▪ Abstract  Most of our knowledge of biodiversity and its causes in the deep-sea benthos derives from regional-scale sampling studies of the macrofauna. Improved sampling methods and the expansion of investigations into a wide variety of habitats have revolutionized our understanding of the deep sea. Local species diversity shows clear geographic variation on spatial scales of 100–1000 km. Recent sampling programs have revealed unexpected complexity in community structure at the landscape level that is associated with large-scale oceanographic processes and their environmental consequences. We review the relationships between variation in local species diversity and the regional-scale phenomena of boundary constraints, gradients of productivity, sediment heterogeneity, oxygen availability, hydrodynamic regimes, and catastrophic physical disturbance. We present a conceptual model of how these interdependent environmental factors shape regional-scale variation in local diversity. Local communities in the deep sea may be composed of species that exist as metapopulations whose regional distribution depends on a balance among global-scale, landscape-scale, and small-scale dynamics. Environmental gradients may form geographic patterns of diversity by influencing local processes such as predation, resource partitioning, competitive exclusion, and facilitation that determine species coexistence. The measurement of deep-sea species diversity remains a vital issue in comparing geographic patterns and evaluating their potential causes. Recent assessments of diversity using species accumulation curves with randomly pooled samples confirm the often-disputed claim that the deep sea supports higher diversity than the continental shelf. However, more intensive quantitative sampling is required to fully characterize the diversity of deep-sea sediments, the most extensive habitat on Earth. Once considered to be constant, spatially uniform, and isolated, deep-sea sediments are now recognized as a dynamic, richly textured environment that is inextricably linked to the global biosphere. Regional studies of the last two decades provide the empirical background necessary to formulate and test specific hypotheses of causality by controlled sampling designs and experimental approaches.

X-ray diffraction studies confirm that, with few exceptions, each skeletal element of echtinoderms is a single crystal of magnesium-rich calcite and that a relation exists between the shape of the element and the crystallographic a- and c-axes. The exceptions incluide the teeth of echinoids, and the calcareous ring as well as the anal teeth of holothurians. The tubercles of an echinoid plate begin their growth as parts of the single crystal of the plate; under the mechanical action of the spines that are attached to them, they become partly polycrystalline, as shown by scanning electron microscopy and by x-ray powder diffraction. The interface between inorganic crystalline and organic amorphous matter in the skeletal element appears to be the first example reported in nature of a periodic mninimal suirface.

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Pawson, David L. The Echinoderm Fauna of Ascension Island, South Atlantic Ocean. Smithsonian Contributions to the Marine Sciences, number 2, 31 pages, 11 figures, 1978.-Two recent intertidal collecting expeditions and existing museum collections have added much to knowledge of the Ascension Island echinoderm fauna. Twenty-five species are now known from Ascension; eight are new records. One new species, Holothuria (Halodeima) manningi, and one new subspecies, Echinometra lucunter polypora, are described. Diadema ascensionis Mortensen is regarded as a subspecies of D. antillarum Philippi, and Pseudoboletia atlantica H. L. Clark is regarded as a subspecies of P. maculata Troschel. The echinoderm fauna of Ascension Island includes 8 amphi-Atlantic species, 3 western Atlantic species, 4 eastern Atlantic species, 5 circumtropical species, 4 species shared only with St. Helena, and 1 endemic species. There are in addition three endemic subspecies. Twelve species are shared with St. Helena, and both islands are closely similar in terms of numbers and relationships of their faunal components. Colonization of both islands by planktonic larval stages is suggested. Dendrochirotid holothurians, which lack such larval stages, are not represented at either St. Helena or Ascension. The structure of the Ascension fauna seems to have been determined by vagaries of ocean surface and subsurface currents. In contrast, Bermuda, which sits astride the Gulf Stream, has a fauna that is entirely typical of the West Indian region to the south. OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SERIES COVER DESICN: Seascape along the Atlantic coast.

The preparation and physical properties of the new complexes Cs,[Ru(N) X,] and R[M(N)X,] (M = Ru or 0 s ; R = Ph4As or Bu"4N ; X = CI or Br) are described. New binuclear nitrido-bridged complexes of ruthenium(1v) with carbonyl, cyanide, and chelate ligands, the polymeric ni'trido-bridged species [Os(N) Br41nn-and [Os,(N),X,,-(NH3),I3-(X = CI or Br), and oxo-and dioxo-complexes of ruthenium are also reported. The structures of the species are discussed on the basis of vibrational spectra and other properties.THE nitride ion (N3-), like the isoelectronic oxide ion (02-), can function as a terminal ligand or, less commonly, bridges two,2 three,3 or four4 metal atoms in linear, triangular, or tetrahedral arrays. Recently we briefly described the preparation of ruthenium(v1) terminal nitrido-salts Cs,[Ru(N)X,] (X = C1 or Br) and related dioxo-~pecies,~ and here we give fuller details of these and of other terminal nitrido-complexes. We also report an extension of our previous work on binuclear and polynuclear nitrido-bridged complexes of ruthenium and osmium.6 RESULTS AND DISCUSSION Terminal Nitrido-conzpZexes.-Mononuclear species containing MEN groups have been established for very few metals, viz. vanadium,' molybdenum and tungsten,s r h e n i ~m , ~ and osmium.1° In general the MEN distance is short (ca. 1.7 A), and the metal is in a high oxidation state due to the very effective 0-and x-donor properties of the nitrido-1igand.l Despite the considerable stability of nitrido-complexes of osmium(v1) and osmium(vm), the only ruthenium nitrido-complexes hitherto established are binuclear with symmetric Ru-N-Ru units.6 We found that reaction of the complexes tra.n~-[Ru(O),X~]~-(X = C1 or Br) in ice-cold HX solution with an excess of azide ions

New information on swimming behavior of four species of deep-sea holothurians has been obtained using the research submersibles Johnson-Sea-Link (Harbor Branch Oceanographic Institution) and Pisces V (University of Hawaii, HURL Program). Hansenothuria benti Miller and Pawson and Enypniastes eximia Theel were studied off the Bahama Islands, Paelopatides retifer Fisher off the Hawaiian Islands, and Pelagothuria natatrix Ludwig off the Galapagos Islands. Video recordings were made of swimming behavior, and individuals of all species were collected at the time of observation. Four contrasting life modes are represented: H. benti lives and feeds on the seafloor, but when disturbed it can swim vigorously for several minutes by rapidly flexing the anterior and posterior ends of the body into S curves. Enypniastes eximia swims almost continuously, briefly settling to the seafloor to ingest surface sediments. The bulbous body is propelled upwards by rhythmic pulsation of a webbed anterodorsal veil; stability during swimming is maintained by counteractive flexing of posterolateral veils. Paelopatides retifer lives on or near the seafloor and has been found up to 300 meters above the seafloor. The swimming behavior of this species combines locomotory movements of the two preceding species. An anterior veil pulsates, and the posterior half of the body flexes into S curves. Pelagothuria natatrix is truly pelagic, floating or drifting near the seafloor or high in the water column. Swimming is effected by infrequent and irregular pulsation of an enormous anterior veil. There is no evidence to suggest that P. natatrix descends to feed on the seafloor. Published data on the approximately 25 known species of swimming holothurians are summarized Probable reasons for swimming behavior are discussed Swimming appears to be most useful in predator avoidance, escape from physical hazards, locomotion, seeking out suitable substrata for feeding, and dispersal of juveniles or adults. OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: Seascape along the Atlantic coast of eastern North America. Library of Congress Cataloging-in-Publication Data Miller, John E. Swimming sea cucumbers (Echinodermata, Holothuroidea) : a survey, with analysis of swimming behavior in four bathyal species / John E. Miller and David L. Pawson p. cm.-(Smithsonian contributions to the marine sciences ; no. 35) Includes bibliographical references.

Chiridota heheva new species is described from cold seeps off Georgia and Florida, a shipwreck off Georgia, and an artificial wood-block habitat near Puerto Rico, in bathyal-abyssal depths of 2,200 3,300 meters. C. heheva is similar in some respects to C. hydrothermica Smirnov & Gebruk from Western and Southeastern Pacific hydrothermal vents, but it differs in structure of the tentacles and in color.

The deep ocean is home to a group of broad-collared hemichordates--the so-called 'lophenteropneusts'--that have been photographed gliding on the sea floor but have not previously been collected. It has been claimed that these worms have collar tentacles and blend morphological features of the two main hemichordate body plans, namely the tentacle-less enteropneusts and the tentacle-bearing pterobranchs. Consequently, lophenteropneusts have been invoked as missing links to suggest that the former evolved into the latter. The most significant aspect of the lophenteropneust hypothesis is its prediction that the fundamental body plan within a basal phylum of deuterostomes was enteropneust-like. The assumption of such an ancestral state influences ideas about the evolution of the vertebrates from the invertebrates. Here we report on the first collected specimen of a broad-collared, deep-sea enteropneust and describe it as a new family, genus and species. The collar, although disproportionately broad, lacks tentacles. In addition, we find no evidence of tentacles in the available deep-sea photographs (published and unpublished) of broad-collared enteropneusts, including those formerly designated as lophenteropneusts. Thus, the lophenteropneust hypothesis was based on misinterpretation of deep-sea photographs of low quality and should no longer be used to support the idea that the enteropneust body plan is basal within the phylum Hemichordata.