In situ recordings of large gelatinous spheres from NE Atlantic, and the first genetic confirmation of egg mass of Illex coindetii (Vérany, 1839) (Cephalopoda, Mollusca).

In total, 90 gelatinous spheres, averaging one meter in diameter, have been recorded from ~ 1985 to 2019 from the NE Atlantic Ocean, including the Mediterranean Sea, using citizen science. More than 50% had a dark streak through center. They were recorded from the surface to ~ 60-70 m depth, mainly neutrally buoyant, in temperatures between 8 and 24°C. Lack of tissue samples has until now, prohibited confirmation of species. However, in 2019 scuba divers secured four tissue samples from the Norwegian coast. In the present study, DNA analysis using COI confirms species identity as the ommastrephid broadtail shortfin squid Illex coindetii (Vérany, 1839); these are the first confirmed records from the wild. Squid embryos at different stages were found in different egg masses: (1) recently fertilized eggs (stage ~ 3), (2) organogenesis (stages ~ 17-19 and ~ 23), and (3) developed embryo (stage ~ 30). Without tissue samples from each and every record for DNA corroboration we cannot be certain that all spherical egg masses are conspecific, or that the remaining 86 observed spheres belong to Illex coindetii. However, due to similar morphology and size of these spheres, relative to the four spheres with DNA analysis, we suspect that many of them were made by I. coindetii.

Whole mitochondrial genome of the Ram's Horn Squid shines light on the phylogenetic position of the monotypic order Spirulida (Haeckel, 1896).

The phylogenetic position of the only known species within the order Spirulida, the Ram's Horn Squid, Spirula spirula, may be the key to resolving relationships within Decapodiformes (squids and cuttlefishes). Spirula spirula possesses several unique features including an internal calcareous chambered shell unlike the familiar cuttlebone of Sepiidae (cuttlefishes). The shell is reduced to a gladius or absent in other decapod clades. To resolve decapodiform phylogenetic relationships we sequenced the mitochondrial genome of S. spirula and Sepiadarium austrinum and analysed these along with other mitochondrial genomes. Sequence analyses found that S. spirula and Sepiidae, the only two extant phragmocone bearing groups, were not sister taxa. Rather, in most analyses S. spirula was placed within a clade containing Bathyteuthoidea and Oegopsida either as the sister taxon to Bathyteuthoidea+Oegopsida or the sister taxon to Bathyteuthoidea only, depending upon the analysis method. Sepiidae was the sister taxon to a clade containing all remaining decapods. Spirulid mitochondrial gene order was identical to that of Octopodiformes, which we recognize as close to that of ancestral molluscs. The phylogenetic position of Idiosepiidae differed among analysis methods of molecular sequence data. However, gene order analysis resolved a highly supported monophyletic relationship containing Idiosepiidae and Sepiolida.

Association of deep-sea incirrate octopods with manganese crusts and nodule fields in the Pacific Ocean.

Incirrate octopods (those without fins) are among the larger megafauna inhabiting the benthic environments of all oceans, commonly in water depths down to about 3,000 m. They are known to protect and brood their eggs until the juveniles hatch, but to date there is little published information on octopod deep-sea life cycles and distribution. For this study, three manganese-crust and nodule-abundant regions of the deep Pacific were examined by remote operated-vehicle and towed camera surveys carried out between 2011 and 2016. Here, we report that the depth range of incirrate octopods can now be extended to at least 4,290 m. Octopods (twenty-nine individuals from two distinct species) were observed on the deep Ka'ena and Necker Ridges of the Hawaiian Archipelago, and in a nodule-abundant region of the Peru Basin. Two octopods were observed to be brooding clutches of eggs that were laid on stalks of dead sponges attached to nodules at depths exceeding 4,000 m. This is the first time such a specific mineral-biota association has been observed for incirrate octopods. Both broods consisted of approximately 30 large (2.0-2.7 cm) eggs. Given the low annual water temperature of 1.5oC, it is likely that egg development, and hence brooding, takes years [1]. Stalked-sponge fauna in the Peru Basin require the presence of manganese nodules as a substrate, and near total collapse of such sponge populations was observed following the experimental removal of nodules within the DISCOL (DISturbance and COLonisation) area of the Peru Basin [2]. Stalked fauna are also abundant on the hard substrates of the Hawaiian archipelago. The brooding behavior of the octopods we observed suggests that, like the sponges, they may also be susceptible to habitat loss following the removal of nodule fields and crusts by commercial exploitation.

The study of deep-sea cephalopods.

"Deep-sea" cephalopods are here defined as cephalopods that spend a significant part of their life cycles outside the euphotic zone. In this chapter, the state of knowledge in several aspects of deep-sea cephalopod research are summarized, including information sources for these animals, diversity and general biogeography and life cycles, including reproduction. Recommendations are made for addressing some of the remaining knowledge deficiencies using a variety of traditional and more recently developed methods. The types of oceanic gear that are suitable for collecting cephalopod specimens and images are reviewed. Many groups of deep-sea cephalopods require taxonomic reviews, ideally based on both morphological and molecular characters. Museum collections play a vital role in these revisions, and novel (molecular) techniques may facilitate new use of old museum specimens. Fundamental life-cycle parameters remain unknown for many species; techniques developed for neritic species that could potentially be applied to deep-sea cephalopods are discussed. Reproductive tactics and strategies in deep-sea cephalopods are very diverse and call for comparative evolutionary and experimental studies, but even in the twenty-first century, mature individuals are still unknown for many species. New insights into diet and trophic position have begun to reveal a more diverse range of feeding strategies than the typically voracious predatory lifestyle known for many cephalopods. Regular standardized deep-sea cephalopod surveys are necessary to provide insight into temporal changes in oceanic cephalopod populations and to forecast, verify and monitor the impacts of global marine changes and human impacts on these populations.

First in situ observations of the deep-sea squid Grimalditeuthis bonplandi reveal unique use of tentacles.

The deep-sea squid Grimalditeuthis bonplandi has tentacles unique among known squids. The elastic stalk is extremely thin and fragile, whereas the clubs bear no suckers, hooks or photophores. It is unknown whether and how these tentacles are used in prey capture and handling. We present, to our knowledge, the first in situ observations of this species obtained by remotely operated vehicles (ROVs) in the Atlantic and North Pacific. Unexpectedly, G. bonplandi is unable to rapidly extend and retract the tentacle stalk as do other squids, but instead manoeuvres the tentacles by undulation and flapping of the clubs' trabecular protective membranes. These tentacle club movements superficially resemble the movements of small marine organisms and suggest the possibility that G. bonplandi uses aggressive mimicry by the tentacle clubs to lure prey, which we find to consist of crustaceans and cephalopods. In the darkness of the meso- and bathypelagic zones the flapping and undulatory movements of the tentacle may: (i) stimulate bioluminescence in the surrounding water, (ii) create low-frequency vibrations and/or (iii) produce a hydrodynamic wake. Potential prey of G. bonplandi may be attracted to one or more of these as signals. This singular use of the tentacle adds to the diverse foraging and feeding strategies known in deep-sea cephalopods.

Does presence of a mid-ocean ridge enhance biomass and biodiversity?

In contrast to generally sparse biological communities in open-ocean settings, seamounts and ridges are perceived as areas of elevated productivity and biodiversity capable of supporting commercial fisheries. We investigated the origin of this apparent biological enhancement over a segment of the North Mid-Atlantic Ridge (MAR) using sonar, corers, trawls, traps, and a remotely operated vehicle to survey habitat, biomass, and biodiversity. Satellite remote sensing provided information on flow patterns, thermal fronts, and primary production, while sediment traps measured export flux during 2007-2010. The MAR, 3,704,404 km(2) in area, accounts for 44.7% lower bathyal habitat (800-3500 m depth) in the North Atlantic and is dominated by fine soft sediment substrate (95% of area) on a series of flat terraces with intervening slopes either side of the ridge axis contributing to habitat heterogeneity. The MAR fauna comprises mainly species known from continental margins with no evidence of greater biodiversity. Primary production and export flux over the MAR were not enhanced compared with a nearby reference station over the Porcupine Abyssal Plain. Biomasses of benthic macrofauna and megafauna were similar to global averages at the same depths totalling an estimated 258.9 kt C over the entire lower bathyal north MAR. A hypothetical flat plain at 3500 m depth in place of the MAR would contain 85.6 kt C, implying an increase of 173.3 kt C attributable to the presence of the Ridge. This is approximately equal to 167 kt C of estimated pelagic biomass displaced by the volume of the MAR. There is no enhancement of biological productivity over the MAR; oceanic bathypelagic species are replaced by benthic fauna otherwise unable to survive in the mid ocean. We propose that globally sea floor elevation has no effect on deep sea biomass; pelagic plus benthic biomass is constant within a given surface productivity regime.

Evolution of the cephalopod head complex by assembly of multiple molluscan body parts: Evidence from Nautilus embryonic development.

Cephalopod head parts are among the most complex occurring in all invertebrates. Hypotheses for the evolutionary process require a drastic body-plan transition in relation to the life-style changes from benthos to active nekton. Determining these transitions, however, has been elusive because of scarcity of fossil records of soft tissues and lack of some of the early developmental stages of the basal species. Here we report the first embryological evidence in the nautiloid cephalopod Nautilus pompilius for the morphological development of the head complex by a unique assembly of multiple archetypical molluscan body parts. Using a specialized aquarium system, we successfully obtained a series of developmental stages that enabled us to test previous controversial scenarios. Our results demonstrate that the embryonic organs exhibit body plans that are primarily bilateral and antero-posteriorly elongated at stereotyped positions. The distinct cephalic compartment, foot, brain cords, mantle, and shell resemble the body plans of monoplacophorans and basal gastropods. The numerous digital tentacles of Nautilus develop from simple serial and spatially-patterned bud-like anlagen along the anterior-posterior axis, indicating that origins of digital tentacles or arms of all other cephalopods develop not from the head but from the foot. In middle and late embryos, the primary body plans largely change to those of juveniles or adults, and finally form a "head" complex assembled by anlagen of the foot, cephalic hood, collar, hyponome (funnel), and the foot-derived epidermal covers. We suggest that extensions of the collar-funnel compartment and free epidermal folds derived from multiple topological foot regions may play an important role in forming the head complex, which is thought to be an important feature during the body plan transition.

'Lophenteropneust' hypothesis refuted by collection and photos of new deep-sea hemichordates.

The deep ocean is home to a group of broad-collared hemichordates--the so-called 'lophenteropneusts'--that have been photographed gliding on the sea floor but have not previously been collected. It has been claimed that these worms have collar tentacles and blend morphological features of the two main hemichordate body plans, namely the tentacle-less enteropneusts and the tentacle-bearing pterobranchs. Consequently, lophenteropneusts have been invoked as missing links to suggest that the former evolved into the latter. The most significant aspect of the lophenteropneust hypothesis is its prediction that the fundamental body plan within a basal phylum of deuterostomes was enteropneust-like. The assumption of such an ancestral state influences ideas about the evolution of the vertebrates from the invertebrates. Here we report on the first collected specimen of a broad-collared, deep-sea enteropneust and describe it as a new family, genus and species. The collar, although disproportionately broad, lacks tentacles. In addition, we find no evidence of tentacles in the available deep-sea photographs (published and unpublished) of broad-collared enteropneusts, including those formerly designated as lophenteropneusts. Thus, the lophenteropneust hypothesis was based on misinterpretation of deep-sea photographs of low quality and should no longer be used to support the idea that the enteropneust body plan is basal within the phylum Hemichordata.