Burrowing by small polychaetes – mechanics, behavior, and muscle structure of Capitella sp

Meeting Abstract

P2.95  Sunday, Jan. 5 15:30  Burrowing by small polychaetes – mechanics, behavior, and muscle structure of Capitella sp. GRILL, S.*; DORGAN, K. M.; Hochschule Bremen; Dauphin Island Sea Lab sgrill@stud.hs-bremen.de

Most worms extend burrows in mud, which acts as an elastic solid, by fracture. To extend a burrow by cracking, the worm applies force dorso-ventrally, which is amplified at the crack tip. Smaller worms are limited in the extent to which they can displace sediments, and therefore in how much force they can apply to burrow walls. We hypothesized that a transition in burrowing strategy, specifically the ability to burrow by fracture and muscle morphology, would indicate a minimum body size below which burrowing by fracture would not be feasible. Kinematics of burrowing in a mud analog, external morphology and muscle structure were examined in juveniles and adults of the polychaete, Capitella sp., which is small enough that burrowing by fracture may potentially be limited by body size. Capitella sp. moves by peristalsis, and no obvious differences were observed among worms of different sizes; even very small juveniles were able to burrow through a clear mud analog by fracture. Interestingly, we found that in addition to longitudinal and circular muscles needed for peristaltic movements, left- and right-handed helical muscles wrap around the thorax of worms of all sizes. We developed a physical model to test whether contraction of these helical muscles may increase the internal pressure in the thorax, enabling even small worms to extend burrows by fracture. Further research is needed, however, to determine whether surficial sediments inhabited by small worms fail by fracture or plastically deform under forces applied by Capitella sp. Our results raise questions about whether worms in a size range close or below to the limit of being able to extend burrows by fracture, including juveniles of larger species, might show additional adaptions to enable locomotion.

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