POLYPIDE MORPHOLOGY AND FEEDING BEHAVIOR IN MARINE ECTOPROCTS

Observations on living colonies of 56 species of marine bryozoans from Florida and Panama have shown that these organisms possess a variety of morphological and behavioral adaptations related to feeding activities. In the species studied mean lophophore diameter varies from 187 to 1,012 fivn, mouth size from 15 to 91 ium, and tentacle number from 8 to 31. Polypide morphology, particularly introvert length and lophophore symmetry, also varies from species to species, and this variation is linked to behavioral strategy. With respect to individual polypide behavior species can range from passive filterers (e.g. Crisia elongala), to tentacle feeders (e.g. Pasylhea lulipifera), to cage-captors (e.g. Bugiila neriiina), to particle jugglers (e.g. Siindanelta sibogae). Colony-wide patterns of morphology and behavior also reflect various methods of dealing with water currents. These range from weakly integrated patterns characterized by separation and a high degree of functional independence of individual polypides to highly integrated patterns in which both skeletal morphology and polypide orientation serve to enhance and/or channel feeding currents. Similar strategies have evolved in all three orders of marine bryozoans, apparently in response to the common problem of changing the characteristics of water flow in the immediate vicinity of the colony so that food particles may be extracted. Behavior is not a word one commonly associates with colonial marine organisms, particularly those as sessile and apparently inactive as ectoprocts. Seeing the calcified crusts or seaweed-like festoons of their colonies among the rocks of breakwaters or on the undersurfaces of platy corals, it is hard to imagine writing of any of them as, “remarkable among an active tribe for the vivacity of its movements,” or, “A colony in full health and vigor affords a rare display of delicate structure, vivacious movement and graceful form” (Hincks, 1880). Yet to 19th century naturalists, enchanted by the newly discovered miniature world of the tide-pool, the ectoprocts were indeed active creatures. In most species feeding activities of individual zooids are limited to movements of the polypide: protrusion, retraction, expansion and bending of the lophophore, and associated actions of the ciliated tentacles. The basic features of the anatomy of the ectoproct polypide were understood by the early 19th century. Farre (1837) was able to make detailed and accurate observations on the structure of the polypide in several species, noting size and activity of the tentacles, distribution of cilia and “bristles,” the form of various portions of the gut, the fate of food particles and the action of swallowing. Hincks (1880) included in his survey of the British marine Polyzoa much information indicating his understanding of individual morphology and behavior, including the presence of sensory cells on the tentacles, though most of this information is buried in species descriptions. Yet the comparative aspects of polypide morphology have not received attention, and, indeed, examination of later 19th and 20th century literature shows a gradual loss of information on polypide structure and function. Although the 19th century knowledge of individual (polypide) behavior was never codified, it is apparent from species descriptions and illustrations (Grant, 1827; Lister, 1834; Farre, 1837; Hincks, 1880, and BULLETIN OF MARINE SCIENCE, VOL. 28, NO. 1, 1978 Others) that individual behavior has been observed. Even the process of feeding was studied (Grant, 1827; Farre, 1837; Hincks, 1880), and, while the language in which it was described is overly metaphorical for present-day scientific tastes, the observations themselves are generally correct. These authors noted both that the current generated by the cilia of the tentacles acts to “create a very maelstrom in the water, which sweeps the passing animalcule or the floating food particle toward the central mouth” (Hincks, 1880, p. xiv), and that the tentacles themselves might play an important role in feeding: “The tentacula are exquisitely sensible, and we frequently observe them either singly or all at once, striking in their extremities to the centre of the bell-shaped cavity, when any minute floating body comes in contact with them” (Grant, 1827, p. 114). While individual polypide behavior was understood by those early workers, the phenomena of colony-wide patterns in feeding behavior do not seem to have been discovered until much more recently. Banta, McKinney, and Zimmer (1974) showed the presence of excurrent chimneys, based on polypide morphology and orientation in Membranipora membranácea and speculated on the possible function of monticules and other skeletal modifications in fossil and living ectoprocts in providing effective water circulation throughout colonies. In reviewing the feeding biology of marine ectoprocts (Winston, in press) I became aware of the limited knowledge, the controversies, and the possibilities, regarding polypide morphology and feeding behavior in these animals. The research reported here was started in order to learn (1 ) the range and variation of morphology possible in the gymnolaemate polypide, with specific reference to variation in lophophore shape, and in the positioning of possible sensory structures, (2) what different types of behavior patterns were possible for individual polypides and for colonies, and (3) in what ways these behavior patterns could be related to parameters of morphology, ecology and taxonomy. This paper covers qualitative observations on morphology and behavior. The quantitative relationships between them will be explored in a future publication (Winston, in prep.). MATERIALS AND METHODS Ectoprocts were collected in various subtropical and tropical habitats; in Florida, from estuarine grassbeds, fouling panels, breakwaters, and intertidal beachrock ledges, in Panama, from coral reef and intertidal and subtidal rocky areas. No attempt was made to collect all the ectoprocts from any one habitat, rather the emphasis was on collecting as many different kinds of colonies and as many representatives of the different groups, cheilostomes, cyclostomes, and ctenostomes, as possible. Animals were taken to the laboratory where they were observed and measured in seawater under the dissecting microscope. Most observations were made as soon as possible after collection, as the behavior of many species changes markedly within a few hours after being collected. Some species could be kept in aquaria without harm, and these were maintained and fed with Dunal¡ella or Isochrysis. Because there was so little information available on the ways in which polypides behave, the first few weeks of the project were spent in making detailed obsei-vations on a variety of species in order to learn what behavioral characters occurred and how they could be combined in a data sheet that could be used with other species. Table 1 summarizes the characteristics for each of 56 species of marine ectoprocts from Florida and Panama studied.