Morphology, Anatomy, and Systematics of the Cinctiporidae, New Family (Bryozoa: Stenolaemata)

Abstract

The study of thin sections, peels, and SEM micrographs of skeletons, and sections of skeletons and soft parts together, has revealed new morphology and anatomy resulting in new growth and functional interpretations in a new stenolaemate family, the Cinctiporidae. Cinctiporids are found primarily in the New Zealand region and range from upper Cretaceous to Recent. In contrast to the present classification of stenolaemates, the family includes eight species grouped into two free-walled genera, one fixed-walled genus, and one mixed free-/fixed-walled genus. This unconventional family is inferred to be monophyletic based upon a number of shared character states, zones of astogenetic change with fixed, free, and fixed/free apertures, and zones of repetition with both fixed- and free-walled zooids. These taxa are described using both external and internal skeletal morphology and soft part anatomy. Zooids of cinctiporids are typically several times larger than those of other stenolaemates, facilitating detailed observations. In dendroid growth habits, growth rates of zooids are greatest in endozones at growing tips of branches, and in cinctiporids skeletal and fully regenerated polypide sizes are roughly proportional. Growth rates decrease greatly as young zooids reach exozones by saltation in a series of polypide cycles. In exozones, attachment organs become fixed in position, some in attachment scars in skeletal linings, resulting in regenerated polypides being fixed in position in subsequent cycles. During regenerating phases of any single cycle, polypides grow inward from attachment organs, ingesting and eliminating as they grow. Retractor muscles must function, therefore, and must slide their skeletal connections inward also as polypides increase in length. In early phases of a regeneration the developing polypides ingest and eliminate from within their living chambers. Elimination within living chambers is apparently facilited by faecal pellets passing out through the atrium and vestibule. The funiculus of stenolaemates generally ends blindly against skeletal walls preventing connection to neighboring zooids by that means as in gymnolaemates. A large funicular muscle or muscles aids in retracting polypides of the cinctiporids. Skeletal walls calcified from one side necessarily form against pre-existing membranes. Exterior skeletal walls in stenolaemates calcify against outer cuticles, preserving the shapes of the cuticles as they are calcified, explaining growth undulations on frontal walls and intimate contacts that basal colony walls make with substrates.