New Records of Stylasteridae (hydrozoa: Hydroida) from the Galapagos and Cocos Islands

— Based on the collections of the Johnson-SeaLink I submersible, new records of 14 stylasterid species are reported from the Galapagos Islands, including one new species: Lepidopora concatenata. Five stylasterid species are reported from Cocos Island, including two new species: Pliobothrus fistulosus and Stylaster cocosensis. These are the first records of stylasterids from Cocos Island, three of the five species also shared with the Galapagos Islands. These specimens are also the first records of the genera Lepidopora and Pliobothrus in the eastern Pacific, from the Galapagos and Cocos Islands, respectively. Both the Galapagan and Cocos Island stylasterid faunae are considered to be derived from the western Pacific, having no affinity with the shelf and slope fauna of the American continents in the eastern Pacific. A rich fauna of fourteen stylasterid species, all endemic to the Galapagos Islands and all based on only six Albatross stations made at the turn of the century, was reviewed by Cairns (1986b). Therefore, it was anticipated that a more intensive collecting effort (27 stations in the Galapagos and 8 off Cocos Island) using more efficient and selective collecting methods (a manned submersible) would certainly yield many more species. Although stylasterids were sighted on every submersible dive and collected at 21 of the 27 sites in the Galapagos, in which all 14 previously collected species were represented, only one specimen of one new species was collected. This surprising result might be explained by assuming that all of the Galapagan stylasterid species are uniformly and abundantly distributed throughout the archipelago, such that even a cursory sampling would have a high probability of collecting most of the resident species. This hypothesis would explain both the paucity of new species and the re-collection of all previously known species. The history of our knowledge of the Galapagos stylasterid fauna was given by Cairns (1986b) and is not repeated here. One of the species previously reported, Stenohelia robusta Boschma, 1964a, is herein synonymizcd with Stenohelia concinna Boschma, 1964a, and one new species is described, which maintains the number of species known from the Galapagos at 14. The additional specimens collected by the Johnson-Sea-Link /, however, did: allow an extension of the geographic, bathymetric, and temperature ranges of all species; provide information on the range of variation of various morphological characters; and establish maximum colony sizes for half of the species. Stylasterids were also abundant off Cocos Island, being collected from four of the eight stations. Since no stylasterids had previously been reported from Cocos Island, the five species reported herein are all new records for this island, including two new species. Material and methods. —The new records on which this report is based originated primarily from collections of the R/ V Seward Johnson and Johnson-Sea-Link I submersible expedition to the Galapagos and Cocos 210 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON Table 1. —List of Johnson-Sea-Link I (JSL) stations at which stylasterids were collected (Fig. 32). Station Latitude Longitude CW) Depth (m) Date Bottom temperature (•C) 1911 0°32.7'S 90°07.0' 426^62 12 Nov 1986 8.3-10.3 1912 0°21.9'S 90°15.7' 713-806 14 Nov 1986 5.9-6.7 1913 r32.7'S 90°25.8' 84-227 14 Nov 1986 13.5-14.5 1914 1°17.3'S 90'"17.4' 166-172 15 Nov 1986 14.3-14.4 1915 l''17.2'S 89"'48.7' 650-652 15 Nov 1986 7.4-10.8 1916 1°18.7'S 89°48.8' 545-562 16 Nov 1986 7.3-10.8 1920 1°46.6'S 89°30.8' 64-104 17 Nov 1986 1921 0°17.0'N 89''59.8' 680-720 18 Nov 1986 6.0-6.7 1922 0°23.7'N 90''26.3' 475-578 19 Nov 1986 7.3-8.9 1923 0°23.7'N 90°32.3' 348-384 19 Nov 1986 9.9-10.