“You are what you eat,” so the health food devotees claim, but if you are a bryozoan, “you are where you eat,” as well. Bryozoans are suspension feeders, dependent for their food on extracting edible particles from the water currents surrounding them. Most bryozoans are also sessile, unable to move from the place where the larva attached (except by that slow “movement” over the substratum that occurs by growth and decay of portions of the colony). Thus, colony morphology is inextricably linked to the way in which the colony processes water for food.

A fundamental morphological and ecological division among sessile colonial invertebrates and sponges is that between encrusting and erect growth habits. The distributions of such organisms results both from their patterns of larval recruitment onto the substratum and their subsequent growth and interactions (Buss 1979b; Jackson 1979a). Sessile encrusting organisms [runners, sheets, and mounds of Jackson (1979a)] grow primarily out over the substratum. Such growth sets no special mechanical constraints for colony support and growth is potentially infinite, although limited by extrinsic factors such as the extent of the substratum, interactions with other organisms, or physical environmental factors. The alternative pattern is one of growth primarily up or away from the substratum surface [plates, vines, and trees of Jackson (1979a)]. This may set overall size constraints relative to mechanical support and attachment (Cheetham 1971; Cheetham et al. 1981; Cheetham and Thomsen 1981; Schopf et al. 1980), often with approximately determinate growth as for solitary animals (Jackson 1977a, 1979a).

Duncan (1957) and Osburn (1957) provided excellent literature surveys on the paleoecology and ecology of bryozoans; this report is intended as an updating of Duncan's work. Publications on modern bryozoans are not included here except for certain papers directed toward paleontologic problems. Since Duncan, and Osburn, ecological and paleoecological summaries have been published by Hyman (1959), Cheetham (1963), Ryland (1970) and Cuffey (1970). Schopf (1969) surveyed bryozoan paleoecology from the viewpoint of colony growth habits and Heckel (1974) and Cuffey (1977) summarized knowledge of bryozoan occurrences in reefs. Most authors have emphasized cheilostomes; information on stenolaemates is limited.

The individual functioning units (zooids) in stenolaemate bryozoan colonies include skeletal portions called zooecia (singular, zooecium). Within a zooecium there may be basal diaphragms that make the occupied portion (living chamber) shorter than the full length of the zooecium, and there may be various skeletal parts that project into and modify the shape of the living chamber. The entire zooecium constitutes a record of zooidal ontogeny and of the geometrical relationships between neighboring zooecia or between zooecia and the surrounding colonial tissues. Therefore, evolutionary changes in zooecial shape reflect changes in all stages of zooidal ontogeny and in relationships between zooids and their surrounding intracolonial environment. In addition, evolutionary changes in zooidal size have affected zooecial shape in some stenolaemate groups.

Bryozoa are the only phylum in which all known species form colonies. A colony consists of one or more kinds of physically connected zooids and supporting parts, all assumed to be genetically uniform. The physically connected zooids of a colony generally grow from the sexually produced first zooid, the ancestrula (Fig. 1). Growth in asexually produced colonies is similar, but originates from the ancestrula of a parent colony.

Many taxonomic studies of bryozoans have been published since the late 19th century and most of these studies contain biostratigraphic information about the occurrences of the bryozoans described. Unfortunately, very few attempts have been made to arrange this information into usuable zonation schemes at either the provincial or worldwide level. Most published studies are faunal studies of a particular stratigraphic unit and are concerned primarily with taxonomy.

Brachiopods are characterized by being solitary, bivalved, bilaterally symmetrical coelomates. A ciliated, filament-bearing lophophore occupies much of the mantle cavity of all living representatives and functions as the principal food-gathering and respiratory organ of the animal. The coelom is divided into two principal spaces. The largest one is the posteriorly located metacoel that forms the body cavity and encloses most of the organs. The smaller mesocoel is the coelomic space inside the lophophore.

Over a decade has passed since Rudwick (1965b, 1970) and Ager (1967) reviewed the ecology of brachiopods, a hiatus partially filled by Brunton (1975) and Steele-Petrovic (1979). With the widespread use of SCUBA, we are finally beginning to learn about these dominantly subtidal (both Recent and fossil) organisms in their proper environment. A renaissance of ecologic interest in the phylum has produced much, and promises more. Already many text-book dogmas have been refuted and others questioned.

Methods of interpretation of living habits of ancient brachiopods.–The most obvious means to interpret life habits of ancient brachiopods is by analogy with living ones. Increased knowledge of the living ones, however, is revealing progressively more pitfalls in the path of using their examples to arrive at easy conclusions regarding the ancient ones. As the analogies are applied to ever more ancient forms, the similarities decrease and the interpretations become increasingly tenuous. Even the supposed “safe” interpretations of ancient terebratulids and rhynchonellids on the basis of analogy with their living relatives are being challenged by new research. Formerly, presence of a pedicle foramen was considered prima facie evidence that the shell lived attached to a substrate of some kind, but this can no longer be assumed, and further evidence for attachment must be sought.

Interest in historical biogeography has risen tremendously since 1971. During the period 1971 to present there have been five important compilations of paleontologic information cast into an historical biogeographic framework (Gray and Boucot, 1979; Hallam, 1973; Hughes, 1973; Middlemiss, Rawson, and Newall, 1971; Ross, 1974). All of these volumes contain a certain amount of material dealing directly with brachiopod historical biogeography. More important, however, is the fact that all of them have a large number of papers devoted to shallow water, marine, benthic historical biogeography of organisms other than brachiopods, which provides a useful comparative background for future efforts in brachiopod historical biogeography. It is clear that efforts in historical biogeography are finally beginning to form a more routine part of the overall paleontologic effort. However, at the present time we still lack a really uniform, reasonably agreed upon, biogeographic framework for the Phanerozoic. This means that we have differing biogeographic terminologies for the basic units. There is no agreed upon definition of how to define the commonly used heirarchy, realm, region, province, subprovince–some prefer to do it with percentages of genera, some by considering families, still others by important presences or absences, or by mixtures of these approaches. One also quickly becomes aware of the fact that there is a confusing, commonly overlapping nomenclature applied to the same and different biogeographic units. For example, for much of Paleozoic time there is a Southern Hemisphere cold or cool water biogeographic unit termed Atlantic in the Cambrian, Atlantic, Mediterranean, Proto-Tethyan or Malvinokaffric in the Ordovician, Malvinokaffric in the Silurian and Devonian, and Gondwana in the Permian-Carboniferous. The warmer water units of the Paleozoic may also be considered in this time successive, confusing manner. It will probably be another decade or so before we have gained enough experience, by making all the conceivable types of mistakes, in the naming of Phanerozoic biogeographic units to enable us to come up with the most universally useful set of terms for the realms, regions, provinces and subprovinces. The fact that some realms begin their history as subprovinces and then “evolve” into realms further complicates the issue. The fact that some biogeographic units become extinct must also be considered.

Brachiopods have been successfully used for many years to provide local, regional, and worldwide biostratigraphic control. Their value as phylogenetic time-markers is somewhat impaired by the fact that as sessile filter feeders they are particularly susceptible to the impress of varying local environmental conditions. The situation is especially troublesome where precise, finely tuned biostratigraphic zonation is attempted, as it becomes difficult to separate out the effects of time (phylogeny) from the effects of paleoenvironmental variations. Paleoenvironmental interpretations involve many uncertainties, as they are based on indirect evidence, a problem compounded by differences of opinion concerning the data used to provide the basic underpinning.

The present state of knowledge permits only the grossest assessment of nutritional physiology of living brachiopods since most of the knowledge available on brachiopods is not addressed from this aspect and when it is, much of the information is derived from studies made without the use of modern investigative methods. Additionally, of the few studies that have been made on the physiology of the brachiopod digestive system, most have been on the genus Lingula. Unfortunately, this is one of only 2 genera that occupy an infaunal habitat, all other living genera are epifaunal forms (Table 1). The geographic distribution, habitat preference, and digestive modifications suggest that there are some differences in dietary characteristics between the infaunal and epifaunal brachiopods. With these limitations in mind, studies on physiology of digestive systems in other phyla will be used for comparison.

Most major topics that bear on the lophophorate condition have been ably treated in preceding contributions for either the Bryozoa or Brachiopoda. Accordingly I shall attempt a comparative approach, first characterizing the lophophorates as a whole and then contrasting the groups with an eye towards the evolutionary implications of resemblances and differences. To set a practical target I shall attempt contrasts between the feeding systems, because they seem to be particularly important to the present habits, habitats and distribution patterns of these groups. From this approach, questions naturally arise as to the evolutionary history of the lophophorates and in particular of extinct types of Brachiopoda for which modern analogues are unknown; these problems form potential research areas of special interest. To conserve space I have tried where possible to cite only more recent and/or general works that themselves contain ample references. I have assumed that by this point in the volume the reader will be acquainted with the gross morphology of bryozoans and brachiopods and with the major descriptive terms applied thereto. Because phoronids are not specifically covered in other contributions, I have included a wider range of phoronid references including some historically important works.