Clionaids are excavating sponges, which live in and grow into calcareous substrates. We studied the sexual reproductive cycles of two clionaid sponges coexisting in a Mediterranean coastal basin (Porto Cesareo, Italy), Cliona viridis and Cliona celata, by analyzing monthly tissue samples of ten specimens of each species collected over a 2-year period. From May to June of the second study year, supplementary samples were taken weekly. Up to 90% of the specimens of C. viridis and 70% of those of C. celata sampled were reproductive during the study. In both species, but particularly in C. viridis, reproductive investment, measured as the percentage of sponge tissue occupied by gametes, was high. Oocytes were present almost year-round in both species, except for a 1–4-month period after zygote release. In contrast, spermatogenesis occurred most frequently in May in both species, when (May–June) oocytes reached their greatest diameters. Cliona viridis and C. celata are hermaphrodites, with oocytes and spermatic cysts coexisting in 10% of the studied individuals in the first year of the study, and in 30% during the second. No developing embryos or larvae were incubated in the sponge tissues, and fertilization was not observed. Temperature may play a role in triggering some important phases of the reproduction of these Cliona, such as oocyte maturation and spermatogenesis, which occurred when water temperature increased from 17°C to 25°C between May and June.

Cnidarians have extracellular matrix, or mesoglea, situated between an outer epidermis and an inner gastrodermis. In this article, we describe the ultrastructure of the mesoglea of polyps of Nematostella vectensis during development and regeneration. The column wall of recently metamorphosed polyps had basal laminae composed of a meshwork of thin filaments underlying each epithelium and a network of unstriated thick (20–25 nm in diameter) and thin fibrils (∼ 5 nm) decorated with particulate matter. In juvenile polyps with eight tentacles, the system of thick fibrils was concentrated near the gastrodermis. In the column wall and mesenteries of the adult there were bundles of thick fibrils that ran parallel to the myonemes. In regenerating polyps 2 days after transection, the network of thin fibrils and particulate material as well as the basal lamina largely disappeared in the healing part of the oral, but not aboral, half. In the regenerating portion of the aboral half 1 and 2 days after transection, the bundles of thick fibrils were smaller and less organized, and the basal laminae were thicker than in the column wall of untransected polyps. In both regenerating halves, the general organization of the mesoglea of normal polyps was reattained by 5 days after transection. At all stages the mesoglea contained cellular processes that may belong to amebocytes; nucleated amebocytes with a range of shapes were present in the mesoglea of the column wall and mesenteries of adult polyps. Certain features of the mesoglea of members of N. vectensis and Hydra are similar, especially the ultrastructure of the basal laminae, but the fibrillar systems of these two model cnidarians are different. Temporal and spatial differences in the composition of the mesoglea of N. vectensis point to different roles for its components during development and regeneration.

Araucaria forests are among the most threatened biomes of one of the world's 25 biodiversity hotspots, the south Brazilian Atlantic Rain Forest. This study was focused on flatworm community structure in three protected areas located on the eastern border of the Araucaria Plateau in south Brazil. We addressed three main questions: (1) How species-rich are Araucaria forests? (2) Are there any differences in the community structure within the three areas? (3) What is the distribution pattern of land flatworms in this type of forest? A total of 51 flatworm species in ten genera and two subfamilies were found. Non-metric multidimensional scaling analysis showed that the assemblage structure differed within the three areas. The abundance and richness varied in time, being affected by an interaction between season and areas. Araucaria forests on the eastern border of the Araucaria Plateau should be considered a hotspot of land planarian diversity, harboring an estimated 64 species. The high combined species richness in the protected areas studied emphasizes the importance of their preservation. Notwithstanding their close proximity, they are not redundant in maintaining regional biodiversity.

The intertidal hoplonemertean Prosorhochmus americanus is a common inhabitant of the fouling community of rock jetties of the southeast coast of the United States. We undertook a laboratory investigation of the feeding rate of this nemertean, which is a suctorial predator of amphipod crustaceans that co-occur in abundance in the fouling community. While submerged in water (simulating high tide), worms fed on the tube-building amphipods Jassa falcata and Corophium cf. insidiosum at rates of 0.19 amphipods nemertean¯¹ d¯¹ (n = 10) and 0.26 amphipods nemertean¯¹ d¯¹ (n = 14), respectively. These predation rates were not significantly different (two-tailed t-test, p>0.05), and are similar to those estimated in laboratory studies of other suctorial nemerteans. Many nemerteans are typically more active at night, and indeed, adults of P. americanus consumed more individuals of J. falcata during dark periods than during light periods (χ² analysis, p<0.05). However, no difference in consumption of individuals of C. cf. insidiosum was observed in dark versus light. We attribute these contrasting results to differences in tube-building behavior exhibited by these two species of amphipod under laboratory conditions. Our results and those of other laboratory investigations suggest that nemerteans that prey on amphipods feed at a rate of ∼0.2 prey items nemertean¯¹ d¯¹, but under natural conditions this rate may not be obtained because of limited feeding time, longer foraging distances, and emigration of prey from regions of high nemertean activity.

Blue crabs (Callinectes sapidus) prey on hooked mussels (Ischadium recurvum) growing epizoically on oyster clumps in estuaries along the Louisiana coast. In prey size-selection experiments, blue crabs preferred small mussels (<30-mm shell length) to larger mussels, possibly because handling time increased with mussel size. When crabs were given a choice of solitary mussels versus mussels in clumps on oysters in the laboratory, mortality was lower by 86% in clumped mussels. However, no size selection by crabs occurred with mussels in clumps, likely because smaller mussels escaped predation in crevices between larger mussels or oysters. When individuals of two size classes of mussels were exposed to water containing the scent of crabs and of mussels consumed by blue crabs, an increase in byssal thread production was induced in all mussels, but byssal thread production rate was higher for small mussels than for large mussels. We conclude that increased predation risk for small mussels has resulted in higher size-specific production of byssal threads, and that predator-induced production of byssal threads, which may increase clumping behavior, may reduce their risk of mortality to predatory blue crabs.

Semelparity is one of the most drastic reproductive strategies found among marine invertebrates. It is frequently found in species whose members have small adult sizes and brood embryos internally. In this study, we describe the reproductive strategy of the bivalve Gaimardia bahamondei to explore the possible causes of the association between semelparity and internal brooding. Males of this species exhibit continuous gonadal activity throughout the breeding season. Apparently continuous spawning of sperm is associated with an abundance of captured sperm in the adfrontal region of the gill filaments of both males and females. Females are capable of brooding three cohorts of embryos simultaneously while also producing three new cohorts of oocytes. This suggests that females are able to generate at least six cohorts of embryos during the breeding season. Embryos are brooded in the suprabranchial chamber and are individually surrounded by a membrane with a projecting peduncle; embryos are anchored by this peduncle to the adfrontal region of the gill filaments. Members of the youngest cohort differ in size, color, and shell ornamentation from members of the two older cohorts. There is no difference between members of the two older cohorts in size, but there is with respect to coloring and shell ornamentation. The importance of the embryonic cohorts in terms of their percentage of the total number of embryos varied among brooding females, suggesting among-female variation in the timing of release of the oldest cohort of embryos. Members of this cohort break loose from the gills, lose their surrounding membrane, and fall into the ventral region of the suprabranchial chamber, from which they are evacuated to the exterior. Continuous sperm production in males and the production of at least six cohorts of embryos in females suggest that the costs of reproduction are high, which may partly explain the semelparity identified in this species.

Intraspecific variation in eye size in relation to ecological factors has not been well studied. Here, for the first time, we show that larger eyes in a freshwater crustacean may be associated with the presence of predators. In central Pennsylvania (USA), individuals of the amphipod crustacean Gammarus minus have significantly larger eyes in two freshwater springs with numerous fish predators (Cottus cognatus) than in three springs with few or no fish predators. Although we do not know the precise causes of these differences, this study and previous work on cave populations of G. minus suggest that eye size is an evolutionarily malleable trait that may respond to multiple selection pressures, either directly or indirectly. Three plausible explanations for the eye-size variation observed among our study populations include (1) larger eyes may enable amphipods to better detect and avoid fish predators, (2) fish predation favors nocturnal or shallow interstitial activity that is facilitated by larger, more light-sensitive eyes, or (3) the presence of fishes is associated with other environmental factors that may favor relatively large eyes. Available evidence suggests that the first hypothesis is the most viable explanation, but further study is required.

A paucity of data on the reproductive cycle of crabs in the family Lithodidae inhibits both the development of management strategies and the formulation of hypotheses regarding the evolution of lithodid life histories. Life-history parameters of Lopholithodes foraminatus from British Columbia, Canada, were investigated based on 26 females maintained in the laboratory and supplementary observations on other living and preserved animals. The rate of embryonic development was determined by measuring the percentage area occupied by yolk in lateral views of eggs removed from brooding females throughout development. Females of L. foraminatus exhibited biennial reproduction including an 18-month brooding period. Females molted, mated, and extruded eggs in mid-summer, and did not release larvae until late winter or early spring of the second year after fertilization. Embryo-genesis included a 12-month diapause at the gastrula stage. Females released larvae over a mean interval of 69 d, the longest reported for any lithodid. While the development stage of embryos was observed to be heterogeneous within a brood, no spatial gradient in development rate was observed, calling into question the oxygen limitation hypothesis of extended hatching. Biennial reproduction of individuals of L. foraminatus may be a consequence of a relatively low-quality habitat. Relative to annual reproduction, biennial reproduction halves the potential rate of increase of a population and increases vulnerability to overharvesting, suggesting that L. foraminatus is not a good candidate for commercial exploitation. The adaptive value of embryonic diapause is uncertain and warrants further research.

According to anecdotal evidence, some spiders are inaccurate mimics of ants, that is, they resemble one or several ant models in coloration, but not in body form. Here, we studied the mimetic accuracy of individuals of three myrmecomorphic species, Liophrurillus flavitarsis, Phrurolithus festivus, and Micaria sociabilis, and their association with ant models to find evidence in support of hypotheses suggested to explain the maintenance of inaccurate mimicry. We found that all three species occur together with their models. Individuals of L. flavitarsis and P. festivus associated with a few ant species, while specimens of M. sociabilis only associated with a single species. The density of spiders was several hundred times lower than that of their models. The myrmecomorphs resembled their models in color, body length, and speed of movement but not in some aspects of behavior (specifically, gait and opisthosoma bobbing). Behavioral resemblance might markedly improve the inaccurate static visual resemblance, resulting in overall high accuracy. However, the constant movement of mimics and models may not allow operators to discriminate between them, thus relaxing selection for more accurate visual mimicry.