Bernard Guy
email: bernard.guy15@wanadoo.fr

Striped icebergs. Preliminary discussion on the respective roles and positionings of sea ice, marine ice, glacier ice and ice shelf

Keywords: icebergs, ice, sea ice, glacier ice, ice shelf, seawater, freezing, constitutional supercooling, columns, parallel planes, NaCl, solidification, self-organization, basalt columns

We offer a few comments on the formation of striped icebergs. We discuss the different types of ice as distinguished by the authors: glacier ice, ice shelf, marine ice, sea ice. We rely on the hypothesis exposed in Guy (<hal-03559083>, 2022): the planar and columnar structures characterizing such icebergs result from the fingered solidification of sea water under the iceshelf ice (instability of the planar freezing front due to constitutional supercooling). We propose to separate marine ice into two types: -type 1 -marine ice, restricted to ice formation by nucleation within the water beneath the ice shelf; -type 2 -marine ice, for the fingered ice formed at the ice-water front below the ice shelf. The complete succession of zones may thus comprise, from top to bottom: glacier ice / type 2 -marine ice / type 1 -marine ice / seawater. Some results from the article by Warren et al. (JGR Oceans, 124, 2019) are discussed.

Introduction

The present text supplements the HAL notice submitted two years ago [START_REF] Guy | Planar and columnar structures observed in some icebergs: a hypothesis[END_REF], which contained preliminary proposals on the formation of striped icebergs. In this addition, we have endeavored to distinguish between the different types of ice discussed by the authors, which we had not done. The whole is of a "preliminary" nature, outside any rigorous quantitative approach.

Reminder of Guy (2022)

During an exhibition on Antarctica, our attention was drawn to some spectacular structures visible in certain icebergs (views of such structures in icebergs of various origins can be found on the Internet). These consist of sets of vertical ice columns, or parallel planes (also vertical), forming colonnades. The latter are separated by horizontal surfaces from the rest of the iceberg above (the tilting of which modifies these directions); the diameters of the columns and the thicknesses of the planes appear decimetric to multi-decimetric.

The structures are inscribed in the mass of ice, with marine erosion and melting highlighting them (under overhangs of the massive iceberg). To the best of our knowledge, there does not seem to be any reasoned description or proposed explanation. We are content here to sketch out a potential interpretative framework. We do not go into detail about the reasons that guide us; they are inspired by our knowledge of the solidification of geological magmas giving comparable structures: columns and planes [START_REF] Guy | Réflexions sur la prismation des basaltes : l'instabilité du front plan de solidification[END_REF][START_REF] Guy | Discussion: Comments on "Basalt columns: Large scale constitutional supercooling? by John Gilman (JVGR, 2009) and presentation of some new data[END_REF][START_REF] Guy | Columnar structures in pyrometamorphic rocks associated with coal-bearing spoil-heaps burned by self-ignition[END_REF].

We thus imagine that, when it enters the sea, a piece of glacier (or, on a larger scale, an ice shelf such as those surrounding the Antarctic continent), constituting a significant reservoir of coldness, can, under certain conditions, cause the sea to freeze on contact with it in its submerged parts (new ice is thus formed; we will call this ice: type 2 -marine ice, see section 2). As the sea is rich in NaCl, the solidification (freezing) point of the water depends on the salt content in the vicinity of the ice/seawater contact. Depending on the temperature gradients involved, the phenomenon of supercooling may come into play, and the ice/water interface show instability; this is responsible for the formation of digitations, i.e. fingers, or parallel planes of ice, protruding into the water during freezing. Materials scientists discuss the threedimensional temperature gradients that enable a bifurcation between the columnar and planar regimes. As a result of their growth, the fingers/planes will weld together, leaving joints between them that correspond to more fragile zones, highlighted by later erosion / melting processes, when the iceberg rises or tilts. If water ice cannot contain salt, it can neither contain a whole range of chemical elements, including gases, which will be "expelled" to the outside.

Could this explain the gaseous releases observed along the joints by some people (Raphaël Sané, pers. com., 2022) and sometimes considered to be responsible for the structures (when in fact they are a consequence of them)?

Preliminary semi-quantitative estimates (...) involving the main parameters of the problem (temperatures, enthalpy of fusion, heat capacities, thermal and molecular diffusivities, thermal gradients, slope of the liquidus in the phase diagram, involvement of solutal convection) are encouraging.

The different types of ice

We extend the previous lines after reading an article on "green icebergs" [START_REF] Warren | Green icebergs revisited[END_REF] 1 .

Vocabulary, nucleation process and competition between two "marine ices".

We need to link up with existing words, which the previous article mentions: glacier ice, marine ice, sea ice, ice shelf, iceberg. What we proposed in section 1 is marine ice, but we are now saying that we need to make a distinction between two type of marine ice: type 1-marine ice and type 2 -marine ice.

Type 2 -marine ice is the plane-or column-structured marine ice; it is similar to metallurgists' cells or to rock columns and planes we discussed in the texts quoted in section 1 (arising from the solidification of geological magmas). Type 2marine ice forms directly from the ice shelf (or possibly iceberg) ice in its lower part (see Figures 1 and2). There is no need to nucleate new ice; new ice grows from old ice (glacier ice); if thermal gradients allow, this ice can be structured into planes or columns (cf. supercooling).

Type 1 -marine ice 2 forms in mid-water ahead of the formation front of type 2 marine ice (or simply ahead of the base of the ice shelf or iceberg if type 2 marine ice does not form, see figures). A nucleation threshold corresponding to a certain degree of supercooling must be exceeded (this is known as homogeneous nucleation). This ice will rise and stick to the ice of the ice shelf (whether primary glacier ice or type 2 -marine ice).

When the two marine ice types (type 1, type 2) develop simultaneously, we have two different layers (see Fig. 2). This raises the question of contact between the two types of marine ice. It is likely that type 2 -marine ice pushes back type 1 -marine ice and that there is no "mixing", resulting in an overall clear contact at the macroscopic level. There may be cases where the contact is more irregular, but this remains to be seen (depending on possible observations).

Sea ice is similar to type 1 -marine ice in its formation (homogeneous nucleation in the water), but it would take more observation and reflection to understand the differences with type 1marine ice: according to the authors, sea ice retains more salt and gas. If we compare it to type 2 -marine ice, we can understand why there is less salt and bubbles in type 2 -marine ice than in sea ice (efficient expulsion of everything that does not fit into the ice network, during cell growth). As the authors did not distinguish between the two types of marine ice (they would not always have done so anyway, given the observation conditions), it is possible that, when they say that the solid phase is less rich in salt in marine ice than in sea ice, they mean type 2marine ice.

Note that the previous figures, showing the succession:

-Exterior solid or cold wall (in this case glacier ice) / Solid consisting of ice structured into cells (in the sense of metallurgists), i.e. type 2 -marine ice / Solid consisting of type 1 -marine ice ("equiaxed" in the sense of metallurgists) / Liquid (sea water) is strictly what is observed in metallurgical ingots (before complete solidification, the liquid eventually disappearing inside the equiaxed zone). The equiaxed zone (or type 1 -marine ice) corresponds to the entablature of volcanic flows; the colonnade corresponds to type 2 -marine ice. What is new here is that the system is not completely symmetrical. In the case of metallurgical ingots, as in the case of volcanic flows, solidification takes place from two "cold" surfaces: the edges of the ingot on both sides, the outside of the magmatic flow (cold air) and its base (cold ground); in both cases, zones are repeated, giving: wall / cell zone / equiaxed zone / cell zone / wall columns nor planes (for which the designation is 2); but depending on the conditions of observation, the authors cannot distinguish between the two types of marine ice.

for ingots or compact zone (+/-scoria) / (upper) colonnade / entablature / (lower) colonnade / compact zone (+/-scoria) with frozen zones at the top and bottom (outer surfaces) in the case of volcanic flows.

Depending on the overall size of the ingot or the magma flow, the succession may be not complete. In the case of ice, if there were also cooling from below and not just from above, we could have (purely "theoretical") : glacier ice / type 2 -marine ice / type 1 -marine ice / then back to type 2 -marine ice / glacier ice

Other observations reported by the authors

When the authors talk about marine ice (they obviously do not specify whether it is type 1 or 2), we think it could be type 1 -marine ice, or type 2 -marine ice, or both. It depends on the case and/or the observation conditions. Indeed, if the observation is made by drilling into the ice shelf down to its base (or by geophysics), the structures of the possible type 2 -marine ice cannot be easily seen. We "simply" see ice that is different from the glacier ice of the mass. When we see the green color 3 , it is more likely to be type 1 -marine ice.

Type 2 -marine ice has indeed been seen, as the article just quoted devotes a paragraph to it: "striped icebergs". But the authors cannot hide their embarrassment at the explanation of its formation, writing "probably result from tension...". This story of basal crevasses filling with seawater that immediately freezes seems highly improbable to us; how can we account for the regularity of alternating glacier ice and type 1 -marine ice? As far as we are concerned, striped icebergs typically show type 2 -marine ice, structured in the course of its development.

We also wonder why the isotopic profiles (δ 18 O ratio across a strip of marine ice from a striped iceberg), seem incomplete, without documenting all the ice zones that contain them (i.e. also including strips of primitive glacier ice whose supposed crevasses would be filled with marine 3 According to the authors of the article cited, the green color is caused by a combination of effects due to the interaction of light with ice (giving a blue color) and effects due to the incorporation by the ice of fine organic or mineral particles (iron oxides in particular). In the case of type 2 -marine ice, all kinds of impurities are expelled from the growing ice cell. ice). Put another way, we cannot see how the analyzed strip relates to any adjacent strips (which should be glacier ice according to the model?). On the contrary, in our view, the isotopic profile, showing an increase in the ratio δ 18 O inside the band of marine ice compared with its edges, can be explained by a distillation phenomenon; this is well known in other contexts: the ice that forms preferentially incorporates 18 O, and the remaining water, which will then freeze, is depressed in heavy isotope at the edges of the advancing digitation. It would have been interesting to carry out the isotopic profiles overlapping several strips including the supposed glacier ice strips.

Conclusion

For the moment, we are not looking at the various papers on the subject that should be consulted.

The preceding lines are simply a progress report. We are therefore maintaining our initial proposal (the strips in striped icebergs are due to fingering during water freezing at their base because of constitutional supercooling), while adjusting it to associate it with other facts of which we were unaware (type 1-marine ice). We will see in the future whether this framework should be kept as it is, amended, or abandoned. It invites us to make new observations, to take measurements of various kinds (chemical, petrofabric), to read about related subjects, and to debate with experts.

Figure 1

Formation of two types of marine ice, added from below to the glacier ice of the ice shelf. If thermal gradient conditions allow, type 2 -marine ice, structured in prismatic or planar cells, forms directly at the contact with the lower part of the ice shelf. If supersaturation conditions allow, type 1 -marine ice forms within the sea water, by homogeneous Because of its lower density than water, this type 1 -marine ice will rise and stick to the lower surface of the platform, or to the lower boundary of the growing type 2 -marine ice; it will form a layer by agglomeration (as shown in the following figure; we will assume that the two types 1 and 2 of marine ice do not mix, with type 2 ice pushing back type 1, which is debatable).

Figure 2

Overall chart showing the different types of ice that can be observed (under the hypotheses discussed in the text and according to the mode of formation shown in Figure 1). In a) (top) b) (bottom), two slightly different scenarios are presented for the lateral arrest (in the shallower part and in the deeper part) of the two superimposed layers of type 1 and type 2 marine ice. Additional knowledge (temperature values, pressures, salinities, temperature gradients, water movements, etc.) will be needed to choose among the two scenarios (or propose another one).

When we refer to the "authors" below, they are first those of this article.

We have kept number 1 for what is already described in the literature, and encompasses types 1 and 2 in this article. We now restrict the designation 1 s.s. (type 1 -marine ice sensu stricto) to that which is not structured in

Acknowledgements

We would like to thank our glaciology colleagues in Toulouse and Grenoble for their initial exchanges (among them Frédérique Rémy and Christian Vincent), as well as, in a special way, MM Sané and Bidart (naturalist guides) for their photographs and useful comments (without wishing to compromise any for accepting the hypotheses presented). Our thanks also go to the mediators at La Rotonde (CCSTI de la Loire and Ecole des Mines) for the exhibition (autumn 2021) at the origin of this reflection. Jean Le Coze, now deceased, also took part in the discussion.


From Lost to the River: Embracing Sort Proliferation Gaëtan Gilbert, Pierre-Marie Pédrot, Matthieu Sozeau, and Nicolas Tabareau Inria Rennes -Bretagne Atlantique, LS2N

Since their inception, proof assistants based on dependent type theory have featured some way to quantify over types. Leveraging dependent products, the most common way to do so is to introduce a type of types, known as a universe. Care has to be taken, as paradoxes lurk in the dark. Martin-Löf famously introduced in his seminal type theory MLTT a universe U with the typing rule U : U, only for Girard to show that this system was inconsistent. The standard solution is to introduce a hierarchy of universes (U i ) i∈N and mandate that U i : U i+1 .

While trivial from the point of view of the typing rules, this additional index is a major source of non-modularity. One has indeed to pick a level in advance for every universe instance they write, leading to potential conflicts later on. Historically, the first answer to this problem was the introduction of floating universes, i.e. replacing N with a well-founded graph and checking constraints on-the-fly. This solution is simple and works for most practical uses, but is too limited for in-depth universe manipulation as it still forces a global assignment of levels.

Properly solving the issue requires a bit more expressivity, provided by universe polymorphism. Several variants of such a mechanism exist, which can roughly be put on a spectrum of internalization, from McBride's crude but effective stratification [START_REF] Mcbride | Crude but effective stratification[END_REF], to Agda where universe levels are inhabitants of a bona fide type [START_REF] Agda Team | The Agda manual[END_REF]. On the midpoint sit the type theories of Coq [START_REF] Sozeau | Universe Polymorphism in Coq[END_REF] and Lean [START_REF] Carneiro | The type theory of Lean[END_REF] which only allow an external, prenex form of universe polymorphism. These systems are a sweet spot as they are conservative while restoring the lost modularity. So, is everything perfect in the best of all universes? Unfortunately for the user, but fortunately for us, the answer is no. Universe polymorphism is optimal only when there is a single hierarchy of universes. In proof assistants based on CIC, like Coq or Lean, the universe structure follows the PTS tradition, insofar as it has not one single hierarchy, but actually two. Namely, while there is on the one hand the Type i hierarchy that corresponds to U i from MLTT, there is also a universe of propositions Prop1 . The Prop universe is a hodgepodge of several features, mixing impredicativity, compatibility with proofirrelevance and erasability. In order to make this sound, inductive types living in Prop cannot be eliminated in general into Type. This is a source of non-monotonicity, and as a result Prop cannot be treated as a level in universe polymorphism. Not only this forces code duplication between Type and Prop, but this has also annoying consequences in unification where some sorts must be explicitly annotated.

The situation in Coq has recently gotten even worse with the introduction of a third kind of universe, SProp, which classifies definitionally irrelevant types. Thus we have to triplicate all our definitions, but that is the least of our problems. Conversion now depends on the knowledge that a type lives in SProp, which in the Coq case prevents the cumulativity relation SProp ⊆ Type. This introduces even more code duplication compared to Prop. Worse, this completely breaks unification. Up to Coq 8.17, unification picked the sort of a type eagerly to be Type. This worked with a few quirks for Prop ⊆ Type, but this prevented conversion from relying on irrelevance without explicit SProp annotations. The kernel also had to perform a hackish "repair" of ill-annotated terms produced by elaboration.

One could claim that the existence of three hierarchies is an annoyance. We claim that in reality one should desire many more hierarchies. The literature abounds in examples, e.g. the opposition between strict and fibrant types of 2LTT [START_REF] Annenkov | Two-level type theory and applications[END_REF] and the one between pure and effectful types [START_REF] Pédrot | A reasonably exceptional type theory[END_REF]. A decent proof assistant should thus make it possible to write modular code not only w.r.t. universe levels, but also w.r.t. universe hierarchies! As a solution, we propose a novel mechanism of sort polymorphism complementary to the universe polymorphism mechanism.

In a nutshell, it introduces a new algebra of sorts s, which in the case of Coq is

s ::= α | Type | Prop | SProp
where α ranges over sort variables. Sorts are then factorized as a single term constructor Sort s i where s is a sort and i is a level. The usual sorts are then defined as e.g. Type i := Sort Type i and Prop := Sort Prop 0 . Just like levels, we now allow prenex quantifications over sort variables. For this to work properly, we need the typing rules to be stable by sort instantiation. For the negative fragment, we expect the sort of a sort to be Type and the sort of a product to be the sort of its codomain, as per the rules below. for all levels i, j. More generally, these rules seems to be valid for every instance from the literature.

We are currently working on porting this system from the negative fragment to the more complex case of inductive types. The avowed goal is to emulate the infamous template polymorphism feature of Coq, which is a primitive form of level polymorphism with a bit of sort polymorphism blended in. Notably, this allows Coq to type A × B : Prop whenever A, B : Prop. We envision a system leveraging the difference between squashed types, with identity eliminations for sort variables and explicit elimination rules for ground sorts, and unsquashed types, allowing all eliminations.

This mechanism has been partially implemented in the unification algorithm of Coq 8.18. The kernel does not feature a way to quantify over sorts at the level of definitions yet, but the elaboration algorithm now manipulates algebraic sorts. In particular, relevance annotations are parameterized by sort variables, solving the aforementioned issues with SProp. As a byproduct longstanding issues due to the eager choice of Type vs. Prop were solved.

  Sort s i : Type i+1 ⊢ A : Sort s ′ i x : A ⊢ B : Sort s j ⊢ Π(x : A). B : Sort s i∨jThis allows transparently handling impredicative universes, setting e.g. Sort Prop i ≡ Sort Prop j

We voluntarily ignore the case of impredicative Set.


Colmar, France *Corresponding author e-mail: llorrain.lea@gmail.com Phoresy is a specific form of commensalism where a mobile organism affords transport to a less mobile one (White, Morran, & de Roode, 2017). Many phoretic associations have been described [START_REF] Clausen | Phoresy among entomophagous insects[END_REF][START_REF] Binns | Phoresy as Migration -Some functional aspects of phoresy in mites[END_REF][START_REF] Bartlow | Phoresy in animals: review and synthesis of a common but understudied mode of dispersal[END_REF] of which several examples involve freshwater molluscs; presumably because they have limited ability to make long distance dispersal by themselves. Charles [START_REF] Darwin | On the dispersal of freshwater bivalves[END_REF] made pioneering observation of such dispersal in the freshwater mussel Unio complanatus attached to the toe of a duck, as well as supposedly Sphaerium corneum (then named Cyclas cornea) caught on the toes of newts (species not defined). Since then, multiple studies have reported phoretic associations between freshwater bivalves and lizards [START_REF] Lopez | Phoretic behaviour of bromeliad annelids (Dero) and ostracods (Elpidium) using frogs and lizards as dispersal vectors[END_REF], frogs and toads [START_REF] Kolenda | A possible phoretic relationship between snails and amphibians[END_REF], and newts [START_REF] Audibert | Tritons et Sphaeriidae[END_REF].

Among amphibians, newts appear to be often used as 'hosts' by freshwater mussels for two reasons. First, mussels can attach easily to the toes of newts whereas attaching to the skin folds of anurans is more difficult [START_REF] Kolenda | A possible phoretic relationship between snails and amphibians[END_REF]. Second, newt species may move between ponds during breeding season [START_REF] Denoël | Dispersal and alternative breeding site fidelity strategies in an amphibian[END_REF] which would facilitate local mussel dispersal [START_REF] Lopez | Phoretic behaviour of bromeliad annelids (Dero) and ostracods (Elpidium) using frogs and lizards as dispersal vectors[END_REF]. Accordingly, multiple studies have described examples of different newt species carrying small freshwater mussels of the genus Sphaerium. For instance, Sphaerium corneum has been found attached on the toes of Lissotriton helveticus [START_REF] Laza-Martínez | Anfibios y reptiles como potenciales agentes de dispersión de moluscos en el norte ibérico[END_REF][START_REF] Audibert | Tritons et Sphaeriidae[END_REF], Triturus marmoratus [START_REF] Boissinot | Observations de Cyclades communes Sphaerium corneum (Linnaeus, 1758) sur des Tritons marbrés Triturus marmoratus (Latreille, 1800)[END_REF], Ichthyosaura alpestris [START_REF] Audibert | Tritons et Sphaeriidae[END_REF], and Sphaerium nucleus was found to be attached to Lissotriton helveticus and Triturus cristatus [START_REF] Wood | Interactions between freshwater mussels and newts: A novel form of parasitism?[END_REF]. The frequency of this phenomenon may differ widely between sites. For example, a study in Luxembourg, very high mussel densities were found at one site of around 3000 per m², where 23% of the 161 captured newts had Sphaerium nucleus or Pisidium obtusale attached to their toes while occurrence was less frequent at two other sites where mussel attachment to newt toes was recorded on 3.6% and 7% of newts [START_REF] Wood | Interactions between freshwater mussels and newts: A novel form of parasitism?[END_REF].

In this study, we report the observation of Sphaerium nucleus attached to the toes of L.

helveticus. We sampled newts on 15 April 2022 around 23:00 h in two small forest ponds (France; 0 °25' 27.85'' W, 46° 8.0' 49.56'' N, 0° 25' 29.28'' W, 46° 8.0'4 5.24'' N, 70m a.s.l) of about 26 and 75 m 2 respectively. In addition to Lissotriton helveticus, we observed (but not capture) Rana dalmatina and Alytes obstetricans in Pond 1, and Triturus marmoratus, Triturus x blasii, Bufo spinosus, Rana dalmatina, Alytes obstetricans and Pelophylax esculentus in Pond 2. The two ponds host several aquatic plant species. In pond 1, we captured 37 L. helveticus individuals (21 females and 16 males), out of which 8 individuals (21.6 % of individuals, 5 females and 3 males) presented clams attached to their toes (see Figure 1), and 13 presented wounds to their toe (35.1% individuals, 8 females and 5 males). Clams were attached to the toes of forelegs (4 females and 2 males) and hind legs (1 female and 1 male). All individuals had only one clam attached. In pond 2, we caught 69 L. helveticus individuals (57 females and 12 males). Surprisingly, while this pond was situated a hundred meters from the first pond and free living mussels have been seen at the bottom, we did not find clams attached to L. helveticus toes.

Freshwater clams clamped onto newt toes were collected and subsequently identified as belonging to the Sphaerium corneum group, within which it is sometimes difficult to assign a species name based on morphological characters alone. The specimens sampled exhibited a general shell shape intermediate between Sphaerium corneum (Linneaus, 1758) and S. nucleus (Studer, 1820). However, the high porosity of the shells and the size and shape of the hinge teeth allowed these specimens to be assigned to S. nucleus [START_REF] Kořínková | Recent distribution of Sphaerium nucleus (Studer, 1820) (Bivalvia: Sphaeriidae) in the Czech Republic[END_REF].

To our knowledge, this is the first report of Sphaerium nucleus attached to L. helveticus in France although this clam species has been observed attached to L. helveticus in Luxembourg [START_REF] Wood | Interactions between freshwater mussels and newts: A novel form of parasitism?[END_REF]. In the same geographic area of our observation (6 km from our study sites), the closely related S. corneum was found on larger newt species (e.g., [START_REF] Boissinot | Observations de Cyclades communes Sphaerium corneum (Linnaeus, 1758) sur des Tritons marbrés Triturus marmoratus (Latreille, 1800)[END_REF], while in other parts of France, and Spain, S. corneum has been found on L. helveticus [START_REF] Laza-Martínez | Anfibios y reptiles como potenciales agentes de dispersión de moluscos en el norte ibérico[END_REF][START_REF] Audibert | Tritons et Sphaeriidae[END_REF]. Such observations highlight the fact that both Sphaerium species can attach to different newt species, regardless of their size. However, we emphasize the complex identification of species from the Sphaerium corneum group which also include a third species, S. ovale (Férussac, 1807), whose taxonomic validity is still debated [START_REF] Prié | Environmental DNA metabarcoding for freshwater bivalves biodiversity assessment: methods and results for the Western Palearctic (European sub-region)[END_REF]. The morphologic similarities of these taxa may obscure the identification of, but also the true diversity of, the freshwater clam species involved in these phoretic interactions.

Our report suggests that phoresy may be site specific. Indeed, this phenomenon can either be rare [START_REF] Audibert | Tritons et Sphaeriidae[END_REF] or frequent [START_REF] Wood | Interactions between freshwater mussels and newts: A novel form of parasitism?[END_REF] within a population and with variations between sites [START_REF] Wood | Interactions between freshwater mussels and newts: A novel form of parasitism?[END_REF]. The observed differences between the two ponds in the frequency of mussel attachment to newts may be explained by the density of the mussel populations (a parameter we did not assess) and of the presence of other amphibian species.

'Host' selection by phoretic bivalves, if any, still needs to be explored. Indeed, [START_REF] Boissinot | Observations de Cyclades communes Sphaerium corneum (Linnaeus, 1758) sur des Tritons marbrés Triturus marmoratus (Latreille, 1800)[END_REF] have shown that in a pond where L. helveticus, T. cristatus, and T. marmoratus co-occurred, only T. marmoratus was affected, despite the fact that L. helveticus and T. cristatus were more abundant. This suggests that 'host' selection may occur, a process for which chemical orientation of the phoront has already been assessed to play a role in frog and lizard 'hosts' [START_REF] Lopez | Phoretic behaviour of bromeliad annelids (Dero) and ostracods (Elpidium) using frogs and lizards as dispersal vectors[END_REF]. [START_REF] Wood | Interactions between freshwater mussels and newts: A novel form of parasitism?[END_REF] suggest alternatively that newt species behaviours and habitat use, or simply toe size and structure, must also impact the likelihood of attachment of sphaerid mussels. As mussel attachment can cause damage to individuals toes [START_REF] Wood | Interactions between freshwater mussels and newts: A novel form of parasitism?[END_REF], this makes the relationship appear to be parasitic, because the mussels benefits by being facilitated in dispersal while the newts are harmed. Indeed, such damage may interfere with oviposition [START_REF] Wood | Interactions between freshwater mussels and newts: A novel form of parasitism?[END_REF] and eventually reduce newts displacements; however these potential disadvantages are likely to be temporary as newts are capable of limb regeneration [START_REF] Scadding | Limb regeneration in adult amphibia[END_REF].

11

  Hitchhiking freshwater clams: First report of Sphaerium nucleus attached toLissotriton helveticus in FranceLEA LORRAIN-SOLIGON 1* , JEAN-MICHEL BICHAIN 2 , FRANÇOIS BRISCHOUX 1 , JEAN-PIERRE VACHER 1 Centre d'Etudes Biologiques de Chizé, CEBC UMR 7372 CNRS -La Rochelle Université, 79360 Villiers en Bois, France 2 Musée d'Histoire Naturelle et d'Ethnographie de Colmar, 11 rue Turenne, 68000

Figure 1 .

 1 Figure 1. Sphaerium nucleus found on a female Lissotriton helveticus, in a pond in the Deux-Sèvres

ACKNOWLEDGEMENTS

We would like to thank Michal Horsák from Masaryk University (Czech republic) for help with the identification of clam specimens and Mathieu Denoël for his comments on the first draft of the manuscript.