Organization of Buccal Cone Musculature in the Pteropod Mollusc Clione limacina.

The pteropod mollusc Clione limacina is a feeding specialist, preying on shelled pteropods of the genus Limacina. Specialized prey-capture structures, called buccal cones, are hydraulically everted from within the mouth to capture the prey. Once captured, the prey is manipulated so the shell opening is over the mouth of Clione. Analyses of high-speed cine sequences of prey capture suggest that the mouth is actively opened rather than passively forced open by buccal cone eversion. The inflated buccal cones are initially straight and form a wide angle (maximum, 113°) prior to prey contact. Individual buccal cones bend orally following prey contact, suggesting a sensory trigger. To determine the muscular basis of buccal cone movements, the musculature of the buccal cones is described. Three distinct muscle fiber types include circular smooth muscle, longitudinal smooth muscle, and longitudinal striated muscle. The organization, distribution, and innervation of the muscle types suggest that circular muscle is used during buccal cone eversion, longitudinal smooth muscle is used for buccal cone withdrawal, and longitudinal striated muscle is used for oral bending of the buccal cones after prey contact and for manipulation of the prey.

Changes in wingstroke kinematics associated with a change in swimming speed in a pteropod mollusk, Clione limacina.

In pteropod mollusks, the gastropod foot has evolved into two broad, wing-like structures that are rhythmically waved through the water for propulsion. The flexibility of the wings lends a tremendous range of motion, an advantage that could be exploited when changing locomotory speed. Here, we investigated the kinematic changes that take place during an increase in swimming speed in the pteropod mollusk Clione limacina. Clione demonstrates two distinct swim speeds: a nearly constant slow swimming behavior and a fast swimming behavior used for escape and hunting. The neural control of Clione's swimming is well documented, as are the neuromuscular changes that bring about Clione's fast swimming. This study examined the kinematics of this swimming behavior at the two speeds. High speed filming was used to obtain 3D data from individuals during both slow and fast swimming. Clione's swimming operates at a low Reynolds number, typically under 200. Within a given swimming speed, we found that wing kinematics are highly consistent from wingbeat to wingbeat, but differ between speeds. The transition to fast swimming sees a significant increase in wing velocity and angle of attack, and range of motion increases as the wings bend more during fast swimming. Clione likely uses a combination of drag-based and unsteady mechanisms for force production at both speeds. The neuromuscular control of Clione's speed change points to a two-gaited swimming behavior, and we consider the kinematic evidence for Clione's swim speeds being discrete gaits.

Serotonergic cerebral cells control activity of cilia in the foregut of the pteropod mollusk Clione limacina.

Bilaterally symmetrical pair of serotonergic cells, named C1 in Clione, has been described in the cerebral ganglia of all gastropod species. Here we describe a new role of C1 cells in gastropod mollusks: control of activity of ciliated epithelium in the foregut. Detailed morphological investigation of C1 neurons in the pteropod mollusk Clione limacina revealed that these cells among other destinations send their neurites into foregut where they produce intense arborization with large varicosities along the processes. Intracellular stimulation of a single C1 induced pronounced activation (often followed by inhibition) of cilia lining the foregut. This activation was substantially reduced by serotonin antagonist mianserin. Bath application of serotonin also induced transient increase in ciliary transport rate, followed by inhibition of ciliary activity up to its full cessation in some areas of isolated foregut. These data suggest that C1 in Clione may use serotonin to influence cilia in the foregut. Taking into account high homology of serotonergic cerebral cells across studied species we can speculate that these cells may be involved in the neural control of cilia in the foregut in other gastropod mollusks.

Buccal neurons activate ciliary beating in the foregut of the pteropod mollusk Clione limacina.

Beating of cilia lining the foregut of gastropods facilitates the swallowing of food and, therefore, plays a role in feeding behavior. Despite the fact that neural control of feeding is well studied in mollusks, no neurons controlling ciliary beating in the foregut have been identified to date. Here we describe for the first time a pair of buccal neurons innervating the foregut of Clione. Intracellular stimulation of these neurons induced vigorous activation of cilia lining the foregut in a semi-intact preparation. Using immunochemistry labeling, buccal foregut cells were found to contain peptides similar to CNP neuropeptides of the terrestrial snail Helix lucorum. Application of DYPRL-amide, a member of the Helix CNP peptide family, mimicked the effect of buccal foregut cell stimulation on ciliary activity. Induction of fictive feeding in an isolated CNS preparation resulted in the activation of buccal foregut cells suggesting that these cells control ciliary beating in the foregut during feeding. Thus, cilia-activating buccal neurons may represent a new intrinsic element of the neural control of feeding in gastropods.

Trade-off between aerobic capacity and locomotor capability in an Antarctic pteropod.

At -1.8 degrees C, the waters of Antarctica pose a formidable physiological barrier for most ectotherms. The few taxa that inhabit this zone have presumably made specific adjustments to their neuromuscular function and have enhanced their metabolic capacity. However, support for this assertion is equivocal and the details of specific compensations are largely unknown. This can generally be attributed to the fact that most Antarctic organisms are either too distantly related to their temperate relatives to permit direct comparisons (e.g., notothenioid fishes) or because they are not amenable to neuromuscular recording. Here, as a comparative model, we take advantage of 2 pelagic molluscs in the genus Clione to conduct a broadly integrative investigation on neuromuscular adaptation to the extreme cold. We find that for the Antarctic congener aerobic capacity is enhanced, but at a cost. To support a striking proliferation of mitochondria, the Antarctic species has shed a 2-gear swim system and the associated specialized neuromuscular components, resulting in greatly reduced scope for locomotor activity. These results suggest that polar animals have undergone substantial tissue-level reorganizations to accommodate their environment, which may reduce their capacity to acclimate to a changing climate.