Meeting Abstract

P2.151  Saturday, Jan. 5  Seawater flow into the digestive system of actinotroch larvae (Phoronida) JAECKLE, W.B.*; Ill. Wesleyan Univ, Bloomington wjaeckle@iwu.edu

Collection of particle foods by actinotroch larvae involves the cilia of the larval tentacles, the muscular elevation of the preoral lobe, and the ciliature of the vestibular epithelium. Particles, ingested by larvae, are likely to be contained within a volume of seawater that enters the digestive system. However, the existence of this seawater flow in the absence of particulate foods is unknown. To test for the presence of a constitutive flow of seawater into the digestive system, larvae of Phoronis architecta were exposed to the iron-containing protein, ferritin (0.5-1.0 mg/mL), for < 5 h. Larvae were collected from plankton tows, transferred into 0.2 µm-filtered seawater, and then incubated in filtered seawater containing ferritin. The presence and distribution of the iron-containing label in experimental and control larvae was detected using the ferrocyanide reaction. The blue reaction product was present in the digestive system of all larvae exposed to ferritin; no label was detected in the digestive system of control larvae. In whole mounts and sectioned larvae, the label was located within apparent vesicles in cells of all regions of the digestive system except the distal proctodaeum. In the lumen of the proximal proctodeum the reaction product was also found within a consolidated, acellular mass. The presence of an iron-containing label in larvae previously incubated in particle-free seawater containing ferritin supports the existence of a constitutive flow of seawater into the digestive system. The appearance of the label in vesicles within cells of the digestive system indicates pinocytosis of the dissolved protein and presents potential alternate sites in feeding larvae for the assimilation of dissolved organic materials present in seawater.