Halichondria panicea or Halichondria bowerbanki

Halichondria (Halichondria) panicea  (Pallas, 1766) 

Breadcumb sponge - Broodspons

or

Halichondria (Halichondria) bowerbanki  (Burton, 1930) 

Bowerbank's halichondria - Sliertige broodspons

In a recent publication (see at the bottom of the page) the authors state that the taxa of Halichondria panicea and H. bowerbanki are not diagnosable with traditional morphological characters. That implies that you have to do DNA-research to be 100% sure about the identity of the species. The identification of the specimens shown at this page is merely a guess based on their habitus.

PART 1: More likely Halichondria (Halichondria) panicea

Sint-Annaland, the Netherlands, 19-3-2019.

Sint-Annaland, the Netherlands, 8-12-2015. Specimen A.

Sint-Annaland, the Netherlands, 8-12-2015. Specimen A.

PART 2: More likely Halichondria (Halichondria) bowerbanki

Watervalletje, the Netherlands, 3-11-2015.

Sint-Annaland, the Netherlands, 1-3-2017. Specimen B.

Sint-Annaland, the Netherlands, 1-3-2017. Specimen B.

Sint-Annaland, the Netherlands, 1-3-2017. Specimen B.

Zeelandbrug, the Netherlands, 17-09-2012.

Sint-Annaland, the Netherlands, 3-4-2018.

Watervalletje, the Netherlands, 3-11-2015. Specimen C.

Watervalletje, the Netherlands, 3-11-2015. Specimen C.

A common garden of Halichondria sponges: taxonomic revision of Northeast

Pacific Halichondriidae reveals many cryptic introduced species. Thomas Turner, Christine Morrow, Bernard Picton, Claire Goodwin, Robert Thacker, 2024-11. BioRxiv 2024, 11. 

https://doi.org/10.1101/2024.11.04.621922