Soft‐bottom tube worms: from irregular to programmed shell growth

Like other secondary soft‐bottom dwellers, serpulid and sabellid tube worms used particular strategies in order to cope with their earlier loss of mobility. This is expressed by the transition from irregular to genomically programmed morphologies of their calcareous shells that guarantee a stable horizontal resting position. In contrast to permanent recliners, however, this attitude was probably only the starting position for active resurrection after the muddy tail of storm sediments had settled on top of the displaced animal.     

Contributions to the taxonomy of Sabellidae (Polychaeta)

The genus Potamilla Malmgren is particularly characterized by dorsal lips which lack any radiolar midrib; Pseudopotamilla Bush by compound radiolar eyes, dorsal collar lappets and flanges alongside the bases of the most dorsal radioles; Demonax Kinberg by a wide dorsal collar gap and companion setae with big heads and narrow blades; and Potamethus Chamberlin by an elongated first segment, enlarged ventral sacs, very long shafts to the thoracic uncini, and inferior abdominal setae much shorter than the superior ones. Perkinsiana gen. nov . lacks most of these characters, but the type species 'Potamilla' rubra Langerhans is remarkable in having red blood. It bores into limestone abundantly off S Wales and is here redescribed. Oriopsis hynensis sp. nov . from SW Ireland has a smooth collar set low on the first segment, with its ventral margin entire and free from the apex of the peristome. The new name Demonax langerhansi is proposed for Sabella (Potamilla) incerta Langerhans non Demonax incertus Kinberg.     

Morphological comparison of the regeneration process in Sabella spallanzanii and Branchiomma luctuosum (Annelida,Sabellida)

Within Annelida, the family Sabellidae is a particularly interesting clade in which to carry out comparative studies of regeneration, as its members vary in regeneration potential, with some even lacking this ability completely. However, data on the regenerative potential of sabellids are available only for a few species investigated early in the last century, and even for those, many aspects of regenerative ability are yet to be determined. In the present study, we compared the morphology of the regeneration process of anterior and posterior ends in Sabella spallanzanii and Branchiomma luctuosum, two sabellids that belong to closely related genera. Members of S. spallanzanii exhibited lower mortality in response to wounding and greater regenerative ability, with amputees able to complete the regeneration process more rapidly than in B. luctuosum. Moreover, results from this study suggest that adults of S. spallanzanii and B. luctuosum use different mechanisms to restore lost anterior body parts. In S. spallanzanii, both morphallaxis and epimorphosis appear to be important in anterior end regeneration, but in B. luctuosum, only epimorphosis appears to be important. Such variation among closely related taxa sharing similar body plans has rarely been reported, but might be profitably examined using molecular approaches in these and other species of sabellids. Results of such studies interpreted in the context of phylogeny may ultimately provide insight into the evolution of regeneration.     

Factors influencing latitudinal pattern of biodiversity: An example using Sabellidae (Annelida, Polychaeta)

The latitudinal gradient of biodiversity hypothesis was tested utilising the geographical distribution of species taxa belonging to the family Sabellidae (Annelida: Polychaeta), one of the polychaete families studied by only a few specialists around the world. An increase in species richness towards the Tropical region was revealed, with an asymmetric distribution between the two hemispheres. Data show that most of the species were found in Northern latitudes, producing a Northern area much richer than the Southern one. The Atlantic-Mediterranean Region was particularly rich, with the number of species close to those from the Indo-Pacific Region. Mediterranean species richness is discussed in the light of the particular history of the basin, also emphasising the importance of naturalistic studies that have made the Mediterranean marine flora and fauna one of the best known in the world. The existence of extrinsic factors that obscure the real pattern of distributions is hypothesised. Differences found between the two hemispheres could be attributed primarily to the higher number of specialists working in the Boreal Domains, including the Mediterranean area. Global trends produced by some representative genera are also discussed with respect to the distribution of the taxonomic specialists.     

The genera <Emphasis Type="Italic">Bispira</Emphasis> Krøyer, 1856 and <Emphasis Type="Italic">Stylomma</Emphasis> Knight-Jones, 1997 (Polychaeta,Sabellidae): systematic revision,relationships with close related taxa and new species from Australia

A cladistic analysis undertaken to test monophyly of Bispira and Stylomma (including new species of both genera) and to ascertain relationships with related taxa reveals that Bispira is paraphyletic without the inclusion of Pseudobranchiomma and Branchiomma, and that Stylomma is monophyletic due to the presence of a structure on the dorsal basal flanges which has never been described before. New species of Bispira and Stylomma from Australia are described. Bispira serrata n. sp., differs from the other species of the genus in having serrated radiolar flanges whereas all other Bispira species have smooth flanges or lack them, and also by the shape of the thoracic and abdominal uncini, which are short-handled and have 2–3 rows of big teeth above the main fang, instead of having medium-sized handles and small, numerous rows of teeth over the main fang. Stylomma juani n. sp., is characterized by the presence of serrated radiolar flanges and unpaired compound eyes along the branchial radioles, whereas other species in the genus have smooth radiolar flanges and subterminal compound radiolar eyes. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: K. Martens     

Biology of Pseudopotamilla reniformis (Müller 1771) in the White Sea,with description of asexual reproduction

The tube-dwelling polychaete Pseudopotamilla reniformis (Sabellidae) forms dense and complex aggregations of flexible tubes on hard substrates in the subtidal zone of the White Sea. No sexual reproduction was observed in this study and recruitment appeared to be due to asexual reproduction by architomy in winter, from October to March. The posterior part of the abdomen undergoes spontaneous fission into from 2 to 4 fragments and depending on their position, the fragments regenerate their anterior ends or both anterior and posterior ends. Regeneration in P. reniformis takes place via a combination of epimorphosis (replacement of missing parts by cell proliferation and the growth of new tissue) and morphallaxis (the remodelling of pre-existing structures without cell proliferation). The morphogenetic events during regenerative restoration include de novo formation of branchial crown, formation of thoracic segments and restoration of the posterior end. Asexual reproduction appears to play a crucial role for formation of P. reniformis aggregations and is very important for the population in the White Sea, at the margin of the species’ range.     

To avoid or deter: interactions among defensive and escape strategies in sabellid worms

Numerous studies demonstrate how sessile marine organisms utilize chemical, structural, and nutritional deterrents to persist in predator-rich environments. Little is known, however, about how mobile, more behaviorally complex species minimize predation by integrating avoidance and deterrence strategies. We investigated this using sabellid polychaete worms from the Caribbean and temperate western Atlantic. Sabellids extend their feather-like radioles beyond their protective tubes for feeding and respiration; the body remains inside the tube and the radioles retract when threatened. We used co-occurring consumers to determine the palatability of radioles and bodies for each of the eight species tested. In addition, we examined chemical or structural traits affecting palatability and evaluated predator escape traits, such as tube strength, speed of radiole retraction, completeness of retraction, and sensitivity to a nearby disturbance. All species had unpalatable radioles that were chemically or structurally defended, but only two species had unpalatable bodies. Thus, most species allocated defenses to tissues that were most exposed to predation. The two species with chemically defended bodies, Bispira brunnea and Bispira variegata, relied less on behavioral escapes than the other species. Their tubes were weak, they did not retract until disturbances were very close, and B. brunnea retracted slowly and incompletely even when touched. Other species generally had stronger tubes and/or retracted when disturbances were farther away. This trade-off of deterrence versus escape even occurred within a single species when populations differed in palatability. Populations of B.variegata from North Carolina and Georgia were chemically deterrent to both temperate and tropical consumers, while populations from Panama and Florida were palatable. The more palatable Panama population retracted in response to distant movement, while the unpalatable North Carolina population did not retract until nearly touched. Thus, most species utilize a combination of predator avoidance and deterrence strategies, but more deterrent populations of species utilized avoidance less.     

Evidence of regenerative ability in Myxicola infundibulum (Annelida,Sabellida): evolutionary and systematic implications

Members of only a few species of annelids are reported as being incapable of regeneration; of these, Myxicola infundibulum is the only example in the family Sabellidae. Interestingly, its congener Myxicola aesthetica exhibits noteworthy regenerative ability. Unambiguously identifying non‐regenerating species is critical to reconstructing how regenerative abilities evolved within the phylum. However, studies designed specifically to assess the regenerative potential of M. infundibulum have never been performed. In this study, we aimed to confirm the lack of regeneration ability of M. infundibulum, reported previously for Atlantic specimens, or to determine the extent to which regeneration occurs. Our results showed that individuals from the Mediterranean Sea (Adriatic Sea) do undergo regeneration of lost body parts, although to a lesser extent than do other sabellids. Therefore, M. infundibulum should no longer be considered a non‐regenerating species. At present, uncertainties regarding phylogenetic relationships of Sabellidae prevent inferences about the polarity of change in M. infundibulum. Since our findings are counter to those of previous studies which describe Atlantic specimens as non‐regenerating, more extensive analysis is required to ascertain if they could actually belong to a different species than Mediterranean M. infundibulum, accounting for these differences in reported regenerative capacity.