Natural History Observations on the Gastropod Shell-Using Amphipod Photis Conchicola Alderman, 1936

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Photis conchicola is a tube-building marine amphipod that uses empty gastropod shells as a portable shelter. Observations in San Luis Obispo County, California, revealed that small (1-10 mm) empty shells are used as domiciles to contain soft tubes constructed from silk spun by P. conchicola in intertidal and subtidal regions. Domiciles are attached to marine plants in maximum densities of 38 per 1/16 m2. Selection of plants is nonspecific with attachment accomplished by cementing a portion of the tube to the chosen plants, principally algae. Typical habitats included pockets of sand and shell debris with a low level (=30 cm) algal canopy. Although the adult sex ratio is near unity, the majority of solitary domicile inhabitants were males within intertidal and subtidal regions. Adult males with gravid females were the most common cohabitants in the intertidal area. Solitary juveniles were collected most frequently within the subtidal region where initial shell-searching is presumed to occur. Empty gastropod shells typically selected as domiciles were of the same species of gastropods sympatric on algae to which domiciles were attached. Over 80 per cent of all gastropod taxa selected for occupancy were generally in good condition (no broken apertures, spines, or shells with encrusting bryozoans) with natural colors and banding patterns apparent. Increased survivorship of P. conchicola due to reduced predation may result from appearing as an unpalatable, cryptic, or disruptively colored prey item.