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Genus Polyphysia Quatrefages, 1866 Polyphysia crassa fauveli (Laubier, 1959) DISTRIBUTION: NA, CA. LITERATURE RECORDS: Amoureux 1983 c; Požar-Domac 1994; Zavodnik & Kovačić 2000; Castelli et al. 2008. OTHER REPORTED NAMES: Eumenia crassa fauveli Laubier, 1959; Eumenia crassa Laubier, 1959., Published as part of Mikac, Barbara, 2015, A sea of worms: polychaete checklist of the Adriatic Sea, pp. 1-172 in Zootaxa 3943 (1) on page 102, DOI: 10.11646/zootaxa.3943.1.1, http://zenodo.org/record/244663, {"references":["Amoureux, L. (1983 c) Annelides Polychetes de l'Adriatique. Thalassia Jugoslavica, 19, 15 - 21.","Pozar-Domac, A. (1994) Index of the Adriatic Sea Polychaetes (Annelida, Polychaeta). Natura Croatica, 3, (Supplement 1), 1 - 23.","Zavodnik, D. & Kovacic, M. (2000) Index of marine fauna in Rijeka Bay (Adriatic Sea, Croatia). Natura Croatica, 9 (4), 297 - 379.","Castelli, A., Bianchi, C. N., Cantone, G., Cinar, M. E., Gambi, M. C., Giangrande, A., Iraci Sareri, D., Lanera, P., Licciano, M., Musco, L. & Sanfilippo, R. (2008) Annelida Polychaeta. In: Relini, G. (Ed), Checklist della flora e della fauna dei mari italiani (Parte I). Biologia Marina Mediterranea, 15 (Supplement 1), pp. 327 - 377."]}

The burrowing mechanisms of two soft-bodied marine invertebrates, Polyphysia crassa (Annelida: Polychaeta) and Priapulus caudatus (Priapulida) were re-examined and extended utilizing computer image analysis. Predetermined points on sequential photographs of animals burrowing in methylcellulose (an artificial medium of high transparency) were digitized and stored as x, y coordinates from which were calculated segment length, width, and volume in addition to producing real and straightened images of the animal on a plotter. Both species are adapted to soft substrata and both utilize a direct peristaltic wave to advance the body into a cavity or loosened area formed by anterior structures. Polyphysia displaces and loosens the substratum with lateral scraping movements of its anterior six segments (the “head region”) while Priapulus makes a large cavity anteriorly by the forceful eversion and dilation of the praesoma. Unlike Priapulus, Polyphysia utilizes a different method of locomotion when moving on the mud surface as opposed to burrowing, the former involving two direct peristaltic waves at a time and negligible internal pressures resulting in nearly continuous advance. However when burrowing, Polyphysia, like Priapulus, utilizes a single direct peristaltic wave alternating with phasic pressure pulses which advance the animal in step-wise fashion.