The ultrastructure of chondrocytes in the cartilage of Sepia officinalis and Octopus vulgaris (Mollusca, Cephalopoda)

Thin sections of cartilage from the chondrocranium of cuttle fish and octopus were examined using the transmission electron microscope. It was found that cephalopod chondrocytes differed considerably from the chondrocytes of vertebrate cartilage; in particular they possessed many long and ramifying cytoplasmic processes and had an ultrastructure typical of protein-secreting cells. They did not, however, contain secretory granules; while vesicles and rough endoplasmic reticulum cisternae seemed to open directly to the cell surface. The cell body and processes contained cytoskeletal structures: microtubules were easily recognized, but intermediate and thin filaments were difficult to make out as they were frequently clumped into bundles. Some chondrocytes contained conspicuous accumulations of hemocyanin. The cytoplasmic processes possessed intercellular contacts similar to gap junctions. Also present on processes and the cell body were cell-extracellular matrix focal adhesions. The chondrocytes were not polarized or arranged in any preferential spatial order, however, with their processes they formed a three-dimensional network throughout the cartilage tissue. Ultrastructural findings are discussed in relation to the singular morphofunctional characteristics of cephalopod cartilage which shares features with both the cartilage and bone of vertebrates.     

Drilling by Octopus vulgaris(Mollusca: Cephalopoda) in the Mediterranean

Octopus vulgaris drills holes in the shells of a variety of molluscs. The walls of the cavities drilled exhibit dissolution of mineral and organic material. The features which characterize the cavities have been described. The composition and structure of the shell itself is important in determining the size, shape and form of the cavity drilled, and not the size of the octopus. Capture, drilling the shell, and eating the occupant may take less than one hour.     

Foraging, feeding and prey remains in middens of juvenile Octopus vulgaris (Mollusca: Cephalopoda)

Juvenile Octopus vulgaris foraged by chemotactile exploration, mainly in crevices and under rocks. They caught small crustaceans and molluscs, including Lima bivalves, and preferred crabs and Lima in a simple laboratory choice test. Octopuses consumed 30% of their prey away from home, and small remains of prey deposited in the midden were selectively removed by waves and currents resulting in an underestimate of the octopus' intake and diet.     

Digestive absorption in Octopus vulgaris (Cephalopoda: Octopoda)

In Octopus , the caecum, the pancreas and the liver are involved in the absorption of ³H-glycine-labelled food. The caecum exhibits the highest specific activity while the liver absorbs the largest proportion of labelled material. The administration of stained food shows in vivo alternating phases of absorption and secretion in the liver and continuous absorption in the caecum.     

A new dicyemid from Octopus hubbsorum (Mollusca:Cephalopoda:Octopoda)

A new species of dicyemid mesozoan is described from Octopus hubbsorum Berry, 1953, collected in the south of Bahia de La Paz, Baja California Sur, México. Dicyema guaycurense n. sp. is a medium-size species that reaches about 1,600 μm in length. It occurs in folds of the renal appendages. The vermiform stages are characterized as having 22 peripheral cells, a conical calotte, and an axial cell that extends to the base of the propolar cells. Infusoriform embryos consist of 39 cells; 1 nucleus is present in each urn cell and the refringent bodies are solid. This is the first of a dicyemid species from a host collected in the Gulf of California.     

A physiologically discrete population of chromatophres in Octopus vulgaris (Mollusca)

Specimens of Octopus vulgaris (Cuvier) immersed in cold sea-water (4°C) exhibit a flashing display of brown chromatophores that we call "brown spots". The spots, which flashed approximately once every three seconds, are distributed over the dorsal skin of the head, mantle and arms and correspond mainly with the distribution of the white spots and white streaks previously described, and appear to act as a screen for the patches composing the white spots. Flashing brown spots could be evoked in animals with the supraoesophageal brain removed but not in animals with local denervation of the skin.
The precise site of action of the cold is unknown but it is proposed that the nerves supplying the brown spot units are normally tonically inhibited and that the cooling process removes this inhibition and allows the spots to flash. They are particularly useful for the in vivo study of the control of chromatophores because they can be reliably activated and isolated from responses of other chromatophores.     

Crab and mollusc shell drilling by Octopus vulgaris (Mollusca: Cephalopoda) in the Ria de Vigo (north-west Spain)

Octopus vulgaris living in the Ria de Vigo, north-west Spain, sometimes drills a cavity in the carapace of crabs and shells of molluscs. These holes have features with the same characteristics as those made in molluscs by O. vulgaris and in crabs by Eledone cirrhosa when isolated in aquaria. This is the first report of drilling the carapace of crabs by Octopus vulgaris .     

'Home' choice and modification by juvenile Octopus vulgaris (Mollusca: Cephalopoda): specialized intelligence and tool use?

Analysis of 'homes' occupied by juvenile Octopus vulgaris shows flexible behaviour which may indicate specialized intelligence and tool use. Octopuses occupied sheltered areas for a short time, average 10 days, but stayed longer in larger homes and in areas where preferred prey was available. They did not simply respond to perceptual characteristics of a site, but instead chose locations potentially suitable and modified them by removing rocks and sand and bringing in items partially to block the aperture.     

Larval nematodes (Spiruroidea: Cystidicolidae) in Octopus vulgaris (Mollusca: Cephalopoda: Octopodidae) from the northeastern Atlantic Ocean.

Larval nematode parasites (Spiruroidea: Cystidicolidae) are recorded for the first time in Octopus vulgaris Cuvier, 1797 in the northeastern Atlantic Ocean. Prevalence was 16% and mean intensity was 1.46 worms/host. Body length of larval nematodes ranges from 8.3 to 9.3 mm, with a distance from the anterior end to nerve ring from 187.5 to 200 microm, and to excretory pore 194.6-350 microm. Anatomical characteristics, such as deirid, nerve ring, cephalic alae, excretory pore, pseudolabia amphids, sclerotized protuberance, and anus, examined using light microscopy (LM) or scanning electron microscopy (SEM), are illustrated. The nematode was designed as a cystidicolid "Type A" larva. The hemocytic infiltration present in the host tissue around the nematode capsule and the mechanical compression in the infected organs denote the pathogenicity of this nematode. In the study area, O. vulgaris may play the role of an intermediate or paratenic host in the nematode life cycle.     

Three new dicyemids from Octopus sasakii (Mollusca: Cephalopoda: Octopoda)

Three new species of dicyemid mesozoan are described from Octopus sasakii Taki, 1942, collected from Tosa Bay and Kii Strait in Japan. Dicyema shimantoense n. sp. is a medium-size species that reaches about 3,000 microm in length, and lives in folds of the renal appendages. The vermiform stages are characterized by having 22 peripheral cells, a conical calotte, and an axial cell that extends to the base of the propolar cells. Infusoriform embryos consist of 37 cells; a single nucleus is present in each urn cell, and the refringent bodies are solid. Dicyema codonocephalum n. sp. is also a medium-size species that reaches about 2,000 microm in length. It too lives in folds of the renal appendages. The vermiform stages are characterized by having 17-22 peripheral cells, an elongated calotte, and an axial cell that extends to the middle of propolar cells. Infusoriform embryos consist of 37 cells; a single nucleus is present in each urn cell, and the refringent bodies are solid. Dicyemennea pileum n. sp. is a medium species that reaches about 2,000 microm in length. It attaches to the surface of the renal appendages. The vermiform stages are characterized by having 23 peripheral cells, a disc-shaped calotte, and an axial cell that extends to the propolar cells. An anterior abortive axial cell is absent in vermiform embryos. Infusoriform embryos consist of 38 cells; 2 nuclei are present in each urn cell, and the refringent bodies are liquid. These are the first dicyemids to be described from Octopus sasakii.     

Oxygen consumption and ammonia excretion rates in Octopus maya,loligo forbesi and Lolliguncula brevis (Mollusca: Cephalopoda)

Oxygen consumption and ammonia excretion rates were investigated in young Octopus maya (hatching to 139 days old; 0.11–81.23 g wet body weight, BW; 22.5–23.9°C), young squids of Loligo forbesi (hatching to 45 days old; 9.4–115.3 mg BW; 12.3–13.1°C) and young squids of Lolliguncula brevis (2.00–39.98 g BW; 23.8–24.7°C). Except at hatching, oxygen consumption and ammonia excretion rates on an individual basis (M) of these three cephalopods increased linearly with increasing body weight (BW) expressed as M = aBW^b . Values of b for oxygen consumption were 0.900, 0.910 and 0.848 and for ammonia excretion were 0.744, 0.809 and 0.751 for O. maya, L. forbesi and L. brevis, respectively. Among the three species the value a varied widely, while b was similar for both oxygen consumption and ammonia excretion rates. Based upon these data, metabolism for hatchlings of O. maya and L. forbesi was estimated to be relatively lower than that of older juveniles. The O/N ratios for hatchlings of O. maya and L. forbesi were relatively high and indicate an apparent dependence upon lipids in the immediate post‐hatching period, followed by standard protein energy utilization thereafter.     

A new look at geographic and phylogenetic relationships within the species group surrounding Octopus vulgaris (Mollusca, Cephalopoda): indications of very wide distribution from mitochondrial DNA sequences

The distribution of Octopus vulgaris has not yet been completely clarified. For a long time, a cosmopolitan distribution with unknown distribution limits had been assumed. This assumption has recently been questioned and it has been postulated that the distribution is restricted to the Mediterranean and the northeastern Atlantic. However, as our previous studies show, the existence of O. vulgaris can be confirmed for the Mediterranean and the whole eastern Atlantic, and evidence is provided for its occurrence in the western Atlantic. The aim of the present work is to extend our previous data matrix and to clarify whether O. vulgaris exists in the northwestern Pacific. Therefore, the sequence variation in ostensible O. vulgaris from 13 localities in the Mediterranean (France), the Atlantic Ocean [Lanzarote, Senegal, South Africa (Atlantic, Indian Ocean), Tristan da Cunha, north, middle and south Brazil], the Caribbean Sea (Venezuela) and the Pacific Ocean (Taiwan, Japan and Costa Rica) was examined using the mitochondrial genes coding for the 16S rRNA and cytochrome oxidase subunit III (COIII). Sequence divergence was relatively low between populations of O. vulgaris from the Mediterranean, the eastern and western Atlantic (except north Brazil), Venezuela, Taiwan and Japan compared with other species of the genus Octopus . Trees constructed by using maximum likelihood, neighbour joining and maximum parsimony algorithms (PAUP) show the above-mentioned populations from the Mediterranean, the western and eastern Atlantic, Venezuela and the northwestern Pacific (Japan and Taiwan) as a monophyletic cluster. Thus, even if the Octopus vulgaris -like octopus from north Brazil should turn out a cryptic species, the data of this work not only support our hypothesis of the distribution of O. vulgaris in the Mediterranean, the eastern and western Atlantic but also show that O. vulgaris is present in the northwestern Pacific, namely in the waters of Taiwan and Japan.     

A comparative ultrastructural investigation of the cephalic sensory organs in Opisthobranchia (Mollusca, Gastropoda)

Cephalic sensory organs (CSOs) are specialised structures in the head region of adult Opisthobranchia involved in perception of different stimuli. The gross morphology of these organs differs considerably among taxa. The current study aims at describing the cellular morphology of the CSOs in order to reveal cellular patterns, especially of sensory epithelia, common for opisthobranchs. Transmission electron microscopy was used to characterise the fine structure of the organs and to compare the CSOs of four different opisthobranch species. The cellular composition of the sensory system is conserved among taxa. The epidermal cells in sensory regions are always columnar and ciliated cells are frequently apparent. The sensory cells are primary receptors arranged in subepidermal cell clusters. They extend dendrites which penetrate the epithelium and reach the surface. Some of the dendrites bear cilia, whereas others only build a small protuberance. Processing of sensory information takes place in the peripheral glomeruli of all species. Moreover, few taxa possess additional peripheral ganglia at the base of their CSOs. The results of the present study might support other investigations indicating that the posterior CSOs are primarily involved in distance chemoreception, whereas the anterior CSOs might be used for contact chemoreception and mechanoreception.     

The stalked eyes of Bathothauma (Mollusca, Cephalopoda)

In the larvae of some cranchiid squids the eyes are carried sideways on long stalks and also possess a presumed luminous organ. The structure of this organ is described but the only sign of light producing tissues is some possible luminescent bacteria. The stalked eye may be connected with plankton feeding at great depths, perhaps improving distance judgement. The older animals of these species carry a different form of luminous organ.     

Growth of Octopus maya (Mollusca: Cephalopoda) of the Yucatan coast, Mexico: a long-term analysis]

Growth of the octopus (Octopus maya) off Yucatan (Mexico) was estimated from a long-term study (seven years) by the length-based methods ELEFAN, PROJMAT and SLCA. Some 19,251 octopuses with a range of mantle length between 50 and 240 mm were sampled from commercial landings in 1983-1987, 1989 and 1992. The jackknife technique was applied to deal with uncertainty in growth estimates resulting from chance variations in sampling design. The growth index phi' was used for comparative purposes. Results differed markedly among methods: ELEFAN produced parameter estimates within the range reported in the literature, whereas PROJMAT and SLCA showed problems to converge in an optimum combination of parameters, and tended to underestimate them. Jackknife analysis revealed very low intraannual variability in phi' but high variability among years, especially when applying PROJMAT. No significant differences were found in precision parameters--percent error and coefficient of variation--among methods. Estimates of phi' derived by ELEFAN varied between 4.19 and 5.23 and agreed with those reported in the literature (between 4.25 and 4.91), whereas PROJMAT and SLCA estimates were significantly lower. We suggest the use of ELEFAN, together with jackknife, to estimate growth parameters of Octopus maya.     

Extraintestinal gamogony of Aggregata octopiana in the reared common octopus (Octopus vulgaris) (Cephalopoda: Octopodidae)

Aggregata octopiana (Apicomplexa, Aggregatidae) is the most prevalent coccidian in the wild common octopus (Octopus vulgaris), whose heteroxenous life cycle includes gamogony and sporogony undergoing in the octopus digestive tract. In the infected reared octopi, we observed an unusual extraintestinal distribution of the coccidian, with both gamogony and sporogony ongoing in dermal and gill tissue. Oocysts and macrogamonts were embedded in the dermal connective tissue of octopian arms, demarcated by a thin cyst wall or multilayered dark membrane. In gill connective and epithelial tissue all developmental stages were observed, eliciting hemocytic infiltration. Sometimes a complete substitution of the tissue by cysts and developmental stages occurred, resulting in necrosis of gill tissue.     

Octopus joubini (Mollusca: Cephalopoda): a detailed study of growth through the full life cycle in a closed seawater system

Twenty individual pygmy octopuses, Octopus joubini , were reared at 25°C from hatching to maturity on a quantified diet of live crabs in closed (recirculating) natural seawater systems. At 24 week intervals the animals were narcotized, weighed and measured. There was 85% survival to sexual maturity.
Growth rates were highest during the first four weeks of exponential growth. Beyond four weeks, growth rates steadily declined and growth became logarithmic in form. Female octopuses grew slightly faster than males and attained a larger size at maturity. The length-weight relationship showed male Octopus joubini to weigh more than females at a given mantle length. This species displays slight allometric growth resulting in changing body proportions through the life cycle. Relative food intake is highest at hatching and decreases with age. Mean gross growth efficiency over the life span was approximately 40%.