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Longitudinal sections, ultrathin of specimen #542 ( a , b ) and semithin of specimen #675 ( c , d ). a Prostomium anterior to peristomium with prototroch (pr), tentacle (te), foregut (fg), and midgut (mg) with adjacent ventral blood vessel (vv); b prostomium with unpaired coelomic cavity (cp) anterior to peristomium with prototroch (pr) and mouth opening (mo), segment 1 with tentacle (te), foregut (fg), and
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Vestimentiferans (Siboglinidae, Polychaeta) live as juveniles and adults in an obligate mutualistic association with thiotrophic bacteria. Since their development is aposymbiotic, metatrochophores of vestimentiferans from the East Pacific Rise colonizing deep-sea hydrothermal vents are infected with the specific symbiont, develop the trophosome, an...
Context in source publication
Context 1
... molecular studies point to a sister taxa relationship of vestimentiferans and Sclerolinum , Osedax being the sister taxon to the vestimentiferans + Sclerolinum , and the frenulates being the sister taxon to the three above-mentioned taxa (Halanych et al. 2001; McHugh 1997, 2005; Rouse et al. 2004; Rousset et al. 2004, 2007; Glover et al. 2005, Hilário et al. 2011). However, combined molecular and morphological analyses showed that the positions of frenulates and Osedax are not well supported (Zrzavy et al. 2009). In the terminology of higher taxa within siboglinids, we follow Rouse (2001). An exception is the term Monilifera, which was created for all Sclerolinum species by Ivanov (1991) but is used by Rouse (2001) for the taxon vestimentiferans + Sclerolinum . Comparable metatrochophore stages and development into the juvenile have been studied in frenulates species (Bakke 1974, stages 1-3; Bakke 1977, stage 4; Brattegard 1966, Fig. 3; Callsen-Cencic and Flügel 1995, stages 3-5; Webb 1964, Fig. 1b-g; Webb 1969, Fig. 11), but only few studies also contain information on the inner organization (Callsen-Cencic and Flügel 1995, stage V; Ivanov 1975, Abb. 12,14,15; Jägersten 1957; Nørrevang 1970, stage 4). Only a brief description of a settled metatrochophore of Osedax is published (Rouse et al. 2009). No developmental information is available for Sclerolinum. We suggest that, also in frenulates and Osedax , the general composition of body regions of the metatrochophore (prostomium, peristomium, two chaetigers, and a pygidium) is overall similar to that of vestimentiferans. The most conspicuous character is the occurrence of two chaetigers in the metatrochophore in all three taxa versus the three almost simultaneously formed larval segments found in many other polychaetes (Anderson 1966, 1973; Jägersten 1972; Potswald 1981; Heimler 1988; McDougall et al. 2006; Seaver et al. 2005; Brinkmann and Wanninger 2008). In frenulates, the metatrochophore exhibits a digestive system including mouth, but no anus, and it shows larval organs such as the prototroch, the neurotroch, telotroch, apical organ, photoreceptors, and protonephridia [the latter three characters described in Siboglinum poseidoni Callsen-Cencic and Flügel (1995)]. In addition, already developed juvenile/ adult organs such as tentacles, frenulum, uncini, and pyriform glands are also present. In Osedax “ orange collar, ” the metatrochophore showed no traces of a digestive system, mouth, or anus, but a prototroch, an apical organ, and paired bundles of uncini were developed (Rouse et al. 2009). In frenulates, the prostomial coelom exhibits a double layer of epithelio-muscle cells and a small coelomic space, which apparently is unpaired (stage V, Callsen-Cencic and Flügel 1995). In a somewhat smaller metatrochophore still lacking tentacles, however, Nørrevang (1970) described this coelom as being either single or double. Ivanov (1963) initially described one unpaired coelom, later re-evaluated his own interpretation, and concluded that a paired coelomic cavity is present (Ivanov 1975). Nevertheless, according to Callsen-Cencic and Flügel (1995), the mesoderm in this prostomial region is clearly separated from the mesoderm of the first chaetiger by a septum located posterior to the two tentacles. Instead, Ivanov (1963) described the separation between this and the posteriorly located paired coelom taking place at a later stage. Regardless of time of formation, a septum is present in frenulates separating the peristomium and tentacles from the first chaetiger. This stands in contrast to our findings in vestimentiferans. Moreover, the lining of this prostomial coelomic cavity is myoepithelial, while in the metatrochophore of vestimentiferans we studied, it is non-muscular. In both frenulates and vestimentiferans, the tentacles are located posterior to the larval prototroch. In none of these tentacles was the innervation studied, which is one of the reasons that we do not apply the term palps for these head appendages (see above).The tentacles arise from the prostomium in frenulates but from the first chaetiger in vestimentiferans. Support for this interpretation comes from the location of the septum between the peristomium and first chaetiger: in frenulates it is present posterior to the tentacles, as detailed in drawings of Ivanov (1975). With respect to such a different origin of the tentacles, the sister group relationship of frenulates with all other siboglinids would suggest that tentacles arising from the first segment in vestimentiferans replaced the prostomial tentacles of frenulates or the other way round. Note here that the adult organization of head appendages also differs considerably in frenulates and vestimentiferans. Frenulates exhibit up to hundreds of tentacles, whereas vestimentiferans develop an obturacular region composed of a brachial plume with filaments/tentacles and an obturaculum. Considering the different development as well as adult config- uration of the tentacles, such conditions rather point to their basically analogous origin in vestimentiferans and frenulates. In contrast, according to Ivanov (1963, 1975) the septum – located in frenulates anterior to the first chaetiger (posterior of the tentacles) – differentiates late; thus, this septum could be a secondary one, formed after an anterior shift of the tentacles (onto the prostomium) had taken place because of limited space in the tube-dwelling animals (comp. Salvini-Plawen 2000). The first and second chaetiger exhibited paired coelomic cavities and, behind these, Nørrevang (1970) described a proliferation zone giving rise to all but the anteriormost segment of the opisthosoma (second chaetiger), similar to vestimentiferans. A peculiarity of frenulates is the formation of a muscular septum in the first chaetiger, separating the so- called forepart from the trunk. Because the neurotroch is located ...
Citations
... However, detailed descriptions of its larval development and ontogenesis have not yet been provided. Thus, there remains a lack of comprehensive descriptions of neurogenesis within the family Siboglinidae, with only a few studies addressing siboglinid larval morphologies (Nørrevang, 1970;Bakke, 1977;Gardiner and Jones, 1994;Callsen-Cencic and Flügel, 1995;Bright et al., 2013;Rimskaya-Korsakova et al., 2021;Temereva and Rimskaya-Korsakova, 2023). The post-embryonic development of Osedax has been briefly described, primarily based on light microscopy observations for O. packardorum Rouse, Goffredi, Johnson & Vrijenhoek, 2018(Rouse et al., 2018 (as O. "orange collar" in Rouse et al., 2009) and O. japonicus (Miyamoto et al., 2013). ...
... However, the internal ciliated structure found in some of the older (potentially female) metatrochophores and in young females might represent a residual gut structure due to its position and configuration. A temporary gut is found in other genera of siboglinids, though in these cases, there is a posterior anus, and a mouth that serves as an entry for uptake of symbionts (e.g., Bright et al., 2013). Further examinations and analyses are necessary to determine the homology and function of this structure in O. japonicus. ...
Most species of the bone-devouring marine annelid, Osedax, display distinct sexual dimorphism with macroscopic sedentary females rooted in bones and free-living microscopic dwarf males. The paedomorphic male resembles the non-feeding metatrochophore larva in size, presence of eight pairs of chaetae, and a head ciliation potentially representing a residual prototroch. The male development may thus uniquely reiterate and validate the theoretical heterochrony process “progenesis”, which suggests that an accelerated sexual maturation and early arrest of somatic growth can lead to a miniaturized and paedomorphic adult. In this study, we describe the postembryonic larval and juvenile organogenesis of Osedax japonicus to test for a potential synchronous arrest of somatic growth during male development. Five postembryonic stages could be distinguished, resembling day one to five in the larval development at 10°C: (0D) first cleavage of fertilized eggs (embryos undergo unequal spiral cleavage), (1D) pre-trochophore, with apical organ, (2D) early trochophore, + prototroch, brain, circumesophageal connectives and subesophageal commissure, (3D) trochophore, + telotroch, four ventral nerves, (4D) early metatrochophore, + protonephridia, dorsal and terminal sensory organs, (5D) metatrochophore, + two ventral paratrochs, mid-ventral nerve, posterior trunk commissure, two dorsal nerves; competent for metamorphosis. The larval development largely mirrors that of other lecithotrophic annelid larvae but does not show continuous chaetogenesis or full gut development. Additionally, O. japonicus larvae exhibit an unpaired, mid-dorsal, sensory organ. Female individuals shed their larval traits during metamorphosis and continue organogenesis (including circulatory system) and extensive growth for 2–3 weeks before developing oocytes. In contrast, males develop sperm within a day of metamorphosis and display a synchronous metamorphic arrest in neural and muscular development, retaining a large portion of larval features post metamorphosis. Our findings hereby substantiate male miniaturization in Osedax to be the outcome of an early and synchronous offset of somatic development, fitting the theoretical process “progenesis”. This may be the first compelling morpho-developmental exemplification of a progenetic origin of a microscopic body plan. The presented morphological staging system will further serve as a framework for future examination of molecular patterns and pathways determining Osedax development.
... It should be noted that monociliary collar sensory cells have also been described using TEM in the opisthosoma of the frenulate Siboglinum fiordicum Webb, 1963(Southward 1975. Also, Gardiner and Jones (1993), Miyamoto et al. (2013), and Bright et al. (2013) have provided TEM evidence on ciliary sensory elements in the epidermis of adults and larvae of several vestimentiferans. Unfortunately, other microscopic studies, not only in frenulates, but in all siboglinids lack information on ciliary sensory cells (Gupta et al. 1966;Gupta and Little 1969Nørrevang 1974;Southward 1984Southward , 1993Jones and Gardiner 1989;Callsen-Cencic and Flügel 1995;Worsaae and Rouse 2010;Karaseva et al. 2012;Worsaae et al 2016;Rimskaya-Korsakova et al. 2021). ...
The general morphology of the body, including the distribution of putative sensory ciliary cells, was studied using scanning electron microscopy (SEM) in the siboglinid Nereilinum murmanicum Ivanov, 1961 collected from the Barents Sea and at a new, deeper locality in the Greenland Sea outside the known range of this species. The fine features of cuticular structures in N. murmanicum, including the bridle and cuticular plaques from different parts of the body, were described for the first time. Since we have previously shown in the closely related siboglinid Oligobrachia haakonmosbiensis Smirnov, 2000 using SEM and confocal laser scanning microscopy (CLSM) that all epidermal cilia except for the ventral ciliary band belong to sensory cells, we consider all ciliary structures detected in N. murmanicum as sensory. The tentacles, clusters of ciliary cells along the dorsal furrow, areas around the openings of the multicellular glands, papillae, and the ciliary patch located on the cephalic lobe at the base of the tentacles can be regarded as specialized sensory areas. Based on our current knowledge of sensory structures in annelids, a number of assumptions were made about possible functional characteristics of putative sensory structures in siboglinids.
... The latter is composed of transversal and longitudinal nerves of the body wall, the stomatogastric nervous system (lacking in all pogonophorans), and peripheral nerve centers, such as parapodial or pharyngeal ganglia [15,19]. Among pogonophorans, the anatomy of the brain and other parts of the central nervous system (CNS) of Osedax and several vestimentiferans has been studied in the greatest detail using light microscopy, histological techniques [20][21][22][23], as well as electron and confocal microscopy [24][25][26][27][28][29][30][31][32][33][34]. The structure of the CNS of females and dwarf males of several species of Osedax was described by combining immunohistochemistry with confocal microscopy [35,36]. ...
... Tubiparous glands of vestimentiferans are situated primarily on the vestimental wings and it is these wings rather than papillae that are used by the worms when they build the walls and funnels of the tube [26,32,68]. The papillae are also lacking in the region of the pogonophoran body that may correspond to the vestimentum (see, however, the discussion on the homology of different body regions in pogonophorans, e.g.: [8,31,36]), but multicellular tubiparous glands are present in all frenulate pogonophorans, and the bridle and epidermal [69]. ...
Background
The nervous system of siboglinids has been studied mainly in Osedax and some Vestimentifera, while data in Frenulata – one of the four pogonophoran main branches – is still fragmentary. In most of the studies, the focus is almost always on the central nervous system, while the peripheral nervous system has traditionally received little attention. In contrast to other annelids, the structure and diversity of sensory structures in siboglinids are still quite undescribed. Meanwhile, the peripheral nervous system, as well as sensory elements, are extremely evolutionarily labile, and information about their organization is of high importance to understand lifestyles and behavior as well as main trends that lead siboglinids to their peculiar organization.
Results
The structure of the peripheric nervous system, sensory elements, and neuromuscular relationships of Oligobrachia haakonmosbiensis were studied using both scanning electron and confocal laser microscopy. A significant number of monociliary sensory cells, as well as sensory complexes located diffusely in the epithelium of the whole body were revealed. The latter include the cephalic tentacles, sensory cells accumulations along the dorsal furrow and ciliary band, areas of the openings of the tubiparous glands, and papillae. The oval ciliary spot located on the cephalic lobe at the base of the tentacles can also be regarded as a sensory organ. Most of the detected sensory cells show immunoreactivity to substance P and/or acetylated α-tubulin. FMRFamide- and serotonin-like immunoreactivity are manifested by neurons that mainly innervate tentacles, muscles, body wall epithelium, skin glands, tubiparous glands, and papillae. In the larva of O. haakonmosbiensis, monociliary sensory elements were revealed in the region of the apical organ, along the body, and on the pygidium.
Conclusions
The diversity of sensory structures in O. haakonmosbiensis comprises epidermal solitary sensory cells, sensory spots around tubiparous glands openings, and putative sensory organs such as cephalic tentacles, an oval ciliary spot on the cephalic lobe, the dorsal furrow, and papillae. Sensory structures associated with papillae and tubiparous glands play presumable mechanosensory functions and are associated with regulation of tube building as well as anchorage of the worm inside the tube. Sensory structures of the dorsal furrow are presumably engaged in the regulation of reproductive behavior. An overall low level of morphological differentiation of O. haakonmosbiensis peripheral nervous system is not typical even for annelids with the intraepithelial nervous system. This can be considered as a plesiomorphic feature of its peripheral plexus’s organization, or as evidence for the neotenic origin of Siboglinidae.
... Это предположение основывалось на том факте, что у ювенильных особей сохраняются рот и рудиментарный кишечник, в клетках которого были обнаружены неидентифицированные бактерии. Однако, по данным авторов [13,14], исследовавших механизм заражения ювенильных особей вестиментифер, сульфидокисляющие бактерии проникают в организм червя из внешней среды не через рудиментарный кишечник, а через стенку тела в передней части туловищного отдела. Тот факт, что трофосома представляет собой совокупность тяжей, осью каждого из которых является кровеносный сосуд, позволяет предполагать, что трофосома связана в своем происхождении с кровеносной системой. ...
Вестиментиферы – это бескишечные морские беспозвоночные, которые существуют за счет хемоавтотрофных сульфид-окисляющих бактерий. Особый интерес к этой группе возник после открытия богатой фауны гидротермальных сообществ в рифтовых зонах Мирового океана. По современным представлениям Vestimentifera – одно из подсемейств в семействе Siboglinidae, которое относится к типу кольчатых червей. Органом бактериального питания вестиментифер является трофосома – тканевый тяж, расположенный в туловищном отделе. В трофосоме были обнаружены хемоавтотрофные сульфид-окисляющие бактерии, которые осуществляют окисление сульфида и фиксацию углекислоты в цикле Кальвина-Бенсона. В проведенных ранее исследованиях клеточный состав трофосомы был изучен на ультраструктурном уровне, что позволило выявить в составе этого органа несколько типов клеток, в частности, бактериоциты, клетки внешней обкладки трофосомы и клетки, образующие стенки кровеносных сосудов. При этом общая анатомия трофосомы и гистологическое строение ее тяжей не описаны, а происхождение этого органа у вестиментифер остается загадочным.
... The benthic phase is marked by the uptake of the symbiont into the metatrochophore larvae and growth into an adult, which completely reduces its mouth, gut, and anus. Instead, a unique mesodermal nutritional organ, the trophosome, functionally replaces the digestive system (Nussbaumer et al. 2006;Bright et al. 2013). The adult body is organized into four distinct regions, the obturacular region, the vestimentum, the trunk, and the opisthosoma ( fig. ...
... The trunk region, the single elongated first segment, harbors the trophosome and the gonads. The posterior part, the opisthosoma, contains a typical segmented annelid region with serially arranged chaetae (Bright et al. 2013). It is so far unknown how this unusual body plan lacking the entire digestive system is reflected in their developmental genes and signaling pathways. ...
... Combining the genomic information with tissue-specific transcriptomes allows us to hypothesize that the mesodermal trophosome (Nussbaumer et al. 2006;Bright et al. 2013) is a multifunctional organ with ancestral inherited functions such as hematopoiesis. This trait, we hypothesize belongs to the functional repertoire known from mesodermal chloragogen (extravasal tissue surrounding the gut and blood vessels) derived from the visceral mesoderm in annelids like the trophosome in vestimentiferans (Nussbaumer et al. 2006;Bright et al. 2013). ...
The mutualism between the giant tubeworm Riftia pachyptila and its endosymbiont Candidatus Endoriftia persephone has been extensively researched over the past 40 years. However, the lack of the host whole genome information has impeded the full comprehension of the genotype/phenotype interface in Riftia. Here we described the high-quality draft genome of Riftia, its complete mitogenome, and tissue-specific transcriptomic data. The Riftia genome presents signs of reductive evolution, with gene family contractions exceeding expansions. Expanded gene families are related to sulphur metabolism, detoxification, anti-oxidative stress, oxygen transport, immune system, and lysosomal digestion, reflecting evolutionary adaptations to the vent environment and endosymbiosis. Despite the derived body plan, the developmental gene repertoire in the gutless tubeworm is extremely conserved with the presence of a near intact and complete Hox cluster. Gene expression analyses establishes that the trophosome is a multi-functional organ marked by intracellular digestion of endosymbionts, storage of excretory products and haematopoietic functions. Overall, the plume and gonad tissues both in contact to the environment harbour highly expressed genes involved with cell cycle, programmed cell death, and immunity indicating a high cell turnover and defence mechanisms against pathogens. We posit that the innate immune system plays a more prominent role into the establishment of the symbiosis during the infection in the larval stage, rather than maintaining the symbiostasis in the trophosome. This genome bridges four decades of physiological research in Riftia, whilst simultaneously provides new insights into the development, whole organism functions and evolution in the giant tubeworm.
... Данная стадия по своей морфологии занимает промежуточное положение между второй и третьей стадиями, описанными у S. poseidoni [39], так как опистосомальные хеты у личинок уже развиты, но щупальцевых зачатков не обнаружено. По своей морфологии данная стадия близка к поздней метатрохофоре [26,39,41]. ...
... По положению и строению клеток-бактериоцитов можно предположить, что трофосома имеет энтодермальное происхождение, что уже предполагалось некоторыми авторами при изучении других зибоглинид [2,8,26,39,43]. Однако проведенные ранее исследования трофосомы указывали на ее мезодермальное происхождение [41,44,45]. ...
This article deals with the external and internal morphology in the adult stages of Nereilinum murmanicum Ivanov, 1961, a widespread species of Siboglinidae in the Barents Sea. Since Siboglinidae is currently a taxon within the phylum Annelida, we revised the commonly held view of the body segmentation pattern typical of the species and provided the first description of its opisthosoma. Furthermore, the postannular region and trophosome were structurally analyzed using histology and electron microscopy. The endodermal origin of the trophosome was suggested from its structure and position. The juvenile and larval stages of the species were described. The early larvae were found to resemble the trochophores in Annelida. The late larvae look like the late metatrochophora in Annelida and lack parapodia. The juvenile specimens retain no larval traits and are morphologically comparable to the adult stages. New data on the ecology of the species were obtained: it appears to also inhabit deeper water layers. The boundaries of its range in the Barents Sea were expanded and specified. The abundance distribution of the species in the Barents Sea (30–40 ind/m2 for the major part of the sea, up to 72–113 ind/ m2 for certain areas of the sea in particular years) was considered.
... Current knowledge on the anatomy of siboglinid larvae is mainly based on ultrastructural studies of vestimentiferans [29][30][31][32][33], and immunolabeling and confocal scanning microscopy on larva-like male of Osedax [34]. Only few histological [35][36][37] and ultrastructural [38] data on frenulate larvae exist and their full anatomy needs to be reconstructed with advanced microscopy techniques and considering their current position within Annelida. ...
... Sequence of septa formation and regionalization of the body In the frenulate larva the border between the prostomium and the peristomium, bearing the ventral mouth and dorsal tentacle, is distinguishable and the regionalization follows that of other annelid larvae [38,49]. But the division of the rest of the body raised questions [33,50]. ...
Background
Many annelids, including well-studied species such as Platynereis , show similar structured segments along their body axis (homonomous segmentation). However, numerous annelid species diverge from this pattern and exhibit specialised segments or body regions (heteronomous segmentation). Recent phylogenomic studies and paleontological findings suggest that a heteronomous body architecture may represent an ancestral condition in Annelida. To better understand the segmentation within heteronomous species we describe the myogenesis and mesodermal delineation of segments in Siboglinum fiordicum during development.
Results
Employing confocal and transmission electron microscopy we show that the somatic longitudinal musculature consists of four separate strands, among which ventrolateral one is the most prominent and is proposed to drive the search movements of the head of the late metatrochophore. The somatic circular musculature lies inside the longitudinal musculature and is predominantly developed at the anterior end of the competent larva to support the burrowing behaviour. Our application of transmission electron microscopy allows us to describe the developmental order of the non-muscular septa. The first septum to form is supported by thick bundles of longitudinal muscles and separates the body into an anterior and a posterior region. The second group of septa to develop further divides the posterior body region (opisthosoma) and is supported by developing circular muscles. At the late larval stage, a septum reinforced by circular muscles divides the anterior body region into a forepart and a trunk segment. The remaining septa and their circular muscles form one by one at the very posterior end of the opisthosoma.
Conclusions
The heteronomous Siboglinum lacks the strict anterior to posterior sequence of segment formation as it is found in the most studied annelid species. Instead, the first septum divides the body into two body regions before segments are laid down in first the posterior opisthosoma and then in the anterior body, respectively. Similar patterns of segment formation are described for the heteronomous chaetopterid Chaetopterus variopedatus and serpulid Hydroides elegans and may represent an adaptation of these annelids to the settlement and transition to the sedentarian-tubiculous mode of life.
... In the frenulate larva the border between the prostomium and the peristomium, bearing the ventral mouth and dorsal tentacle, is distinguishable and the regionalization follows that of other annelid larvae (37,55). But the division of the rest of the body raised questions (32,56). ...
Background
Many annelids, including well-studied species such as Platynereis , show similar structured segments along their body axis (homonomous segmentation). However, numerous annelid species diverge from this pattern and exhibit specialised segments or body regions (heteronomous segmentation). Recent phylogenomic studies and paleontological findings suggest that a heteronomous body architecture may represent an ancestral condition in Annelida. To better understand the segmentation within heteronomous species we describe the myogenesis and mesodermal delineation of segments in Siboglinum fiordicum during development. ResultsEmploying confocal and transmission electron microscopy we show that the somatic circular musculature lies inside the longitudinal musculature and is predominantly developed at the anterior end of the larva. The longitudinal musculature consists of four separate strands at the ventral, dorsal, and ventrolateral body sides. Posteriorly, the longitudinal strands form a continuous layer. Our application of transmission electron microscopy allows us to describe the developmental order of the non-muscular septa. The first septum to form is supported by thick bundles of longitudinal muscles and separates the body into an anterior and a posterior region. The second group of septa to develop further divides the posterior body region (opisthosoma) and is supported by developing circular muscles. At the late larval stage, a septum reinforced by circular muscles divides the anterior body region into a forepart and a trunk segment. The remaining septa and their circular muscles form one by one at the very posterior end of the opisthosoma. Functionally, the prominent ventrolateral longitudinal muscles in the larva are proposed to drive the search movements of the head, while the anterior circular muscles and the posterior continuous layers of longitudinal muscles support the burrowing behaviour of the larva.Conclusions
The heteronomous Siboglinum lacks the strict anterior to posterior sequence of segment formation as it is found in the most studied annelid species. Instead, the first septum divides the body into two body regions, before segments are layed down in first the posterior opisthosoma and then in the anterior body, respectively. Similar pattern of segment formation is described for the heteronomous chaetopterid Chaetopterus variopedatus and may represent an ancestral segmentation process in Annelida.
... The wing-like folds between the cephalic lobe and the bridle on the dorso-lateral sides of the forepart of the species of Galathealinum have a different degree of development, from very strong lappets in G. bruuni to weakly pronounced lobes in G. arcticum. Although it is likely that the dorso-lateral ridges on the anterior part of the moniliferan (sclerolinid) body should be recognised as the initial structure for the origin and further evolution of the so-called vestimental wings of the vestimentiferans (Bright et al., 2012;Eichinger et al., 2013), no one has yet paid attention to how similar the wings on the forepart of Galathealinum are to the vestimental wings of the vestimentiferans. Indeed, these structures are in fact epidermal or epidermal-muscular folds located both on the anterior part of the body, fusing ventrally and being divided dorsally. ...
... No matter how the problem of homology of the anterior body part of different pogonophoran clades is resolved (Rouse, 2001;Rousset et al., 2004;Southward et al., 2005;Nussbaumer et al., 2006;Hilário et al., 2011;Eichinger et al., 2013;Worsaae et al., 2016), it is obvious that at least the region anterior to the bridle in the frenulates is homologous to the anterior part of the vestimental region of the vestimentiferans and to the anterior part of the body of the moniliferans. According to Bright et al. (2012), the forepart in the frenulates and the vestimentum in the vestimentiferans each contain the prostomium, peristomium and some portion of the anterior (first) chaetiger, while Worsaae et al. (2016) assumes that both forepart and vestimentum comprise only the anterior chaetiger. Thus, the forepart wings of Galathealinum and the vestimental wings of the vestimentiferans can be considered homoplasic in the sence of Beklemishev (1964), since they develop in closely related taxa as a Fig. 5. Infographic explaining characters mentioned in the paper. ...
A new species of Pogonophora obtained from one station at a depth of 25 m from near the Dikson Island in the Kara Sea is described. Galathealinum karaense sp. nov. is one of the largest pogonophorans, the first known representative of the rare genus Galathealinum Kirkegaard, 1956 in the Eurasian part of the Arctic Ocean and a highly unusual finding for the desalted shallow of the Yenisey Gulf. Several characters occurring in the new species are rare or unique among the congeners: under-developed, hardly discernible frills on the tube segments, extremely thin felted fibres in the external layer of the tube, and very faintly separated papillae in the anterior part of the trunk. Morphological characters useful in distinguishing species within the genus Galathealinum are defined and summarised in a table. Diagnosis of the genus Galathealinum is emended and supplemented by new characters. Additionally, three taxonomic keys are provided to the species of Galathealinum and to the known species of the Arctic pogonophorans using either animals or their empty tubes only, with the brief zoogeographical information on each Arctic species.
... As in active vents, some animal taxa in inactive vent fields may obtain their nutrition in association with chemoautotrophic microbial production (Erickson et al. 2009;Copley et al. 2016;Thomas et al. 2018). Many animals from the next generation recruit their symbionts from the environment independently of the previous generation (Van Dover 2000; Bright et al. 2013;Thomas et al. 2018), so disruptions to the composition of the ambient seawater microbial communities could affect the ability of these animals to persist in areas adjacent to mining activities even if their own habitat is not directly affected (Fig. 3). ...
Interest in extracting mineral resources from the seafloor through deep‐sea mining has accelerated in the past decade, driven by consumer demand for various metals like zinc, cobalt, and rare earth elements. While there are ongoing studies evaluating potential environmental impacts of deep‐sea mining activities, these focus primarily on impacts to animal biodiversity. The microscopic spectrum of seafloor life and the services that this life provides in the deep sea are rarely considered explicitly. In April 2018, scientists met to define the microbial ecosystem services that should be considered when assessing potential impacts of deep‐sea mining, and to provide recommendations for how to evaluate and safeguard these services. Here, we indicate that the potential impacts of mining on microbial ecosystem services in the deep sea vary substantially, from minimal expected impact to loss of services that cannot be remedied by protected area offsets. For example, we (1) describe potential major losses of microbial ecosystem services at active hydrothermal vent habitats impacted by mining, (2) speculate that there could be major ecosystem service degradation at inactive massive sulfide deposits without extensive mitigation efforts, (3) suggest minor impacts to carbon sequestration within manganese nodule fields coupled with potentially important impacts to primary production capacity, and (4) surmise that assessment of impacts to microbial ecosystem services at seamounts with ferromanganese crusts is too poorly understood to be definitive. We conclude by recommending that baseline assessments of microbial diversity, biomass, and, importantly, biogeochemical function need to be considered in environmental impact assessments of deep‐sea mining.
