Ysgol Gwyddorau Eigion
- Cyhoeddwyd
Basic assessment of Portunus segnis (Forskål, 1775) – A baseline for stock management in the Western Arabian Gulf
Giraldes, B. W., Al-Maslamani, I., Al-Ashwel, A., Chatting, M. & Smyth, D., Maw 2016, Yn: The Egyptian Journal of Aquatic Research. 42, 1, t. 111-119Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
The benthic sea-silk-thread displacement of a sessile bivalve, Pinctada imbricata radiata (Leach, 1819) in the Arabian-Persian Gulf
Giraldes, B. W., Leitao, A. & Smyth, D., 1 Mai 2019, Yn: PLoS ONE. 14, 5, e0215865.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Species richness in North Atlantic fish: Process concealed by pattern
Gislason, H., Collie, J., MacKenzie, B. R., Nielsen, A., de Fatima Borges, M., Bottari, T., Chaves, C., Dolgov, A. V., Dulcic, J., Duplisea, D., Fock, H. O., Gascuel, D., de Sola, L. G., Hiddink, J. G., ter Hofstede, R., Isajlovic, I., Pall Jonasson, J., Jorgensen, O., Kristinsson, K., Marteinsdottir, G., Masski, H., Matić-Skoko, S., Payne, M. R., Peharda, M., Reinert, J., Sólmundsson, J., Silva, C., Stefansdottir, L., Velasco, F. & Vrgoc, N., Mai 2020, Yn: Global Ecology and Biogeography. 29, 5, t. 842-856Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- E-gyhoeddi cyn argraffu
Variation in coral rubble cryptofauna is scale-dependent and driven by small-scale habitat characteristics
Goberdhan, L., Robertson, C., Egerton, J., Fox, M., Johnson, M., Graham, N. & Williams, G. J., 5 Rhag 2024, (E-gyhoeddi cyn argraffu) Yn: Marine Ecology Progress Series. 750, t. 19-36Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Fundamentals of in situ digital camera methodology for water quality monitoring of coast and ocean.
Goddijn-Murphy, L., Dailloux, D., White, M. & Bowers, D. G., 1 Gorff 2009, Yn: Sensors. 9, 7, t. 5825-5843Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
SEASTAR: A Mission to Study Ocean Submesoscale Dynamics and Small-Scale Atmosphere-Ocean Processes in Coastal, Shelf and Polar Seas
Gommenginger, C., Chapron, B., Hogg, A., Buckingham, C., Fox-Kemper, B., Eriksson, L., Soulat, F., Ubelmann, C., Ocampo-Torres, F., Nardelli, B. B., Griffin, D., Lopez-Dekker, P., Knudsen, P., Andersen, O., Stenseng, L., Stapleton, N., Perrie, W., Violante-Carvalho, N., Schulz-Stellenfleth, J., Woolf, D., Isern-Fontanet, J., Ardhuin, F., Klein, P., Mouche, A., Pascual, A., Capet, X., Hauser, D., Stoffelen, A., Morrow, R., Aouf, L., Breivik, Ø., Fu, L.-L., Johannessen, J. A., Aksenov, Y., Bricheno, L., Hirschi, J., Martin, A. C. H., Martin, A. P., Nurser, G., Polton, J., Wolf, J., Johnsen, H., Soloviev, A., Jacobs, G. A., Collard, F., Groom, S., Kudryavtsev, V., Wilkin, J., Navarro, V., Babanin, A., Martin, M., Siddorn, J., Saulter, A., Rippeth, T., Emery, B., Maximenko, N., Romeiser, R., Graber, H., Azcarate, A. A., Hughes, C. W., Vandemark, D., Silva, J. D., Leeuwen, P. J. V., Naveira-Garabato, A., Gemmrich, J., Mahadevan, A., Marquez, J., Munro, Y., Doody, S. & Burbidge, G., 13 Awst 2019, Yn: Frontiers in Marine Science. 6, t. 1-7 8 t., 457.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Representative range of acoustic point source measurements in the Chukchi Sea
Gonzalez, S., Horne, J. K., Danielson, S. L., Lieber, L. & Lopez, G., 30 Meh 2022, Yn: Elementa: Science of the Anthropocene. 10, 1Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Flow regime in a restored wetland determines trophic links and species composition in the aquatic macroinvertebrate community
Gonzalez Ortegon, E., Walton, M., Moghaddam, B., Vilas, C., Prieto, A., Kennedy, H., Canavate, J. P. & Le Vay, L., 15 Ion 2015, Yn: Science of the Total Environment. 503-504, t. 241-250Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Individual and mixture effects of selected pharmaceuticals on larval development of the estuarine shrimp Palaemon longirostris
Gonzalez-Ortegon, E., Blasco, J., Nieto, E., Hampel, M., Le Vay, L. & Gimenez, L., 7 Gorff 2015, Yn: Science of the Total Environment. 540, t. 260-266Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
The Baltic prawn Palaemon adspersus Rathke, 1837 (Decapoda, Caridea, Palaemonidae): first record, possible establishment, and illustrated key of the subfamily Palaemoninae in northwest Atlantic waters
Gonzalez-Ortegon, E., Sargent, P., Pohle, G. & Martinez-Lage, A., 15 Tach 2014, Yn: Aquatic Invasions. 10, 3, t. 299-312Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Environmentally mediated phenotypic links and performance in larvae of a marine invertebrate
Gonzalez-Ortegon, E. & Gimenez, L., 15 Ebr 2014, Yn: Marine Ecology Progress Series. 502, t. 185-195Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Maternal trophic status and offspring phenotype in a marine invertebrate
Gonzalez-Ortegon, E., Le Vay, L., Walton, M. & Gimenez, J., 25 Meh 2018, Yn: Scientific Reports.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Floating plastics as a potential dispersal vector for rafting marine non-native species
González -Ortegó , E., Demmer, J., Robins, P. & Jenkins, S., 1 Hyd 2024, Yn: Marine Pollution Bulletin. 207, 116919.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Emergent patterns of reef fish diversity correlate with coral assemblage shifts along the Great Barrier Reef
González-Barrios, J., Keith, S., Emslie, M., Ceccarelli, D., Williams, G. J. & Graham, N., 13 Ion 2025, Yn: Nature Communications. 16, 303.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Effects of food limitation and pharmaceutical compounds on the larval development and morphology of Palaemon serratus
González-Ortegón, E., Giménez, L., Blasco, J. & Le Vay, L., 15 Ion 2015, Yn: Science of the Total Environment. 503-504, t. 171-178 8 t.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
A multiple stressor approach to study the toxicity and sub-lethal effects of pharmaceutical compounds on the larval development of a marine invertebrate
González-Ortegón, E., Blasco, J., Le Vay, L. & Giménez, L., Rhag 2013, Yn: Journal of Hazardous Materials. 263, Part 1, t. 233-238 6 t.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Connectivity and Dispersal Patterns of Protected Biogenic Reefs: Implications for the Conservation of Modiolus modiolus (L.) in the Irish Sea
Gormley, K., Mackenzie, C., Robins, P. E., Coscia, I., Cassidy, A., James, J., Hull, A., Piertney, S., Sanderson, W. & Porter, J., 1 Rhag 2015, Yn: PLoS ONE. 10, 12, t. e0143337Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Local Biomass Baselines and the Recovery Potential for Hawaiian Coral Reef Fish Communities: Hawaiian Reef Fish Recovery Potential
Gorospe, K., Donahue, M., Heenan, A., Gove, J., Williams, I. & Brainard, R., 9 Mai 2018, Yn: Frontiers in Marine Science. 5, 162.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
A new Holocene relative sea-level curve for western Brittany (France): Insights on isostatic dynamics along the Atlantic coasts of north-western Europe
Goslin, J., Van Vliet Lanoe, B., Spada, G., Bradley, S., Tarasov, L., Neill, S. P. & Suanez, S., 5 Tach 2015, Yn: Quaternary Science Reviews. 129, t. 341-365Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Shifting Trophic Control of Fishery–Ecosystem Dynamics Following Biological Invasions
Goto, D., Dunlop, E. S., Young, J. D. & Jackson, D. A., 1 Hyd 2020, Yn: The Bulletin of the Ecological Society of America. 101, 4, t. e01764Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl
- Cyhoeddwyd
Phylogeny of Echiura updated, with a revised taxonomy to reflect their placement in Annelida as sister group to Capitellidae
Goto, R., Monnington, J., Sciberras, M., Hirabayashi, I. & Rouse, G. W., 10 Chwef 2020, Yn: Invertebrate Systematics. 34, 1, t. 101-111Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Coral reefs benefit from reduced land–sea impacts under ocean warming
Gove, J. M., Williams, G. J., Lecky, J., Brown, E., Conklin, E., Counsell, C., Davis, G., Donovan, M., Falinski, K., Kramer, L., Kozar, K., Li, N., Maynard, J. A., McCutcheon, A., McKenna, S., Neilson, B., Safaie, A., Teague, C., Whittier, R. & Asner, G., 21 Medi 2023, Yn: Nature. 621, 7979, t. 536-542 7 t.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Near-island biological hotspots in barren ocean basins
Gove, J. M., McManus, M. A., Neuheimer, A. B., Polovina, J. J., Drazen, J. C., Smith, C. R., Merrifield, M. A., Friedlander, A. M., Ehses, J. S., Young, C. W., Dillon, A. K. & Williams, G., 16 Chwef 2016, Yn: Nature Communications. 7, 10581.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Prey-size plastics are invading larval fish nurseries
Gove, J. M., Whitney, J., McManus, M. A., Lecky, J., Carvalho, F., Lynch, J., Li, J., Neubauer, P., Smith, K., Phipps, J., Kobayashi, D., Balagso, K., Contreras, E., Manuel, M., Merrifield, M., Polovina, J., Asner, G., Maynard, J. A. & Williams, G. J., 26 Tach 2019, Yn: Proceedings of the National Academy of Sciences of the USA. 116, 48, t. 24143-24149 7 t.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Coral reef benthic regimes exhibit non-linear threshold responses to natural physical drivers
Gove, J. M., Williams, G. J., McManus, M. A., Clark, S. J., Ehses, J. S. & Wedding, L. M., 2 Maw 2015, Yn: Marine Ecology Progress Series. 522, t. 33-48Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Tidal energy extraction in three-dimensional ocean models
Goward Brown, A., Neill, S. & Lewis, M., Rhag 2017, Yn: Renewable Energy. 114, A, t. 244/257Allbwn ymchwil: Cyfraniad at gyfnodolyn › Rhifyn Arbennig › adolygiad gan gymheiriaid
- Cyhoeddwyd
The influence of wind gustiness on estimating the wave power resource
Goward Brown, A., Neill, S. & Lewis, M., 10 Tach 2013, Yn: International Journal of Marine Energy. 3-4, t. e1-e10Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
New insights about the introduction of the Portuguese oyster, Crassostrea angulata, into the North East Atlantic from Asia based on a highly polymorphic mitochondrial region.
Grade, A., Chairi, H., Lallias, D., Power, D., Ruano, F., Leitao, A., Drago, T., King, J., Boudry, P. & Batista, F., Rhag 2016, Yn: Aquatic Living Resources. 29, 4, 6 t., 404.Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Interpreting LISST-100X measurements of particles with complex shape using digital in-line holography
Graham, G. W., Davies, E. J., Nimmo-Smith, W. A., Bowers, D. G. & Braithwaite, K. M., 1 Mai 2012, Yn: Journal of Geophysical Research Oceans. 117, C5, t. C05034Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Evaluating assessment feedback in Higher Education: Principles of good practice
Grange, L., Gorff 2019.Allbwn ymchwil: Cyfraniad at gynhadledd › Crynodeb › adolygiad gan gymheiriaid
- Cyhoeddwyd
Problems in the field: Using formative field-skills training to improve student outcomes
Grange, L., Harding, I., Zhu, X., Chiorean, C. & Evans, C., Gorff 2019.Allbwn ymchwil: Cyfraniad at gynhadledd › Crynodeb › adolygiad gan gymheiriaid
- Cyhoeddwyd
Multi-year observations on the gametogenic ecology of the Antarctic seastar Odontaster validus (vol 153, pg 15, 2007)
Grange, L. J., Tyler, P. A. & Peck, L. S., Gorff 2011, Yn: Marine Biology. 158, 7, t. 1681-1681Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Multi-year observations on the gametogenic ecology of the Antarctic seastar Odontaster validus
Grange, L. J., Tyler, P. A. & Peck, L. S., Tach 2007, Yn: Marine Biology. 153, 1, t. 15-23Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Megafaunal Communities in Rapidly Warming Fjords along the West Antarctic Peninsula: Hotspots of Abundance and Beta Diversity
Grange, L. J. & Smith, C. R., 3 Rhag 2013, Yn: PLoS ONE. 8, 12Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Long-term interannual cycles of the gametogenic ecology of the Antarctic brittle star Ophionotus victoriae
Grange, L., Tyler, P., Peck, L. & Cornelius, N., 2004, Yn: Marine Ecology Progress Series. 278, t. 141-155Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Supporting STEM Students’ Self-Regulatory Skills through Developing their Assessment Literacy and Evaluative Judgement Capabilities
Grange, L., Evans, C. & Zhu, X., Hyd 2024, Research Handbook on Innovations in Assessment and Feedback in Higher Education: Implications for Teaching and Learning. Evans, C. & Waring, M. (gol.). Edward Elgar Publishing Ltd, t. 170-195Allbwn ymchwil: Pennod mewn Llyfr/Adroddiad/Trafodion Cynhadledd › Pennod › adolygiad gan gymheiriaid
- Cyhoeddwyd
Fertilization success of the circumpolar Antarctic Seastar Odontaster validus: A diver-collected study
Grange, L., Tyler, P. & Peck, L., 2011, Proceedings of the American Academy of Underwater Sciences 30th Symposium. Pollock, N. W. (gol.). t. 140-151 12 t.Allbwn ymchwil: Pennod mewn Llyfr/Adroddiad/Trafodion Cynhadledd › Cyfraniad i Gynhadledd
- Cyhoeddwyd
Chemical properties of brackish water ice in the Bothnian Bay, the Baltic Sea.
Granskog, M. A., Virkkunen, K., Thomas, D. N., Ehn, J., Kola, H. & Martma, T., 1 Ion 2004, Yn: Journals of Glaciology. 50, 169, t. 292-302Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Sea ice in the Baltic Sea – A Review.
Granskog, M., Kaartokallio, H., Kuosa, H., Thomas, D. N. & Vainio, J., 1 Hyd 2006, Yn: Estuarine, Coastal and Shelf Science. 70, 1-2, t. 145-160Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Influence of freshwater inflow on the inorganic nutrient and dissolved organic matter within coastal sea ice and underlying waters in the Gulf of Finland (Baltic Sea).
Granskog, M. A., Kaartokallio, H., Thomas, D. N. & Kuosa, H., 1 Hyd 2005, Yn: Estuarine, Coastal and Shelf Science. 65, 1-2, t. 109-122Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Small-scale spatial variability in physical, chemical and biological properties of landfast sea ice in the Baltic Sea.
Granskog, M. A., Kaartokallio, H., Thomas, D. N., Ehn, J. & Evans, D. W., 1 Ion 2003.Allbwn ymchwil: Cyfraniad at gynhadledd › Papur
- Cyhoeddwyd
Chemical processes during formation of brackish water ice in the Baltic Sea.
Granskog, M. A., Ehn, J., Virkkunen, K., Martma, T., Thomas, D. N. & Kola, H., 1 Ion 2002.Allbwn ymchwil: Cyfraniad at gynhadledd › Papur
- Cyhoeddwyd
Scales of horizontal patchiness in chlorophyll-a, chemical and physical properties of landfast sea ice in the Gulf of Finland (Baltic Sea).
Granskog, M. A., Kaartokallio, H., Kuosa, H., Thomas, D. N., Ehn, J. & Sonninen, E., 1 Maw 2005, Yn: Polar Biology. 28, 4, t. 276-283Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Attribution of global lake systems change to anthropogenic forcing
Grant, L., Vanderkelen, I., Gudmundsson, L., Tan, Z., Perroud, M., Stepanenko, V. M., Debolskiy, A. V., Droppers, B., Janssen, A. B. G., Woolway, R. I., Choulga, M., Balsamo, G., Kirillin, G., Schewe, J., Zhao, F., del Valle, I. V., Golub, M., Pierson, D., Marce, R., Seneviratne, S. I. & Thiery, W., 18 Hyd 2021, Yn: Nature Geoscience. 14, 11Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Intercomparison results of sand transport models based on ‘blind’ benchmarking test cases
Grasmeijer, B. T., Davies, A. G., Guizien, K., Van Der Werf, J. J., Van Rijn, L. C., Walther, R., Sutherland, J., Biegowski, J., Soulsby, R. L. (Golygydd), Hoekstra, P. (Golygydd) & Davies, A. G., 1 Ion 2005, SANDPIT: Sand Transport and Morphology of Offshore Mining Pits. 2005 gol. Aqua Publications, t. 1-10Allbwn ymchwil: Pennod mewn Llyfr/Adroddiad/Trafodion Cynhadledd › Pennod
- Cyhoeddwyd
On effects of trawling, benthos and sampling design.
Gray, J. S., Dayton, P., Thrush, S. & Kaiser, M. J., 1 Awst 2006, Yn: Marine Pollution Bulletin. 52, 8, t. 840-843Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Fishing for facts on the environmental effects of trawling and dredge fisheries: Reply to Lokkeborg.
Gray, J. S., Dayton, P., Thrush, S. & Kaiser, M. J., 1 Ebr 2007, Yn: Marine Pollution Bulletin. 54, 4, t. 497-500Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
From policy to practice in developing ecologically sustainable fisheries: Reply to Valdimarsson?
Gray, J. S., Dayton, P., Thrush, S. & Kaiser, M. J., 1 Ebr 2007, Yn: Marine Pollution Bulletin. 54, 4, t. 491-493Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Interlaboratory comparison study of calibration standards for foraminiferal Mg/Ca thermometry.
Greaves, M., Caillon, N., Rebaubier, H., Bartoli, G., Bohaty, S., Cacho, I., Clarke, L. J., Cooper, M., Daunt, C., Delaney, M., De Menocal, P., Dutton, A., Eggins, S., Elderfield, H., Garbe-Schoenberg, D., Goddard, E., Green, D., Groeneveld, J., Hastings, D., Hathorne, E., Kimoto, K., Klinkhammer, G., Labeyrie, L., Lea, D. W., Marchitto, T., Martinez-Boti, M. A., Mortyn, P. G., Ni, Y., Nuernberg, D., Paradis, G., Pena, L., Quinn, T., Rosenthal, Y., Russell, A., Sagawa, T., Sosdain, S., Stott, L., Tachikawa, K., Tappa, E., Thunell, R. & Wilson, P. A., 1 Awst 2008, Yn: Geochemistry Geophysics Geosystems. 9, t. Q08010Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid
- Cyhoeddwyd
Non-assimilated tidal modeling of the South China Sea
Green, J. A. & David, T. W., 24 Ebr 2013, Yn: Deep Sea Research Part I: Oceanographic Research Papers. 78, t. 42-48Allbwn ymchwil: Cyfraniad at gyfnodolyn › Erthygl › adolygiad gan gymheiriaid