The structure of the kinetid (flagellar or ciliary apparatus) is known to be of phylogenetic significance in sponges (Phylum Porifera) and can provide information about evolutionary relationships. Here, we report on the larval kinetid structure of two closely related species, Oscarella lobularis and O. tuberculata (Homoscleromorpha, Oscarellidae). Cells belonging to the four previously recognized morphological regions (anterior pole, lateral zone, paracrystalline belt, and posterior pole) were studied. The cells of the paracrystalline belt have pear-shaped nuclei with a paracrystalline inclusion connected to the roots of the kinetid. In the cells of other zones, the nucleus is separated from the kinetid, and the roots adjoined the Golgi apparatus only. In kinetids of the studied larval cells, we observed the accessory centriole arranged immediately under the kinetosome, and two unequal fibrillar roots. These features are unique for sponge larvae. Comparing kinetids of the Homoscleromorpha with those in its sister group, the Calcarea, we propose an ancestral composition for the kinetid in the lineage Calcarea + Homoscleromorpha. This proposed kinetid structure includes a kinetosome–nucleus link, striated roots, simple basal foot, orthogonal centriole, and a long transition zone of the flagellum. The position of the centriole under the kinetosome in homoscleromorph larvae and the stout fibrillar or microtubular bundle on the kinetosome in calcarean larvae might be the apomorphies of these groups.

Isopod parasites in the family Cymothoidae can cause reduced growth, castration, or even mortality in their hosts. Olencira praegustator is a cymothoid that parasitizes the mouth and gill chamber of Brevoortia tyrannus (Atlantic menhaden), which is the basis for the largest fishery along the eastern coast of the USA and an important link within estuarine food webs. To better characterize interactions between O. praegustator and B. tyrannus, including parasite-induced pathology, we sampled hosts and parasites from three estuarine sites on Kiawah Island, South Carolina. Over 5 weeks, we collected, measured, and weighed 169 juvenile menhaden; remarkably, 96% of these fish were infected with O. praegustator, typically with one isopod found in the mouth of each host. Based on the external morphologies of 163 examined isopods, 58 were female (35.6%), 9 of which were gravid, and 105 were male (64.4%). Although fish size was unrelated to isopod length or mass, isopod length was a direct predictor of the amount of damage observed on the host operculum, which in severe cases involved tissue atrophy and hemorrhage. Considering the high infection prevalence, significant damage associated with infections, as well as the impairing effects of other cymothoids on their hosts, the consequences of interactions between B. tyrannus and O. praegustator warrant additional investigation for understanding the management and ecology of Atlantic menhaden.

Cupelopagis vorax is a sessile, predatory rotifer with indirect development. The topology of its nervous system is partly known through histological examination of the female adult. However, there is no information on the larval stage, and so, no understanding of how metamorphosis might affect the configuration of neurites. Here, we use immunohistochemistry and confocal laser scanning microscopy to map the position of serotonin-like immunoreactive (SLIR) neurites, which are hypothesized to be important in sensory innervation and stimulating locomotory activity. We found that the relative position and number of SLIR neurites were similar between larvae and adults despite differences in their ecologies and the drastic changes that occur at metamorphosis. Both life stages possess at least four pairs of perikarya in the cerebral ganglion, a pair of lateral nerve cords, and a pair of neurites that appear to innervate a portion of the digestive tract. The larval stage also possesses an SLIR neurite ring at the base of the corona that is postulated to function in stimulating ciliary activity and receiving sensory information from the apical field. Although the adult did not appear to possess this ring, we cannot rule out its presence, because immunoreactive signals in the anterior end were weak. In contrast to the larvae, the adult possessed a pair of SLIR neurites that appeared to innervate the neck region. We hypothesize that these neurites form a circuit that functions in prey detection and capture. Based on these results, it appears that despite their overall similarities, the two life stages show some unique neural patterns that correspond to their ecologies; neurites that function in the planktonic environment of larvae and neurites that likely function in prey detection in the sessile adults.

The present study provides the first assessment of the reproductive cycle of three common and widespread species of the genus Chiton, sympatric in rocky shores of Coquimbo, northern Chile (∼30°S): C. granosus, C. cumingsii, and C. magnificus. From specimens seasonally sampled during a 2-year period, a histological study was performed in order to describe the gonad structure and stages of gonadal development for each species. The morphological structure of the gonad was similar in the three species, with sexual cells developing from the gonad wall towards its center. The three species were gonochoric and iteroparous, with asynchronous gamete maturation at population level; in all seasons, sexual maturity was evident in small to large individuals of each species (≥25 mm in total length for C. cumingsii and C. granosus, and ≥47 mm for C. magnificus).

As part of a project to document the diversity of larval invertebrates on both coasts of Panama, we collected and photographed 141 larval asteroids and sequenced fragments of their mitochondrial cytochrome c oxidase subunit I (COI) and 16S ribosomal DNA. We uncovered 10 Caribbean operational taxonomic units (OTUs) and five Pacific OTUs. We could identify six of the 15 OTUs based on >99% similarity with reference sequences in GenBank: The Pacific species Astropecten verrilli and Pentaceraster cumingi and the Caribbean species Astropecten marginatus, Astropecten antillensis, Oreaster reticulatus, and Mithrodia clavigera. Two other OTUs were placed in BINs in the Barcode of Life Database (BOLD) with unpublished sequences that were identified as Pharia pyramidata from the Pacific and Valvaster striatus, now known from the Caribbean as well as the Indo-West Pacific. The remaining seven species appear likely to belong to Luidia, as 16S sequences from each have 87%–95% identity with various species of Luidia, and the sequences nest among species of Luidia in neighbor-joining trees. The low diversity of asteroid larvae reflects ∼10% of the diversity of adult sea stars reported from Panama, and highlights the need for broader collection efforts and improved coverage of DNA barcode reference sequences for Luidia and other soft-bottom species.

The invasiveness of Corbicula largillierti has been underestimated, but this bivalve is currently receiving more attention. The first study of the distribution of this species along one of the major basins of central Argentina showed that it was completely absent in the major central reservoir, but was present along its tributary and effluent rivers. Ten years later, this discontinuous distribution has not changed, despite the bivalve's high dispersion capacity. The main environmental differences between the reservoir and the rivers are that the former has finer sediment grain size, higher temperatures, and lower oxygen concentration during summer months. This study aimed to evaluate whether one of these factors could be limiting the distribution of C. largillierti. We assessed the metabolic response and burial behavior (under different grain sizes) of C. largillierti over 8 weeks at 30°C against a control condition at 20°C. We also analyzed the oxygen consumption (vO₂) as a function of environmental oxygen concentration (pO₂) at 25°C, estimating its metabolic regulation capacity (R). This showed the existence of an environmental oxygen concentration threshold (P_t) that could be an indicative of physiological limiting concentrations that compromise species survival and settlement. After 8 weeks at 30°C, the metabolic rate of individuals of C. largillierti increased and their burial behavior was slightly compromised but mostly for coarser sediments. Concerning environmental oxygen availability, C. largillierti is an oxyconformer with a low R (39.9%), a clear pattern of negative regulation, and a low P_t (48.4% air saturation). The lack of any regulation capacity of C. largillierti under environmental oxygen limitations and the extremely low pO₂ at the bottom of the reservoir during summer months may explain its failure to colonize and survive there

The ink gland in cephalopods is a modified part of the digestive tract that generates melanin used in defense activities against predators. In the present study, we document the histological structure of the ink gland of the cuttlefish Sepia pharaonis following light microscopy (LM) and transmission electron microscopy (TEM) examinations. Based on the observations, we infer the series of cellular events leading to the formation and secretion of melanin. LM observations revealed that the cuttlefish ink gland was cord-like, and could be separated into two distinct regions with different functions, based on markedly different cellular and biochemical characteristics. The region with the function of secreting ink was the epithelial cell region (i.e., mature ink gland cells) and was mainly composed of melanosomes, rough endoplasmic reticulum, Golgi apparatus, and mitochondria. Conversely, the connective tissue region was the site of formation of cells and energy supply. In addition, the most probable sequence of activities from melanogenesis to the release, based on TEM observations, is as follows: (a) formation of a matrix of opaque electronic substances (melanin precursors); (b) melanization in the precursor matrix to form melanin-like particles; (c) further melanin granule development and enlargement, and gradual intensifying of the hue; (d) production of melanin granules (melanosomes) in the precursor matrix; (e) binding of melanosomes to the cytoskeleton and migration to the cell surface; (f) fusion of melanosomes with the cell membrane at the apical pole, and discharge of melanin granules into intercellular spaces or lumen by exocytosis or cell fragmentation. We also investigated how the process of continuous ink release influences ink gland histology and ultrastructure. Inking stimulation induced the release of large amounts of ink by epithelial cells, and was associated with cell disorganization, and severe cellular vacuolization, in addition to severe organelle damage.

The feather duster worm Schizobranchia insignis is an abundant marine annelid found subtidally and in the low intertidal of the northeastern Pacific Ocean. As in other sabellids, the anterior appendages, used for feeding and respiration, can be damaged by physical or biological means. Limited information is available on the regeneration of radioles leading us to study this process on a worm with radioles that dichotomously branch. First, we documented the occurrence of natural radiole damage in two populations of S. insignis found at environmentally distinct sites: a subtidal marina and an intertidal, rocky bench. All 21 worms collected from the exposed intertidal bench had branchial crown damage, whereas 15 of 22 worms (68%) sampled in the marina exhibited natural radiole damage. In the laboratory, we observed radiole regeneration on individuals of S. insignis from the marina by removing a single radiole. Radiole regrowth was a continuous process in which functionality was restored through radiole bifurcation, elongation, and the development of internal support structures. The regrowth of a single radiole of S. insignis took more than 35 days. However, in one of our studies, after 21 days, although not all individuals recovered, four of 12 worms (33%) had completed bifurcation. Pointed tips on the distal-most branches signified the end of bifurcation. During recovery, individuals of S. insignis did not consistently regenerate the same number of branches observed prior to damage. In addition, a majority of the radiole elongation during recovery occurred after branching. The radiole regeneration in Eudistylia vancouveri, a closely related species found in the marina, was observed to compare regeneration in co-occurring species. We found that the radiole regeneration in E. vancouveri was less complex because of the absence of branching. Since Schizobranchia is the only genus in which radioles are branched, our study of S. insignis provides a unique examination of natural radiole damage and regrowth.

The invasive freshwater jellyfish Craspedacusta sowerbii, native from East Asia (Yangzi Jiang River), was introduced in Europe for the first time in the basins of the Royal Botanic Garden in London. From the beginning of the 20th century, worldwide reports of the presence of C. sowerbii have been increasing (USA, Canada, Europe, Australia, Russia). Despite its now worldwide distribution, C. sowerbii has rarely been the subject of recent studies. Moreover, C. sowerbii is difficult to rear in the laboratory, and individuals generally from the wild have only been reared for short periods. Many aspects of laboratory cultures have proven to be problematic for all stages of the life cycle (from frustule to medusae): lack of optimal growing system (circular current or not), water quality (physical and chemical conditions), diet (the type of food), and temperature. In this article, we present a technique for culturing all life stages of C. sowerbii, from polyps to medusae, to study its life history in the laboratory. To demonstrate the success of our culture protocol, the growth of polyps was measured for 80 days at 19 and 29°C. Colony growth increased at both temperatures in our culture system, and data were similar to those presented in the literature, illustrating the success of this protocol. Medusae were cultured for 70 days, and their bell diameter increased from 0.60 ± 0.08 mm (Day 0) to 9.0 ± 2.1 mm (Day 32). We developed a closed culture system that allowed specimens (i.e., polyps and medusae) to be maintained for more than 2 months (80 days for polyps, 72 days for medusae). This culture system will allow researchers in the future to study more precisely the metabolism (growth, ingestion, longevity) of polyps and medusae to understand life-history characteristics important to this species'ecology (periods of medusae production, predation, and diet).

John Stuart Pearse, Professor Emeritus in the Department of Ecology and Evolutionary Biology (EEB) at the University of California, Santa Cruz, died on July 31, 2020, at the age of 84. John was the consummate invertebrate biologist with far-reaching interests and expertise. He was also an amazing teacher and mentor to a cadre of postdocs and graduate students, and to the hundreds of undergraduates who took his courses in invertebrate zoology, intertidal biology, and kelp forest ecology.