these depths lie within the bathypelagic zone. still extending to about 40 percent of the arm Examination of the specimen revealed that it length in the latter. The web is almost com­ was a brooding female. pletely lacking between the ventral arms. The arms and web, therefore, form a capacious pouch which, very likely, held the larvae (Fig. 1A). DESCRIPTION Unfortunately all of the young had been dis- In formalin, the small female specimen has a lodged by the time the specimen was examined lateral mantle length of 30 to 35 mm and a total and no remnants of egg capsules, stalks, or any of about 75 mm. Although fragile-it has the special modifications for egg attachment were consistency of a jellyfish-it was only slightly found. damaged in the trawl. A number of larval octo- The buccal mass, which lies at the posterior pods were fortuitously attached to the head and end of this pouch is entirely sealed except for a body of the adult by radiolarian skeletons. minute central pore. This closure is not formed Nearly all of the fragile deep-living octopods by the fusion of the lips that surround the buccal that have come to my attention have had radio- mass; rather, it is the integument of the oral larians stuck to their bodies as a result of con- surface of the buccal crown that extends over the tact within the trawl. The larval octopods are lips and buccal mass. Careful examination ini­ equally susceptible to empalement by radiolar- tially failed to reveal the presence of any open­ ians, and it was by this means that they were ing. Only when the overlying integument was attached to the surface of the adult specimen. being dissected, did pressure by the scissors -'-A~.----.tolaLoLlLlar.Yae--.ReRLecjL"-eftd~~.duding,--=-f~or::.'c:.:-e---a te~fl",oc,":,cu=le..,.nc"t ___ ...s-.-m-:oa=-I---1 a_:om.:.-o:.:_u...n:.:-t of w...h...i... m=at"e",n...·a",I 1 a few that were found in the bottom of the through the integument, indicating the presence specimen jar; all were at the same stage of de- of a minute pore. Although it was still impos­ velopment. sible to see the pore, a short canal was detected The arms of the female are in a rather un- leading from a cavity around the lips and beaks to the area where the pore was presumed to be. 1 This work was supported by National Science The presence of this canal suggests that a pore Foundation Grant GB 20993. Manuscript received and not a rupture allowed the material to es­ 10 May 1972. cape. The flocculent material consisted of a 2 Department of Oceanography, University of Ha­ waii, Honolulu, Hawaii 96822. cellular debris heavily infested with several 400 Brooding in a Bathypelagic Octopus-YOUNG 401 A St. B Cae. c Br. H.--+--~~"" Hep. Int. FIG. 1. A, lateral view of Bolitaena microcotyla. Dashed line indicates extent of brood chamber; B, larva of B. microcotyla; C, mature egg from ovary. SYMBOLS: Br. H., branchial heart; Cae., caecum; Cr., crop; Es., esophagus; Fu. 0., funnel organ; G., gill; Hep., hepatopancreas; Int., intestine; Int. Y. S., internal yolk sac; M., mantle; Op. L., optic lobe; P. Sal. Gl., posterior salivary gland; St., stomach; Stat., statocyst; Ste. G., stellate ganglion; Subes. M., subesophageal mass of brain; Sue., suckers. types of ciliate protozoans. This same material The larvae measured 2 mm in lateral mantle could be squeezed from the buccal mass, and length (Fig. 1 B). The eight stubby arms each similar debris including the ciliates was found carry four large suckers. The distal two suckers --in-the-stoma'chohneOLtopus. frequently he on opposite sides of the arm, ap­ The ovary is depleted except for a single large parently due to crowding. The eyes are large, egg and a residue of deteriorating ovarian tis­ elliptical in outline, and directed forward. A sue. The egg is ovate, 2 by 1.5 mm, and pos­ thin layer of iridophores lies on the surface of sesses a short stalk (Fig. Ie). The digestive each eye. The mantle is thick and gelatinous. tract apparently is in a state of degeneration. The Large reddish brown chromatophores are scat­ crop is collapsed and the stomach is contracted tered over the surfaces of the mantle, head, and infested with ciliates. The hepatopancreas is arms, and dorsal surface of the visceral mass. very small and the posterior salivary glands are The larva has the same general appearance as small and flaccid. the adult, except that it has relatively shorter 402 PACIFIC SCIENCE, Volume 26, October 1972 arms and larger eyes that face anteriorly. The generally are regarded as benthic animals but largest portion of the viscera consists of the six of the nine families are wholly pelagic. (The internal yolk sac which suggests that the young vast majority of species, however, occurs in the octopods had only recently hatched from the benthic family Octopodidae.) The pelagic in­ egg capsules. In several larvae an elongate pel­ cirrate octopods are probably derived from let was found in the digestive tract at the junc­ benthic ancestors since their general morphology ture between the esophagus and crop. The pel­ retains many of the benthic adaptations found let is composed of a mass of droplets of varying in their bottom-living relatives. The pelagic sizes, presumably yolk. realm has been invaded by octopods on more than one occasion during their history. A great number of species of octopods lay small eggs CONCLUSIONS which produce small larvae that spend con- The evidence, summarized below, clearly in- siderable periods in the plankton. These larvae dicates that this specimen of Bolitaena micro- generally are similar to juveniles or subadults cotyla was brooding larvae at the time of cap- except for their relative body proportions, and ture. they may reach considerable size while in the 1. Twelve recently hatched larvae are associated plankton. A mantle length of 25 mm and an with a female octopus. arm spread of over 100 mm was recorded for a 2. The arms and web form a large chamber pelagic larva taken off California (Young, in suitable as a brood pouch. press). This larva is larger than the adults of 3. The mouth is almost completely sealed and, some benthic octopods (Robson, 1929:1) . apparently, incapable of ingesting food Seemingly the transition to a wholly pelagic particles. existence by an octopus with an extended larval 4. The digestive tract appears degenerate and stage would not be great, although a number nonfunctional. of modifications would be required. One of 5. The deteriorated and depleted condition of these concerns the reproductive habits. the ovary indicates that the octopus had As far as is known, all shallow water benthic spawned. octopods attach their eggs to some solid sub­ strate, usually rocks, coral, or shells. After de- Shallow water octopods feed rarely or not at positing the eggs, the female broods them until all while brooding their embryos (Nixon, hatching. The brooding process apparently as­ 1969). Therefore the apparent cessation of sures (among other things) that the eggs are feeding in this animal is not unexpected. Feed- properly ventilated. Pelagic incirrate octopods, ing, seemingly, would be incompatible with as far as is known, have not adopted what might oral brooding. Since the web between the ventral seem to be the simplest solution to this problem, arms is almost totally lacking, the funnel, pre- i.e., abandonment of the brooding habit and the sumably, could extend into this gape or, at least, production of free-floating eggs or egg masses. reach between the ventral arms when the oral Rather, they have retained the brooding habit, crown is flexed ventrally. In either case insertion which has necessitated considerable adaptation. of the funnel into the brood chamber would There are three families of octopods which ____provide a means of depositing~Dgs,,----,ac:::n,,-,d,,----,o:c:f,-_a_r,e.-e~p~ipLe:-.l~ag,;-ic:Argonautidae, Tremoctopodidae, directing water currents over the embryos. and Ocythoiaae. (A fourtnfamJ1y,theA:n'-:cop=o=---~ sidae, has been reported many times in the near­ DISCUSSION surface plankton, but species in this family are also found associated with the bottom [Thore, The order Octopoda consists of two sub­ 1949]. Their habits are not clearly under­ orders: the Cirrata, the finned octopods, whose stood.) Female members of the monotypic members are benthic, benthopelagic, or pelagic genus Argonattta form delicate shells through (Roper and Brundage, in press); and the In­ secretions of the dorsal arms.