An illustrated key to the Malacostraca (Crustacea) of the northern Arabian Sea. Part 3: Euphausiacea

The key includes twenty-one species of euphausiids belonging to two families and six genera. The key was prepared following Brinton (1975). Since several authors attributed a fundamental importance to thelycum in systematics of euphausiids therefore the available figures of thelycum are also included

Female chromosome X mosaicism is age-related and preferentially affects the inactivated X chromosome

To investigate large structural clonal mosaicism of chromosome X, we analysed the SNP microarray intensity data of 38,303 women from cancer genome-wide association studies (20,878 cases and 17,425 controls) and detected 124 mosaic X events >2 Mb in 97 (0.25%) women. Here we show rates for X-chromosome mosaicism are four times higher than mean autosomal rates; X mosaic events more often include the entire chromosome and participants with X events more likely harbour autosomal mosaic events. X mosaicism frequency increases with age (0.11% in 50-year olds; 0.45% in 75-year olds), as reported for Y and autosomes. Methylation array analyses of 33 women with X mosaicism indicate events preferentially involve the inactive X chromosome. Our results provide further evidence that the sex chromosomes undergo mosaic events more frequently than autosomes, which could have implications for understanding the underlying mechanisms of mosaic events and their possible contribution to risk for chronic diseases

Female chromosome X mosaicism is age-related and preferentially affects the inactivated X chromosome

To investigate large structural clonal mosaicism of chromosome X, we analysed the SNP microarray intensity data of 38,303 women from cancer genome-wide association studies (20,878 cases and 17,425 controls) and detected 124 mosaic X events42Mb in 97 (0.25%) women. Here we show rates for X-chromosome mosaicism are four times higher than mean autosomal rates; X mosaic events more often include the entire chromosome and participants with X events more likely harbour autosomal mosaic events. X mosaicism frequency increases with age (0.11% in 50-year olds; 0.45% in 75-year olds), as reported for Y and autosomes. Methylation array analyses of 33 women with X mosaicism indicate events preferentially involve the inactive X chromosome. Our results provide further evidence that the sex chromosomes undergo mosaic events more frequently than autosomes, which could have implications for understanding the underlying mechanisms of mosaic events and their possible contribution to risk for chronic diseases

Detectable clonal mosaicism and its relationship to aging and cancer

In an analysis of 31,717 cancer cases and 26,136 cancer-free controls from 13 genome-wide association studies, we observed large chromosomal abnormalities in a subset of clones in DNA obtained from blood or buccal samples. We observed mosaic abnormalities, either aneuploidy or copy-neutral loss of heterozygosity, of >2 Mb in size in autosomes of 517 individuals (0.89%), with abnormal cell proportions of between 7% and 95%. In cancer-free individuals, frequency increased with age, from 0.23% under 50 years to 1.91% between 75 and 79 years (P = 4.8 × 10(-8)). Mosaic abnormalities were more frequent in individuals with solid tumors (0.97% versus 0.74% in cancer-free individuals; odds ratio (OR) = 1.25; P = 0.016), with stronger association with cases who had DNA collected before diagnosis or treatment (OR = 1.45; P = 0.0005). Detectable mosaicism was also more common in individuals for whom DNA was collected at least 1 year before diagnosis with leukemia compared to cancer-free individuals (OR = 35.4; P = 3.8 × 10(-11)). These findings underscore the time-dependent nature of somatic events in the etiology of cancer and potentially other late-onset diseases

Variable Factors Affecting the Apparent Range and Estimated Concentration of Euphausiids in the North Pacific

The quantitative and qualitative contents of a zooplankton sample are influenced by two kinds of variables: (1) natural variables such as temperature of the water, currents, latitudinal and seasonal variations in sunlight intensity, water transparency, amount of food or nutrients, oxygen content of the water, which may modify or maintain the horizontal and vertical distribution of species and condition their breeding and growth cycles; (2) artificial variables associated with (a) the method used to present the data, (b) the method used to take aliquots and count the plankton, and (c) the collecting method-type of net, depth of tow, hour of day of sampling

The distribution of Pacific euphausiids

A study has been made of the distribution of 59 euphausiid species in the Pacific Ocean, based upon oceanic surveys carried out from 1949 to 1961 by the Scripps Institution of Oceanography, California Cooperative Oceanic Fisheries Investigations (CalCOFI), and Pacific Oceanic Fisheries Investigations (POFI). Quantitative aspects of the vertical and horizontal distributions are presented. The species belonging to the genera Bentheuphausia and Thysanopoda are typically deep-living. Bentheuphausia ambloyops, Thysanopoda cornuta, and T. egregia are widely ranging bathypelagic species, the adults of which inhabit depths greater than 1,500 meters. Of the ten genera, six (Thysanopoda, Euphausia, Thysanoessa, Nematoscelis, Nematobrachion, and Stylocheiron)contain some species that inhabit a mesopelagic zone between depths of about 500 and 1,500 meters and other species that are characteristically epipelagic, living mainly above 500–700 meters. The epipelagic species are designated in accord with the analogous water masses inhabited. The Pacific water masses are (1) subarctic, situated to the north of the North Pacific Drift, including only the northern part of the California Current (typical species: Thysanoessa longipes, Tessarabrachion oculatus); (2) transitionzone, including the cooler part of the California Current south of 40°–45° N. and a belt extending westward to Japan in the region of the North Pacific Drift (typical species: Thysanoessa gregaria, Nematoscelis difficilis); (3) central, occupying the oceanic gyrals of mid-latitudes 15°–40° in both hemispheres (typical species: Nematoscelis atlantica, Euphausia brevis); and (4) equatorial, occupying a broad tropical belt in the eastern Pacific and a narrower belt to the west (typical species: Euphausia diomediae, E. distinguenda). Equatorial species occupy equatorial water masses in the Pacific and Indian oceans. A zone occupied by the transition-zone species Thysanoessa gregaria and Nematoscelis megalops (corresponding to N. difficilis of the Northern Hemisphere) occurs near 35°–45° S. Subantarctic and antarctic species are found south of the Subantarctic Convergence. The composite range of a tropical western Pacific group of species (e.g., Euphausia pseudogibba, E. fallax, E. sibogae) extends eastward across the Pacific in a zone 10°–20° S., while an eastern tropical group (e.g., Euphausia distinguenda, E. eximia) extends westward in a tongue having an axis near 10° N. Ekman’s zones of the Pacific littoral fauna each have a counterpart species in the coastal or boundary euphausiid fauna. Seasonal changes in euphausiid distribution are discussed with respect to five regions: (1) the Kuroshio and East China Sea, (2) the North Pacific Drift Current, (3) the California Current, (4) the Peru Current, and (5) the equatorial mid-Pacific

Euphausiids of Southeast Asian waters

Euphausiids collected by R/V Stranger during 1959-61 were examined with respect to 1) seasonal change in distribution, abundance and recruitment in the Gulf of Thailand and South China Sea and 2) range through the Indo-Australian seas. Discussion of the species is preceded by a description of the distribution of zooplankton biomass. In the Gulf of Thailand, biomass was found to be three to five times greater than in the open South China Sea. In eastern waters of the Gulf, the peak appeared during the intermonsoon period following northeast winds. The western and northern parts of the Gulf were richest under the influence of the southwest monsoon. Northern coastal waters of South Viet Nam were richest toward the end of each season: 1) the northeast monsoon when coastal upwelling and southerly flow from the Gulf of Tonkin took place and 2) the southwest monsoon season of northerly flow. The southern shelf and the basin region of the South China Sea yielded the greatest biomass during the southwest monsoon season when flow was from the direction of adjacent neritic waters to the southwest. The Sunda Shelf waters, including the Gulf of Thailand, constitute the extensive neritic province in which Pseudeuphausia lives. The South China Sea basin, though the largest basin in the inter-ocean region, is essentially a cul-de-sac with respect to its oceanic euphausiid assemblage, the species of which are derived from both the tropical and subtropical Pacific to the northeast. They are transported southwestward as far as the Sunda Shelf. During the northeast monsoon season many of the oceanic species tend to extend into shelf waters. Evidently the presence over the shelf of a dense neritic plankton, together with the shallowness of the water which prevents the normal range of euphausiid vertical migration, precludes presence of the oceanic species. Only Stylocheiron species, which do not migrate vertically, extend much beyond the edge of the shelf, rarely entering the Gulf of Thailand. The taxonomic diversity of the predominant species of the South China Sea (each belongs to a different species group) indicates that this assemblage is part of a regional plankton community. The annual reproductive cycles of the oceanic species were like that of neritic Pseudeuphausia, with larvae produced year-round but with maximum spawning taking place during, and at the end of, the northeast monsoon season. Production of Pseudeuphausia in the Gulf of Thailand shifted seasonally from southwest to northeast, evidently in response to coastal enrichment processes initiated by southwest and northeast monsoon winds respectively. Of the parameters measured, only low salinity (‰) correlates with the paucity of larvae. Local occurrences of the species are considered in relation to the global distributions in a study of the effectiveness of the inter-ocean seas in maintaining or interrupting flow between Pacific and Indian Ocean populations and in providing local habitats. The pelagic connection between the two oceans is limited to a succession of deeper seas: Celebes-Molucca-Banda and Flores-Timor. The large number (46) of euphausiid species in this inter-ocean region apparently reflects complexity in the oceanography rather than in the plankton community. Regularly occurring species are either endemic (e.g. Stylocheiron insulare), Indo- Pacific equatorial (e.g. Euphausia diomedeae) or broadly ranging warm-water cosmopolites (e.g. epipelagic Stylocheiron carinatum and mesopelagic Nematobrachion boöpis). Species associated primarily with central water masses of the Indian and Pacific Oceans are sparse though seasonally consistent in occurrence. The most widely-ranging species in the global sense (e.g. Nematobrachion boöpis, Stylocheiron carinatum) exhibit inter-oceanic and inter-hemispheric continuity that appears to have long been firmly established. These species do not have close relatives, with the exceptions Stylocheiron longicorne and S. maximum, each a member of a sub-generic species group. This suggests that the speciation process (population isolations + re-invasions) in Stylocheiron, a genus consisting of members which do not migrate vertically, each occupying a discrete depth interval, may differ from that process in strongly migrating genera such as Euphausia and Thysanopoda. The importance of the Indo-Australian region in the evolution of sub-tropical and tropical species is indicated by 1) the large number of species found there, 2) the present partitioning of central water mass species distributions (e.g. Euphausia brevis exists globally in five sub-populations), and of Indo-Pacific equatorial distributions (E. paragibba exists in separated Pacific and Indian Ocean populations), 3) the patchy confluence of some central and subtropical species through this waterway (e.g. E. mutica), and 4) the existence of Indo- Australian endemics (e.g. E. fallax, E. sanzoi, Nematoscelis lobata). The species of the region, including larval stages of most South China Sea species, are illustrated and briefly described. Thysanopoda subaequalis Boden is synonymized with T. aequalis Hansen, the type material of T. aequalis having been found to possess the characteristics defining T. subaequalis. The species presently called T. aequalis is redescribed as T. astylata. A third geographical form of Stylocheiron longicorne is described as the "North Indian Ocean Form.

The distribution of Pacific euphausiids

A study has been made of the distribution of 59 euphausiid species in the Pacific Ocean, based upon oceanic surveys carried out from 1949 to 1961 by the Scripps Institution of Oceanography, California Cooperative Oceanic Fisheries Investigations (CalCOFI), and Pacific Oceanic Fisheries Investigations (POFI). Quantitative aspects of the vertical and horizontal distributions are presented. The species belonging to the genera Bentheuphausia and Thysanopoda are typically deep-living. Bentheuphausia ambloyops, Thysanopoda cornuta, and T. egregia are widely ranging bathypelagic species, the adults of which inhabit depths greater than 1,500 meters. Of the ten genera, six (Thysanopoda, Euphausia, Thysanoessa, Nematoscelis, Nematobrachion, and Stylocheiron)contain some species that inhabit a mesopelagic zone between depths of about 500 and 1,500 meters and other species that are characteristically epipelagic, living mainly above 500–700 meters. The epipelagic species are designated in accord with the analogous water masses inhabited. The Pacific water masses are (1) subarctic, situated to the north of the North Pacific Drift, including only the northern part of the California Current (typical species: Thysanoessa longipes, Tessarabrachion oculatus); (2) transitionzone, including the cooler part of the California Current south of 40°–45° N. and a belt extending westward to Japan in the region of the North Pacific Drift (typical species: Thysanoessa gregaria, Nematoscelis difficilis); (3) central, occupying the oceanic gyrals of mid-latitudes 15°–40° in both hemispheres (typical species: Nematoscelis atlantica, Euphausia brevis); and (4) equatorial, occupying a broad tropical belt in the eastern Pacific and a narrower belt to the west (typical species: Euphausia diomediae, E. distinguenda). Equatorial species occupy equatorial water masses in the Pacific and Indian oceans. A zone occupied by the transition-zone species Thysanoessa gregaria and Nematoscelis megalops (corresponding to N. difficilis of the Northern Hemisphere) occurs near 35°–45° S. Subantarctic and antarctic species are found south of the Subantarctic Convergence. The composite range of a tropical western Pacific group of species (e.g., Euphausia pseudogibba, E. fallax, E. sibogae) extends eastward across the Pacific in a zone 10°–20° S., while an eastern tropical group (e.g., Euphausia distinguenda, E. eximia) extends westward in a tongue having an axis near 10° N. Ekman’s zones of the Pacific littoral fauna each have a counterpart species in the coastal or boundary euphausiid fauna. Seasonal changes in euphausiid distribution are discussed with respect to five regions: (1) the Kuroshio and East China Sea, (2) the North Pacific Drift Current, (3) the California Current, (4) the Peru Current, and (5) the equatorial mid-Pacific

Euphausiacea (Crustacea) of the North Pacific

As a part of the Marine Life Research Program of the Scripps Institution of Oceanography (a member of the California Coöperative Oceanic Fisheries Investigations) an increased effort is being made to describe and evaluate the various organic factors that are important in the biological economy of the sea. In attacking the problem, the most expedient procedure is to study in detail the various components of the plankton, for it is well known that these components in varying degrees of importance provide directly the basic food for the plankton-feeding fishes, such as the sardine, and also directly or indirectly for larger but less abundant pelagic fishes, as well as benthonic life. Among the several groups of zoöplankton organisms that are being studied are the euphausiid shrimp. These highly pelagic crustaceans, popularly known as “krill,” occur in large swarms in all oceans in both neritic and oceanic waters. They are considered second in importance only to the copepods as basic animal food in the sea but often exceed the copepods in mass and numbers, especially at greater depths. The present report deals with the group taxonomically on a wide geographic basis. The chief purpose here is to provide an essential tool with complete descriptions and illustrations to facilitate further study of the biology of the euphausiids and their relation to the pelagic community of the Pacific. Such a study is now under way, and it is believed that application of knowledge of the various species, their geographic ranges, concentrations, and reproductive areas will yield pertinent information relative to the importance of different oceanic currents and water masses in the marine ecology of our coasts. Among the marine animals that are known to feed upon the euphausiids are especially such fish as the herring and sardine, and also the whalebone whales whose diet is, despite their huge size, almost exclusively plankton. A literature too voluminous to review here bears this out for both the fish and mammals. The catch of baleen whales is remarkably closely correlated with the abundance and swarming of euphausiids in the Atlantic and Antarctic waters. Locally, the California gray whale is known to feed at least in part upon Euphausia pacifica, the most common euphausiid off our coast. Similarly, the humpback whales of our coast were found to have fed upon “shrimp.” The place of euphausiids in the diet of the California sardine and other local fishes is presently under investigation in connection with the Marine Life Research program. The euphausiids are food not only to fish and other aquatic animals but to a lesser extent also to sea birds. The euphausiids usually live at depths beyond the range of surface-feeding animals, but during swarming, vast hoards may migrate to the very surface within reach of large flocks of birds. These swarmings may be within restricted areas as in the passages between Passamaquoddy Bay and the Bay of Fundy. Here Meganyctiphanes norvegica and Thysanoëssa spp. rise in the turbulent water within reach of sea gulls and other birds. On the open coast off La Jolla, California, swarms of female Thysanoëssa spinifera that had migrated to the upper water layers were swept ashore and stranded upon the beach. In Australian waters “rafts” of Nyctiphanes australis, covering an acre in extent, may occur at the surface where they are fed upon by the muttonbird. Finally, euphausiids may hold a place directly in the diet of man himself. Japanese fishermen sometimes catch vast numbers of these crustaceans, which periodically swarm in the deep bays of Honshu Island. The niche occupied by the euphausiids in the food chain of the sea requires also a consideration of the food upon which they themselves subsist. Some progress along this line has been made by various workers. Much remains to be done. Einarsson (1945) reviews briefly pertinent literature which brings evidence to show that the diet of euphausiids consists of both diatoms and microcrustaceans, but chiefly of the phytoplankton diatoms. Floating detritus is also an item of diet, but further study is needed in determining the efficiency of the feeding mechanisms in screening out the very finest particulate organic material known to be present in the sea water. The feeding mechanism of the euphausiids consists of a basket formed by the thoracic appendages, the inner margins of which are provided with long plumose bristles or setae. Water is strained through the bristles, and the small organisms and detritus are screened out as the animal swims through the water propelled by the swimming feet (pleopods) on the abdomen. Important also are the mouth parts. The mouth parts are situated immediately in front of the thoracic appendages. From anterior to posterior, they consist of labrum, mandibles (with “teeth” and palps), labia, first maxillae, and second maxillae. There are no maxillipeds differing from the thoracic appendages. The first and second maxillae are small, but they are well provided with many rather short setae and spines which are apparently used mainly in holding or transferring food particles to the labia and mandibles. The active feeding process of euphausiids was not studied but, from consideration of the structure of the feeding mechanisms, it appears that at least in Euphausia pacifica an important nonscreening device is the pair of mandibular palps. These palps are designed to move the food particles from the basket and maxillae into reach of the labia and mandibles and doubtless to hold larger particles against the mandibles during mastication. The end segment of each palp is provided with a row of strong, curved spines along the posterior edge. The palps are rotated somewhat toward the mid-line to show the orientation of the spines. In Nematoscelis difficilis the mandibular palps are much shorter and may therefore serve a more restricted function. In the genus the second pair of thoracic legs are enormously elongated, but it is not clear with what feeding function this modification may be associated. Although much of the food material consists of detrital particles or organisms of very small size, this is only a fraction of the diet. Larger objects such as copepod larvae, and even adults, form a part of the food of Meganyctiphanes norvegica. The well-developed mandibles with chitinized gnathobase attest to this fact. They are each provided with a cutting incisor process and a molar process useful in crushing