P2.48 Thursday, Jan. 5 The kinematics and anatomical features of undulatory burrowing in Armandia brevis LAW, C. J.*; DORGAN, K. M.; ROUSE, G.; Scripps Institution of Oceanography email@example.com
Recent work has shown that diverse polychaetes extend burrows through muddy sediments by fracture. Radial body expansions near the anterior, achieved both by peristalsis and eversible pharynges and proboscis, apply forces that are amplified at the tip of the crack-shaped burrow, resulting in fracture. The opheliid annelid, Armandia brevis (Moore 1906), lacks an expansible anterior consistent with burrowing by fracture. Instead, A. brevis burrows with a lateral undulatory motion in heterogeneous sediments. We hypothesized that surficial sediments on the scale of this small burrower are granular aggregates rather than a cohesive elastic solid. Kinematic analysis of worms burrowing in clear granular analog materials (cryolite and gelatin grains) showed a wave efficiency during burrowing close to one, indicating minimal slipping and that the grains are not fluidized. In addition, histological 3D reconstruction (Amira 5.3) of the internal anatomy shows transverse muscles extending from the ventral groove that act antagonistically to the longitudinal muscles along the interior of the body wall. Circular muscles—used to contract the body radially during peristaltic locomotion—are lacking in this sinusoidal burrower. Further kinematic analysis of Ophelina acuminata (Oersted 1843), a larger and morphologically similar opheliid species that inhabits fine-grained porous muds, revealed similar non-slipping sinusoidal locomotion. Behaviors and anatomies of both species differ substantially from peristaltic burrowers and are consistent with living in loosely packed granular sediments rather than consolidated elastic muds.