Diego G. Zelaya

The Genera Thyasira and Parathyasira in the Magellan Region and Adjacent Antarctic Waters (Bivalvia: Thyasiridae)

ABSTRACT This study provides a revision of the Magellanic and Antarctic species of Thyasira and Parathyasira. The status of all species previously reported from the area is revised and a new species described. Five species are recognized as valid: Thyasira falklandica (Smith, 1885); Thyasira scotiana, n. sp.; Thyasira debilis (Thiele, 1912), new combination; Parathyasira magellanica (Dall, 1901), new combination; and Parathyasira dearborni (Nicol, 1965), new combination. Cryptodon fuegiensis Dall, 1890, previously reported under the genus Thyasira, is reallocated into Conchocele Gabb, 1866. Loripes pertenuis Smith, 1881, and Thyasira bongraini Lamy, 1911, are considered nomen dubia.

Tellimya Tehuelcha, New Species: First Record of Tellimya Brown, 1827, In South America (Bivalvia: Lasaeidae), with Notes on Life History and Reproduction

Galeommatoids are small bivalves usually living as epibionts on other invertebrates. Among them, a number of genera, such as Waldo Nicol, 1966, Scioberetia F. Bernard, 1895, Montacuta Turton, 1822, Tellimya Brown, 1827, Brachiomya Jespersen, Lützen & Nielsen, 2004, and Montacutella Jespersen, Lützen & Nielsen, 2004, are associated with sea urchins. Only Scioberetia and Waldo were reported from the southern tip of South America (F. Bernard, 1895a–c; Zelaya & Ituarte, 2002). Tellimya was proposed to include Mya suborbicularis Montagu, 1803, Ligula substriata Montagu, 1808, Mya ferruginosa Montagu, 1808, Tellimya lactea Brown, 1827, T. tenuis Brown, 1827, T. elliptica Brown, 1827 (based on Mya ferruginosa Montagu, 1808, and an objective synonym thereof), T. glabrum Brown, 1827, and T. ovata Brown, 1827. Subsequently, Gray (1847) designated Mya ferruginosa as its type species. Pérès (1937), Pophan (1940), Deroux (1961) and Oldfied (1961) provided information on the gross anatomy and functional morphology of the type species, and Kamenev (2008) clarified the details of the hinge morphology of the genus. Tellimya has sometimes been regarded as a subgenus of Montacuta (e.g., Pelseneer, 1925; Ponder, 1968), but currently regarded as a full genus (e.g., Chavan, 1969; Aartsen, 1997; Marshall, 2002; Kamenev, 2008). In the present paper, a new species of Tellimya from the Magellan Region, which constitutes the first record of the genus in South America, is described.

A New Species of Leptochiton (Polyplacophora: Leptochitonidae) from the Southwestern Atlantic

ABSTRACT Leptochiton sanmatiensis, new species, is described from shallow-waters of Argentina. The species is characterized by having a quincuncial arrangement of tegmental granules on head valve, lateral areas of intermediate valves and postmucronal area of tail valve, and a longitudinal arrangement of these structures on the central areas of intermediate valves; each granule having a macraesthete and four micraesthetes. In addition, the new species has pectinated dorsal scales, with 14–21 ridges; a low number of ctenidia (up to six on each side in the largest specimens); and the second lateral tooth with three denticles in the cusp. The species lives on small gravel and shells.

A New Generic Placement for “Calliostoma” Blakei Clench & Aguayo, 1938 (Gastropoda: Trochoidea)

ABSTRACT “Calliostoma” blakei Clench & Aguayo, 1938, described from Río Negro Province, Argentina, appears in the literature either under the genera Calliostoma, Photinula (Calliostomatidae) or as a member of the Umboniinae (Trochidae). The study of live-collected specimens allows to revise its generic placement.The species is characterized by a bipectinate ctenidium with short afferent membrane, isolated appendices in the left side of the neck, and the rachidian and the first lateral teeth reduced to their base. This set of characters, not present in any other trochoid, leads us to propose the new genus Carolesia for this species.

Neactaeonina argentina, New Species, and Family Placement of the Genus Neactaeonina Thiele, 1912 (Mollusca: Gastropoda)

ABSTRACT Neactaeonina argentina, a new species from the outer Argentine shelf off Buenos Aires province, is described. The species is characterized by the elongate, low-spired shell, with shouldered, nearly straight whorls, deep suture, and sculpture composed of numerous, broad, flat spiral cords. The radula is similar to that previously described for the type species, Neactaeonina cingulata Thiele, 1912, except in having a greater number of teeth. The present study provides the first information on the anatomy and histology of the genital system, and details of the radula anatomy of Neactaeonina, both unknown to date. The study of anatomical characters demonstrates that Neactaeonina has clear similarities with other Acteonidae, with a combination of features present in Acteon (such as the presence of a strongly calcified shell, with well-developed operculum; mantle cavity opening anteriorly; nervous system with only the cerebropleural ganglia fused; a single allosperm sac associated with the female system; radula without cardinal tooth; and oral cuticle with rod-like processes); and some characters present in acteonid genera other than Acteon (e.g., the number and morphology of teeth, and processes of the oral cuticle). However, Neactaeonina shows some characters thus far not reported for any other genus currently placed into the Acteonidae: salivary glands with laminar structure, male genital system with an open portion, a single allosperm sac opening distally, and a flat and triangular copulatory organ.

Species of Iothia (Gastropoda: Lepetidae) from Shallow Waters of the Magellan Region

ABSTRACT The Lepetidae are currently assumed to be represented by only one valid species in the Magellan region: Iothia emarginuloides (Philippi, 1868), of which Tectura (Pilidium) coppingeri Smith, 1881, and Iothia coppingeri magellanica Linse, 2002, were regarded as synonyms. The extant records of this species are scarce, although they suggest a wide distributional range in the Pacific Ocean, from off Concepción (36°S) to the Beagle Channel (55°S), and a restricted distribution in the Atlantic Ocean, where the species is only known from the Malvinas / Falkland Islands and Isla de los Estados (about 54.5°S). This study provides new information on the occurrence of the genus Iothia in the Magellan region, including morphological, anatomical and molecular evidence. The synonymy of Tectura (Pilidium) coppingeri, Iothia coppingeri magellanica and Iothia emarginuloides is ratified. The species is properly redescribed and figured, and its intraspecific variability discussed, particularly regarding its relation with depths. Furthermore, the distribution of this species in the southwestern Atlantic is extended north to San Matías Gulf (about 41°S). Iothia megalodon Warén, Nakano & Sellanes, 2011, previously known from deep waters off Concepción (36°S), is here reported for the first time for the Magellan region. Its finding in shallow waters from the Beagle Channel greatly extends its distribution both latitudinally and bathymetrically.

A New Species of Mysella angas, 1877 from Southern Chile (Bivalvia: Galeommatoidea)

Fil: Guller, Marina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biologia Experimental; Argentina

A Case of Phoresis of Sphaeriids by Corixids: First Report for the Americas

Dispersal represents a key process in determining the genetic structure and demography of populations. This process reduces competition among siblings, reduces competition between parents and offspring, reduces the likelihood of inbreeding, increases recolonization following local extinctions, also decreasing the risk of local extinction (Pechenik, 1999). Similarly, the modes of reproduction and dispersal can play a major role in species longevity, geographic distribution, and rate of speciation (Mayr, 1970; Stanley, 1979). In freshwater bivalves, a free-living larval stage is frequently suppressed; consequently, the dispersal of a species relies on the capacities of juvenile and adult stages. Dispersal mechanisms include rafting (i.e., the transport of an organism on a drifting object); currentmediated dispersal of juveniles suspended in water (McKillop & Harrison, 1982); airborne dispersal (anemochory) of juveniles and adults (e.g., hurricanes, tornadoes, and other twisters) (Rees, 1965, and references therein); and dispersal by biotic (either natural or anthropogenic) vectors, with vertebrates or invertebrates acting as carriers (Kappes & Haase, 2012, and references therein).

On the Generic Allocation of “Aligena” Pisum Dall, 1908

additional records. Harry (1969), in the context of a systematic revision of the genus Aligena Lea, 1846, concluded that Aligena pisum was wrongly located under this genus, and proposed its tentative reallocation in the genus Axinulus Verrill & Bush, 1898, a decision not followed by cies under Aligena. Bernard (1983) considered Aligena pisum as a nomen dubium. The genus Adontorhina was proposed by Berry (1947) to include Lower Pleistocene specimens of his new species A. cyclia. The species was subsequently reported as also living by Howard (1952). Other species currently regarded under Adontorhina are: A. sphaericosa Scott, 1986, A. lynnae Valentich Scott (in Coan, Valentich Scott & Bernard), 2000, A. keegani Barry & McCormack, 2007, and A. similis Barry & McCormack, 2007. In this paper, Aligena pisum is redescribed, properly illustrated, and reallocated to Adontorhina. MALACOLOGIA, 2011, 53(2): 373 378

Bivalves from the Chilean Fjords Region: Knowns and Unknowns*

Abstract: The Chilean Fjords Region has been regarded as one of the most complex coastal systems of the world, with a high level of mollusk diversity. Contradictorily, bivalves from this region have been recently considered both well and insufficiently known. This study critically evaluates the current state of knowledge on bivalves from the Chilean Fjords Region, by combining information coming from previously published literature, the study of material housed at museum collections, and new data coming from recently collected material. Although a total of 223 species appear listed in the literature for the area, only 81 valid species have documented records, the remaining corresponding to nomina dubia/nuda, synonyms, misidentifications, species complexes or species which were listed for the area, but based on unknown sources. The present study makes evident that, after more than two centuries the knowledge on bivalve diversity from the Chilean Fjords Region still remains at its first stages.