The Internal-Brooding Apparatus in the Bryozoan Genus Cauloramphus (Cheilostomata: Calloporidae) and Its Inferred Homology to Ovicells

Abstract

We studied by SEM the external morphology of the ooecium in eight bryozoans of the genus Cauloramphus Norman, 1903 (Cheilostomata, Calloporidae): C. spinifer, C. variegatus, C. magnus, C. multiavicularia, C. tortilis, C. cryptoarmatus, C. niger, and C. multispinosus, and by sectioning and light microscopy the anatomy of the brooding apparatus of C. spinifer, C. cryptoarmatus, and C. niger. These species all have a brood sac, formed by invagination of the non-calcified distal body wall of the maternal zooid, located in the distal half of the maternal (egg-producing) autozooid, and a vestigial, maternally budded kenozooidal ooecium. The brood sac comprises a main chamber and a long passage (neck) opening externally independently of the introvert. The non-calcified portion of the maternal distal wall between the neck and tip of the zooidal operculum is involved in closing and opening the brood sac, and contains both musculature and a reduced sclerite that suggest homology with the ooecial vesicle of a hyperstomial ovicell. We interpret the brooding apparatus in Cauloramphus as a highly modified form of cheilostome hyperstomial ovicell, as both types share 1) a brood chamber bounded by 2) the ooecium and 3) a component of the distal wall of the maternal zooid. We discuss Cauloramphus as a hypothetical penultimate stage in ovicell reduction in calloporid bryozoans. We suggest that the internal-brooding genus Gontarella, of uncertain taxonomic affinities, is actually a calloporid and represents the ultimate stage in which no trace of the ooecium remains. Internal brooding apparently evolved several times independently within the Calloporidae.

Diversity of brood chambers in calloporid bryozoans (Gymnolaemata, Cheilostomata): comparative anatomy and evolutionary trends

“…11b, 12e). There were no brooding sacs with embryos in the material studied, however we saw it functional in some other species (Ostrovsky et al 2007). The brooding sac consists of a main chamber connecting with the exterior via a narrow neck.…”

“…The anatomical structure of the internal brood sacs has been recently studied in eight species of the genus Cauloramphus from the PaciWc (Ostrovsky et al 2007), including C. spinifer. In contrast, we investigated colonies of supposedly the same species from the White Sea, but found no diVerence in the internal structure of the brood sac.…”

“…Levinsen mainly studied cleaned skeletons, so the information about epithelia and tissues is often missing in his works. The anatomy of the internal brood chambers has been recently studied in eight species of the calloporid genus Cauloramphus (Ostrovsky et al 2007). …”

Cribrimorph and OtherCauloramphusSpecies (Bryozoa: Cheilostomata) from the Northwestern Pacific

“…Reproductive zooids have a reduced, vestigial kenozooidal ooecium (e.g., Figs. 2C, 2F, 4D, 5C) with a median ooecial pore; brooding is endozooidal (Ostrovsky et al, 2007). Zooids interconnect by tubular pore chambers (most evident in Figs.…”

“…Within Calloporidae, species of Cauloramphus Norman, 1903, are unusual in having, in addition to circumopesial spines, avicularia attached to the lateral gymnocyst by a flexible cuticular joint, a reduced kenozooidal ooecium (Ostrovsky et al, 2007), and internal brooding.…”