We examined the female reproductive system of the yellowline arrow crab Stenorhynchus seticornis by means of histological and histochemical techniques. Mature specimens obtained in the field were kept in the laboratory for mating experiments. After 24 h, newly mated females were dissected, and their reproductive trait routinely processed for embedding in historesin. The specimens examined each possessed a pair of kidney-shaped seminal receptacles (SR), and these we classified as ventral type, based on the location of the oviduct opening. The mesodermal dorsal region (DR) of SR consisted of a stratified epithelium with scaly cells, while the ectodermal ventral region (VR) was composed of a simple epithelium covered by a cuticle. The oviduct opened at the transition region (TR) between DR and VR and had no velum. The simple epithelium of TR had more folds on the face of the oviduct opening. The vagina exhibited the same features as the TR epithelium and was contiguous to VR, anchored by muscles. In the lumen, from one to three strata of sperm packets were observed, the dorsal one containing free sperm, and the most ventral stratum, spermatophores. An acidophilic glycoprotein layer enclosed the strata. Spermatophores in the ventral stratum were enclosed in a voluminous secretion, composed by acid polysaccharides most likely from the last male mated. The ventral-type receptacle, stratified sperm packets, and polyandry, usually observed in females of Majoidea, suggest the occurrence of sperm competition in S. seticornis, favoring the sperm of the last male mated, as its sperm mass is located near the opening of the female oviduct.

Hatching plasticity has been documented in diverse terrestrial and freshwater taxa, but in few marine invertebrates. Anecdotal observations over the last 80 years have suggested that intertidal neritid snails may produce encapsulated embryos able to significantly delay hatching. The cause for delays and the cues that trigger hatching are unknown, but temperature, salinity, and wave action have been suggested to play a role. We followed individual egg capsules of Nerita scabricosta in 16 tide pools to document the variation in natural time to hatching and to determine if large delays in hatching occur in the field. Hatching occurred after about 30 d and varied significantly among tide pools in the field. Average time to hatching in each pool was not correlated with presence of potential predators, temperature, salinity, or pool size. We also compared hatching time between egg capsules in the field to those kept in the laboratory at a constant temperature in motionless water, and to those kept in the laboratory with sudden daily water motion and temperature changes. There was no significant difference in the hatching rate between the two laboratory treatments, but capsules took, on average, twice as long to hatch in the laboratory as in the field. Observations of developing embryos showed that embryos in the field develop slowly and continuously until hatching, but embryos in the laboratory reach the hatching stage during the first month of development and remain in stasis after that. Instances of hatching plasticity in benthic marine invertebrates, like the one in N. scabricosta, could greatly enhance our ability to investigate the costs and benefits of benthic versus planktonic development, a long-standing area of interest for invertebrate larval biologists.

Prey organisms reduce predation risk by altering their behavior, morphology, or life history. Avoiding or deterring predators often incurs costs, such as reductions in growth or fecundity. Prey minimize costs by limiting predator avoidance or deterrence to situations that pose significant risk of injury or death, requiring them to gather information regarding the relative threat potential predators pose. Chemical cues are often used for risk evaluation, and we investigated morphological responses of oysters (Crassostrea virginica) to chemical cues from injured conspecifics, from heterospecifics, and from predatory blue crabs (Callinectes sapidus) reared on different diets. Previous studies found newly settled oysters reacted to crab predators by growing heavier, stronger shells, but that adult oysters did not. We exposed oysters at two size classes (newly settled oyster spat and juveniles ∼2.0 cm) to predation risk cue treatments including predator or injured prey exudates and to seawater controls. Since both of the size classes tested can be eaten by blue crabs, we hypothesized that both would react to crab exudates by producing heavier, stronger shells. Oyster spat grew heavier shells that required significantly more force to break, an effective measure against predatory crabs, when exposed to chemical exudates from blue crabs as compared to controls. When exposed to chemical cues from injured conspecifics or from injured clams (Mercenaria mercenaria), a sympatric bivalve, shell mass and force were intermediate between predator treatments and controls, indicating that oysters react to injured prey cues but not as strongly as to cues released by predators. Juvenile oysters of ∼ 2.0 cm did not significantly alter their shell morphology in any of the treatments. Thus, newly settled oysters can differentiate between predatory threats and adjust their responses accordingly, with the strongest responses being to exudates released by predators, but oysters of 2.0 cm and larger do not react morphologically to predatory threats.

The anterior pericardial wall or amebocyte-producing organ (APO) is a site of hemocyte formation in the schistosome-transmitting snail Biomphalaria glabrata. Histological sections of the APOs of adult schistosome-resistant Salvador strain snails, and two schistosome-susceptible M-line strains, BRI-M and USF-M, showed qualitatively differing amounts of hemopoietic tissue (HT), with Salvador>BRI-M>USF-M. Adult Salvador snails also had a significantly higher concentration of hemocytes in the hemolymph than the two M-Line strains. In juvenile snails of the same three strains, measurements of total APO HT volume confirmed the qualitative differences seen in adults, and differences between the three strains were statistically significant. Crosses between Salvador (large HT volume) and USF-M (small HT volume) show that a large HT volume is dominant in juvenile F₁s. Analysis of the distribution of HT volume among F₂s shows it to be a quantitative trait. Although USF-M juvenile F₀s had a significantly lower APO HT volume than that of BRIM F₀s, they had a significantly higher mitotic index, possibly as a compensatory mechanism. Salvador APO allografts maintained HT volume and mitotic activity equally well in USF-M and Salvador recipients after 2 weeks, suggesting that the low HT volume in USF-M snails may result from a developmental defect rather than a lack of HT-supportive plasma factors.

There are conflicting reports as to whether Ocypode gaudichaudii individuals switch from carnivory as juveniles to deposit-feeding primarily on diatoms as adults, or whether they expand diet range and become omnivorous with maturity. At the onset of deposit-feeding, crabs develop specialized claws with truncated ends that they use to shovel sediment during foraging. Eighty-eight crabs were collected from Culebra Island (Republic of Panama) to study how the diet of this crab shifts with changes in claw shape, mouthpart proportions, and setation, as well as gastric mill width. Forty-four crabs had identifiable material in their foreguts: 30 had animal material, 12 had diatoms, and two had a mix of both. There were no differences between the gastric mill, mandibles, and the proximal endites of the first maxillipeds of predators and deposit-feeders, but extra rows of plumose setae were present on the second maxilliped of deposit-feeding crabs with carapace length (CL) >10.6 mm. All individuals with CL <12.3 mm and non-truncated claws ate animals, but those with larger CL and truncated claws had animal, diatom, or mixed diets; hence, claw truncation does not restrict the crab's diet to diatoms but, instead, broadens the diet to include both animals and diatoms. Perhaps this is a strategy to balance the economics of foraging on animals and diatoms on medium to low-energy beaches that lack the larger invertebrates that adults of other species of ghost crabs eat. More generally, our study shows that specialized feeding structures need not imply a narrow or specialist diet.

Arthropods are well known to biomineralize and metallize their exoskeletons with naturally occurring elements that function to stabilize the protein component and add hardness to surfaces that endure wear. In this study, we provide the first description of the trace elements in the cuticle of a marine intertidal pseudoscorpion, Halobisium occidentale, using energy-dispersive x-ray spectroscopy. We characterized the trace element composition of six regions on four specimens: the prosoma, opisthosoma, tarsal claws, arolia, chelicerae, and pedipalps. In addition to the elements C, O, and N that make up the α-chitin component of the cuticle, we found 11 trace elements across the body, but only five of these elements were present at significant levels (≥1% wt): Ni, P, Al, Zn, and Fe. The only trace element on both tagmata is P, while the appendages and their structures contain varying amounts of other elements. The tarsal claws are supplemented with Zn and Ni, while the adhesive arolia contain either Ni or P. The pedipalps are enriched with Al along their proximodistal axis, with P, Zn, and Fe present only around the venom pore. The chelicerae have P, Zn, and Fe present only on the distal regions. This study confirms that pseudoscorpions, like many other arthropods, enrich their cuticle with specific elements at precise locations that are important in predation (cheliceral fingers, pedipalps, venom pore) and locomotion (tarsal claws, arolia). This is also the first study to reveal the presence of Al and Ni in any significant quantities in the arthropod exoskeleton.

Bryozoans are impressively active suspension feeders, with diverse feeding behaviors. These have been studied extensively in marine bryozoans, but less so in their freshwater counterparts. Here we identified 16 distinct behaviors in three phylactolaemate species and classified them into behaviors involving separate tentacles, groups of tentacles, lophophore arms, the introvert, or multiple zooids. We examined (1) the repertoire of behaviors in each species, and each behavior's (2) absolute frequency, (3) relative frequency and (4) duration in each of the three species, at two flow velocities (0 and 0.2 cm s^–1). Nine feeding behaviors were shared by all three species, but the occurrence of other behaviors in a given species was limited by its morphology. Behaviors involved in particle capture were the most frequent, and were often faster than the reactions involved in particle rejection. By contrast, the absolute frequency of behaviors varied widely among species without clear associations with species form, or function of the behavior. Flow velocity had only minor effects on the feeding behaviors exhibited by a species, or their frequencies or durations. Our results show that phylactolaemates have the same key feeding behaviors of the individual polypides (especially involving separate tentacles) as previously described in gymnolaemate and stenolaemate bryozoans, although their behaviors tend to be carried out more slowly than those of stenolaemates or gymnolaemates. Feeding behaviors involving multiple zooids were nearly absent in the studied phylactolaemates, but are common in gymnolaemates. Freshwater bryozoans appear to be intermediate between stenolaemate and gymnolaemate bryozoans in terms of richness of the repertoire of feeding behaviors.

Gnathorhynchidae is a diverse taxon of predatory eukalyptorhynch flatworms characterized by an armed proboscis. Their present taxonomy is not concordant with what we know of their phylogeny. Further progress in this area is hindered by a lack of information concerning their morphology. As recent studies have shown, a historical reliance on live observations for species descriptions has resulted in a number of errors and omissions. Here, we redescribe the anatomy of the male copulatory organ of Prognathorhynchus busheki using transmission electron and confocal microscopy, correcting several errors in the original description. Furthermore, we use these results to update our understanding of the anatomy and evolution of male copulatory organs in Gnathorhynchidae and in Platyhelminthes more generally.

There is considerable variation in structures known to function in the transfer and storage of sperm in female decapod crustaceans. The thelycum is a secondary sexual character that forms from the posterior thoracic sterna of female shrimps (especially penaeoids and sergestoids). Females in the caridean shrimp family Processidae have a thelycum-like structure which rarely occurs in other caridean females. We tested the hypothesis that the processid thelycum serves as a spermatheca for either short-term attachment or long-term sperm storage. When inseminated females of the processid Ambidexter symmetricus were isolated after mating, newly spawned and then incubated embryos hatched, but in the continued absence of a male, females were unable to fertilize a subsequent spawn. Our observations on A. symmetricus show that sperm were not retained after female spawning, and thus the thelycum is not used for long-term sperm storage as in many penaeoids. In A. symmetricus, the thelycum may serve as an external median spermatheca (seminal receptacle) for temporary attachment and storage of a sperm mass during the 2–3 h interval between mating and spawning. Observations on mating behavior support the hypothesis of a pure-search (promiscuous) mating system in A. symmetricus, with males showing little interest before, and copulating with females only after, the female parturial molt. Mating encounters were short (<2 min). This mating system is like that of other caridean shrimps with populations structured similarly to those in A. symmetricus: a relatively high density of mobile individuals and sexual dimorphism in body size (reproductive females larger than males) but not in cheliped weaponry (similar in males and females).