Diversity of macrociliary size, tooth patterns, and distribution in Beroe (Ctenophora)

Revision of Beroidae (Ctenophora) in the southern seas of Europe: systematics and distribution based on genetics and morphology

Genetic and morphological analyses were used to revise historical controversies in identities of Beroe species in the southern seas of Europe. DNA analyses with ITS sequences were used to explore their phylogenetic relationships. Three species of Beroe were initially listed as occurring in the Mediterranean Sea. Recently, the specimens were often re-identified using genetic analyses, causing confusions of identity. In 1997, a non-native Beroe was introduced into the Black Sea, which established there and spread to the adjacent seas, adding more controversy and confusion to species identification in this group of comb jellies.

Our revisions suggest the following systematic changes: (1) re-naming of the species from what was initially labelled as Beroe ovata, and later as B. cucumis (sensuMayer, 1912), to Beroe pseudocucumis sp. nov.. (2) Beroe mitrata but not Beroe ‘anatoliensis’ inhabits the Aegean Sea, as was reported previously. (3) Beroe ovata is the only species of Beroidae that became invasive and should be used with the authority of Bruguière, 1789, but not in the sense of Mayer, 1912. (4) Beroe forskalii appears to be represented by two species in the Mediterranean and in the Antarctic, but further justification is needed. (5) Beroe cucumis is a species of bipolar occurrence, inhabiting both subpolar areas and its recent definition as Beroe ‘norvegica’ is incorrect.

Dynamic control of reversible cell adhesion and actin cytoskeleton in the mouth of Beroë

Cell-cell adhesion in the various types of intercellular junctions of differentiated tissues is relatively stable and permanent. In migrating cells of embryos, or in wound closure, inflammatory responses and tumors of adult tissues, however, bonds between cells are made and broken and made again, i.e., cell-cell adhesions are transient and reversible. These nonjunctional contacts lack the organized structure of intercellular junctions, but may initiate their tissue-specific formation during development. Investigation of dynamic, nonjunctional cell-cell adhesions has been hampered by the asynchronous and heterogeneous distribution of these transient contacts among groups of moving cells. We recently discovered a novel system of reversible cell adhesion in a differentiated tissue that overcomes this difficulty. Here I review our current knowledge of this system, particularly its unique experimental advantages for investigating the mechanisms and control of dynamic cell adhesion.

Middle Cambrian ctenophores from the Stephen Formation, British Columbia, Canada

The Ctenophora are a marine phylum of gelatinous swimmers and crawlers, with a minimal fossilization potential. To date only two acceptable fossil specimens are known, both from the Devonian Hunsruck Slate. Here we re-describe the single specimen of Fasciculus vesanus from the Phyllopod bed of the Burgess Shale (Middle Cambrian). The globose body bore two sets of comb-rows: one elongate and estimated to total ca.16, the other shorter and totalling ca. 64, so giving a total of ca. 80. Internally there were at least two and possibly four prominent organs, each consisting of an elongate series of lobes. Xanioascus canadensis gen. nov., sp. nov. is recorded from a horizon low in the Stephen Formation, from the Glossopleura zone. It is more similar to extant ctenophores than F. vesanus , but the comb-rows total ca. 24. These converge on the aboral pole, where there is evidence for the polar fields. The comb-rows stop short of the oral area, which is poorly defined. Internally prominent ovoid bodies are sometimes present, but their significance is uncertain. Ctenorhabdotus capulus gen. nov., sp. nov. occurs in the Bathyuriscus-Elrathina zone of the Stephen Formation. It is best known from the Raymond Quarry of the Burgess Shale, but also occurs in the underlying strata, including the Phyllopod bed. The comb-rows appear to have totalled 24, and converged towards the aboral pole, adjacent to which they amalgamate as groups of three rows each. In the fossils the comb-rows then join eight strands, possibly representing the meridional canals, that meet as a ring. In addition, in each group of three comb-rows the central row appears to have been conspicuously shorter than those flanking it. The aboral pole also bore a prominent capsule, presumably housing the statocyst. The oral area, which lacks the comb-rows, bore a voluminous mouth, apparently surrounded by a folded margin with possible musculature. These Cambrian ctenophores differ from the Devonian and Recent taxa in a number of ways. They have a larger number of comb-rows and apparently an absence of tentacles. In addition, structures found in the Cambrian ctenophores, such as the lobed organs of F. vesanus and the ovoid bodies of X. canadensis lack obvious counterparts in living species. The wider affinities of the ctenophores remain mysterious, but they probably evolved very early in the metazoan radiations, perhaps from an animal with an anterio-posterior axis and a ciliated surface.