I'm 98% certain of the species ID but have not had it confirmed by an expert. There are 180 species of Echinoderms in the Pacific Northwest, but this one seems pretty unique in the descriptions (largest seastar in the PNW; 16-24 arms -- this specimen appears to have 16), and matches the pictures of it online.
Ed Bierman|sourceurl=https://flickr.com/photos/26216388@N02/6003890397%7Creviewdate=2019-01-19 13:42:00|reviewlicense=cc-by-2.0|reviewer=FlickreviewR 2
Wikimedia Commons
Summary[edit] Description: This giant spined star (Pisaster giganteus) with one arm around a warty sea cucumber (Apostichopus californicus) - Monterey, California. Date: 30 July 2011, 14:10. Source: Best Palls. Author: Ed Bierman from CA, usa.
Summary[edit] Description: English: Giant Pink Seastar (Pisaster brevispinus), Ganges Harbour, Salt Spring Island, British Columbia. Date: 4 June 2008. Source: Own work. Author: D. Gordon E. Robertson.
Description: Placa madrepórica; probablemente Asterias sp. Date: 30 September 2007. Source: Own work. Author: Luis Fernández García. : This file is licensed under the Creative CommonsAttribution-Share Alike 2.5 Spain license.:. https://creativecommons.org/licenses/by-sa/2.5/es/deed.en CC BY-SA 2.5 es Creative Commons Attribution-Share Alike 2.5 es truetrue.
Asterias rubens Linnaeus, 1758 Coordinate uncertainty in metres 10 Country or area Norway Country code NO County Møre og Romsdal Decimal latitude 62.869515 Decimal longitude 8.308482 Geodetic datum WGS84 Georeference remarks None Locality Bruksgrenda småbåthamn, Tingvoll, Mr
Summary[edit] Description: English: Asterias rollestoni Bell, 1881 - Preserved specimen - Dry ossicles, pedicellaria Asterias rollestoni (YPM IZ 080407). Digital Image: Yale Peabody Museum of Natural History; photo by Daniel J. Drew 2016 ; Location Country or area Japan Municipality Sagami Bay State province Kanagawa Prefecture Water body Pacific Ocean. Source: https://www.gbif.org/occurrence/1269525403. Author: Daniel J. Drew Gall L (2019). Invertebrate Zoology Division, Yale Peabody Museum. Yale University Peabody Museum. Occurrence dataset https://doi.org/10.15468/0lkr3w accessed via GBIF.org on 2019-02-04. https://www.gbif.org/occurrence/1269525403.
Summary[edit] Description: English: Eleven armed starfish Coscinasterias muricata at Rapid Bay Jetty, Gulf St Vincent, South Australia. Date: 2 February 2014, 14:23:26. Source: Own work. Author: Peter Southwood. Camera location35° 31′ 08.44″ S, 138° 11′ 04.27″ EView all coordinates using: OpenStreetMap - Google Earth.