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Aspects of the functional morphology of cirrate octopods: Locomotion and feeding
Abstract
Cirrate octopods swim by a combination of fin action and medusoid propulsion by the arm/web complex. The fins of cirrate octopods are associated with a unique cartilage-like shell in a shell sac. In cross-section, the fins have distinct proximal and distal regions, both of which are covered by a thin surface sheath of muscle. The distal region is characterized by dorsal and ventral layers of muscle somewhat similar to a typical decapod fin. In the proximal region, the fin cartilage forms a flat central core within the fin and provides skeletal support for attachment of densely packed muscle. Whereas Stauroteuthis maneuvers slowly by sculling with the fins, Grimpoteuthis swims primarily using powerful fin strokes. In Stauroteuthis, the mantle is extensively modified. The mantle opening closely surrounds the funnel, and the posterior mantle muscle is thickened and probably controls water flow for respiration. The "secondary web" in some cirrate species results from a modification of the way the web muscles attach to the arms. The more benthic opisthoteuthids lack this modification. The secondary web enables larger volumes of water to be trapped in the web in some postures. The entrapment of water resulting in a bell-shaped posture in Stauroteuthis could be related to predator defense or to feeding. Buccal secretory glands found in Stauroteuthis and the presence of small copepods in the digestive tract, suggest that this benthopelagic species feeds by entrapping planktonic prey in mucus.
... Cirrate octopods are easily recognized by a pair of fins on the body, resembling the ears of the flying elephant in Dumbo, the Disney movie of 1941, which has resulted in the name 'dumbo' or 'jumbo' octopus being commonly used for some cirrate taxa [3]. The limited stomach contents data of cirrate octopods report a diet of predominantly Crustacea and Polychaeta, and occasional records of Gastropoda, Bivalvia, Cephalopoda and Osteichthyes [3,[22][23][24][25]. The only observations of confirmed feeding behaviour in cirrates are based on a single female of Opisthoteuthis sp. that was kept in an aquarium for 53 days [3,26]. ...
... Compared to Opisthoteuthis, the cirri of Cirroteuthis are relatively long and with reduced musculature [3,22,23]. The cirri may be used to scan the seafloor for prey during feeding sequences and also help manipulating the entrapped prey towards the oral cavity as in other cirrates [24]. External glands around the lips [22] may facilitate capture or transport of food and explain the release of mucus as observed in this study, and in other cirrates [24]. ...
... The cirri may be used to scan the seafloor for prey during feeding sequences and also help manipulating the entrapped prey towards the oral cavity as in other cirrates [24]. External glands around the lips [22] may facilitate capture or transport of food and explain the release of mucus as observed in this study, and in other cirrates [24]. ...
Deep-sea cephalopods are diverse, abundant, and poorly understood. The Cirrata are gelatinous finned octopods and among the deepest-living cephalopods ever recorded. Their natural feeding behaviour remains undocumented. During deep-sea surveys in the Arctic, we observed Cirroteuthis muelleri. Octopods were encountered with their web spread wide, motionless and drifting in the water column 500-2600 m from the seafloor. Individuals of C. muelleri were also repeatedly observed on the seafloor where they exhibited a repeated, behavioural sequence interpreted as feeding. The sequence (11-21 s) consisted of arm web spreading, enveloping and retreating. Prey capture happened during the enveloping phase and lasted 5-49 s. Numerous traces of feeding activity were also observed on the seafloor. The utilization of the water column for drifting and the deep seafloor for feeding is a novel migration behaviour for cephalopods, but known from gelatinous fishes and holothurians. By benthic feeding, the octopods benefit from the enhanced nutrient availability on the seafloor. Drifting in the water column may be an energetically efficient way of transportation while simultaneously avoiding seafloor-associated predators. In situ observations are indispensable to discover the behaviour of abundant megafauna, and the energetic coupling between the pelagic and benthic deep sea.
... Stauroteuthis syrtensis Verrill (1879) and Cirroteuthis muelleri Eschricht (1836) are the best-known representatives of their respective families. S. syrtensis has been redescribed (Collins and Henriques, 2000), collected in trawl catches, observed by submersibles a few times (Vecchione and Young, 1997;Johnsen et al., 1999a,b;Collins et al., 2001b;Collins, 2002;Vecchione and Pohle, 2002;Jacoby et al., 2009;Vecchione et al., 2010;Shea et al., 2017;Richards and Vecchione, 2020), and stomach contents analyzed in several individuals (Vecchione and Young, 1997;Jacoby et al., 2009). C. muelleri was described in detail by Reinhardt and Prosch (1846), translated into English in Knudsen and Roeveld (2002), and revised later by Voss and Pearcy (1990). ...
... Stauroteuthis syrtensis Verrill (1879) and Cirroteuthis muelleri Eschricht (1836) are the best-known representatives of their respective families. S. syrtensis has been redescribed (Collins and Henriques, 2000), collected in trawl catches, observed by submersibles a few times (Vecchione and Young, 1997;Johnsen et al., 1999a,b;Collins et al., 2001b;Collins, 2002;Vecchione and Pohle, 2002;Jacoby et al., 2009;Vecchione et al., 2010;Shea et al., 2017;Richards and Vecchione, 2020), and stomach contents analyzed in several individuals (Vecchione and Young, 1997;Jacoby et al., 2009). C. muelleri was described in detail by Reinhardt and Prosch (1846), translated into English in Knudsen and Roeveld (2002), and revised later by Voss and Pearcy (1990). ...
... Reports on S. syrtensis are scarce and imply that it consumes copepods, including Calanus spp. (Vecchione and Young, 1997;Jacoby et al., 2009), and employs a hunting strategy trapping its prey in a mucous web produced by buccal secretory glands (Vecchione and Young, 1997). Jørgensen (unpublished; Institute of Marine Research, Tromsø, Norway) reports six individuals of C. muelleri from the Barents Sea, whose stomach contents included Mysidacea, Cumacea, Amphipoda, and Isopoda (Anisopoda). ...
Stauroteuthis syrtensis and Cirroteuthis muelleri were studied based on representative material collected in Greenland, Iceland, and the Barents Sea and adjacent deep-sea areas (96 stations and 165 individuals for S. syrtensis, and 82 stations and 215 individuals for C. muelleri). The species occur on the border of the Arctic and the northern North Atlantic; S. syrtensis is a southern species and C. muelleri is a northern species, in the area from the Denmark and Davis Straits and associated underwater ridges. These species were demonstrated to be ecological analogues since they: a) occupy the same depths; b) reach the same abundance density; c) reach virtually the same biomass density when corrected for size differences; and d) their food spectra largely coincide. Temperature, not depth, is a principal factor that prevents these species from crossing the border between the Arctic and the northern North Atlantic, with mean habitat temperatures of 3.5 ± 0.06 °C for S. syrtensis and 0.3 ± 0.06 °C for C. muelleri. This study provides unprecedented density estimates for the North Atlantic and Arctic Cirrata: the highest in the world ocean in terms of biomass and second highest in terms of numerical abundance. Food spectra of the studied species consist of Calanoida (including eurybathic Paraeucheta spp. and Calanus spp., and deep-sea Bradyidius similis), Mysidacea and Isopoda (including deep-sea Eurycopinae) (Crustacea), and in C. muelleri also Cumacea, Amphipoda (Crustacea) and Polychaeta (Polynoidae). Additionally, this study: a) provides specific growth and morphometric equations; b) provides equations to estimate mantle length (ML) and body mass (BM) from beak measurements, and BM of fresh individuals (for modelling purposes or predators diet analyses) from BM of fixed individuals; c) reports maximum sizes for C. muelleri (ML 170 mm, total length 400 mm, BM 781.0 g); and d) reports findings of rarely encountered juvenile cirrates.
... nov. and Pearceiteuthis buyi (Fig. 6) and the enormous space of the lateral fields in relation to the reduced state of the median field even provides evidence that patelloctopodids were capable of performing powerful fin strokes similar to living Vampyroteuthis (Seibel et al. 1998) and cirrates Cirroteuthis and Grimpoteuthis (Vecchione and Young 1997;Villanueva et al. 1997). Mesozoic records of fin cartilage in gladius-bearing octobrachians as well as palaeoctopodids (see Donovan and Fuchs 2015) strongly suggest that the fins of patelloctopodids were likewise supported by fin cartilage. ...
... Mesozoic records of fin cartilage in gladius-bearing octobrachians as well as palaeoctopodids (see Donovan and Fuchs 2015) strongly suggest that the fins of patelloctopodids were likewise supported by fin cartilage. Mantle jetting in cirrates (and incirrates) is ineffective compared to gladius-bearing forms (Vecchione and Young 1997). Instead, cirrates move by means of fin contractions and/or medusoid propulsion with the arm/web complex, a mode of locomotion that is also conceivable for Patelloctopus and Pearceiteuthis. ...
Limpet-like and non-mineralized fossils from the upper Kimmeridgian Nusplingen Plattenkalk are identified as internal
shells of coleoid cephalopods, more specifically as octobrachian gladii. The significantly reduced median field provokes
us to consider this new gladius type to be shorter than the mantle length. It is consequently seen as a vestigial gladius. The
first recognition of an unpaired gladius vestige in the fossil record sheds new light on the evolutionary history of the gladius
vestiges of incirrate and cirrate Octopoda. Patelloctopus ilgi sp. nov. is most similar to Callovian Pearceiteuthis buyi in
having a rudimentary median field with an extraordinary large opening angle and radiating ribs on the lateral fields. Both P.
ilgi sp. nov. and P. buyi are therefore combined in the new family Patelloctopodidae. The patella-shaped lateral fields of the
gladius vestige exposes Patelloctopus and Pearceiteuthis as members of the superfamily Muensterelloidea, which includes,
apart from Patelloctopodidae, the Muensterellidae and Enchoteuthidae. The unpaired patelloctopodid gladius vestige is
morphologically intermediate between the muensterelloid gladius type and the paired (bipartite) gladius vestige of Late
Cretaceous Palaeoctopodidae (Palaeoctopus, Keuppia). The gladius vestige morphology suggests that the mode of locomotion
and the life style of these shallow water inhabitants were similar to those of extant deep-sea octopods (Cirrata) and that
the Patelloctopodidae represents the stem group of the Octopoda (Cirrata and Incirrata), although Patelloctopus ilgi sp. nov.
might alternatively be a stem incirrate.
... nov. and Pearceiteuthis buyi (Fig. 6) and the enormous space of the lateral ields in relation to the reduced state of the median ield even provides evidence that patelloctopodids were capable of performing powerful in strokes similar to living Vampyroteuthis (Seibel et al. 1998) and cirrates Cirroteuthis and Grimpoteuthis (Vecchione and Young 1997;Villanueva et al. 1997). Mesozoic records of in cartilage in gladius-bearing octobrachians as well as palaeoctopodids (see Donovan and Fuchs 2015) strongly suggest that the ins of patelloctopodids were likewise supported by in cartilage. ...
... Mesozoic records of in cartilage in gladius-bearing octobrachians as well as palaeoctopodids (see Donovan and Fuchs 2015) strongly suggest that the ins of patelloctopodids were likewise supported by in cartilage. Mantle jetting in cirrates (and incirrates) is inefective compared to gladius-bearing forms (Vecchione and Young 1997). Instead, cirrates move by means of in contractions and/or medusoid propulsion with the arm/web complex, a mode of locomotion that is also conceivable for Patelloctopus and Pearceiteuthis. ...
Limpet-like and non-mineralized fossils from the upper Kimmeridgian Nusplingen Plattenkalk are identified as internal shells of coleoid cephalopods, more specifically as octobrachian gladii. The significantly reduced median field provokes us to consider this new gladius type to be shorter than the mantle length. It is consequently seen as a vestigial gladius. The first recognition of an unpaired gladius vestige in the fossil record sheds new light on the evolutionary history of the gladius vestiges of incirrate and cirrate Octopoda. Patelloctopus ilgi sp. nov. is most similar to Callovian Pearceiteuthis buyi in having a rudimentary median field with an extraordinary large opening angle and radiating ribs on the lateral fields. Both P. ilgi sp. nov. and P. buyi are therefore combined in the new family Patelloctopodidae. The patella-shaped lateral fields of the gladius vestige exposes Patelloctopus and Pearceiteuthis as members of the superfamily Muensterelloidea, which includes, apart from Patelloctopodidae, the Muensterellidae and Enchoteuthidae. The unpaired patelloctopodid gladius vestige is morphologically intermediate between the muensterelloid gladius type and the paired (bipartite) gladius vestige of Late Cretaceous Palaeoctopodidae (Palaeoctopus, Keuppia). The gladius vestige morphology suggests that the mode of locomotion and the life style of these shallow water inhabitants were similar to those of extant deep-sea octopods (Cirrata) and that the Patelloctopodidae represents the stem group of the Octopoda (Cirrata and Incirrata), although Patelloctopus ilgi sp. nov. might alternatively be a stem incirrate.
... IX fig. 2;Vecchione and Young 1997). While Robson (1924bRobson ( , 1932 made no mention of them in S. gilchristi, according to Collins and Henriques (2000) both this species and S. syrtensis have four small glands (in two pairs). ...
New deep-sea finned octopods (Octopoda: Cirrata) in the genera Stauroteuthis and Cirrothauma (Cirroteuthidae) are reported from Australian waters. One new species of Stauroteuthis, S. kengrahami n. sp., is reported from southeastern Australia, a second, S. ? gilchristi from off Macquarie Island, and one specimen collected from off Heard Island is provisionally referred to Cirrothauma magna. A single female Luteuthis dentatus (Grimpoteuthididae) is also reported from Macquarie Island, and additional specimens of Grimpoteuthis greeni are reported from the Great Australian Bight. These new records and new species increase the diversity of Australian cirrate octopuses from six to 10 species, covering all recognised cirrate genera excepting Cryptoteuthis, and emphasise how much remains to be learned regarding Australia's deep-sea cephalopods.
... Such a feature can effectively increase the grasping reliability when gasping large object and living animal by preventing the animal from escaping from the gap between the arms and increasing the grasping friction force. [34,35] In this study, inspired by the predation behavior of the glowing sucker octopus (Stauroteuthis syrtensis), and benefited from 3D printing and casting technology, we developed a novel soft gripper with a similar geometric structure and grasping ability to the glowing sucker octopus (Stauroteuthis syrtensis). The gripper features excellent abilities to suck and grasp objects with any shapes (flat or nonflat) and dimensions, scattered multiple objects, living bodies, super-weight, and objects beyond the grasping range. ...
A soft gripper inspired by the glowing sucker octopus (Stauroteuthis syrtensis)' highly evolved grasping capability enabled by the umbrella-shaped dorsal and ventral membrane between each arm is presented here, comprising of a 3D-printed linkage mechanism used to actuate a modular mold silicone-casting soft suction disc to deform. The soft gripper grasp can lift objects using the suction generated by the pump in the soft disc. Moreover, the protruded funnel-shaped end of the deformed suctorial mouth can adapt to smooth and rough surfaces. Furthermore, when the gripper contacts the submerged target objects in a turbid environment, local suctorial mouth arrays on the suction disc are locked, causing the variable flow inside them, which can be detected as a tactile perception signal to the target objects instead of visual perception. Aided by the 3D-printed linkage mechanism, the soft gripper can grasp objects of different shapes and dimensions, including flat objects, objects beyond the grasping range, irregular objects, scattered objects, and a moving turtle. The results report the soft gripper's versatility and demonstrate the vast application potentials of self-adaptive grasping and sensing in various environments, including but are not limited to underwater, which is always a key challenge of grasping technology.
... Several external characters supporting that identification are visible in our frame grabs. These include (a) the large lobe-shaped fins in Fig. 3B, D, (b) single long web nodules in Fig. 3C, reminiscent of those in Cirroteuthis muelleri, and (c) possible narrow "secondary webs" (Vecchione and Young 1997) between the arms and the "primary webs". Cirroteuthids are known to swim far above the bottom, but they have been seen near bottom (Vecchione and Young 2016). ...
During a manned submersible dive in the Philippine Trench, a solitary oegopsid squid of the monogeneric family Magnapinnidae was observed swimming close to the seafloor at 6212 m. The estimated mantle length of the squid was ca. 10 cm. The long slender terminal arm and tentacle filaments characteristic of adult Magnapinna were not obvious in the video. The filaments may have been contracted or may not yet have developed. This observation is the first record of squid at hadal depths and extends the known bathymetric range for any squid by 1477 m; an increase of ca. 30%. We also observed four cirrate octopods between 6212 and 6224 m. Although the video quality was poor, these octopods did not appear to be the same species as those reported previously in the Java Trench. These observations extend the known hadal occurrence of cirrates, and cephalopods in general, from the Indian Ocean to the equatorial North Pacific Ocean, suggesting that their global presence in depths > 6000 m may be more extensive than previously recognized.
... Although cirrate octopods are usually found in depths greater than 300 m and dominate the benthic cephalopod fauna at depths greater than 1500 m , Collins & villanueva 2006, very little is known about their biogeography, biology and ecology. A few behavioural studies of cirrate octopods, using deep-water video cameras, have been undertaken (vecchione 1987(vecchione , vecchione & young 1997(vecchione , villanueva et al. 1997(vecchione , villanueva 2000(vecchione , Collins & villanueva 2006. They are apparently predated by certain marine mammal species (santos et al. 2001a,b). ...
Cephalopods play a significant role in coastal and oceanic ecosystems, both as consumers of invertebrates and small fish and as the prey of some fish, seabirds and marine mammals and other large predators. Approximately 30 species of cephalopod have been recorded in the north-eastern Atlantic and adjacent waters, including 18 teuthid (squid), seven sepiolid (bobtail), three sepiid (cuttlefish) and 10 octopod (octopus) species. A number of these are exploited commercially and support important target and by-catch fisheries in Western Europe. During the past decade, annual landings of cephalopods from the north-eastern Atlantic (International Council for the Exploration of the Sea [ICES] area) have ranged from 40,000 to 55,000 t, including substantial catches of long-fin (loliginid) squid (7000-11,000 t per annum), short-fin (ommastrephid) squid (3000-10,000 t), cuttlefish (including sepiolids; 16,000-24,000 t) and octopods (12,000-18,000 t). The most important exploited species in the north-eastern Atlantic are Eledone cirrhosa, Illex coindetii, Loligo forbesi, Loligo vulgaris, Octopus vulgaris, Todarodes sagittatus, Todaropsis eblanae and Sepia officinalis. Other species including Alloteuthis subulata, Gonatus fabricii and certain sepiolids, appear to be abundant and may be marketable. Cephalopods tend to rapidly concentrate heavy metals and other toxic substances in their tissues and this plays an important role in the bioaccumulation of these pollutants in marine predators as well as having implications for human consumption. High levels of cadmium and mercury are often recorded in cephalopod tissues. Another important environmental issue concerns the potential impact of widespread human activity on cephalopod spawning areas, particularly bottom-fishing operations but also shipping, and oil exploration and production. In contrast to many finfish species that spawn annually over a number of years, most cephalopods live only 1-2 yr and die after spawning. Therefore, failure to reproduce and recruit adequately in any given year may seriously impact the long-term viability of cephalopod stocks. Climate change is expected to have a significant effect on many species in the north-eastern Atlantic. This review provides a detailed account of the zoogeography, biology and ecology of cephalopods in the north-eastern Atlantic, on a species-by-species basis. Important economic, ecological and conservation issues affecting cephalopods in this area are also discussed.
... These typical deep-sea cephalopods with a gelatinous consistency and well-developed fins, spawn very large eggs suggesting direct developing juveniles [252]. However, the cirrate octopod family Cirroteuthidae (Cirrothauma, Cirroteuthis, Stauroteuthis) are essentially pelagic, but live generally close to the sea floor, and are characterized by very large fins and swimming behaviour [253][254][255]. The Cirroteuthidae morphology suggests a possible planktonic or benthopelagic mode of development for large hatchlings in the deep-sea, because very large fins were observed in advanced cirrate embryos of 9 mm ML [256]. ...
Cephalopods (nautiluses, cuttlefishes, squids and octopuses) exhibit direct development
and display two major developmental modes: planktonic and benthic. Planktonic hatchlings
are small and go through some degree of morphological changes during the planktonic
phase, which can last from days to months, with ocean currents enhancing their dispersal
capacity. Benthic hatchlings are usually large, miniature-like adults and have comparatively
reduced dispersal potential. We examined the relationship between early developmental
mode, hatchling size and species latitudinal distribution range of 110 species hatched in
the laboratory, which represent 13% of the total number of live cephalopod species
described to date. Results showed that species with planktonic hatchlings reach broader
distributional ranges in comparison with species with benthic hatchlings. In addition, squids
and octopods follow an inverse relationship between hatchling size and species latitudinal
distribution. In both groups, species with smaller hatchlings have broader latitudinal distribution
ranges. Thus, squid and octopod species with larger hatchlings have latitudinal distributions
of comparatively minor extension. This pattern also emerges when all species
are grouped by genus (n = 41), but was not detected for cuttlefishes, a group composed
mainly of species with large and benthic hatchlings. However, when hatchling size was
compared to adult size, it was observed that the smaller the hatchlings, the broader the latitudinal
distributional range of the species for cuttlefishes, squids and octopuses. This was
also valid for all cephalopod species with benthic hatchlings pooled together. Hatchling size
and associated developmental mode and dispersal potential seem to be main influential
factors in determining the distributional range of cephalopods.
Cephalopods play an important role in polar marine ecosystems. In this review, we compare the biodiversity, distribution and
trophic role of cephalopods in the Arctic and in the Antarctic. Thirty-two species have been reported from the Arctic, 62 if
the Pacific Subarctic is included, with only two species distributed across both these Arctic areas. In comparison, 54 species
are known from the Antarctic. These polar regions share 15 families and 13 genera of cephalopods, with the giant squid
Architeuthis dux the only species confirmed to occur in both the Arctic and Antarctic. Polar cephalopods prey on crustaceans,
fish, and other cephalopods (including cannibalism), whereas predators include fish, other cephalopods, seabirds, seals and
whales. In terms of differences between the cephalopod predators in the polar regions, more Antarctic seabird species feed on
cephalopods than Arctic seabirds species, whereas more Arctic mammal species feed on cephalopods than Antarctic mammal
species. Cephalopods from these regions are likely to be more influenced by climate change than those from the rest of
the World: Arctic fauna is more subjected to increasing temperatures per se, with these changes leading to increased species
ranges and probably abundance. Antarctic species are likely to be influenced by changes in (1) mesoscale oceanography (2)
the position of oceanic fronts (3) sea ice extent, and (4) ocean acidification. Polar cephalopods may have the capacity to adapt
to changes in their environment, but more studies are required on taxonomy, distribution, ocean acidification and ecology.
After studying (and eating) smaller squid for years, the Smithsonian's cephalopod man is now ready to face the biggest calamari of all.
The diet of Opisthoteuthis agassizi and O. vossi in the southeast Atlantic was studied from 171 and 121 individuals respectively. Small epibenthic and suprabenthic crustaceans and polychaetes are the most frequent prey items in both species, suggesting that they feed on suprabenthic and epibenthic material. Diel analysis of feeding by O. agassizi at 490 m and O. vossi at 836 m depth demonstrated a pattern of continuous feeding. Relationships of total body length and beak measurements to total weight were also studied. The ultrastructure of sucker and cirri are described for both species and their relationship with prey detection mechanisms is discussed.
The first cephalopods, recognized as such by their possession of a chambered shell with a siphuncle, appeared in the late Cambrian. They are assumed to have been crawling animals. Lightening the shell, made possible by ion and water removal and the consequent appearance of gas in the chambers would have allowed the animal to escape upwards, using the jet resulting from a sudden withdrawal of the body into the shell. Nautilus still produces a propulsive jet in this manner. It can also generate a low pressure stream using the wings of the funnel to waft a flow through the gills. It is argued that all the other ectocochleates would have had propulsive mechanisms based on one or other (or both) of the means by which Nautilus develops a jet. One consequence of this conclusion is that none of them were powerful swimmers. The momentum imparted by a jet depends upon the ejected mass multiplied by the velocity of the jet. But E = ½mv2 so that while slow speed propulsion using the ventilation stream can result in a very low cost of transport any attempt to achieve high speeds is very costly. Only marginal improvements could be made by lightening or streamlining the shell. More economical fast locomotion could only be achieved by increasing the volume of the mantle cavity, and this meant scrapping or internalizing the shell. It also necessitated the development of a new set of propulsive muscles, in the wall of the mantle. Mantle musculature now took on both locomotor and ventilatory functions. The two functions have incompatible requirements; for efficient jet propulsion the stream volume should be maximized, while efficient oxygen uptake should minimize the flow. Octopods have optimized oxygen extraction, the squids, in general are specialized for jet propulsion. In the teuthoids and octopods progressive shell reduction also led to the loss of neutral buoyancy, regained in some forms by ion-substitution in the tissues and an associated return to relatively slow-moving lifestyles. Jet propulsion remained an extravagant form of propulsion at all but the slowest speeds. Many coleoids, as a result, have moved on to develop yet another locomotor system, replacing jet propulsion by undulant fins.
THE bathymetric distribution of marine organisms collected during oceanographic expeditions is often difficult to ascertain because retrieval methods (nets, dredges, and so on) do not always indicate the precise depth at which an organism is entrapped. The level at which organisms dwell can, however, be accurately defined by deep ocean bottom photography.