Biological Studies of the Bermuda Ocean Acre: Planktonic Ostracoda Mfe LOUIS S. KORNICKER, SHELDON WIRSING, and MAURA McMANUS I SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 223 SERIAL PUBLICATIONS OF THE SMITHSONIAN INSTITUTION The emphasis upon publications as a means of diffusing knowledge was expressed by the first Secretary of the Smithsonian Institution. In his formal plan for the Insti- tution, Joseph Henry articulated a program that included the following statement: "It is proposed to publish a series of reports, giving an account of the new discoveries in science, and of the changes made from year to year in all branches of knowledge." This keynote of basic research has been adhered to over the years in the issuance of thousands of titles in serial publications under the Smithsonian imprint, com- mencing with Smithsonian Contributions to Knowledge in 1848 and continuing with the following active series: Smithsonian Annals of Flight Smithsonian Contributions to Anthropology Smithsonian Contributions to Astrophysics Smithsonian Contributions to Botany Smithsonian Contributions to the Earth Sciences Smithsonian Contributions to Paleobiology Smithsonian Contributions to Zoology Smithsonian Studies in History and Technology In these series, the Institution publishes original articles and monographs dealing with the research and collections of its several museums and offices and of professional colleagues at other institutions of learning. These papers report newly acquired facts, synoptic interpretations of data, or original theory in specialized fields. These pub- lications are distributed by mailing lists to libraries, laboratories, and other interested institutions and specialists throughout the world. Individual copies may be obtained from the Smithsonian Institution Press as long as stocks are available. S. DILLON RIPLEY Secretary Smithsonian Institution SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 223 Biological Studies of the Bermuda Ocean Acre: Planktonic Ostracoda Louis S. Kornicker, Sheldon Wirsing, and Maura McManus SMITHSONIAN INSTITUTION PRESS City of Washington 1976 ABSTRACT Kornicker, Louis S., Sheldon Wirsing, and Maura McManus. Biological Studies of the Bermuda Ocean Acre: Planktonic Ostracoda. Smithsonian Contributions to Zoology, number 223, 34 pages, 20 figures, 9 tables, 1976.—Planktonic Ostra- coda from depths of surface to 1170 m collected aboard the Research Vessels Trident, Albatross IV, and USNS Sands during 1967 to 1970 on Ocean Acre Cruises 1, 7, 9, and 10 are studied with main emphasis on Cypridinacea and on Cruise 10. The data suggest that the cypridinid species Macrocypridina castanea and the Halocyprididae migrate upward nightly. The collections indicate that M. castanea is primarily an inhabitant of the bathypelagic zone, and that G. muelleri is primarily an inhabitant of the bathypelagic and upper abyssalpelagic zones. Halocyprids were collected at all depths but occurred in the greatest frequency in the epipelagic zone. The reported upper temperatures range of G. muelleri is increased by 10°, to 14.9°C by the distribution of the species in samples from Cruise 10. The stomach contents of M. castanea indicate that the species is a predator. Ovigerous females of M. castanea have previously been reported from collections made during May and July; the present cruises show that ovigerous females also are present during June, early September, late October, and early November. Reproduction may be less during winter months. The phenomenon of the swallowing of the bristles of the 1st antenna by specimens of M. castanea is studied, and it is suggested that this may take place during the throes of being captured or killed. Swallowing of bristles of the 2nd antenna by this species is reported for the first time. SEM studies of M. castanea and G. muelleri reveal that both species bear lateral glandular fields on the upper lips in addition to previously reported anteroventral fields, and that the comb teeth of the 7th limbs bear terminal pores. The shells of both species have pores and are laminated. The copulatory organ of the adult male M. castanea has pores in the clawlike spine of the anterior proximal lobe and at the tip of the 2nd joint of the posterior, distal lobe. OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SI PRESS NUMBER 6164. SERIES COVER DESIGN: The coral Montastrea cavernosa (Linnaeus). Library of Congress Cataloging in Publication Data Kornicker, Louis S. 1919— Biological studies of the Bermuda Ocean Acre. (Smithsonian contributions to zoology ; no. 223) Bibliography: p. Supt. of Docs, no.: SI 1.27:223 1. Ostracoda. 2. Marine zooplankton. I. Wirsing, Sheldon, joint author. II. McManus, Maura, joint author. III. Title. IV. Series: Smithsonian Institution. Smithsonian contributions to zoology ; no. 223. QL1.S54 no. 223 [QL444.08] 591'.08s [595'.33] 75-619399 Contents Page Introduction 1 Acknowledgments 1 Methods 2 Station Data 2 Diel Migration 5 Relationship between Depth and Frequency of Capture 5 Macrocypridina castanea 5 Gigantocypris muelleri 8 Halocyprididae 8 Relationship between Water Temperature and Salinity and Ostracode Distribution 8 Food Requirements of Planktonic Ostracodes 8 Reproduction of Macrocypridina castanea 9 Phenomenon of Swallowing Bristles of First Antenna 11 Macrocypridina castanea (Brady, 1897) 13 Gigantocypris muelleri Skogsberg, 1920 16 Literature Cited 34 Biological Studies of the Bermuda Ocean Acre: Planktonic Ostracoda Louis S. Kornicker, Sheldon Wirsing, and Maura McManus Introduction grouped under the category Halocyprididae in the present paper, and were not identified further. The Project "Ocean Acre" is a group effort of The specimens of M. castanea and G. muelleri scientists representing the University of Rhode provided the opportunity to examine in detail the Island, the National Marine Fisheries Service, and morphology of the carapace, upper lip, and 7th the Smithsonian Institution. The object of the limb of these species using the scanning electron project is to make a comprehensive study of the microscope. biology and oceanography in the upper 1000 m of ACKNOWLEDGMENTS.—We thank Mr. Michael J. water within a one degree square southeast of Ber- Sweeney and Mr. Charles Karnella, Smithsonian muda with its center at 32°N, 64°W (Roper et al., Institution, for their assistance in obtaining station 1970). The present paper is concerned with ostra- data and background information concerning the codes from Cruises 1 and 10, and in a few samples Ocean Acre Program. The collections were made from Cruises 7 and 9 (see "Station Data"). with the financial support of the Naval Under- Our analyses of distribution are based almost water Systems Center, Contract No. N00140-70- completely on samples collected during Cruise 10 C-O3O7. We are grateful to Dr. Clyde F. E. Roper in discrete depth sampling equipment, because and Dr. Martin V. Angel for reviewing the manu- more discrete depth samples were collected during script. The assistance of Mr. Walter R. Brown and that cruise. The distribution of ostracodes captured Miss Mary J. Mann, who operated the scanning in samples collected during the other cruises we electron microscope is acknowledged. Freeze-drying studied is consistent with the distributions observed of specimens for photography was done in the lab- on Cruise 10. oratory of Mr. Rolland Hower, Smithsonian In- The samples contained 2 species in the suborder stitution. We also thank the numerous individuals Myodocopina: Macrocypridina castanea (Brady, aboard the R/V Trident, R/V Albatross IV, and 1897) sensu Poulsen (1962:119), and Gigantocy- R/V USNS Sands, who collected the specimens pris muelleri Skogsberg, 1920; and many species in upon which this paper is based. The specimens the suborder Halocypridina. The latter were were sorted by personnel at the Smithsonian Oceanographic Sorting Center. We thank Mrs. Louis S. Kornicker and Maura McManus, Department of Mary Frances Bell of the Smithsonian Institution Invertebrate Zoology, National Museum of Natural History, Press for editing and preparing the manuscript and Smithsonian Institution, Washington, D.C. 20560. Sheldon illustrations for publication. Wirsing, Wells College, Aurora, New York, 13026. SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY Methods 2152-2213 EST; whole sample; discrete-depth sampler (second chamber). The attempt was made to take 4 samples during Halocyprididae: 1 each trawling period of about 1 hour using a 10-ft. Station 1-4B; 27 October 1967; 32°18'N, 64°20'W; 125-150 m; 0023-0053 EST; whole sample; discrete-depth sampler Isaacs-Kidd Midwater trawl with a cod-end (second chamber). Discrete-Depth Plankton Sampler. All gates were Macrocypridina castanea: 2 left open and no sample was obtained until the de- Station 1-9A; 27-28 October 1967; 32°33'N, 64°21'W; 125 m; sired depth was reached. Then, the rear gate was 2307-0007 EST; whole sample; discrete-depth sampler closed forming a chamber. After 1 hour, the 2nd (first chamber). Macrocypridina castanea: 1 gate was closed isolating the 1st sample, and form- Station 1-9C; 28 October 1967; 32°33'N, 64°21'W; 75 m; ing a new collection chamber. This was repeated 0015-0115 EST; whole sample; discrete-depth sampler for the 3rd chamber. When the final gate was (third chamber). closed isolating the 3rd chamber, the gear was Halocyprididae: 1 raised to the surface providing the 4th sample, Station 1-11 A; 28 October 1967; 32°37'N, 64°10'W; 200 m; which is called the oblique sample. For details con- 0550-0620 EST; whole sample; discrete-depth sampler (first chamber). cerning the mechanics and operation of the Macrocypridina castanea: 1 discrete-depth sampler see Aron et al. (1964) and Station 1-15A; 28 October 1967; 32°46'N, 64°00'W; 420- Bourbeau et al. (1966). 700 m; 2003-2103 EST; whole sample; discrete-depth The sample collected in the 1st chamber is des- sampler (first chamber). ignated "A," the 2nd chamber "B," the 3rd cham- Macrocypridina castanea: 1 Station 1-15M; 28 October 1967; 32°46'N, 64°00'W; 0-283 m; ber "C," and the oblique sample "M." Samples la- 2232-2308 EST; whole sample; oblique sampler from beled with "P" are oblique samples combined with depth to surface (last chamber). 1 or more discrete-depth samples, due to a malfunc- Macrocypridina castanea: 2 tion of the instrument. Samples labeled with "N" Station 1-16A; 29 October 1967; 32°44'N, 63°42'W; 275- are open net samples. 300 m; 0337-0437 EST; whole sample; discrete-depth Information concerning methods may be found sampler (first chamber). Macrocypridina castanea: 1 in a series of reports to the Naval Underwater Sys- Station 1-16B; 29 October 1967; 32°44'N, 63°42'W; 150- tems Center by Roper et al. (1970), Gibbs et al. 275 m; 0437-0458 EST; whole sample; discrete-depth (1971), Brown (1971), and Brown and Brooks sampler (second chamber). (1974). Macrocypridina castanea: 3 For comparison purposes the number of ostra- Station 1-16C; 29 October 1967; 32°44'N, 63°42' W; 175 m; codes per "standard volume" was calculated for 0458-0558 EST; whole sample; discrete-depth sampler (third chamber). each station. Macrocypridina castanea: 3 Number of ostracodes per standard volume = Station 1-18B; 30 October 1967; 32°10'N, 63°48'W; 130 m; 0035-0135 EST; whole sample; discrete-depth sampler Number of ostracodes in samples A+B + C 3 knots (second chamber). L ^ 3 ship's speed Macrocypridina castanea: 1 (knots) Station 1-18C; 30 October 1967; 32°10'N, 63°48'W; 100 m; Most of the ostracodes, especially the halocy- 0145-0245 EST; whole sample; discrete-depth sampler prids, escaped through the netting of the Isaac (third chamber). Macrocypridina castanea: 2 Kick! trawl and were not captured in the discrete- Station 1-18M; 30 October 1967; 32°10'N, 63°48'W; 0-100 m; depth sampler. Therefore, it has been necessary to 0245-0255 EST; whole sample; oblique sampler from assume in the distributional calculations herein depth to surface (last chamber). that the number captured in the discrete-depth Macrocypridina castanea: 1 sampler is representative of the number that Station 1-19A; 30 October 1967; 32°09'N, 63°59'W; 130- entered the trawl. 175 m; 0338-0438 EST; whole sample; discrete-depth sampler (first chamber). Station Data Macrocypridina castanea: 2 Station 1-31N; 1-2 November 1967; 32814'N, 63°26'W; Research Vessel Trident, Cruise 1, October and November 1967 0-1500 m; 0030-0230 EST; whole sample; open net sampler. Station 1-3B; 26 October 1967; 32°16'N, 64°25'W; 320-478 m; Macrocypridina castanea: 3 NUMBER 223 Research Vessel Albatross IV, Cruise 7, September 1969 Station 10-5M; 2 June 1970; 32°33'N, 64°04'W; 0-600 m; 2330-0030 EST; whole sample; oblique sampler from Station 7-15N; 8 September 1969; 32°21'N, 63°29'W; 0-450 m; depth to surface (last chamber); ship speed 3 knots. 2108-2309 EST; part sample; open net sampler. Macrocypridina castanea: 3 Macrocypridina castanea: 2 Halocyprididae: 1 Station 7-19N; 9 September 1969; 32°42'N, 63°49'W; 0-750 m; Station 10-6B; 3 June 1970; 32°22'N, 64°14'W; 290 m; 0746-0946 EST; part sample; open net sampler. 0400-0500 EST; whole sample; discrete-depth sampler Macrocypridina castanea: 1 (second chamber); ship speed 3 knots. Macrocypridina castanea: 1 Research Vessel USNS Sands, Cruise 9, March 1970 Station 10-7A; 3 June 1970; 32°16'N, 64°21'W; 1000-1120 m; 0725-0825 EST; whole sample; discrete-depth sampler Station 9-12N; 19 March 1970; 32°00'N, 64°00'W; 0-55 m; (first chamber); ship speed 2 knots. 0452-0632 EST; part sample; open net sampler. Macrocypridina castanea: 5 (2 ovigerous) Halocyprididae: 1 Station 10-7B; 3 June 1970; 32°16'N, 64°21'W; 970-1060 m; Station 9-21N; 20 March 1970; 31°46'N, 63°47'W; 0-950 m; 0825-0925 EST; whole sample; discrete-depth sampler 0035-0345 EST; part sample; open net sampler. (second chamber); ship speed 2 knots. Gigantocypris muelleri: 1 Macrocypridina castanea: 2 ovigerous $ Station 9-28N; 22 March 1970; 32°07'N, 63°32'W; 0-700 m; Station 10-7M; 3 June 1970; 32°16'N, 64°21'W; 0-970 m; 1320-1635 EST; part sample; open net sampler. 0925-1037 EST; whole sample; oblique sampler from Halocyprididae: 1 depth to surface (last chamber); ship speed 2 knots. Macrocypridina castanea: 1 ovigerous female Research Vessel USNS Sands, Cruise 10, June 1970 Halocyprididae: 6 Station 10-8A; 3 June 1970; 32°02'N, 64°25'W; 90 m; 1305- Station 10-1N; 1 June 1970; 32°OO'N, 64°29'W; 0-925 m; 1405 EST; whole sample; discrete-depth sampler (first 1530-1830 EST; one-fourth sample; open net sampler; chamber); ship speed 2 knots. ship speed 3 knots. Halocyprididae: 3 Macrocypridina castanea: 7 (3 ovigerous $) Station 10-8B; 3 June 1970; 32°02'N, 64°25'W; 90 m; 1405- Halocyprididae: 153 1505 EST; whole sample; discrete-depth sampler (second Station 10-2B; 1 June 1970; 32°13'N, 64°23'W; 100 m; chamber); ship speed 2 knots. 2105-2205 EST; whole sample; discrete-depth sampler Halocyprididae: 3 (second chamber); ship speed 3 knots. Station 10-9A; 3 June 1970; 31°56'N, 64°25'W; 55 m; 1550- Macrocypridina castanea: 1 juvenile (lost) 1650 EST; whole sample; discrete-depth sampler (first Halocyprididae: 3 chamber); ship speed 2 knots. Station 10-3C; 2 June 1970; 32°14'N, 64°13'W; 200 m; Halocyprididae: 1 0615-0715 EST; whole sample; discrete-depth sampler Station 10-lOB; 3 June 1970; 31°5rN, 64°19/W; 825 m; 2325- (third chamber); ship speed 4 knots. 0025 EST; whole sample; discrete depth sampler (second Halocyprididae: 1 chamber); ship speed 3 knots. Station 10-4A; 2 June 1970; 32°18'N, 64°12'W; 800 m; Macrocypridina castanea: 1 1455-1555 EST; whole sample; discrete-depth sampler Gigantocypris muelleri: 1 (first chamber); ship speed 3 knots. Station 10-10M; 3 June 1970; 31°51'N, 64°19'W; 0-825 m; Macrocypridina castanea: 1 0025-0125 EST; whole sample; oblique sampler from Station 10-4B; 2 June 1970; 32°18'N, 64°12'W; 800 m; depth to surface (last chamber); ship speed 3 knots. 1555-1655 EST; whole sample; discrete-depth sampler Macrocypridina castanea: 1 (second chamber); ship speed 3 knots. Halocyprididae: 1 Macrocypridina castanea: 1 Station 10-11 A; 4 June 1970; 32°00'N, 64°16'W; 150 m; Halocyprididae: 2 0200-0300 EST; whole sample; discrete-depth sampler Station 10-4C; 2 June 1970; 32°18'N, 64°12'W; 800 m; (first chamber); ship speed 3 knots. 1655-1755 EST; whole sample; discrete-depth sampler Halocyprididae: 2 (third chamber); ship speed 3 knots. Station 10-11B; 4 June 1970; 32°00'N, 64°16'W; 150 m; Macrocypridina castanea: 3 (one ovigerous female) 0300-0400 EST; whole sample; discrete-depth sampler Halocyprididae: 1 (second chamber); ship speed 3 knots. Station 10-5A; 2 June 1970; 32°33'N, 64°04'W; 600 m; Halocyprididae: 2 2030-2130 EST; whole sample; discrete-depth sampler Station 10-11M; 4 June 1970; 32°00'N, 64°16'W; 0-150 m; (first chamber); ship speed, 3 knots. 0400-0420 EST; whole sample; oblique sampler from Halocyprididae: 2 depth to surface (last chamber); ship speed 3 knots. Station 10-5B; 2 June 1970; 32°33'N, 64°04'W; 600 m; Halocyprididae: 1 2130-2330 EST; whole sample; discrete-depth sampler Station 10-13B; 5 June 1970; 31°23'N, 64°46'W; 400 m; (second chamber); ship speed 3 knots. 0850-1050 EST; whole sample; discrete-depth sampler Macrocypridina castanea: 8 (second chamber); ship speed 4 knots. SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY Halocyprididae: 1 Station 1O-23A; 7 June 1970; 31°45'N, 64°51'W; 630 m; Station 10-14M; 5 June 1970; 31°09'N, 64°42'W; 0-200 m; 1322-1422 EST; whole sample; discrete-depth sampler 1615-1640; whole sample; oblique sampler from depth (first chamber); ship speed 2 knots. to surface (last chamber); ship speed 3 knots. Halocyprididae: 1 Halocyprididae: 1 Station 1O-24A; 7 June 1970; 31°26'N, 64°50^V; 950-1080 m; Station 10-15B; 5 June 1970; 31°24'N, 64°46'W; 210 m; 1855-1955 EST; whole sample; discrete-depth sampler 1926-2020 EST; whole sample; discrete-depth sampler (first chamber); ship speed 2 knots. (second chamber); ship speed 3 knots. Macrocypridina castanea: 1 Halocyprididae: 1 Station 10-24B; 7 June 1970; 31°26'N, 64°50'W; 1080 m; Station 10-15C; 5 June 1970; 31°24'N, 64°46'W; 210 m; 1955-2055 EST; whole sample; discrete-depth sampler 2020-2120 EST; whole sample; discrete-depth sampler (second chamber); ship speed 2 knots. (third chamber); ship speed 3 knots. Halocyprididae: 1 Halocyprididae: 1 Station 10-24C; 7 June 1970; 31°26'N, 64°50'W; 1080 m; Station 10-15M; 5 June 1970; 31°24'N, 64°46'W; 0-210 m; 2055-2155 EST; whole sample; discrete-depth sampler 2120-2137; one-half sample; oblique sampler from depth (third chamber); ship speed 2 knots. to surface (last chamber); ship speed 3 knots. Macrocypridina castanea: 2 ovigerous females Halocyprididae: 1 Gigantocypris muelleri: 1 Station 10-16A; 5 June 1970; 31°29'N, 64°49^V; 205 m; Station 1O-24M; 7 June 1970; 31°26'N, 64°50'W; 0-1080 m; 2215-2315 EST; whole sample; discrete-depth sampler 2155-2320 EST; whole sample; oblique sampler from (first chamber); ship speed 3 knots. depth to surface (last chamber); ship speed 2 knots. Macrocypridina castanea: 1 Macrocypridina castanea: 2 (1 ovigerous female) Station 10-16C; 5 June 1970; 31°29'N, 64°49'W; 205 m; Halocyprididae: 3 0015-0115 EST; whole sample; discrete-depth sampler Station 10-26P; 8 June 1970; 31°41'N, 64°50'W; 0-170 m; (third chamber); ship speed 3 knots. 1125-1325 EST; whole sample; oblique sampler from Macrocypridina castanea: 2 depth to surface plus discrete-depth sampler; ship speed Station 10-17A; 6 June 1970; 31°44'N, 64°57'W; 50 m; 3 knots. 0200-0300 EST; whole sample; discrete-depth sampler Halocyprididae: 4 (first chamber); ship speed 4 knots. Station 1O-27B; 8 June 1970; 31°30'N, 64°53'W; 110 m; Halocyprididae: 1 1910-1930 EST; whole sample; discrete-depth sampler Station 10-17B; 6 June 1970; 31°44'N, 64°57'W; 50 m; second chamber); ship speed 3 knots. 0300-0400 EST; one-half sample; discrete-depth sampler Halocyprididae: 1 (second chamber); ship speed 4 knots. Station 10-28N; 8 June 1970; 31°30'N, 64°53'W; 0-580 m; Halocyprididae: 3 2100-0000 EST; one-half sample; open net sampler; ship Station 10-17M; 6 June 1970; 31°44'N, 64°57'W; 0-50 m; speed 3 knots. 0500-0525 EST; one-half sample; oblique sampler from Macrocypridina castanea: 1 depth to surface (last chamber); ship speed 4 knots. Halocyprididae: 1 Halocyprididae: 1 Station 10-29M; 9 June 1970; 31°10'N, 64°57'W; 0-430 m; Station 10-18A; 6 June 1970; 31°34'N, 64-55^; 100 m; 0415-0443 EST; whole sample; oblique sampler from 0555-0620 EST; whole sample; discrete-depth sampler depth to surface (last chamber); ship speed 3 knots. (first chamber); ship speed 4 knots. Halocyprididae: 2 Halocyprididae: 1 Station 10-31 A; 9 June 1970; 31°17'N, 64°55'W; 300 m; Station 10-19C; 6 June 1970; 31°25'N, 64°54'W; 1160- 0730-0830 EST; whole sample; discrete-depth sampler 1170 m; 1215-1315 EST; whole sample; discrete-depth (first chamber); ship speed 3 knots. sampler (third chamber); ship speed 4 knots. Macrocypridina castanea: 1 Macrocypridina castanea: 1 Station 10-34C; 9 June 1970; 31°33'N, 64°46'W; 520 m; Station 10-19M; 6 June 1970; 31°25'N, 65°54'W; 0-1170 m; 2305-0005 EST; whole sample; discrete-depth sampler 1315-1405 EST; one-fourth sample; oblique sampler from (third chamber); ship speed 3 knots. depth to surface (last chamber); ship speed 4 knots. Macrocypridina castanea: 1 Halocyprididae: 2 Station 1O-35A; 10 June 1970; 31°24'N, 64°48'W; 360 m; Macrocypridina castanea: 2 0215-0315 EST; whole sample; discrete-depth sampler Station 10-20C; 6 June 1970; 31°14'N, 64°52'W; 520 m; (first chamber); ship speed 3 knots. 1800-1900 EST; whole sample; discrete-depth sampler Macrocypridina castanea: 2 (third chamber); ship speed 3 knots. Halocyprididae: 1 Macrocypridina castanea: 1 Station 10-36A; 10 June 1970; 31°14'N, 64°52'W; 630-700 m; Halocyprididae: 2 0710-1010 EST; one-fourth sample; discrete-depth sam- Station 10-21N; 6 June 1970; 31°27'N, 64°49'W; 0-880 m; pler (first chamber); ship speed 3 knots. 2I3O-OO3O EST; one-half sample; open net sampler; ship Halocyprididae: 4 speed 3 knots. Station 10-36M; 10 June 1970; 3I°14'N, 64°52'W; 0-700 m; Halocyprididae: 8 1010-1055 EST; whole sample; oblique sampler from