Lobate Ctenophore Research Articles

Mechanical synchronization of ciliary beating within comb plates of ctenophores.

The mechanism which synchronizes the beating of the hundreds of thousands of long cilia making up a ctenophore comb plate was investigated by microsurgical experiments on single comb plates of Mnemiopsis and Pleurobrachia. Comb plates of lobate ctenophores (e.g. Mnemiopsis) are triggered to beat by ciliated grooves which run between the centres of adjacent plates. By creating gaps or introducing mechanical barriers between two parts of a plate, or by severing the cells at the base of a plate, it was shown that physical proximity of cilia, not tissue continuity, is required for synchronization of beating. In Pleurobrachia only the first comb plate of each row is activated by a ciliated groove, and similar experiments to those done on Mnemiopsis gave identical results. Although adjacent comb plates in Pleurobrachia are triggered mechanically by movements of the preceding plates without the need for an intraplate synchronizing mechanism, unilateral amputation of a plate showed that cilia within these plates may also be synchronized by mechanical coupling. Therefore, in cases where the beating of a comb plate is triggered by a ciliated groove - either at the head of a comb row (in all ctenophores) or along the row (lobates only) - the cilia within the plate are synchronized by hydrodynamic coupling forces between them, not by electrical coupling between their cells as assumed previously.

GIANT SMOOTH MUSCLE FIBERS OF THE CTENOPHOREMNEMIOPSIS LEYDII:ULTRASTRUCTURAL STUDY OFIN SITUAND ISOLATED CELLS

The lobate ctenophore Mnemiopsis leydii possesses giant smooth muscle fibers grouped in two sagittal bundles. Functional isolated cells were obtained by an enzymatic digestion of mesoglea and epithelia.Each bundle is made of 30 to 50 multinucleated cylindrical cells which may reach 35 µm in diameter and 4 cm in length. The nuclei and non-contractile organelles (mitochondria, golgi, rough endoplasmic reticulum) are contained in a discontinuous axial core, surrounded by a thick sheath of myofilaments. Thin (actin) filaments, 5.9 nm in diameter, form irregular rosettes around the thick (myosin) filaments, 16.1 nm in diameter. An actin:myosin filament ratio of 7:2 and a myosin density of 249 filaments per µm2 were found in cross-sections of relaxed in situ cells. No dense bodies nor attachment plates were observed. From the coiled shape of contracted single cells and from the rearrangement of organelles in such coiled cells, we propose that myofilaments are organized in thin long myofibrils attached to the ce...

Laboratory culture of the lobate ctenophore Mnemiopsis mccradyi with notes on feeding and fecundity

Collection and culture of the large lobate ctenophore Mnemiopsis mccradyi Mayer is described, including the requirements for successful development of larvae. Particular attention must be given to the collection of these delicate animals, the handling and provision of live microzooplankton of suitable size for the larvae, and the provision of food densities for the adults which neither stimulate “wasteful” feeding nor limit their growth. Although these ctenophores will ingest detritus and algal cells in high concentration, they lost weight at the same rate as starved individuals unless provided with living zooplankton. Under optimum conditions, specimens would lay eggs within 13 days of their own birth. By the 17th day they laid eggs daily, and had produced an average of 8,000 eggs within 23 days after birth. The maximum number of eggs laid by a single wild individual within 24 h after being brought into the laboratory was 10,000. Their high fecundity, rapid generation time, and ability to self-fertilize help to explain their sudden appearance in bloom proportions at periods of high food concentration in the environment, often referred to in the literature.

Mechanisms of Ciliary Co-ordination in Ctenophores

ABSTRACT An experimental analysis of ciliary metachronism was performed on ctenophores of two types: those with a continuation of the ciliated groove running between adjacent comb plates (lobates), and those in which the ciliated grooves end at the first plate of each comb row (cydippids and beroids). The results showed that the comb plates of cydippids and beroids are co-ordinated by mechanical forces arising from the movement of the plates themselves. Only along the ciliated grooves and at their junctions with the comb rows is a neuroid conduction process likely in this group of ctenophores. Ctenophores with an interplate ciliated groove, on the other hand, do not depend on mechanical interaction between active plates for co-ordination. Instead, the lobates use neuroid conduction at the junction between the interplate ciliated groove and the comb plate, at the junction between adjacent interplate ciliated grooves, and probably along the ciliated grooves and interplate ciliated grooves as well. Ciliary co-ordination may therefore be entirely neuroid in lobate ctenophores. In both types of ctenophores the comb plates may be triggered to beat by depolarization of the comb-plate cells. Electrical excitation of a plate could be caused by mechanical deformation of its base arising from the motion of the preceding plate (in cydippids and beroids), or by a neuroid process at the interplate ciliated groovecomb plate junction (in lobates). These findings resolve a long-standing controversy over the mechanism of ciliary co-ordination in ctenophores.

Feeding of a Ctenophore, Bolinopsis Infundibulum (O. F. Müller)

Bolinopsis infundibulum, a lobate ctenophore, is known to occur from the arctic to the Mediterranean in European waters, and from the arctic to the Gulf of Maine in North American waters1–3. Full taxonomic details are given by Chun1 and Krumbach2.