Sperm chemotaxis in siphonophores
: identification and biochemical properties of the attractant.
According to pioneering midwater explorer Bruce Robison, a biologist at the Monterey Bay Aquarium Research Institute (MBARI) in Moss Landing, California, ignorance of these animals "meant that we probably underestimated the biomass of the sea by a third." The deep ocean's midwaters, he adds, "contain the largest animal communities on Earth." And within these communities, siphonophores
rule, consuming so much food that they compete with big, hard-bodied carnivores such as sharks and whales.
This high trophic availability supports the highest values of zooplankton biomass registered in the same fjords, where Palma & Aravena (2001) have been recorded highest densities of eudoxids (siphonophore
The most important studies focused on broad phylogenetic description of eukaryotic picoplankton diversity, diatom and dinoflagellate, tintinnid ciliate, and siphonophore
diversity, with especially detailed and enlightening studies of tintinnids and siphonophores
(Dolan et al., 2007; Palma & Silva, 2006).
The secretion and development of nematocysts in a siphonophore
While the slugs without shells are able to attack Cnidaria and devour their tentacles--indeed, even those of a Portuguese-man-of-war siphonophore
(Thompson and Bennett, 1969)--they also elegantly creep, move, bend, and swim with a flexible skin, waving their rhinophores and cerata on contact with their prey's tentacles.
In the two siphonophore
species examined, Porpita and Physalia, the tentacles bear large assemblies of cnidocytes, called cnidosacs, that appear as a line of hemispheres or spheres arranged along one edge of each tentacle.
This point circulates in the x-y plane in one direction (clockwise for the ascidian spermatozoa observed in the vicinity of the glass slide surface, and counterclockwise for the siphonophore
spermatozoa), with a radius of curvature that changes depending on the attractant concentration and on time.
Seasonal abundance of the siphonophore
, Nanomia bijuga, in Monterey Bay.
Influence of siphonophore
behavior on their natural diets; evidence for aggressive mimicry.
The most transparent tissues (at 480 nm) were hydromedusa mesoglea (66%), followed by Cystosoma (42%), ctenophore mesoglea (41%), siphonophore
mesoglea (39%), pelagic tunicares (excluding Pyrosoma) (33%), Sagitta (24%), and the translucent portions of the hydromedusae and ctenophores (24%).