RETILAMINA FROM NEW JERSEY: TROPHIC STRATEGY IN A BIZARRE ARCHAEOCYATH

A fluorite-bearing limestone from the Lower Cambrian Leithsville Formation has yielded the first New Jersey specimens of the unusual encrusting archaeocyath Retilamina. Retilamina develops an irregular sheet morphology that flexes upward to form cavity spaces filled with sparry calcite. The New Jersey Retilamina is comparable to R. amourensis from Newfoundland, but shows no evidence for development of stereoplasm. Stolonic projections from individuals of the New Jersey Retilaminaextend into the sheltered cavity spaces beneath the skeletal sheet.

Retilamina occurs in both eastern North America (Labrador, Newfoundland [R. amourensis]; New Jersey [cf. R. amourensis]); and western North America (Great Basin, Sonora [R. debrenneae]). All known occurrences of the genus are found in similar depositional environments, implying a consistent mode of life for Retilamina across its range. Retilamina's trophic strategy, however, is difficult to discern. The passive filter‑feeding method of typical, erect cup‑shaped archaeocyaths would function poorly at the lower current speeds encountered in Retilamina'sseafloor surface habitat.

Retilamina's stolonic projections into cavity spaces pose an additional problem, as flow velocity would presumably be even lower in these cryptic spaces (perhaps 0.1 mm/s or less). Cavity water would be lacking in sufficient suspended particulate food matter to permit efficient filter feeding. We propose that Retilamina fed by direct absorption of dissolved nutrients released by the breakdown of organic matter in cavity pore spaces, supplemented by capture of mobile substrate bacteria as they moved through pore fluids toward the sediment‑water interface.