RESUMO
Juan Fernández and Desventuradas are two oceanic archipelagos located in the southeastern Pacific Ocean far off the Chilean coast that received protected status as marine parks in 2016. Remoteness and access difficulty contributed to historically poor biodiversity sampling and limited associated research. This is particularly noticeable for bivalves, with most prior regional publications focused on single taxa or un-illustrated checklists. This study investigates marine bivalves collected between the intertidal and 415 m depth during (1) the 1997 IOC97 expedition aboard the M/V Carlos Porter, with special focus on scuba-collected micro-mollusks of both archipelagos, (2) two expeditions by the R/V Anton Bruun (Cruise 12/1965 and Cruise 17/1966), and (3) Cruise 21 of USNS Eltanin under the United States Antarctic Program, which sampled at Juan Fernández in 1965. Also, relevant historical material of the British H.M.S. Challenger Expedition (1873-1876), the Swedish Pacific Expedition (1916-1917), and by German zoologist Ludwig H. Plate (1893-1895) is critically revised. A total of 48 species are recognized and illustrated, including 19 new species (described herein) and six other potentially new species. The presence of two species mentioned in the literature for the region (Aulacomya atra and Saccella cuneata) could not be confirmed. The genera Verticipronus and Halonympha are reported for the first time from the Eastern Pacific, as are Anadara and Condylocardia from Chilean waters. Lectotypes are designated for Arca (Barbatia) platei and Mytilus algosus. These findings double the number of extant bivalve species known from the Juan Fernández and Desventuradas archipelagos, highlighting the lack of attention these islands groups have received in the past. A high percentage of species endemic to one or both archipelagos are recognized herein, accounting for almost 78% of the total. The newly recognized level of bivalve endemism supports the consideration of Juan Fernández and Desventuradas as two different biogeographic units (Provinces or Ecoregions) of the Eastern Pacific Ocean.
Assuntos
Biodiversidade , Bivalves , Animais , Oceano Pacífico , Bivalves/classificação , Bivalves/anatomia & histologia , Chile , IlhasRESUMO
Laternula elliptica (P. P. King, 1832) is the sole representative of the anomalodesmatan family Laternulidae and the largest bivalve in the Antarctic and Subantarctic. A keystone species of the regional benthic communities, it has reached model status, having been studied in hundreds of scientific works across many biological disciplines. In contrast, its anatomy has remained poorly known, with prior published data limited to partial descriptions based on chemically preserved specimens. Based on observations of aquarium-maintained living animals at the Brazilian Comandante Ferraz Antarctic Station, gross-morphological dissections, and histological sectioning, the comparative anatomy, functional morphology, and aspects of behavior of L. elliptica are described and discussed. Special focus is placed on the pallial organs (including elucidation of cleansing and feeding sorting mechanisms in the mantle cavity) and the musculature. Among the noteworthy findings are the presence of well-developed siphons furnished with sensory tentacles at its tips, some of which bearing eyes; large, folded gills and labial palps capable of sorting the material entering the mantle cavity; an inter-chamber communication in the posterior region of the mantle cavity; an ample ventral mantle fusion with an anterior pedal gape; the absence of a 4th pallial opening; and the absence of a ligamental lithodesma in adult specimens. This study reevaluates the available anatomical data in the literature, both supplementing and correcting previously published accounts.
Assuntos
Bivalves , Animais , Regiões Antárticas , Bivalves/anatomia & histologia , Movimento Celular , Comunicação , BrasilRESUMO
'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.