The ability to regulate oxygen consumption evolved in ancestral animals and is intrinsically linked to iron metabolism. The iron pathways have been intensively studied in mammals, whereas data on distant invertebrates are limited. Sea sponges represent the oldest animal phylum and have unique structural plasticity and capacity to reaggregate after complete dissociation. We studied iron metabolic factors and their expression during reaggregation in the White Sea cold-water sponges Halichondria panicea and Halisarca dujardini. De novo transcriptomes were assembled using RNA-Seq data, and evolutionary trends were analyzed with bioinformatic tools. Differential expression during reaggregation was studied for H. dujardini. Enzymes of the heme biosynthesis pathway and transport globins, neuroglobin (NGB) and androglobin (ADGB), were identified in sponges. The globins mutate at higher evolutionary rates than the heme synthesis enzymes. Highly conserved iron-regulatory protein 1 (IRP1) presumably interacts with the iron-responsive elements (IREs) found in mRNAs of ferritin (FTH1) and a putative transferrin receptor NAALAD2. The reaggregation process is accompanied by increased expression of IRP1, the antiapoptotic factor BCL2, the inflammation factor NFκB (p65), FTH1 and NGB, as well as by an increase in mitochondrial density. Our data indicate a complex mechanism of iron regulation in sponge structural plasticity and help to better understand general mechanisms of morphogenetic processes in multicellular species.

The Bryozoa (=Ectoprocta) is a large group of bilaterians that exhibit great variability in the innervation of tentacles and in the organization of the cerebral ganglion. Investigations of bryozoans from different groups may contribute to the reconstruction of the bryozoan nervous system bauplan. A detailed investigation of the polypide nervous system of the ctenostome bryozoan Amathia gracilis is reported here. The cerebral ganglion displays prominent zonality and has at least three zones: proximal, central, and distal. The proximal zone is the most developed and contains two large perikarya giving rise to the tentacle sheath nerves. The neuroepithelial organization of the cerebral ganglion is revealed. The tiny lumen of the cerebral ganglion is represented by narrow spaces between the apical projections of the perikarya of the central zone. The cerebral ganglion gives rise to five groups of main neurite bundles of the lophophore and the tentacle sheath: the circum-oral nerve ring, the lophophoral dorso-lateral nerves, the pharyngeal and visceral neurite bundles, the outer nerve ring, and the tentacle sheath nerves. Serotonin-like immunoreactive nerve system of polypide includes eight large perikarya located between tentacles bases. There are two analmost and six oralmost perikarya with prominent serotonergic “gap” between them. Based on the characteristics of their innervations, the tentacles can be subdivided into two groups: four that are near the anus and six that are near the mouth. Two longitudinal neurite bundles - medio-frontal and abfrontal - extend along each tentacle. The zonality of the cerebral ganglion, the presence of three commissures, and location of the main nerves emanating from each zone might have caused by directive innervation of the various parts of the body: the tentacles sheath, the lophohpore, and the digestive tract. Two alternative scenarios of bryozoan lophophore evolution are discussed. The arrangement of large serotonin-like immunoreactive perikarya differs from the pattern previously described in ctenostome bryozoans. In accordance with its position relative to the same organs (tentacles, anus, and mouth), the lophophore outer nerve ring corresponds to the brachiopod lower brachial nerve and to the phoronid tentacular nerve ring. The presence of the outer nerve ring makes the lophophore innervation within the group (clade) of lophophorates similar and provides additional morphological evidence of the lophophore homology and monophyly of the lophophorates.

Eleven species of White Sea invertebrates (sponges, actinians, hydroids, polychaetes, and nudibranch mollusks) were tested for the presence of associated oxygen-evolving phototrophic microorganisms (OPM) (microalgae and cyanobacteria). Two main approaches were applied: (a) light and electron microscopy of intact samples and fixed preparations of invertebrates, and (b) isolation of microorganisms from samples of invertebrates after mild surface sterilization. The obtained results lead to conclusions on the formation of multicomponent associations by White Sea invertebrates and OPM based on the following data: (1) isolation of 27 cultures of OPM from eight species of invertebrates (sponges, hydroids, polychaete trochophore larva), (2) specificity of association between epibiontic communities of microorganisms and macroorganisms within the same biotope, and (3) spatial integration of micro- and macropartners resulting in the formation of morphological structures within the interorganismic contact zones.

Among bryozoans, cyclostome anatomy is the least studied by modern methods. New data on the nervous system fill the gap in our knowledge and make morphological analysis much more fruitful to resolve some questions of bryozoan evolution and phylogeny. The nervous system of cyclostome Crisia eburnea was studied by transmission electron microscopy and confocal laser scanning microscopy. The cerebral ganglion has an upper concavity and a small inner cavity filled with cilia and microvilli, thus exhibiting features of neuroepithelium. The cerebral ganglion is associated with the circumoral nerve ring, the circumpharyngeal nerve ring, and the outer nerve ring. Each tentacle has six longitudinal neurite bundles. The body wall is innervated by thick paired longitudinal nerves. Circular nerves are associated with atrial sphincter. A membranous sac, cardia, and caecum all have nervous plexus. The nervous system of the cyclostome C. eburnea combines phylactolaemate and gymnolaemate features. Innervation of tentacles by six neurite bundles is similar of that in Phylactolaemata. The presence of circumpharyngeal nerve ring and outer nerve ring is characteristic of both, Cyclostomata and Gymnolaemata. The structure of the cerebral ganglion may be regarded as a result of transformation of hypothetical ancestral neuroepithelium. Primitive cerebral ganglion and combination of nerve plexus and cords in the nervous system of C. eburnea allows to suggest that the nerve system topography of C. eburnea may represent an ancestral state of nervous system organization in Bryozoa. Several scenarios describing evolution of the cerebral ganglion in different bryozoan groups are proposed.

The colonies of thecate hydroids are covered with a chitinous tubelike outer skeleton, the perisarc. The perisarc shows a species-specific pattern of annuli, curvatures, and smooth parts. This pattern is exclusively formed at the growing tips at which the soft perisarc material is expelled by the underlying epithelium. Just behind the apex of the tip, this material hardens. We treated growing cultures of Laomedea flexuosa with substances we suspected would interfere with the hardening of the perisarc (l-cysteine, phenylthiourea) and those we expected would stimulate it (dopamine, N-acetyldopamine). We found that the former caused a widening of and the latter a reduction in the diameter of the perisarc tube. At the same time, the length of the structure elements changed so that the volume remained almost constant. We propose that normal development involves a spatial and temporal regulation of the hardening process. When the hardening occurs close to the apex, the diameter of the tube decreases. When it takes place farther from the apex, the innate tendency of the tip tissue to expand causes a widening of the skeleton tube. An oscillation of the position at which hardening takes place causes the formation of annuli.