I thought I would try something new this week - a different geological definition every day. All terms will come from the third edition of the Dictionary of Geologic Terms*. Let me know if you hate this ;) Happy St. Patrick's Day!
arthrophycus (ar-thro-phy'-cus) A sand-filled rounded furrow, curving and branching, with faint but regularly spaced transverse ridges commonly bearing a median depression, probably representing a feeding burrow but also variously regarded as an inorganic structure or a trail produced by a worm, mollusk, or arthropod crawling over a soft-mud surface. The "branches" of the trace fossil may reach 60 cm in length. It was originally described as a plant fossil (seaweed) and assigned to the genus Arthrophycus. (page 29)
"Arthrophycus and other trace fossils in the Red Mountain Formation form a group related by interconnection, intergradation, similar dimensions, and morphologic similarities that, taken together, strongly suggest a common tracemaker." [link]
*Bates, R.L. and J.A. Jackson. 1984. Dictionary of Geologic Terms. American Geological Institute.