TYLER, S.*; HOOGE M.D.: Squeezing through tight spaces–functional morphology of musculature of Gnathostomula armata

Gnathostomulids live in fine-grained sediments with pore sizes that are typically smaller than the diameter of their bodies. How they negotiate such spaces is something of a mystery, but whole-mount preparations of Gnathostomula armata stained with a phalloidin-linked fluorescent marker to reveal its musculature under confocal scanning laser microscopy provides some clues. The musculature is unlike that of other soft-bodied meiofaunal phyla, being dominated by longitudinal fibers that run the full length of the body and having circular fibers only in the posterior half of the body. Conceivably, the strong circular muscles may be used to push the anterior body half through restricting pores, and the longitudinal elements may then pull the rest of the body through. Muscles of the pharynx visible in such preparations are positioned to move the cuticularized mouthparts in ways appropriate to scraping up and grasping the bacteria and fungal hyphae on which gnathostomulids are believed to feed.