(Gastropoda) from the Rockall and Hatton Banks, Northeastern Atlantic Ocean
Total Page：16
File Type：pdf, Size：1020Kb
Miscellanea Malacologica 4(4): 47-61, 31.X.2010 Skeneimorph species (Gastropoda) from the Rockall and Hatton Banks, northeastern Atlantic Ocean L. HOFFMAN1, B. Van HEUGTEN2 & M. S. S. LAVALEYE3 1Zoetermeer, the Netherlands ([email protected]), 2Oosterhout, the Netherlands ([email protected]), 3NIOZ, Texel, the Netherlands ([email protected]) ABSTRACT A record is given on the occurrence and abundance of skeneimorph species in the families Trochaclididae, Pendromidae and Turbinidae (including those species formerly placed in Skeneidae) that have been collected during the NIOZ expeditions to the Rockall and Hatton Banks (2004-2008). A description is provided for two new species: Mikro hattonensis, and Xyloskenea xenos (Skeneinae, Turbinidae, Gastropoda). Their holotypes have been deposited in the Zoological Museum Amsterdam (University of Amsterdam). Two poorly known species have been figured and re-described: Granigyra tenera (Jeffreys, 1883), and Ganesa nitidiuscula Jeffreys, 1883. Key words: Northeastern Atlantic Ocean, Rockall Bank, Hatton Bank, Turbinidae, Skeneidae, Skenea, Ganesa, Mikro, Xyloskenea, Granigyra, taxonomy, new species, HERMES, Moundforce. INTRODUCTION MATERIAL AND METHODS The Rockall and Hatton Banks are sea bottom During expeditions conducted in 2004 (Mienis highs that have developed over Jurassic fault et al., 2004 [Moundforce]), 2005 (van Duyl et blocks. These fault blocks were formed during al., 2005 [HERMES]) and 2006 (Duineveld et early failed continental rifts in the Early al., 2006 [HERMES]), box core samples have Cretaceous. The failed rift systems are been taken from the coral-rich sea-bottom in preceding the successful rift that has developed the southeastern slope of the Rockall Bank and since the Cretaceous between the Western in 2008 (Lavaleye et al., 2008 [HERMES]) on European continent and the East Greenland the Hatton Bank. coastline in the North East Atlantic. The deep Whereas some of these box cores have Rockall Trough separates the Rockall Bank been preserved and retained for other from Ireland and Scotland. The Hatton Bank is investigations, other box core samples have the NW extent of the larger Rockall and Hatton been investigated for their malacofauna. Bank area. The Rockall Bank has a miniscule Unfortunately, the great majority of these island as a tip of a fault block in the North of samples only contained empty shells and, the structure. hence, no material has been available for The Hatton Bank is fully submerged. It anatomical studies. may be assumed that the sea bottom Bottom samples from box cores have environment in the Rockall-Hatton area has been washed thoroughly with fresh water, been in a stable state for at least 65 million dried and sieved in fractions of 10 mm, 3 mm, years, i.e. the end of the Cretaceous. These 1 mm, 0.5 mm. Fractions larger than 10 mm stable and isolated environments are known to and 3 mm contained mostly large coral develop endemic species. The highs of the fragments and few larger Mollusca; these have present day banks form a conglomerate of been hand picked. Fractions of 1-3 mm have cold-water coral reefs. A rich fauna been fully sorted under a microscope. The community populates these highs of which the fractions of 0.5-1 mm have been sampled and a most prominent groups are Mollusca, corals small volume has been fully sorted. The and sponges. remaining material has been enriched in a Typical water depths where these counter-current washing process and the communities thrive are 500-700 m on the enriched fraction has been fully sorted. The Rockall Bank to 600-1100 m on the Hatton smallest fraction has been fully enriched by Bank. The Royal Netherlands Institute for Sea counter-current washing and representative Research (NIOZ) has conducted detailed samples have been sorted. Taxonomy of the studies on the faunal communities of cold- specimen has been largely based on the online water corals in the NE Atlantic Ocean. CLEMAM database for European Mollusca. 47 Hoffman, Van Heugten & Lavaleye, 2010: Skeneimorph species For all box core stations, statistical shell counts In this paper, we add two more new have been carried out such that species species in Skeneinae. Their holotypes have abundance by weight or sea-bottom area could been deposited in the Zoological Museum be estimated. Amsterdam. A few paratypes have been We have used as abundance unit retained in the collections of the authors. shells/kg-dry-sediment-weight and it must be realised that its large uncertainty is caused by inaccuracies introduced by sampling (location ABBREVIATIONS and depth of penetration) as well as in the information gathering (subjective hand sorting, CLEMAM = Check-List of European Marine visual counts, statistical extrapolations, Mollusca HERMES = Hotspot Ecosystem Research of the subjective taxonomic classification). Typical Margins of European Seas dry-weight sediment samples in the box cores n. sp. = new species contain 0.3-20 kg. For large sample sets with NIOZ = Royal Netherlands Institute for Sea high-related abundance it is not meaningful to Research, Texel specify the exact number of shells as this has ZMA = Zoological Museum Amsterdam often been based on statistical extrapolation of sub-samples. For rare species, frequently the ACKNOWLEDGEMENTS fully sorted shell set has been investigated but then the abundance is meaningless with only The authors express their appreciation to NIOZ few specimens available and it has been for allowing to work the unique material and to omitted consequently. publish the results of these studies. We greatly Representatives of most species have acknowledge the assistance of captain, crew, been digitally photographed using a technicians and scientists on board of RV stereomicroscope camera and a computer. ‘Pelagia’ during the cruises. Images have been taken as spherical slices at We particularly thank Robert G. regular focusing distances and the set of Moolenbeek (ZMA) for stimulating images have been synthetically combined into discussions, his knowledgeable advice on the one sharp image using Helicon Focus software. taxonomy and the provision of literature. He Alternatively, rare specimens have been has been most cooperative in allowing the first selected for SEM photography; they have been author to use the SEM facility at the University cleaned in a weak bleach solution, rinsed in of Amsterdam for micro-photographic fresh water, subjected to ultrasonic cleaning. pictures. Bram van der Bijl, Marien J. Faber Subsequently, they have been mounted for and an anonymous referee critically read the SEM photography. manuscript. The class of Archaeogastropoda and in particular the subfamily Skeneinae in the family Turbinidae is predominantly SYSTEMATICS represented in the malacofauna, both in terms of number of specimens as well in the number Family: Trochaclididae of species. In 2008, Hoffman et al. discussed four new skeneid species in the new genus Trochaclis islandicus Warén, 1989 Lopheliella from the Rockall Bank. The holotypes of the genera Trochaclis islandicus Warén, 1989: 9-11, figs 6-7 Lopheliella, Mikro and Xyloskenea are in the collection of the Zoological Museum Material examined.- Amsterdam (formally part of University of ROCKALL BANK: Moundforce 2004/29, depth 1443 m, Amsterdam). All remaining material is either 1 shell; Hermes 2006/12, depth 1091 m, 3 shells; in the collection of the National Museum of HATTON BANK: Hermes 2008/36, depth 700 m, 9 Natural History ‘Naturalis’ in Leiden, the shells; Hermes 2008/117, depth 958 m, 12 shells. Netherlands or in the collections of the authors. 48 Miscellanea Malacologica 4(4): 47-61 Family: Pendromiidae Skenea areolata: Warén, 1991: 58, figs 3A-C Rugulina fragilis (G.O. Sars, 1878) Material examined.- (Figs 1-3) ROCKALL BANK: Moundforce 2004/29, depth 1443 m; Moundforce 2004/41C, depth 784 m; Hermes 2005/15, Adeorbis fragilis G.O. Sars, 1878: 213, tab. 22, figs 19a-c depth 593 m; Hermes 2005/34, depth 767 m; Hermes Rugulina fragilis: Warén, 1991: 71-73, figs 11A-E, 13A- 2006/10C, depth 578 m; Hermes 2006/12, depth 1091 m; B Hermes 2006/23A, depth 578 m; Hermes 2006/56, depth 578 m; Hermes 2006/65, depth 1087 m; HATTON Material examined.- BANK: Hermes 2008/36, depth 700 m; Hermes 2008/92, ROCKALL BANK: Moundforce 2004/37, depth 557 m; depth 822 m; Hermes 2008/117, depth 958 m. Hermes 2005/15, depth 593 m; Hermes 2005/34, depth Abundances are 72.2 shells/kg at 400-600 m, 11.8 767 m; Hermes 2006/10C, depth 587 m; Hermes shells/kg at 600-800 m, 2.2 shells/kg at 1000-1200 m, 2.4 2006/12, 1091 m; Hermes 2006/23A, depth 578 m; shells/kg at 1443 m. Hermes 2006/56, depth 578 m; Hermes 2006/65, depth 1087 m; HATTON BANK: Hermes 2008/35, depth 796 m; Hermes 2008/36, depth 700 m; Hermes 2008/59, Skenea basistriata (Jeffreys, 1877) depth 788 m; Hermes 2008/92, depth 822 m. Abundances are 6.5 shells/kg at 400-600 m, 6.9 shells/kg at 600-800 Cyclostrema basistriata Jeffreys, 1877: 234 m, 2.7 shells/kg at 1000-1200 m. Skenea basistriata: Graham, 1988: 138, fig. 47 Skenea basistriata: Warén, 1993: 176, figs 16A-F, 17A-D Rugulina species Material examined.- (Figs 4-6) ROCKALL BANK: Hermes 2006/12, depth 1091 m; Hermes 2006/65, depth 1087 m. Material examined.- HATTON BANK: Hermes 2008, St.117, depth 958 m, 1 fragmentary shell. Skenea larseni Warén, 1993 Description.- Skenea larseni Warén, 1993: 173, figs 11D-F, 12A, 12C, Fragile well rounded tonnoid-shaped shell, 12E, 13C, 14A-B, 15C-D height 2.3 mm, width 2.3 mm, with radial regular rib structure. Protoconch is eroded and Material examined.- hence unknown. Teleoconch whorls are well ROCKALL BANK: Moundforce 2004/41C, depth 784 rounded but somewhat oval in cross-section. m; Hermes 2005/15, depth 593 m; Hermes 2005/23, The base of the outline is a well-rounded base.