Assessment of serpulid-hydroid association through the Jurassic: A case study from the Polish Basin

The coexistence of sessile, tube-dwelling polychaetes (serpulids) and hydroids, has been investigated. Serpulid tubes bearing traces after hydroids are derived from different stratigraphic intervals spanning the Middle and Upper Jurassic, the rocks of which represent the diverse paleoenvironments of the Polish Basin. Although fossil colonial hydroids classified under the species Protulophila gestroi are a commonly occurring symbiont of these polychaetes during the Late Cretaceous and Cenozoic, they seem to be significantly less frequent during the Jurassic and limited to specific paleoenvironments. The hydroids described here are represented by traces after a thin stolonal network with elongated polyp chambers that open to the outer polychaete tube’s surface with small, more or less subcircular apertures. Small chimney-like bulges around openings are an effect of the incorporation of the organism by in vivo embedment (bioclaustration) within the outer layers of the calcareous tube of the serpulid host. Considering the rich collection of well-preserved serpulid tubes (>3000 specimens), the frequency of bioclaustrated hydroids is very low, with an infestation percentage of only 0.6% (20 cases). It has been noticed that only specimens of the genus Propomatoceros from the Upper Bajocian, Lower Bathonian, Middle Bathonian, and Callovian have been found infested. However, the majority of bioclaustrated hydroids (17 cases) have been recorded in the Middle Bathonian serpulid species Propomatoceros lumbricalis coming from a single sampled site. Representatives of other genera are not affected, which is congruent with previous reports indicating that Protulophila gestroi was strongly selective in the choice of its host. A presumably commensal relationship is compared with the recent symbiosis between the hydroids of the genus Proboscidactyla and certain genera of sabellid polychaetes.

Kleptopredation: a mechanism to facilitate planktivory in a benthic mollusc

Predation occurs when an organism completely or partially consumes its prey. Partial consumption is typical of herbivores but is also common in some marine microbenthic carnivores that feed on colonial organisms. Associations between nudibranch molluscs and colonial hydroids have long been assumed to be simple predator–prey relationships. Here we show that while the aeolid nudibranch Cratena peregrina does prey directly on the hydranths of Eudendrium racemosum , it is stimulated to feed when hydranths have captured and are handling prey, thus ingesting recently captured plankton along with the hydroid polyp such that plankton form at least half of the nudibranch diet. The nudibranch is thus largely planktivorous, facilitated by use of the hydroid for prey capture. At the scale of the colony this combines predation with kleptoparasitism, a type of competition that involves the theft of already-procured items to form a feeding mode that does not fit into existing classifications, which we term kleptopredation. This strategy of subsidized predation helps explain how obligate-feeding nudibranchs obtain sufficient energy for reproduction from an ephemeral food source.

Walking Behavior Observed in Phoxichilidium femoratum (Rathke, 1799) and Nymphon brevirostre Hodge 1863 Collected from Kandalaksha Bay of the White Sea, Russia

In this study, the walking behavior of Phoxichilidium femoratum and Nymphon brevirostre was investigated using video recordings. The walking behavior of P. femoratum while walking over the colonial hydroids that they normally feed on and on relatively smooth glass surfaces was observed. In the case of N. brevirostre, only walking on smooth glass was observed. The movement of the legs while waking does not display a metachronal pattern like that observed in the true spiders. As the animals move, the walking legs on the leading side of the animal are used to pull the animal forward while those on the trailing side make little or no contribution to the motion of the animal. The promoter/remoter motions of the coxa 1-coxa 2 joint of the walking legs are involved in azimuthal changes in the body’s orientation, but not in paraxial locomotion. The extension of the tarsus and propodus segments appears to occur as a result of hydrodynamic drag when the legs are being flexed and/or pressed against a solid substrate.

Associations between the White Sea colonial hydroidDynamena pumilaand microorganisms

Marine sessile invertebrates with outer skeleton constitute additional substrate for a diverse group of epibiotic organisms. Colonial hydroids are no exception. Large numbers of motile and sessile organisms use hydroid colonies covered with chitinous perisarc for permanent or temporal attachment. Such epibiotic associations between colonial hydroids and microorganisms are poorly studied and mostly known for subtropical regions. There are no data about the development of such epibiotic association and type of its specificity yet. The present paper for the first time describes the epibiotic association of the colonial thecate hydroidDynamena pumilafrom the high latitude sea. We reconstruct the spatial and temporal development of such epibiotic community and analyse the organization of the multicomponent biofilm covering the hydroid colony. Comparison of the epibiotic community in different seasons indicates for holding out of the basal features and components of the community during the whole year. Ultrastructural investigations revealed that components of the biofilm affect the outer skeleton of the hydroid colony that results in penetration of the microorganisms into the skeleton and even soft tissues. Our data allow supposing that association of hydroidD. pumilawith a microorganism community has features of a symbiotic system.

Soft tissue organization in some sertulariid colonial hydroids (Hydrozoa: Sertulariidae)

The simplified text-book view holds that hydroids' soft body is composed of a branched double-layered tube, whose wall consists of two epithelial layers (the inner gastrodermis and the outer epidermis) separated by the mesoglea. Some hydroids are characterized by large, complex colonies and likely an even more complicated inner organization. By using three species from the thecate hydroids of the family Sertulariidae we investigated the soft body structure of such hydroids. The anatomical study revealed some new features of colonial hydroids. The double layered coenosarc fills the perisarc (outer skeleton) tube only at the endings of the branched colony. More proximally, the coenosarc tube becomes narrower and a thin epidermal lining covers the inner surface of the perisarc tube. In some species the soft tissues of the shoots form a network of anastomosing canals. The canals are formed by the gastrodermal epithelium and they are embedded in epidermal tissue. In the upper part of the shoot, these canals are located at the periphery, along the inner surface of the perisarc. In more proximal regions of the stem, the whole lumen of the perisarc tube can be occupied by gastrodermal canals; the canals are enclosed in a parenchyma-like epidermal tissue. The organization of the soft tissue in these thecate hydroids is a striking example of structural complexity that does not contravene the limits of the ground plan of the phylum.

Decoding the morphogenetic evolution of thecate hydroids

Modular organization of colonial hydroids is based on cyclic morphogenesis during growth of their body. In many thecate hydroids (Hydrozoa: Leptomedusae) the shoots of the colony consist of a few distinct elements and possess complex spatial organization. In most cases, the evolutionary sequence of morphogenetic modifications that led to present-day organization of shoots is obscure and not obvious. One of the approaches that allow getting insight into the morphogenetic evolution in colonial thecate hydroids is to analyse the spectrum of different minor morphotypes presented in the population of the certain species. In our opinion, some rare morphotypes allow understanding and reconstructing the scenario of morphogenetic evolution of species under consideration. We describe the application of such an approach for reconstruction of the morphogenetic evolution of Dynamena pumila (L.) (Sertulariidae) with some additional conclusions.