2 literature references for Halichondria parasitica (Montagu, 1818):

Author: Montagu, G.
Year: 1818
Title: An Essay on Sponges, with Descriptions of all the Species that have been discovered on the Coast of Great Britain.
Source: Memoirs of the Wernerian Natural History Society 2(1): 67-122,pls III-XVI.
Author: Arndt, W.
Year: 1935
Title: Porifera.
Source: In: Die Tierwelt der Nord- und Ostsee. 3a (27).(Leipzig): 1-140.