Astropectinid seastars typically develop as either feeding bipinnaria larvae or nonfeeding, barrel-shaped larvae. Understanding the direction and frequency of evolutionary transitions between these larval nutritional modes requires knowledge of the distribution of developmental diversity in the family, but the development of only a few astropectinids is known. Here we describe embryogenesis, larval development, and metamorphosis of Astropecten armatus, an astropectinid common in soft-sediment subtidal habitats in southern California. Adults were reproductively mature all year except during the winter months (December–February). Oocytes averaged 137 µm in diameter, the smallest reported in the genus. Fertilized oocytes developed into feeding bipinnaria larvae that fed in the plankton for at least 4 weeks, and in some cases up to 33 weeks, before metamorphosis. The tube feet of juveniles were adhesive, but lacked suckers, contrary to some previous descriptions of suckered tube feet in the juveniles of paxillosidans.

California sage scrub (CSS), a native ecosystem type of low-elevation areas of Southern California, is increasingly threatened by urban development, altered fire regimes, and vegetation-type conversion to non-native grasslands. Using pitfall traps, we examined how suburbanization, type conversion, and fire influence ground-dwelling spider assemblages in eastern Los Angeles County, CA, by surveying spiders in three habitats (CSS, non-native grasslands, and suburban areas) before and after a fire that occurred in a small portion of our study site. Spider assemblages in the suburban habitat differed from those in CSS and non-native grassland habitats, but CSS and grassland assemblages did not significantly differ. This suggests that the urban development, but not vegetation-type conversion to non-native grasslands, has significant effects on ground-dwelling spider assemblages. Fire had no observable effect on assemblages. Because ground-dwelling spiders were not impacted by fire and type conversion, increased fire frequencies, which often result in the establishment of non-native grasses, may not deleteriously influence this animal group, a differing pattern from other taxonomic groups. However, the rapid urban development occurring in low-elevation areas of Southern California means that species requiring non-suburban sites for their survival (15 species, 24.1%) may be threatened and require conservation assessment.

This article describes the reproductive biology and developing young of Amphiura capensis, a small brooding brittle star found in the intertidal zones of Namibia and South Africa. Each month from October 2014 to September 2015, 20 specimens were collected from Mouille Point, Cape Town, South Africa, and dissected for internal examination of brooding characteristics. Disc diameters of 238 analyzed adults ranged 2.5–8.7 mm, with a mean of 6.15 mm (SD = 1.10 mm). Brooding was exhibited in 60.5% of all sampled individuals, of which 30.6% contained young of only one of six subjectively chosen size classes, 31.9% contained two size classes, and the rest (37.5%) contained more than two size classes at the same time. Young within the same bursa were commonly of the same size class, which suggests sequential brooding. However, multiple size classes of young were often present within different bursae of the same parent, which thus exhibited characteristics of both sequential and simultaneous brooding. Of 584 brooded young retrieved from dissections, an average of 2.5 (SD = 3.2) and a maximum of 14 young were recorded within a single parent. As no larval stages were observed, development was assumed to be direct. Three-dimensional visualizations of µCT scans revealed the positions of the brooded young to be quite different from those in other species, facing with their mouths downwards instead of upwards, and not all pressed against the adult's bursal wall. Brooding occurred throughout the year, but numbers of young peaked in austral winter, coinciding with warmer water temperatures at this site. The duration of brooded development was estimated to be ∼6 months, comparable with other species with similar reproductive biology.

Slipper limpets use different ciliary feeding mechanisms as larvae and adults. Veliger larvae of Crepidula fornicata developed part of the adult feeding apparatus, including ctenidial filaments, neck lobe, and radula, before metamorphosis, but ctenidial feeding did not begin until well after loss of the larval feeding apparatus (velum) at metamorphosis. Earlier initiation of ctenidial feeding by individuals that were older larvae when metamorphosis occurred suggests continued development toward ctenidial feeding during delay of metamorphosis. Early juveniles produced a ciliary current through the mantle cavity and moved the radula in a grasping action before they began to capture algal cells on mucous strands or form a food cord. Either early juveniles could not yet form mucous strands or they delayed their production until development of other necessary structures. The neck canal for transporting food from ctenidium to mouth cannot develop before velar loss. In their first feeding, juveniles fed much like the adults except that the neck canal was less developed and the path of the food cord toward the mouth sometimes varied. As suspension feeders, calyptraeids lack the elaborations of foregut that complicate transition to juvenile feeding for many caenogastropods, but a path for the food cord must develop after velar loss. Why individuals can initiate ctenidial feeding sooner when they are older at metamorphosis is not yet known. The juveniles became sedentary soon after metamorphosis and were not observed to feed by scraping the substratum with the radula, in contrast to the first feeding by juveniles of another calyptraeid species, observed by Montiel et al. (2005).

Understanding the spatial patterns of reproductive biology might provide predictions about fitness and population stability in different locations within the geographical range of a particular species. Leptuca uruguayensis is a fiddler crab that breeds year round in tropical estuaries but only in summer months in temperate salt marshes. In this study, we examined several reproductive attributes of the southernmost population of L. uruguayensis, including the proportion of ovigerous females, the proportion of surface-active crabs, the developmental status of the gonads and hepatopancreas, and the fullness of seminal receptacles, and related them to environmental factors such as temperature, photoperiod, and sediment organic matter content. We found that temperature was the environmental factor that was most correlated with the reproductive process of the southernmost fiddler crab, since this environmental factor was related to ovarian development, to the fullness of seminal receptacles, and to the hepatosomatic index. At the southern edge of its distribution, the low temperatures of winter restricted reproduction in L. uruguayensis. These winter temperatures might represent the lower limit of the thermal window of this fiddler crab, limiting its extension toward higher latitudes.

The existence of the platyhelminth clade Adiaphanida—an assemblage comprising the well-studied order Tricladida as well as two lesser known taxa, Prolecithophora and the obligate parasitic Fecampiida—is among the more surprising results of flatworm molecular systematics. Each of these three clades is itself largely well-defined from a morphological point of view, although Adiaphanida at large, despite its strong support in molecular phylogenetic analyses, lacks known morphological synapomorphies. However, one taxon, the genus Genostoma, a parasite of the leptostracan crustacean Nebalia, rests uneasily within its current classification within the fecampiid family Genostomatidae; ultrastructural investigations on this taxon have uncovered a spermatogenesis reminiscent of Kalyptorhynchia, and a dorsal syncytium resembling the neodermatan tegument. Here, we provide molecular sequence data (nearly complete 18S and 28S rRNA) from a representative of Genostoma, with which we test hypotheses on the phylogenetic position of this taxon within Platyhelminthes, expanding upon a recently published phylum-wide analysis, and applying novel alignment algorithms and substitution models. These analyses unequivocally position Genostoma as the sister group of Prolecithophora. However, even in taxon-rich analyses, support for the position of the root of Adiaphanida is lacking, highlighting the need for new data types to study the phylogeny of this clade. Interestingly, our analyses also do not recover the monophyly of several taxa previously proposed, notably Continenticola within Tricladida and Protomonotresidae within Prolecithophora. In light of this phylogeny and the distinctive morphology (especially, spermatogenesis) of Genostoma, we advocate for a redefinition of the family Genostomatidae, outside of both Fecampiida and Prolecithophora, to encompass the members of this unique genus of parasites. Within Fecampiida, the family Piscinquilinidae fam. nov. is erected to accommodate the vertebrate-parasitic Piscinquilinus, formerly Genostomatidae.

The external and internal architecture of crab seminal receptacles are closely associated with mating behavior, sperm transfer, and storage patterns, and ultimately reproductive success. Therefore, describing their anatomy contributes to the development of a greater understanding of crab reproductive biology. In this study, we describe the anatomy and tissue characteristics of the seminal receptacle of the golden crab Chaceon chilensis, a harvested deep-sea species from the Juan Fernández Archipelago (off central Chile). Females in the late mature stage were used as reference for histological description. Morphological features of the seminal receptacle included: (1) a dorsal receptacle–oviduct connection, (2) velum and septum separating the dorsal and ventral chambers, (3) extensive glandular epithelium in both chambers, (4) a ribbed chitin line, (5) a highly folded, bilobulated ventral chamber, and (6) a simple-type vagina. Some of these traits (2, 3, 4, 5) are novel for crab receptacles and could contradict the generalized idea about the pattern of sperm precedence associated with the location of the receptacle–oviduct connection. External sperm plugs were not found in mature females, but variations in the color of opercula occluding the vulva were used to assess sexual maturity. The seminal receptacle of C. chilensis has an unusual internal morphology with vast sperm storage capacity and separate storage areas for sperm ejaculates, which could allow for cryptic female choice. In cases like these, male–male competition is usually intense and males deliver large quantities of sperm in each mating event, which makes them vulnerable to sperm depletion.

Branchiomma bairdi is a Caribbean fan worm introduced in several localities worldwide, including the Mediterranean Sea, where the species' range has rapidly expanded. Reproduction in B. bairdi was previously investigated in both extra-Mediterranean and Mediterranean areas, but no information is available on larval development and post-larval growth. In the present article, we examined these features for a population from the Mar Grande of Taranto (Ionian Sea). The species is hermaphrodite, and fertilization occurs in situ. Mucus seems to play an important role in fertilization, and also in preserving eggs before fertilization. The trochophore stage develops within the mucus and after hatching, larvae swim for about 3 d before settlement. The trochophore showed a distinct prototroch and two red dorsolateral larval eyes. The pelagic stage takes only 96 h even though prototroch is maintained after settlement, disappearing at 5 d, when larvae showed three chaetigers and branchial crown consisted of four radioles. Some interesting observations concerning changes in the morphology of chaetae and in the number of uncini during growth are also reported, together with discussion of the development of stylodes, an important diagnostic feature in Branchiomma species identification.

Abiotic stress is an important source of mortality for cnidarians and is likely to be a major factor shaping their life histories. In freshwater hydra, the ability to withstand exogenous sources of stress varies between species and populations, but little is known about the factors responsible for this variation. Here, we investigated resistance to UV irradiation in Hydra oligactis, a common temperate freshwater cnidarian. We collected polyps from 12 populations and propagated these asexually under standard conditions in the laboratory to obtain 69 laboratory clonal lines with a total of 324 polyps of different age. We measured the size of polyps and recorded their budding rate. In addition, a subset of animals was exposed to hormetic treatment, where experimental animals received a short, sublethal irradiation 2 d before testing their resistance to a higher dose. We investigated how life history traits (age, size, and budding rate), hormetic treatment, and the interaction between life history traits and hormetic treatment relate to the ability of hydra polyps to tolerate high doses of UV irradiation. In multivariate models controlling for the effect of other variables, stress tolerance was positively related to age (lower tolerance in freshly detached buds compared to adult hydra) and size (higher tolerance in polyps with a large body column). Budding rate was negatively associated with stress tolerance. Hormetic treatment increased resistance to UV irradiation, but we found no evidence for an interaction between hormetic response and any of the life history traits, suggesting that the ability to upregulate physiological defense mechanisms after exposure to mild stress does not depend on the life history background of the individuals.

Tropical intertidal organisms tolerate large fluctuations in temperature and high desiccation rates when exposed during low tide. In order to withstand the short-term heat stress, intertidal organisms adopt behavioral responses to maximize their survival. Our previous research showed that tropical littorinids found at the upper and lower intertidal shores in Singapore exhibited different behavioral adaptations during low tide. Most of the upper-shore Echinolittorina malaccana kept a flat orientation, with the aperture against the substrate and the long axis of the shell towards the sun, whereas a majority of the lower-shore individuals of Echinolittorina vidua stood with the edge of the aperture perpendicular to the substrate on the rocky shore during low tide. This prompted analyses of the shells of these two species to determine whether the differences in the shell morphometry, microstructure, and thermal conductivity of shells of E. malaccana and E. vidua were associated with their respective behavioral responses to thermal stress. Analyses of shell morphometry and thermal conductivity showed that shells of E. malaccana were more likely to minimize heat gain, despite having a higher thermal conductivity on the outer surface, due to their light-gray, elongated shell. By contrast, the dark-colored, globose shells of E. vidua probably gain heat more readily through solar radiation. Scanning electron microscopy images of the shells of both littorinid species further revealed that they have cross-lamellar structure; however, only individuals of E. vidua showed the presence of disjointed rod layers and a pigmented inner shell surface. Individuals of E. malaccana had a rough outer shell surface with holes that inter-connect to form water-trapping channels that probably aid cooling. Individuals of E. vidua, however, had a smooth outer surface with rows of kidney-shaped depressions as microsculptures which probably help to stabilize shell shape. In both Echinolittorina species, behavioral responses were used to overcome thermal stress during low tide that was associated with shell morphometry and shell thermal conductivity. Such combined adaptations increase survivability of the littorinids at their respective tidal levels.