Hornera currieae n. sp. (Cyclostomatida: Horneridae): a new bathyal cyclostome bryozoan with reproductively induced skeletal plasticity

Here we describe a new hornerid, Hornera currieae n. sp. (Bryozoa: Cyclostomatida) from bathyal depths across the New Zealand region. Colonies are irregular, finely branched fans attaining ~40 mm or more in height. Key characters include: (1) thick, semi-hyaline porcellanous skeleton; (2) loss or reduction of nervi (longitudinal striae) away from growing tips; (3) sparse, threadlike cancelli; and (4) small (61–87 µm), widely spaced autozooidal apertures. Diagnostic hornerid traits possessed by H. currieae n. sp. include vertical ancestrular tube, periancestrular budding of daughter zooids, and skeletal ultrastructure dominated by hexagonal semi-nacre grading to pseudofoliated fabric. The abfrontal incubation chamber develops from a cryptic tube arising from the frontally positioned aperture of the fertile zooid. We used SEM, micro-CT and electron backscatter diffractometry (EBSD) to investigate the ultrastructure and internal architecture of H. currieae n. sp. EBSD reveals that crystalline c-axes of laminated crystallites are perpendicular to skeletal walls. Threadlike cancelli, which traverse secondary calcification, connect autozooidal chambers to the colony-wide hypostegal cavity. Micro-CT reveals that abfrontal cancelli usually bend proximally towards the base, but turn distally towards reproductively active regions of the colony in synchrony with gonozooid development. The zone of affected cancelli extends for 4–7 branch internodes below the gonozooid. We assessed whether skeletal ultrastructure was similarly affected, but neither cancellus direction, nor gonozooid proximity, were predictive of the crystallite imbrication direction. We hypothesise that (1) hornerid cancelli are active conduits for colonial metabolite transport and (2) that changes in gradients of metabolites and/or reproductive morphogens within the hypostegal cavity affect cancellus morphogenesis. Potentially, H. currieae n. sp. skeletons may preserve a record of intra-colony metabolite translocation dynamics over time.

Morphology and development of the early growth stages of an Indonesian Stylaster (Cnidaria: Hydrozoa)

The aim of this work is to describe the skeletal morphology of the early stages of the colonies of Stylaster sp., settled on artificial panels placed along a coral reef in the Bunaken Marine Park (North Sulawesi, Indonesia). The youngest observed stage deriving from the planula settlement is represented by a well developed primary cyclosystem symmetrically budding two secondary cyclosystems in a very early phase of growth. Successively each cyclosystem starts its vertical growth producing new cyclosystems sympodially arranged. At the same time the basal disc of the first cyclosystem enlarges producing a flattened crust from which new colonies arise. Vertical and encrusting forms are considered different modalities to face the problem of space competition in marine benthic organisms. The colonies of Stylaster sp. grow using both strategies resulting in the asexual reproduction of several colonies from a single settled planula. The new cyclosystems originate as small volcano-like elevations having the centre filled with calcium carbonate. Gradually this calcareous matrix dissolves starting from its perimetric zone and leads to the formation of the gastrostyle and the ring palisade. It is plausible that the cells composing the stolon nets deeply pervading the calcareous structure are responsible for this skeletal plasticity.