Serra do Japi, located in the southeast of São Paulo State, is considered a priority area for conservation, as it houses original Atlantic Forest cover remains. Despite the significant number of studies about vertebrates and invertebrates that were carried out in this region, the meiofauna biodiversity is completely unknown. Thus, the present study aimed to investigate for the first time freshwater Gastrotricha and limnoterrestrial Tardigrada in Serra do Japi Biological Reserve. Samples of sediments, periphyton and floating vegetation in reservoirs and natural lagoons, and mosses growing on native and non-native tree trunks were collected in May 2019. At least five gastrotrichs morphotypes were identified and three of them were formally described: Chaetonotus acanthocephalus, C. dadayi (first record in Brazil), and Heterolepidoderma mariae (first record outside the type locality). In regards to tardigrades, twelve morphotypes were identified and four of them were formally described: Pseudechiniscus juanitae, Minibiotus cf. acontistus, Echiniscus dreyfusi and Itaquascon umbellinae (last two species reported for the first time outside the type locality). This study reinforces that meiofaunal diversity and distribution have been underestimated, even in one of the five largest hotspots in the world.
Siphons represent a remarkable example of evolutionary convergence in different bivalve lineages. In Protobranchia, the siphons, when present, are used exclusively to channel the water currents used for respiration, waste removal and gamete release. Their emergence is thought to be associated with the taxonomic and morphological diversification within the Nuculanida. While siphons have been extensively studied in other bivalve groups, particularly the Heterodonta, gaps remain in the knowledge of protobranch siphons, especially on their morphology, including the musculature and innervation, and their functioning. The few data on Protobranchia siphons are restricted to some Nuculanoidea, and information is still missing for other nuculanid lineages, such as the Sareptoidea. The present study provides a description of the siphonal morphology of Aequiyoldia eightsii, a sareptid bivalve. Histological data were obtained to investigate their organization and infer their functioning. All traits observed were compared with those of heterodont siphons. In A. eightsii, the siphons are fused with each other and distinguished by their reduced longitudinal musculature in bundles that do not form layers, by the presence of a blood lacunal system that fills most of the wall of the siphon and by the innervation that is likely diffuse. This suggests that the siphons are hydrostatic organs with a hydraulic mechanism whose expansion occurs when the lacunar system is filled with blood. Our results provide the first morphological and functional details of a protobranch siphon and thus contribute to knowledge on the comparative anatomy of Bivalvia.
‘Miniaturization’ is a widespread phenomenon among the Metazoa. In the molluscan class Bivalvia, records of miniaturization are numerous. Among the Archiheterodonta, Warrana besnardi (Klappenbach, 1963) has attracted attention for its tiny size, which does not exceed 1.5 mm in shell length, and because it belongs to a group with limited anatomical information and often-debated status, the “Condylocardiidae” (which recent molecular studies place deeply nested within the family Carditidae). All species of Warrana Laseron, 1953 are small-bodied, and so miniaturization presumably occurred from a large-bodied ancestor within the Carditidae sensu lato. South American W. besnardi is here studied in detail. Its small size and the enlargement of the anterodorsal region during growth, reflects (and likely led) to infaunal habit, living as a burrowing bivalve that passively feeds on deposit particles entering the pallial cavity anteriorly. Mantle glands, previously reported as a common feature of other archiheterodonts, are missing in W. besnardi, but spongiform tissue in the antero-ventral portion of the mantle lobes presumably represents a blood sinus that might compensate for the great reduction of the ctenidia. Lecithotrophy is reported, with yolky oocytes bearing a thick non-cellular capsule layer; brooding was not observed, and it is here hypothesized that the extreme miniaturization, with the great reduction of ctenidia, is responsible for a shift in the reproductive mode of condylocardiids, contrasting with the commonly reported ovoviviparity of the carditids.
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