Unlike most rotifers (Rotifera), which are planktonic and direct developers, many gnesiotrochan rotifers (Monogononta: Gnesiotrocha) are sessile and have indirect development. Few details exist on larval metamorphosis in most gnesiotrochans, and considering the drastic transformation that takes place at metamorphosis—the replacement of the ciliated corona with a new head that bears ciliated tentacles (the infundibulum)—it is perhaps surprising that there are limited data on the process. Here, we document part of this metamorphosis by examining the presence and distribution of neurons with serotonin immunoreactivity in the nervous system of both planktonic larvae and sessile adult females. Using antibodies against serotonin combined with confocal laser-scanning microscopy (CLSM) and 3D reconstruction software, we mapped the immunoreactive cell bodies and neurites in both life stages and found that relatively few changes occurred during metamorphosis. The larvae possessed a total of eight perikarya with serotonergic immunoreactivity (5HT-IR) in the brain, with at least two pairs of perikarya outside the brain in the region of the corona. Cells with 5HT-IR in the brain innervated the larval corona and also sent neurites to the trunk via the nerve cords. During metamorphosis, the corona was replaced by the infundibulum, which emerged from the larval mouth to become the new functional head. This change led to a posterior displacement of the brain and also involved the loss of 5HT-IR in the lateral brain perikarya and the gain of two perikarya with 5HT-IR in the anterior brain region. The innervation of the anterior end was retained in the adult; neurites that extended anteriorly to the mouth of the larva formed a distinct neural ring that encircled the infundibulum after metamorphosis. Significantly, there was no innervation of the infundibular tentacles by neurites with 5HT-IR, which suggests that ciliary control is unlikely to be modulated by serotonin within the tentacles themselves.

Females of many organisms mate more than once and with more than one male, suggesting that polyandry confers some advantage to the female or her offspring. However, variation in maternal investment in response to mate choice and mate number can confound efforts to determine if there are benefits of polyandry. Access to multiple mates could increase maternal investment in offspring via a number of different mechanisms. Few studies have determined if investment is influenced by mate choice and number, and data are particularly lacking for marine invertebrates. This study was designed to determine if maternal investment and offspring size increase with access to increasing numbers of mates in the protandrous intertidal slipper snail Crepidula cf. marginalis. Virgin female slipper limpets were exposed to one, three, or five potential mates and their fecundity, egg size, and hatchling size were measured for multiple clutches. Treatment had a significant effect on fecundity, with fecundity increasing with the number of potential mates. Treatment did not have an effect on the size of eggs or hatchlings, on the variation in egg size or hatchling size within broods, or on the frequency of oviposition. Treatment did alter the variation in average offspring size among females, but not in the way predicted by theory. The main result, that access to multiple mates does not have an effect on per offspring maternal investment, makes C. cf. marginalis an ideal candidate to study the effects of polyandry on offspring fitness without having to take into account confounding effects of variation in maternal investment.

The wings of the pteropod mollusc Clione limacina provide forward propulsive force through flapping movements in which the wings bend throughout their length in both dorsal and ventral directions. The musculature of the wings includes oblique, striated muscle bundles that generate the swimming movements of the wings, longitudinal and transverse (smooth) muscle bundles that collapse the wings and pull them into the body during a wing withdrawal response, and dorsoventral muscles that control the thickness of the wings. All muscles act against a hydrostatic skeleton that forms a central hemocoelic space within the wings. Of these muscle types, all have been thoroughly described and studied except the dorsoventral muscles. The fortuitous discovery that the dorsoventral musculature can be intensely labeled with an antibody against the vertebrate hyperpolarization-activated cation channel (HCN2) provided the opportunity to describe the organization of the dorsoventral musculature in detail. In addition, electrical recordings and microelectrode dye injections supported the immunohistochemical data, and provided preliminary data on the activity of the muscle fibers. The organization and activity of the dorsoventral musculature suggests it may be involved in regulation of wing stiffness during the change from slow to fast swimming.

As environmental temperatures increase and become more seasonally variable, the ability of individuals to plastically alter their physiological responses to temperature (=acclimatize) may affect the potential for species persistence. Among marine organisms, the larval stage is often the most physiologically sensitive; larvae are also often the main dispersal stage in the life history. However, studies that address the acclimatization of marine larvae are rare. We investigated whether larvae of the gooseneck barnacle Pollicipes elegans from two temperate populations, one from the Northern Hemisphere (Mexico) and one from the Southern Hemisphere (Peru), show patterns of seasonal acclimatization to temperature. We compared the effects of temperature on swimming activity, oxygen consumption, and mortality of larvae from the two populations in both warm and cold seasons. Larvae from Mexico had higher thermal tolerances when collected in the boreal summer compared to the boreal winter, while no similar indication of seasonal acclimatization was seen in larvae from Peru. The lack of acclimatization in larvae of P. elegans from Peru may be related to recent thermal history, low selection for acclimatization due to irregular patterns of seasonal temperature change during ENSO events, or to different phylogeographic histories of Northern- and Southern-hemisphere populations.

The Asian paddle crab, Charybdis japonica, native to the northwest Pacific, is an invasive species that has established populations within northeastern New Zealand. Here, we provide a detailed examination of C. japonica's reproductive seasonality and gametogenesis, sizes at physiological maturity, and sex ratios outside its native range. Trapping in the Weiti River Estuary, Whangaparoa (36°38.4^'S, 174°43.6^'E) from February 2010 to May 2012 indicated a male-biased population. Reproductive seasonality largely depended on female condition, since males contained ripe spermatozoa year-round. Female gametogenesis began during late autumn, with oocyte development occurring throughout winter to early spring. Based on the presence of mature gametes during late winter and the appearance of gravid females in early November, mating began during early spring, with spawning in mid-spring. Spawning coincided with a large drop in the gonad index, and occurred between sea surface temperatures of 17–22°C and 11.75–13.5 h day length. Females remained reproductive for up to 5 months of the year. Histological observation suggested that CW50 (the carapace width at which 50% of the population is mature) for females was 46.39 mm, while CW50 for males could not be determined due to a paucity of immature males. Histological analysis also suggested that females of C. japonica could produce store sperm and multiple broods annually.

Terrestrial hermit crabs in the family Coenobitidae (genera Coenobita and Birgus) must migrate onto land after completing a pelagic larval stage in the ocean. Better knowledge of emigration behavior would assist in the conservation and management of coenobitid populations by helping identify and protect the habitats they need to complete their life cycles. We cultured laboratory-born individuals of five coenobitid species (Coenobita cavipes, C. purpureus, C. rugosus, C. violascens, and Birgus latro) from megalopae to early juveniles (first, second, and/or third crabs) in vessels containing seawater and a hard substrate, and analyzed their behavior and molting in conjunction with our published data for C. brevimanus. Our results confirm that the coenobitids migrated from sea to land at the megalopal stage. Megalopae and early juveniles tended to select shells based on their body size. Inland-dwelling coenobitids, such as C. brevimanus, C. cavipes, and B. latro, had a longer duration from landing to first molt and had a prolonged first crab intermolt period compared with those of the beach-dwelling coenobitids C. purpureus, C. rugosus, and C. violascens, probably because of the adaptive traits for migrating to inland habitats. Little burrowing behavior was observed by megalopae of B. latro, but they had a strong tendency to be cryptic under shelters. Additionally, megalopae and early juveniles of Coenobita spp. created and utilized burrows somewhat differently. Our results suggest that coenobitids require specific microhabitats for completing their early life stages in the wild. In particular, megalopae of B. latro may need structurally complex refuges to migrate from the sea.

The protein synthetic and secretory activity of spider tubuliform glands is known to be coordinated with the reproductive stage of the spider. For spiders that produce multiple egg cases, such as the black widow Latrodectus hesperus, this means that the cells that make up the tubuliform gland cycle from minimal to maximal silk protein synthesis and exocytosis as the spider transitions from early vitellogenesis to a gravid state and back. The impact of these transitions on the cells that form the tubuliform gland has yet to be characterized. The entire tubuliform gland undergoes an elastic deformation, doubling in size in response to the accumulation and depletion of egg case silk proteins within its lumen. Similarly, the diversity and organization of organelles within the cytoplasm of the secretory epithelial cells that make up the wall of the tubuliform gland change with the reproductive stage of the spider. Progression of a spider from early to late vitellogenesis is accompanied by decondensed nucleoli and distention of the rough endoplasmic reticulum, markers of protein synthetic activity. The presumed silk proteins that fill the lumen of the tubuliform gland of a gravid spider include a fibrous matrix with homogeneous spherical inclusions. These components are also present within the cytoplasm of the cell; however, only the fibrous material appears to be enclosed by membranous organelles. Transition of the tubuliform gland from peak silk synthesis back to a quiescent state is marked by the appearance of multivesicular bodies and organelles resembling phagophores and autophagosomes, suggestive of a role for autophagy in the process of recovery. The reproducible cellular dynamics of the tubuliform silk gland of the black widow spider makes it a potential model system for study of the regulation of silk gene expression, endomembrane transport, and exocytosis of silk proteins and autophagy.

Spermatozoa from four species of echinoids found in New Zealand had morphological characteristics typical of other echinoids, including a conical sperm head with an acrosome-capped nucleus, a midpiece, and a single long flagellum. The spermatozoa of Fellaster zelandiae, Echinocardium cordatum, Evechinus chloroticus, and Centrostephanus rodgersii also showed statistically significant differences in species-specific morphological characteristics. Evechinus chloroticus showed the most variable sperm morphology. The irregular urchins (F. zelandiae and E. cordatum) had short, wide sperm heads (head length: width ratios 2.93:1 & 2.97:1, respectively) with a long acrosome complex, while the regular urchins (E. chloroticus and C. rodgersii) had longer, narrower heads with a short acrosome complex (ratios 5.29:1 & 3.37:1). Spermatozoa of E. cordatum from the New Zealand population shared more characteristics with those of conspecifics from the Sea of Japan than those of conspecifics from the Baltic, reflecting the membership of the former two populations in a distinct Pacific clade. Volumetric calculations showed no evidence of phylogenetic grouping. Mitochondria of E. chloroticus spermatozoa were less than half the volume of those of C. rodgersii and E. cordatum, and those of F. zelandiae were intermediate in volume. These volume measurements will be useful in physiological studies of sperm performance and quality.