Meeting Abstract

P2.113  Saturday, Jan. 5  Mud versus sand: Morphological and behavioral comparison of two species of burrowing orbiniid polychaetes FRANCOEUR, A.A.*; DORGAN, K.M.; University of California, San Diego; Scripps Institution of Oceanography afrancoe@ucsd.edu

Both morphological and mechanical constraints affect how organisms interact with their environments and consequently their distributions and functional roles. For burrowing animals, the mechanical responses of muddy sediments, elastic materials through which worms burrow by fracture, differ substantially from those of sands, non-cohesive granular materials. We focused on two closely related burrowing orbiniid polychaetes with divergent morphological features to address how morphological and environmental differences affect burrowing behaviors. Naineris dendritica lives in sand, has larger parapodia, and a shovel-shaped head, while Leitoscoloplos pugettensis lives in muddy sediments, has smaller parapodia, and a narrow pointed head. To relate morphological differences to the environments they inhabit, burrowing kinematics were analyzed in transparent analogs for mud and sand: gelatin and cryolite, respectively. Both species slipped backward following each cycle of forward movement but this slip was greater for L. pugettensis compared to N. dendritica. The head of N. dendritica widens following forward movement, and friction around this increased surface area may reduce slipping. Both species twist during peristalsis, further increasing the body thickness, but this is more pronounced and regular in L. pugettensis. Twisting increases the dorso-ventral forces applied to burrow walls, thus facilitating crack propagation in mud, while large parapodia and head widening reduce backward slipping, which in sand could result in collapse of the burrow. These divergent burrowing behaviors along with small morphological differences are consistent with the mechanical constraints on burrowing in the environments that these two species inhabit.