Advancing the knowledge of the nematode Echinocephalus pseudouncinatus (Gnathostomatidae, Spirurida): Morphological and molecular identification, new host, and host specificity in two coexisting pen shells (Bivalvia: Pinnidae).

The life cycle of Echinocephalus pseudouncinatus has not been described in detail to date, as is also the case of other species in the genus. This study contributes to the information available about the life history of the genus, particularly E. pseudouncinatus, by (1) using molecular techniques (small subunit rRNA gene [SSU rRNA] sequences) to identify larvae of this species; (2) describing the most conspicuous morphological characteristics that distinguish the species by scanning electron microscopy; (3) describing histological characteristics of the internal anatomy of larvae and the lesions caused by them in the gonads of hosts; (4) reporting new host and reporting evidence of host specificity of E. pseudouncinatus between two species of edible pen shells coexisting in the northern Pacific of Mexico; and (5) analyzing the frequency of infested gonads by host sex, size, and gonadal development stage. The molecular analysis confirmed the morphological and histological diagnosis of E. pseudouncinatus larvae infesting gonads of Atrina maura and Pinna rugosa in Ojo de Liebre and San Ignacio lagoons. The morphological characterization of larvae provides internal details of the cephalic bulb (including rows of hooks and ballonets), neural chord, and cell types of the body wall. Histopathological findings such as degenerated and atretic gametes and the displacement of gonadal tissue in hosts infested with E. pseudouncinatus larvae are discussed in terms of temperature anomalies caused by the "Godzilla El Niño". The frequency of infestation increased with shell length and gonadal development in A. maura, with a higher infestation frequency in females versus males observed at both study sites. Our findings expand the list of hosts of E. pseudouncinatus, which was previously unknown as a parasite of P. rugosa. In P. rugosa, infestation frequencies are noticeably lower (<1 %) compared with those observed in A. maura (>30 %) at both study sites, suggesting host-specific requirements or preferences in E. pseudouncinatus larvae.

Histopathological Alterations in the Gonad of Megapitaria squalida (Mollusca: Bivalvia) Inhabiting a Heavy Metals Polluted Environment.

The gonadal health status of the chocolate clam Megapitaria squalida collected from the Santa Rosalía mining port and San Lucas beach (reference site), Gulf of California, Mexico, was assessed through histological analysis of the reproductive tissue, from which the histopathological alteration index (HAI) was determined. In addition, copper and iron accumulation in tissue was revealed using histochemical techniques. Our results showed a large presence of copper (30%) and iron (45%) only in the gonad tissue of clams from Santa Rosalía, in which histopathological alterations observed were inflammatory responses, degenerative-progressive processes, cell death, and response to infectious agents. The HAI was significantly higher in Santa Rosalía specimens (mean ± SE, 72.18 ± 6.12) than in San Lucas clams (4.60 ± 1.07). At San Lucas beach, a higher prevalence of histopathological alterations occurred in clams in the spent stage (43.2%) and in autumn (18.4%) and winter (17.8%) in concordance with the normal reproductive rest period, whereas at Santa Rosalía a higher prevalence occurred in clams at the ripe stage (76.9%) and in spring (83.7%). In conclusion, our results showed the deteriorated health condition of gonads in M. squalida from the Santa Rosalía mining port, which suggests there is a relationship with chronic exposure to local high levels of heavy metals. The high prevalence and intensity of histopathological alterations in the gonad suggest a strong adverse effect on gametogenesis, gamete quality, and, ultimately, in the reproductive potential of M. squalida at this site.

Human health risk assessment of metals and arsenic via consumption of commercial bivalves in the Gulf of California, Mexico.

Although various studies have reported the bioaccumulation of metals in bivalves of commercial interest from the Gulf of California (GC), the risk associated with their consumption remains poorly understood. In this study, our own and bibliographic concentrations of 14 elements in 16 species of bivalves from 23 locations were used to investigate (1) the species-specific and regional accumulation of metals and arsenic in bivalves, (2) the human health risks by age and sex, and (3) the maximum allowable consumption rates (CRlim). The assessments were done according to the US Environmental Protection Agency guidelines. The results indicate that the bioaccumulation of elements varies markedly between groups (oysters > mussels > clams) and localities (higher on Sinaloa due to intense anthropogenic activities). However, consuming bivalves from the GC remains safe for human health. To prevent health effects for residents or consumers on the GC, we recommend (1) following the CRlim proposed herein; (2) monitoring levels of Cd, Pb, and As (inorganic) in bivalves, as the elements of top concern, mainly when are consumed by children; (3) calculating CRlim for more species and locations, including at least: As, Al, Cd, Cu, Fe, Mn, Pb, and Zn; and (4) determine the regional consumption rates of bivalves.

Contrasting reproductive health of female clams Megapitaria squalida from two nearby metal-polluted sites in the Gulf of California: Potential effects of copper, lead, and cobalt.

We studied the effects of chronic exposure to metals on energy reserves and reproduction in the clam Megapitaria squalida in two nearby populations exposed to different levels of pollution from mining operations in the Gulf of California, Mexico. Female M. squalida from San Lucas beach had good reproductive health status, whereas Santa Rosalia specimens consistently showed low energy reserves, massive oocyte resorption throughout the year, high frequencies of undifferentiated individuals, low proportions of ripe and spawning organisms, smaller and fewer oocytes per follicle, and significantly lower follicular areas. Ovarian levels of Co, Cu, Pb, Mn, and Zn were consistently higher in clams from Santa Rosalia. The poor reproductive health of clams inhabiting this site may be attributed to their long-term exposure to high Co, Cu, and Pb concentrations, as these have been shown to cause toxicity and reproductive impairments in other marine organisms.

Ultraestructura del ovocito maduro y en reabsorción de Spondylus limbatus G. B. Sowerby II, 1847 (= S. calcifer ) (Bivalvia: Spondylidae) / Ultrastructure of the mature and in resorption oocytes of Spondylus limbatus G. B. Sowerby II, 1847 (= S. calcifer ) (Bivalvia: Spondylidae)

Spondylus limbatus es una especie bajo protección especial en México, de la que existe poca información biológica y nada sobre estudios histológicos o de ultraestructura del ovario. El objetivo de esta investigación fue caracterizar la morfología ultraestructural de los gametos femeninos maduros y en degeneración. La gónada femenina de S. limbatus en estado de madurez presentó ovocitos postvitelogénicos de 60-70 µm de diámetro, que presentan el aspecto característico de células metabólicamente activas y altamente sintetizadoras. La membrana citoplasmática posee especializaciones destinadas a aumentar la superficie de absorción de la célula, las microvellosidades; el citoplasma presenta numerosos sistemas membranosos relacionados con la síntesis de material de reserva y secreción; y el patrón de organización nuclear altamente lobulado, y por consiguiente con una gran superficie que asegura el intercambio núcleo-citoplasma, se incorpora de forma estructural al proceso de vitelogénesis. Finalmente, se describen los cambios ultraestructurales resultantes de la lisis de los ovocitos: colapso de las membranas nuclear y citoplásmica, y presencia de células hemocíticas macrófagas.

Spondylus limbatus is a species under special protection in Mexico, of which there is little or no information in the literature of biological, histological or ultrastructural studies of the ovary. The objective of this research was to characterize the ultrastructural morphology of mature and degenerating female gametes. The female gonad of S. limbatus in mature state presented post-vitellogenic oocytes 60-70 µm in diameter, which have characteristics of metabolically active and highly synthesizing cells. The cytoplasmic membrane has specializations designed to increase the absorption surface of the cell, the microvilli; the cytoplasm presents numerous membranous systems related to synthesis of reserve and secretion material as well as the highly lobed nuclear organization pattern; a large surface that ensures core-cytoplasm exchange, is structurally incorporated into the vitellogenesis process. Finally, ultrastructural changes resulting from the lysis of the oocytes are described: collapse of nuclear and cytoplasmic membranes, and the presence of macrophage hemocytic cells.