Boring bryozoans: an investigation into the endolithic bryozoan family Penetrantiidae

Ecology of endolithic bryozoans: colony development, growth rates and interactions of species in the genus Immergentia

Boring bryozoans dissolve calcium carbonate substrates, leaving unique borehole traces. Depending on the shell type, borehole apertures and colony morphology can be diagnostic for distinguishing taxa, but to discriminate among species their combination with zooidal morphology is essential. All boring (endolithic) bryozoans are ctenostomes that, along with other boring taxa, are common in benthic communities. The growth rates of such bryozoans, including Immergentiidae, are largely unknown. For the first time laboratory experiments were conducted to determine growth rates and early colony development of the intertidal species Immergentia stephanieae and the subtidal species I. cf. suecica from Roscoff, France. In growth experiment 1, ancestrular growth rates varied, with the highest rates in I. stephanieae at 96.5 µm day-1 and the lowest at 1.1 µm day-1, during the period of August to October, in which the number of reproductive zooids was comparably higher than in other months of the year. Immergentia cf. suecica had a higher proportion of reproductive zooids from December to March compared to other months. In growth experiment 2, the bryozoans were fed a culture mixture of Chaetoceros calcitrans and Tisochrysis lutea which was compared with a control. The growth rate of small colonies of comparable size was greater in the food-enriched samples compared to the control (non-enriched). In larger colonies, the trend differed with greater growth (cystid appendage expansion) rate reported for some samples in the control. In food-enriched samples ancestrulae of I. stephanieae grew at 23 µm day-1 and I. cf. suecica 9.3 µm day-1 while no growth was observed in the control of I. cf. suecica, but 0.4 µm day-1 was reported for I. stephanieae. Growth patterns in the early developmental stages showed that the budding patterns from the ancestrulae were the same for both species, with different enantiomorphic tendencies. Inter- and intraspecific interactions are also discussed. The distribution of immergentiids is presented, as are records from new locations and the greatest subtidal depth of collection reported to date.

First soft body morphological data on the tracemaker of the endolithic bryozoan trace fossil Terebripora ramosa d'Orbigny, 1842

Terebriporidae is one of the four extant endolithic ctenostome bryozoan families, with colonies immersed into carbonate substrates like molluscan shells. This monogeneric family comprises 17 species, with 11 extant and 6 fossil species. It is currently considered closely related to vesicularioid ctenostomes, a group characterized by colonies interconnected by polymorphic stolons and a distinct gizzard as part of their digestive systems. However, confusion persists regarding the correct species identities and affiliations of many terebriporid species, and even the description of the entire family is based solely on a few external features of their boring traces, rendering the family an ichnotaxon (trace fossil). Our molecular analysis does not support a vesicularioid affinity, but corroborate a close relationship to Immergentia, another genus of boring bryozoans. Consequently, this study aims to untangle the systematic confusion surrounding Terebriporidae by examining the tracemaker of the type species of the family, Terebripora ramosa from Chile, and investigating its morphology and histology using modern techniques. The current analysis could not confirm typical vesicularioid characters such as a gizzard or true polymorphic stolons. Instead, all characters point towards a closer relationship to Immergentiidae as suggested by a recent molecular phylogeny. In fact, these two taxa share several characters such as cystid appendages and duplicature bands, and appear closely related, with the only difference being a characteristic vane with tubulets present in the tracemaker of T. ramosa. The sister-group relationship of the tracemaker and the genus Immergentia infers that these borers share a common boring ancestor, but also emphasizes that additional species from the ichnogenus Terebripora need to be studied for more clarity.

Digging into boring bryozoans: new characters and new species of Immergentiidae

Immergentia is an endolithic genus of ctenostome bryozoans and the sole member of the Immergentiidae. Etchings of their typical spindled-shaped and sometimes enantiomorphic borehole aperture in calcium carbonate substrates are accomplished by chemical dissolution. The tentacle crown of the bryozoan is essentially the only body part that extends beyond the shell surface when protruded. Previously, species were mainly described using external colony and zooidal characteristics or whole mounts, with partial histological sections conducted on a single species in 1947. Modern approaches, however, are hitherto missing. We examined the soft body morphology of Immergentia from different locations with confocal laser scanning microscopy and the production of 3D reconstructions. In addition, zooidal characteristics such as tentacle number, size, tubulets, and interzooidal distances were used to distinguish and describe species. The combination of conventional and modern methods revealed the presence of a cardiac constrictor and intercalary kenozooids that can interpose between the cystid appendages, something not previously reported in immergentiids, thus necessitating an amendment of the family diagnosis. The polypide typically has eight to ten tentacles, and the anus is positioned in the low or mid-lophophoral area. In addition, sequence data, including the mitogenome and the nuclear ribosomal genes (18S and 28S) of four species from five locations, are presented for the first time. Based on molecular and morphological data, a novel intertidal immergentiid from France, Immergentia stephanieae sp. nov., and a subtidal species from New Zealand, I. pohowskii sp. nov., are described. This work supplements the rather sparse existing knowledge on Immergentiidae and proposes additional characteristics to complement existing descriptions in order to enhance future species identification.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13127-024-00645-y.

Boring life: early colony formation and growth in the endolithic bryozoan genus Penetrantia Silén, 1946

As in most colonial and sessile marine invertebrates, bryozoan life history is characterized by asexual propagation of zooids for colonial growth and by sexual production of larvae for dispersal. However, comprehensive life histories, particularly in cryptic species such as endolithic (boring) bryozoans, remain poorly understood. The ctenostome family Penetrantiidae is widespread from temperate to tropical waters and often found in molluscan shells, offering an opportunity to study the boring lifestyle and its potential impact on bioerosion through growth and settlement experiments. Our research focused on Penetrantia clionoides from Guam in the Pacific Ocean, Penetrantia japonica from Japan, and a Penetrantia species from France in the Atlantic Ocean. We found distinct life histories and reproductive patterns potentially influenced by environmental factors such as temperature and food availability. The tropical P. clionoides displayed higher rates of larval production and growth compared to its temperate counterpart. For instance, the mean stolon extension was 335.2 μm/week in P. clionoides versus 232.1 μm/week in Penetrantia sp. Autozooid development took 13 days in P. clionoides and 31 days in Penetrantia sp. Anatomical features like apertural rims aided in species identification and in understanding larval settlement preferences, suggesting a tendency for philopatric settlement behavior. The bioerosional impact of penetrantiids remains little understood, but we generated first projections of bioerosion rates and a protocol for keeping Penetrantia under laboratory conditions, laying a foundation for further research in this field.

Morphology of ctenostome bryozoans: 7. Hislopia, Echinella and Timwoodiellina

Ctenostome bryozoans are a small group of gymnolaemates comprising less than 400 recent species. They are paraphyletic and ctenostome-grade ancestors gave rise to Cheilostomata, the most dominant and speciose taxon of Bryozoa in the present day. Investigations into ctenostomes are important for reconstructing character evolution among Gymnolaemata. As a continuation of studies on a morphological series of ctenostome bryozoans, we herein investigate six species of hislopiids, a small clade of three genera occurring in freshwater habitats. The general morphology of all species is similar in having primarily uniserial chains of encrusting zooids, which are mostly oval to ellipsoid and have a flattened frontobasal axis. Hislopia prolixa and Echinella placoides often have more slender zooids with a higher frontobasal axis. Apertures of hislopiids are quadrangular, lined by a thickened cuticle. Apertural spines are present in various lengths in E. placoides, Hislopia lacustris and Hislopia corderoi. The remaining cuticle is rather thin except at lateral areas, close to the pore-plates which are prominent in hislopiids because of abundant special and limiting cells. All species except H. corderoi and Timwoodiellina natans have a prominent collar obstructing the vestibulum, whereas the latter two species instead have an 'external collar' as cuticular, outer folds projecting over the aperture. Hislopiid lophophores carry eight, or more commonly 12-18 tentacles. The digestive tract is distinguished by an often highly elongated esophagus and/or cardia, with the latter always having a prominent bulbous part in the form of a proventriculus-or gizzard in E. placoides. The caecum is extensive in all species. In Hislopia the intestine is characteristically two-chambered with a proximal and distal part before entering an anal tube of various length. The latter is present in all species except T. natans and terminates in mid-lophophoral area. Oocytes in E. placoides are large and macrolecithal indicating brooding and the production of lecithotrophic larvae. Hislopia species produce small, oligolecithal ones, which suggests zygote spawning and planktotrophy. In general, the morphology is similar among the different hislopiids with characters of the gut aiding in delineating the genera Echinella and Timwoodiellina.