Juan López-Gappa

Redescription and palaeoecological significance of the bryozoan Hippoporidra patagonica (Pallaroni, 1920) in the San Julián Formation (late Oligocene) of Santa Cruz province, Argentina

Hippoporidra is a cheilostome bryozoan that predominantly encrusts gastropod shells inhabited by hermit crabs. The genus has a Pan-Atlantic distribution and its fossil record ranges from the Eocene to Holocene. Cellepora patagonica Pallaroni is here transferred to Hippoporidra and its autozooids and avicularia are described for the first time based on scanning electron microscopy. Hippoporidra patagonica can be distinguished from the remaining species of the genus by the peculiar shape of its interzooidal avicularia and the morphology of its orifice, which is semicircular, with a straight proximal border. In addition, many specimens have adventitious avicularia located on a suboral umbo. The record of Hippoporidra patagonica (Pallaroni) in the Gran Bajo Member of the San Julián Formation (late Oligocene) in Patagonia confirms the presence of this genus at the southern tip of South America and indicates a Pan-Atlantic distribution during the Cenozoic.

New and little-known bryozoans from Monte León Formation (early Miocene, Argentina) and their paleobiogeographic relationships

Abstract. The bryozoan fauna from the South American Cenozoic is poorly known. The study of new material collected in the Monte León Formation (early Miocene), gave us the opportunity to describe four new species: Valdemunitella canui n. sp., Foveolaria praecursor n. sp., Neothoa reptans n. sp., and Calyptotheca santacruzana n. sp. Two of them (V. canui and C. santacruzana) were first recorded by F. Canu and interpreted as recent species from the Australian bryozoan fauna, but are herein described as new species. The stratigraphic range of Otionella parvula (Canu, 1904) is extended to the early Miocene. The present study emphasizes the close relationships between the South American Neogene bryozoan faunas and those of other Gondwanan sub-continents such as New Zealand and Australia.

First record of a fossil selenariid bryozoan in South America

López-Gappa, J., Pérez, L.M. & Griffin, M. February 2017. First record of a fossil selenariid bryozoan in South America. Alcheringa XX, xxx-xxx. ISSN 0311-5518. Selenariidae Busk 1854 (Bryozoa) is considered endemic to Australia and New Zealand. Here we describe a new species of Selenaria Busk 1854 from the lower Miocene Monte León Formation (Patagonia, Argentina). Selenaria lyrulata sp. nov. is characterized by autozooids with a lyrula-like, anvil-shaped cryptocystal denticle, opesiular indentations and lateral condyles, as well as avicularia with a shield of fused costae. This is the first record of a selenariid bryozoan in South America. Juan López-Gappa [lgappa@macn.gov.ar] CONICET—Museo Argentino de Ciencias Naturales. Av. Ángel Gallardo 470, C1405DJR, Ciudad Autónoma de Buenos Aires, Argentina; Leandro Martín Pérez [pilosaperez@gmail.com] and Miguel Griffin [patagonianoyster@gmail.com], CONICET—División Paleozoología Invertebrados, Museo de La Plata. Paseo del Bosque s/n, B1900FWA, La Plata, Argentina.

Recent discovery of non-indigenous bryozoans in the fouling assemblage of Quequén Harbour (Argentina, Southwest Atlantic)

The non-indigenous bryozoans Aspidelectra melolontha (Landsborough) and Amathia verticillata (Delle Chiaje) (= Zoobotryon verticillatum) are recorded for the first time in Argentina. They were found on experimental substrata submerged to study the fouling assemblage of Quequén Harbour (38°34.310′S, 58°42.814′W), an estuarine environment. Biflustra puelcha (d’Orbigny) comb. nov., Conopeum reticulum (Linnaeus), Conopeum seurati (Canu), Cryptosula pallasiana (Moll), Electra monostachys (Busk) and Schizoporella cf. errata (Waters) were also found in this association. Aspidelectra melolontha, a species native to Europe with only one record for San Francisco Bay (United States) based on unpublished data, is here reported for the first time for South America, and the affinity between this species and A. zhoushanica (Wang) is discussed. The presence of C. seurati in brackish water habitats of Argentina is confirmed. B. puelcha was previously unknown as a fouler in harbours. A. verticillata is a well-known marine fouler in many harbours and marinas worldwide. The southernmost record of this species on the Atlantic coast of South America was in Brazil. Thus, its distribution is herein expanded by 14° of latitude towards the south. In view of its great invasive potential, A. verticillata seems to have the ability to continue its dispersal and to become a stable component of this and neighbouring harbours.

The clam Neilonella sulculata in San Jorge Gulf (Argentina, Southwest Atlantic): spatial distribution pattern and inverse relationship between size and density

ABSTRACT Neilonella sulculata is a dominant bivalve on muddy bottoms of the continental shelf and gulfs off Argentina (Southwest Atlantic). Two benthic surveys performed in 2007 and 2009 in San Jorge Gulf, a depositional area characterized by silt/clay sediments, gave us the opportunity to test whether the population of this clam displays a significant spatial structure and to analyse if there is an inverse relationship between size and density. Density, biomass and size–frequency distribution displayed significant spatial structure, being positively autocorrelated at the smallest spatial scales (c. 1.7–14/17 km). Biomass also showed spatial contagion at scales of 25–33 km. A substantial increase in density and biomass occurred between 2007 and 2009. Empty valves in the sediment showed that the maximum size attained by the species may exhibit considerable variation at relatively short temporal scales. Regardless of temporal changes in density and biomass, the spatial structure of these variables remained stable. In densely populated areas, shell size decreased with increasing density, suggesting a density-dependent control of growth. A clear north–south increase in density and biomass was detected, which might be related to a gradient in food availability caused by a thermohaline frontal system associated with wind-related upwelling.

Effect of large predators on the fouling assemblage of a Patagonian harbour (Argentina, SW Atlantic)

Predatory control of community structure, through consumption of herbivores and subsequent positive effects on the biomass or productivity of primary producers is common in marine ecosystems. We designed an experiment to analyse the effect of large-sized predators on the development of the macrofouling assemblage of a harbour. Predation was manipulated by randomly assigning artificial substrata to three treatments: (1) exclosure cages preventing access of large predators, (2) cage controls, i.e. cages with lateral walls but without roofs, allowing predators free access, (3) uncovered panels. Substrata were submersed horizontally and upper surfaces sampled at quarterly intervals over a 1-year period. No differences in species richness were observed among treatments but diversity was lower within exclosure cages than on cage controls/uncovered panels. In sessile assemblages, structure differed between treatments: cage controls/uncovered panels were dominated by algae and associated mesoherbivores, which were scarce/absent within cages. Exposure to predators also affected the structure of mobile assemblages. The sea urchin Pseudechinus magellanicus (Philippi) occurred within exclosure cages but was never found on exposed panels. We conclude that large predators exert a significant effect on assemblage structure and diversity, indirectly promoting the development of filamentous algae and mesoherbivores by controlling the abundance of browsers.

A new genus and species of cheilostome bryozoan associated with hermit crabs in the subantarctic Southwest Atlantic

Some bryozoan species occur on gastropod shells occupied by hermit crabs, often dominating the shell surface to the exclusion of other encrusters. Symbioses between bryozoans and pagurid crabs are known from a wide latitudinal range, including tropical, warm- and cold-temperate regions. Here we describe Burdwoodipora paguricola gen. et sp. nov., a cheilostome bryozoan associated with pagurized shells occupied by the hermit crab Pagurus comptus White in subantarctic waters of the Southwest Atlantic. The association seems to be obligate, as the bryozoan was always found enlarging the last whorl of its gastropod substrate. The new species, however, is not species specific with regard to its shell substrate, as it was found to be associated with 31 species of gastropods with helicoidal coiling. Well-developed colonies may project up to 360° from the outer lip of the shell. The chamber built by the bryozoan is usually larger than the whorl that would have been generated by the gastropod. This is one of the few known cases of an obligate association between a bryozoan and a pagurid crab outside the ascophoran family Hippoporidridae and is also the first bryozoan/hermit crab symbiosis documented in the subantarctic region. The inclusion of Burdwoodipora in the Pacificincolidae, a family currently represented by just four species from the Northern Hemisphere, is discussed.

Taxonomic status of some species of Aspidostomatidae (Bryozoa, Cheilostomata) from the Oligocene and Miocene of Patagonia (Argentina)

Abstract. The bryozoan genus Aspidostoma Hincks, 1881 has been regarded as the only representative of the Aspidostomatidae Jullien, 1888 in Argentina to date. Its type species, Aspidostoma giganteum (Busk, 1854), is presently distributed in the Magellanic Region (Argentina and Chile) and has been recorded in Oligocene and Miocene fossil deposits of Santa Cruz and Chubut, respectively. New material from San Julián (late Oligocene), Monte León (early Miocene), Chenque (early to middle Miocene), and Puerto Madryn (late Miocene) formations suggests, however, that A. giganteum is not represented in the fossil record. Material from Puerto Madryn Formation previously regarded as A. giganteum is here recognized as Aspidostoma roveretoi new species. Aspidostoma ortmanni Canu, 1904 is revalidated for the species from the San Julián Formation. Aspidostoma armatum new species and Aspidostoma tehuelche new species are introduced for material from the Monte León and Chenque formations, respectively. Aspidostoma incrustans Canu, 1908, from the early Miocene, is redescribed. Melychocella Gordon and Taylor, 1999, which differs from Aspidostoma in having vicarious avicularia and lacking a median ridge and a quadrangular process proximal to the opesia-orifice, is so far represented by three Paleogene species from the Chatham Islands (Southwest Pacific). The material from Monte León allowed us to transfer Aspidostoma flammulum Canu, 1908 to Melychocella, resulting in the new combination Melychocella flammula (Canu, 1908). Melychocella biperforata new species is described from the lower Miocene Monte León and Chenque formations. The presence of Melychocella in the Neogene of Patagonia extends its geographic distribution and its temporal range.

Role of the clam Neilonella sulculata as substrate for the hydroid Bougainvillia macloviana on muddy bottoms of San Jorge Gulf (Argentina, Southwest Atlantic)

ABSTRACT The clam Neilonella sulculata is the dominant bivalve on muddy bottoms along the Argentine continental shelf (Southwest Atlantic). The medusa stage of the hydroid Bougainvillia macloviana is one of the most abundant species in the gelatinous zooplankton of the Magellan region. Two benthic surveys carried out in 2007 and 2009 in San Jorge Gulf gave us the opportunity to analyse (1) the interaction between N. sulculata and its epibiont, B. macloviana, and (2) the role of the clam as hard substrate in a depositional area characterized by silt/clay sediments. Bougainvillia macloviana has a high prevalence on the posterior region of live clams. The presence of gonophores shows that these small colonies are able to reproduce there. Hydroid colonies are very rare on dead valves of N. sulculata and also on almost all other live bivalve species in the study area. Specimens of N. sulculata with hydroids were slightly but significantly larger than those without them, both in 2007 and 2009. The high prevalence of B. macloviana on live individuals of N. sulculata and its almost total absence on other clam species suggest that this association may be critical at least for the epibiont and not the result of chance alone.