Functional morphology of prey ingestion by Placetron wosnessenskii Schalfeew Zoeae (Crustacea : Anomura : Lithodidae)

The relationship between the morphology and functions of the feeding append ages of first-stage zoeae of the lithodid crab Placetron wosnessenskii Scha lfeew during ingestion is explored in this study. The preoral chambers of t hese zoeae are bordered on all sides, with the labrum and mandibles forming the anterior borders, the paragnaths;and sternal projection together creat ing the posterior Boundaries, and the maxillules forming the sides. The max illules are the sole pair of appendages responsible for prey manipulation i mmediately preceding ingestion. Maxillules are capable of remarkable plasti city of movement, enabling them to grasp, control, and redirect violently s truggling prey (Artemia sp. metanauplii). The asymmetrical mandibles tear a nd grind the prey, working against each other with rotating motions. Two separate ratchet-like coordinations of the appendages were seen, each o f which enabled the zoea to maintain a firm grasp on the prey while renewin g points of leverage for ingestion. The mandibles hold prey in position whi le the maxillules regrab it to push it farther into the mouth. Similarly, t he labrum holds the prey while the mandibles prepare for a new grinding rot ation. Capture and ingestion of an algal cell by a rapid outward hinging and inwar d clasping of the mouthparts was seen in one videotaped sequence. Gut fluor escence after introduction of various algal species reveals an ability to i ngest a range of particle sizes. This plasticity of feeding behaviors allow s the zoeae to ingest a range of food items, and thus meet their nutritiona l needs.