Independent sucking/swallowing pharynges, as found in members of at least ten animal phyla, are pharynges that are opened by muscles that are not attached to the outer body wall. Their musculature is derived from either mesoderm or ectoderm, the latter taking the form of a myoepithelium. I review results of previous work on the morphology of independent sucking/swallowing pharynges among invertebrates and provide new information on the ultrastructure of the pharynx of the cyclostome bryozoan Crisia eburnea. The various morphologies of this type of pharynx have been used in some phylogenetic considerations, but only the myoepithelial sucking pharynx with a triradiate lumen was considered significant in analyses of relationships between phyla. However, I argue that this shape is the only one that makes an efficient suction pump, and this, together with different orientations of the myoepithelial pharyngeal pump and its phylogenetic distribution, indicates that the triradiate myoepithelial pharynx has evolved convergently in a number of lineages.

Settlement behavior of molluscan veliger larvae prior to metamorphosis requires cessation of swimming, accomplished by arrest of prototrochal cilia on the margin of the velum (the larval swimming organ). Ciliary arrest in larvae of gastropods is mediated by an action potential that occurs synchronously across the velum as a consequence of electrical coupling between the prototrochal ciliated cells. We developed a preparation for extracellular recording of such ciliary arrest spikes from intact swimming and crawling veliger larvae of the caenogastropod Crepidula fornicata, using a fine wire electrode. Ciliary arrest spike rates during bouts of substrate crawling were significantly higher than those recorded during preceding swimming periods in larvae that were competent for metamorphosis, but not in precompetent larvae. Spike rates were similar on clean polystyrene substrates, and on substrates that had been coated with a natural cue for metamorphosis (mucus from conspecific adults). We used immunohistochemical methods to localize neuromodulators that might regulate the function of velar cilia. Labeled terminals for serotonin, FMRFamide, and tyrosine hydroxylase (an enzyme for catecholamine synthesis) were located in positions consistent with modulatory effects on the prototrochal ciliated cells. Prototrochal ciliary arrest spike rates and beat frequencies were measured in isolated velar lobes from competent larvae, which were exposed to serotonin, FMRFamide, and dopamine (10^–5 mol L^–1). Serotonin abolished arrest spiking and increased beat frequency; dopamine also increased beat frequency, and FMRFamide depressed it. Competent larvae tested in a small static water column swam to the top of the column when exposed to serotonin, but occupied lower positions than controls when in the presence of dopamine and FMRFamide. The larval nervous system appears to regulate velar functions that are critical for settlement behavior, and is likely to do so by integrating different sensory modalities in an age-dependent manner.

Crustaceans in the order Spinicaudata display a broad range of reproductive strategies, ranging from pure hermaphroditism to pure dioecy (separate males and females), and intermediate combinations. One particularly interesting genus of these “clam shrimps” is Eulimnadia. Based on offspring sex ratios, it has been suggested that all members of the genus are androdioecious: populations consist of mixtures of males and hermaphrodites. However, only two of the ∼40 species in this genus have been examined histologically to confirm the presence of ovotestes in the purported hermaphrodites of this group. Here, we report both sex ratio and histological evidence showing that populations of five additional Eulimnadia species from India and Thailand are indeed mixes of males and hermaphrodites (four species) or hermaphrodite only (one species). Sex ratios of adults and offspring from isolated hermaphrodites are in accordance with those previously reported for 15 Eulimnadia species, and histological assays of four of the five species show the presence of both testicular and ovarian tissue in these hermaphrodites. As has been previously reported, the testicular tissue in members of these Eulimnadia spp. is located in a small section at the distal end of the gonad. In addition, the sperm produced in these hermaphrodites forms distinct plaques of compacted chromatin. Overall, these data are consistent with a single origin of hermaphroditism in Eulimnadia, and support the notion that all members of the genus are either androdioecious or all-hermaphroditic.

Fiddler crabs are deposit feeders, and use the setae on their mouth appendages to manipulate sediment particles to extract food. The number of spoon-tipped setae on the second maxilliped is frequently related to the distribution of fiddler crabs on estuarine sediments, but no study has compared the morphological diversity of these setae among multiple fiddler crab species. Here, we describe and classify the setae of the second maxillipeds of the nine Uca spp. known from the Brazilian coast. The second maxilliped of each species was examined by scanning electron microscopy. Six types of setae (five papposerrate, and one pappose) were described on the meropodite of the second maxilliped. Among the papposerrate setae, one type had a spoon-like tip, and the morphology of this type, especially the degree of curvature, differed between species. Members of Uca leptodactylus, U. uruguayensis, and U. maracoani had highly concave spoon-tipped setae. In U. rapax and U. cumulanta, the setal tip was moderately curved, while in U. thayeri, U. burgersi, and U. mordax, this curvature was slight. At the other extreme, the meropodite of the second maxilliped of U. vocator lacked setae altogether. This is the first study that describes differences in the degree of curvature of spoon-tipped setae in fiddler crabs. This trait may be strongly related to the distribution of these fiddler crabs on different estuarine substrates.

The population dynamics of threatened invertebrates have important implications for their conservation and restoration. The Seychelles giant millipede (SGM), Sechelleptus seychellarum, is a threatened and functionally important macro-detritivore endemic to the Seychelles granitic islands. Here, we studied the population dynamics of the SGM from 1998 to 2009 on Cousine Island, Seychelles, to make practical restoration recommendations. Large fluctuations in millipede densities were found between 1998 and 2009. In 2002, 2003, 2005, and 2007 millipede densities were low, while densities were high in 1998 and 2009. Although the SGM is active all year round, millipede surface activity was positively correlated with rainfall, with millipede density high during the wet NW monsoon period (i.e., October to April) and low during the SE trade wind period (i.e., May to September). Female:male:juvenile ratios were ∼3:1:1. The implications of these results for restoration are that translocations should preferably be done in years of high millipede densities and during the wet season. Furthermore, chemical control of the invasive ant Pheidole megacephala, which is currently being carried out on Cousine Island and in future could be conducted on other Seychelles islands, should preferably be done during the low rainfall months, as the SGM readily consumes the hydramethylnon-based bait.

The fact that sand dollars are often dislodged and inverted is an inescapable consequence of living at or slightly below the sediment–water interface. Once inverted, however, how do sand dollars effectively right themselves, given their small spines and stiff internal skeletons? Here, we examined the possibility that individuals of Mellita quinquiesperforata and Dendraster excentricus may take advantage of the interaction of their morphology and flow to increase the likelihood of righting. Based on flow tank observations, the critical velocity required to flip an inverted sand dollar varies with orientation and increases with test size. For both species, the critical velocity was lower when inverted sand dollars were oriented with the posterior margin facing directly downstream, compared with when the posterior margin was positioned in an upstream orientation. To test whether inverted sand dollars would actively rotate into a more advantageous position for flipping, we exposed inverted animals in three starting orientations – with their posterior edge directed upstream (the least favored position for flipping), perpendicular, and downstream to flow – to the minimum flow expected to induce flipping and compared their responses. Time-lapse photography showed that regardless of initial orientation, within one hour, a majority of individuals of both species rotated into positions that were not statistically different from the downstream orientation (the most favored position for flipping). These results for D. excentricus were further confirmed in a field experiment. Taken together, these data suggest that inverted sand dollars are able to recognize flow direction and respond by modifying their orientation to maximize lift and drag for righting.

Respiratory trees of holothurians are blind-ended evaginations of the posterior digestive system that are rhythmically inflated with seawater via the anus, and are considered to have respiratory and excretory functions. We tested the assimilatory capability of the respiratory tree epithelium by exposing adults of the oral deposit-feeding aspidochirotid sea cucumber Parastichopus californicus to (1) ¹⁴C-labeled unicellular algae and (2) iron-containing macromolecules, and then following the distribution of the labels in various body regions. The abundance of the ¹⁴C (nmol ¹⁴C g wet weight^–1) varied among body regions. The majority of the label was associated with the respiratory trees. The next greatest concentration was in the rete mirabile of the hemal system. The amount of ¹⁴C within samples of the anterior digestive system, posterior digestive system, and body wall muscle at each sampling time was lower than that of the respiratory trees. The presence and abundance of the ¹⁴C label in samples of the hemal system and the physical association between the respiratory tree and the rete mirabile suggest initial uptake by the respiratory tree and subsequent transfer to the hemal system. The iron label from the protein ferritin and the polysaccharide iron dextran entered cells of the respiratory tree luminal epithelium. The presence of the iron label in mesenchyme cells within the connective tissue compartment of the respiratory trees exposed to ferritin further suggests directional transfer of materials. Holothurians with respiratory trees are nutritionally bipolar; the anus serves as a second mouth.

Relatively little is known about the life cycles of ascidians in temperate seas. Here, we investigated the biological cycle of the colonial ascidian Didemnum fulgens, a dominant species in some shallow localities of the NW Mediterranean Sea. Growth rates and frequencies of fission/fusion events were calculated over a period of 13 months, and the reproductive cycle determined after 32 months of observation. For analyses of reproduction, zooids were dissected in the laboratory and classified into five reproductive categories; these data were used to calculate a maturity index. For growth analyses, underwater photographs of marked colonies were used to estimate the surface area of D. fulgens colonies, calculate monthly growth rates, and document fusion and fission events. Clear seasonal patterns in reproduction and growth were observed, with distinct periods of investment into each function. Gonad maturation started in winter and larval release occurred in early summer, just before maximal sea temperatures were reached. After reproducing, colonies shrank and aestivated during the warmer summer months. Growth occurred during the cooler months, with maximal and minimal growth rates observed in winter and summer, respectively. Fusions and fissions occurred year-round, although fissions were more frequent in fall (coincident with high growth rates) and fusions in spring (coincident with reproduction). These results add to the mounting evidence that ascidian life cycles in temperate seas are characterized by a trade-off between investment in reproduction and growth, triggered by seasonal temperature shifts and constrained by resource availability during summer.