Feeding and the possible role of the prosboscis and mucus cover in the ingestion of microorganisms by rhynchoteuthion paralarvae (Cephalopoda; Ommastrephidae)

Abstract

The diets of 72 rhynchoteuthion paralarvae of Illex argentinus (Catellanos, 1960) (1.0-8.0 mm ML) and two other ommastrephid squids from southern Brazil (28°09'S- 34°20'S) were investigated by examination of their digestive tracts and mucus covering. A great diversity of microorganisms was identified on the mucus cover, on the proboscis suckers and in the digestive tracts of the rhynchoteuthions, including dinoflagellates, flagellates, ciliates, cysts and bacteria. Among the digestive tracts of Illex argentinus rhynchoteuthions examined, 55.6% were empty, 9.7% contained unrecognizable food and 34.7% contained recognizable food, which included microorganisms on mucus as well as copepod appendages. Microorganisms on mucus were found mainly inside the digestive tracts of small paralarvae, which also displayed high bacterial densities on their mucus cover. The presence of bacteria on the mucus cover and of mucus in the digestive tracts decreased with increasing paralarval size. The smallest rhynchoteuthion with copepod appendages in its digestive tract was 3.7 mm ML. These findings suggest that mucus enriched with microorganisms may be important in the diet of small rhynchoteuthions, and it is hypothesized that mucus could act as a substrate for microbial growth. The proboscis may play an important role in the ingestion of mucus.