Tricellaria occidentalis ( Trask, 1857 )

Dyrynda, P. E. J., Fairall, V. R., Ambrogi, A. Occhipinti & d’Hondt, J. - L., 2000, The distribution, origins and taxonomy of Tricellaria inopinata d’Hondt and Occhipinti Ambrogi, 1985, an invasive bryozoan new to the Atlantic, Journal of Natural History 34 (10), pp. 1993-2006 : 1999

Tricellaria occidentalis ( Trask, 1857)

Trask (1857) was brief but very de®nite in describing the presence of three autozooids within each internode with respect to a taxon collected from the Paci®c coast of the USA (at unspeci®ed locations between Santa Barbara and Cape Flattery) and named Menipea occidentalis . The scuta were perceived simply as stout curved spines, and no mention was made of the presence of any marginal bi®d spines. Most autozooids bore lateral avicularia. Hincks (1882), apparently unaware of Trask’s description, introduced Menipea compacta form triplex to describe a taxon from the Queen Charlotte Islands (Paci®c coast of Canada) sharing the fundamental characteristics of T. occidentalis .

Robertson (1905) erected a variety, T. occidentalis var. catalinensis whilst describing bryozoans collected between San Diego and the Queen Charlotte Islands. In addition to recording T. occidentalis (as Menipea occidentalis ), she erected M. occidentalis var. catalinensis in which the internodes were described as usually consisting of 5±7 autozooids. Reference was made to the occurrence of large fanshaped scuta with spiny margins, and some bi®d spines. Robertson’s account can easily be interpreted to mean that the characteristics distinguishing T. occidentalis var. catalinensis from the nominate species are mutually exclusive, e.g., extensive scutum morphology in the former and a simple form in the latter. That this did not accurately describe the situation is apparent from subsequent accounts. The distinction between T. occidentalis and T. occidentalis var. catalinensis was sustained by subsequent authors working in the Paci®c including Yanagi and Okada (1918) and Okada (1929) in Japan, and O’Donoghue and O’Donoghue (1923) and Osburn (1950) in North America. All, however, commented on the variety of certain characteristics, notably scutum morphology, evident within individual colonies of T. occidentalis var. catalinensis . SileÂn (1941), also noted this and concluded that since the two morphologies apparently intergraded within a colony, T. occidentalis and T. occidentalis var. catalinensis were one and the same. We would suggest that this in turn led to more recent Paci®c workers not distinguishing between T. occidentalis and T. occidentalis var. catalinensis . Soule et al. (1995) have retained this position in their recent detailed taxonomic appraisal of T. occidentalis . We believe, however, that T. occidentalis var. catalinensis is more akin, if not identical, to T. inopinata (see above).

Unfortunately, we have been unable to locate type material of Menipea occidentalis and have been led to believe that it may no longer exist. We have, however, had access to early and recent material of T. occidentalis from various localities along the west coast of North America (BMNH 1877.3.7.5ÐSan Francisco; BMNH 1991.9.27.2.3ÐPort Townsend, Washington State; BMNH 1867.1.9.35 ÐVancouver; BMNH 1963.2.14 .2 ÐN.W. America), and paratype material of Menipea compacta form triplex ( Hincks, 1882) from the Queen Charlotte Isles (BMNH 1899.7.1.666 Ð Vancouver, Busk Collection). The material is strikingly distinctive in appearance and very diOEerent from the two taxa described below. In all specimens, branches consist of characteristically`squat’ autozooids occurring in most internodes as triplets, although in some specimens some internodes with ®ve autozooids are evident towards the branch tips. The scuta are invariably slender or slightly spatulate (®gure 2) and we are unable to distinguish any bi®d marginal spines in any of the colonies examined. Another distinctive characteristic is the occurrence of two very prominent, elongate spines in each axil (the angle between bifurcating branches).