Troglobionts are organisms that are specialized for living in a subterranean environment. These organisms reside prevalently in the deepest zones of caves and in shallow subterranean habitats, and complete their entire life cycles therein. Because troglobionts in most caves depend on organic matter resources from the surface, we hypothesized that they would also select the sections of caves nearest the surface, as long as environmental conditions were favorable. Over 1 year, we analyzed, in monthly intervals, the annual distributional dynamics of a subterranean community consisting of 17 troglobiont species, in relation to multiple environmental factors. Cumulative standardized annual species richness and diversity clearly indicated the existence of two ecotones within the cave: between soil and shallow subterranean habitats, inhabited by soil and shallow troglobionts; and between the transition and inner cave zones, where the spatial niches of shallow and deep troglobionts overlap. The mean standardized annual species richness and diversity showed inverse relationships, but both contributed to a better insight into the dynamics of subterranean fauna. Regression analyses revealed that temperatures in the range 7–10°C, high moisture content of substrate, large cross section of the cave, and high pH of substrate were the most important ecological drivers governing the spatiotemporal dynamics of troglobionts. Overall, this study shows general trends in the annual distributional dynamics of troglobionts in shallow caves and reveals that the distribution patterns of troglobionts within subterranean habitats may be more complex than commonly assumed.

Ocean acidification is the decline in seawater pH that results from the absorption of atmospheric carbon dioxide (CO₂). Decreased pH has negative effects on survivability, growth, and development in many marine calcifiers, potentially resulting in reduced coral species richness. This reduction in richness could open new niche space, allowing the spread of invasive species, such as the upside-down jellyfish (Cassiopea spp.). Like corals, this jellyfish forms symbiotic relationships with zooxanthellae, photosynthetic dinoflagellates. This study focused on the effect of seawater acidification in Cassiopea spp. We monitored zooxanthellae density and two measures of health (bell diameter and volume) in individuals of Cassiopea sp. at three pH levels chosen to mimic different open-ocean average conditions: 8.2, representing pre-industrial revolution conditions; and 7.9 and 7.6, representing predicted declines in pH in the next century. Zooxanthellae density and health of the jellyfish were measured twice—prior to experimental manipulations and after four weeks of exposure to experimental pHs—in three consecutive trials. The effects of pH and Trial on proportional change in jellyfish attributes were analyzed using generalized linear mixed models. We found no significant effects of either factor. These results indicate that decreasing seawater pH has no apparent negative effect on zooxanthellae density or health in Cassiopea, which suggests that these jellyfish may be relatively insensitive to the impacts of ocean acidification, heightening its potential as an invasive species.

Reproductive structures, modes, and seasonal patterns of size–class abundances are examined in two benthic platyctene (Family Coeloplanidae) ctenophore species present in dissimilar shallow marine environments in subtropical southeast Florida. Coeloplana waltoni, a minute (1–3 mm body length) epizoic associate of octocorals, occurs in exposed environments often under turbulent conditions, and Vallicula multiformis (2–10 mm) commonly occurs epiphytically on macroalgae in protected, calm-water environments. Reproductive activity in C. waltoni is most active during the warm-water summer season (June–October); gonadal development in V. multiformis occurs year-round, and is most pronounced during sea-warming periods in late spring (May) and late summer to early autumn (August–October), with release of cydippid larvae. Both species are hermaphroditic brooders, exhibiting paedogenesis (early gonadal development) at body lengths approximately one-third (Coeloplana) to one-sixth (Vallicula) of maximum adult size. Juvenile individuals (<0.6 mm) increased in abundance in C. waltoni during the summer reproductive period, and large (≥1 mm) pink-colored individuals comprised 50% or more of samples from July through September. Seasonal abundance of gravid individuals and the timing of cydippid larval release in V. multiformis did not correspond closely with juvenile or adult population densities. Asexual fragmentation occurred in both ctenophore species, but was observed more frequently in individuals of V. multiformis. This asexual mode of reproduction probably accounted in part for the discordance between ctenophore abundances and larval recruitment events by sexual means. Morphological structures and behaviors associated with reproduction are described in this study. Uncommon images of reproductive products (gametes, embryos, larvae), spawning events, brooding, and asexual fragmentation are included, some for the first time in the published literature.

With more than 40,000 species, Malacostraca is the most diverse crustacean class. Most malacostracans are gonochoristic, but simultaneous hermaphrodites are also known. Tanaidacea is one of two malacostracan orders that includes simultaneously hermaphroditic species; so far, simultaneous hermaphroditism has been confirmed externally and internally in only two tanaidacean species, both in the genus Apseudes (Apseudidae). Here we show, through external and internal morphological observations of fixed specimens, that the apseudid Falsapseudes bowmani is a simultaneous hermaphrodite, making Falsapseudes the second tanaidacean genus in which simultaneous hermaphroditism has been confirmed both externally and internally. In this species, the epistome (a projection on the clypeus) was thick and elongate in large specimens but was thin and spiniform in smaller specimens; the brooding of eggs or embryos was observed only in thin-epistome individuals, although a pair of ovaries was confirmed in both thick- and thin-epistome individuals. This suggests that individuals with a thick epistome may act as males while also retaining the female reproductive organs.

Freshwater sponges are important to ecosystem functioning; however, information about their biogeography and interspecific variation is fragmentary, limiting our ability to assess their role. Although the specific epithets of two common species suggest that sponges found in lentic habitats are Spongilla lacustris, and those found in lotic habitats are Ephydatia fluviatilis, the number of sponge species in the UK is unresolved. We sampled sponges in a variety of habitats and used both morphological and molecular (D3 domain of 28S rDNA) methods to identify six species, including the first record of Trochospongilla horrida. We contrasted species in terms of their environmental tolerances, habitats, and variation, and we expanded on the limited information available about the geographic distributions of these sponges. In our study, most sponge species colonized a variety of substrates, but exhibited different distributions. The most widespread sponge, S. lacustris, was present at lower mean water temperatures and was more often located above a latitude of 55°N. Ephydatia fluviatilis was the most common species in rivers, but was also located in lentic habitats. Salinity in anthropogenic habitats was not a significant factor for the presence of E. fluviatilis or the more patchily distributed species Eunapius fragilis. Instead, these species occurred more frequently at sites with negative oxidation–reduction potential. Sponge biodiversity may be affected by substrate availability in anthropogenic habitats, invasive species, and improved ability to recognize sponge taxa. Crucially, we provide foundation data as a prerequisite for future ecological evaluation.

Marine parasite communities can exhibit temporal and spatial changes in response to seasonal and local variations in several biotic and abiotic environmental factors. Limited attention has been given to the influence of abiotic factors, so their effects on parasite community structure remain unclear. A total of 496 specimens of Euthynnus lineatus were collected over a 7-year period (2012–2018) from Acapulco Bay, Mexico. Their parasite communities were analyzed to determine if they experience interannual variations due to local biotic and abiotic factors. Thirty-three metazoan parasite species were recovered and identified: four species of Monogenea (adults); 16 of Digenea (one larvae and 15 adults); two of Acanthocephala (adults); two of Cestoda (larvae); three of Nematoda (two larvae and one adult); and six of Crustacea (three Copepoda, and three Isopoda). Species richness was greatest among the digeneans, which represented 48% of the total species recovered, followed by the crustaceans (19% of total species). Species richness at the component community level (14–24 species) was similar to reported richness in other small tuna species. The component communities and infracommunities of E. lineatus exhibited a similar pattern: high species richness and diversity, and numerical dominance by a single species, mainly by one of the didymozoids Allopseudocolocyntotrema claviforme or Pseudocolocyntotrema yaito. Parasite community structure and species composition varied among sampling years. Variations were possibly caused by a combination of abiotic and biotic factors which generated notable changes in the infection levels of several component species during the study period. These communities may therefore be unpredictable in terms of structure and species composition, as has been suggested for other communities of marine parasites.

We used fluorescently labeled phalloidin to examine the subumbrellar musculature of the scyphozoan jellyfish Aurelia aurita in a developmental series from ephyra to adult medusa. In the ephyra, the swim musculature includes a disc-like sheet of circular muscle, in addition to two radial bands of muscle in each of the eight ephyral arms. The radial muscle bands join with the circular muscle, and both circular and radial muscle act together during each swim contraction. As the ephyra grows into a juvenile medusa, arms tissue is resorbed as the bell tissue grows outward, so eventually, the ephyral arms disappear. During this process, the circular muscle disc also grows outward and the radial muscle bands of the arms also disappear. At this time, a marginal gap appears at the bell margin, which is devoid of circular muscle cells, but has a loose arrangement of radial muscle fibers. This marginal gap is preserved as the medusa grows, and contributes to the floppy nature of the bell margin. Radial distortions in the circular muscle layer involve muscle fibers that run in random directions, with a primarily radial orientation. These are believed to be remnants of the radial muscle of the ephyral arms, and the distortions decrease in number and extent as the medusa grows. Since the mechanics of swimming changes from drag-based paddling in the ephyra to marginal rowing in the adult medusa, the development of the marginal gap and the presence of radial distortions should be considered in terms of this mechanical transition.

Daphnia magna and Daphnia pulex are two important model species in ecotoxicology. In daphniids, studies of the effects of contaminants have mostly focused on female life history traits, yet it would also be important to examine male reproductive traits, particularly in relation to endocrine disruptors. In this study, we developed a protocol that uses flow cytometry to measure sperm number in individual males of different species of Daphnia. We tested our protocol on 114 males from several clones of three common species of Daphnia. Sperm count varied widely among individuals and reached high numbers (up to 1.45 × 10⁵). Positive relationships between male length and sperm number were observed in D. pulex and Daphnia pulicaria, but not in D. magna. Important inter-clonal differences in sperm production were observed in all species, with some clones producing very little sperm. Duplicated sperm samples showed on average only 6% difference in sperm counts. Sperm counts were stable at least over a 2-hr period and up to 5 hr for most samples. This sperm isolation protocol and flow cytometric enumeration approach will be of major interest to ecotoxicologists.

One of the main characteristics of sponges is their capacity for cell dedifferentiation. This capability can allow an impressive amount of asexual reproduction in these animals, because they are able to develop new individuals from just a few somatic cells. Studies of dedifferentiation, however, have focused mainly on sponges of the class Demospongiae. Therefore, we investigated here whether individuals of three different species of Calcarea are able to reconstitute new individuals following artificial fragmentation. We observed that fragmentation releases clumps of choanoderm able to initiate somatic embryogenesis. In Borojevia brasiliensis (asconoid aquiferous system, subclass Calcinea) and Paraleucilla magna (leuconoid aquiferous system, subclass Calcaronea), these clumps started to develop, but they did not pass through the first developmental phases. In Sycettusa hastifera (syconoid aquiferous system, subclass Calcaronea), the choanoderm was reorganized into primmorphs that fused to each other and formed an exopinacoderm. The first primmorphs' spicules were triactines. Despite a large mortality rate, the primmorphs developed into olynthus stages. The somatic embryogenesis and the metamorphosis of the olynthus were similar to those observed during the sexual development of this and other calcareous sponge species. Our results show that in S. hastifera, and perhaps in other syconoid calcareous sponges, somatic embryogenesis occurs mainly from choanocytes, at least in vitro. However, primmorph development does not follow the same pattern observed in post-metamorphic sexual development, as in that case diactines are always the first spicules to be synthesized in calcaronean species.

Fusion to form a chimera has been documented in many marine invertebrate taxa, including poriferans, cnidarians, bryozoans, and colonial ascidians. Allogenic interactions in chimeric ascidian colonies vary widely across taxonomic groups but are poorly characterized in the invasive colonial ascidian Didemnum vexillum. The moderate level of discrimination expressed in the fusion–rejection response of D. vexillum suggests that there is some integration of cells beyond the fusion line in a chimeric colony. We tracked the shifts in representation of microsatellite alleles between fused colonies of D. vexillum to elucidate the extent of genotypic integration in fused colonies and the patterns of changes to the genotypic composition of colonies immediately following chimera formation. By genotyping colonies before and after fusion, we found that allogeneic fusion in D. vexillum may lead to genotypic changes beyond the visible fusion line. Alleles from one colony were found in multiple tissue samples in the chimera 7–10 days after fusion had occurred. In some instances, alleles that were in a single colony prior to fusion were lost following fusion. We observed multiple patterns of allelic change, including both the unidirectional transfer and reciprocal exchange of alleles between fused colonies. Our findings suggest that tissue or cells are exchanged following allogeneic fusion between colonies of D. vexillum and that the genotypic composition of chimeric colonies may be fluid.