hydract

Hydractinia echinata is now considered to be comprised of a sibling species group (see Buss & Yund, 1989. J. Mar. Biol. Assoc. UK, 69:857-874). They are distinguished by features of the crustose base, the nutritive tentacles, by host selection, and by distribution (as well as biochemical characters which lie beyond the scope of this work)

H. polyclina

Littorina littorea

Pagurus acadianus

H. symbiolongicarpus Buss & Yund, 1989. Chitinous colony base does not exceed margin of host shell; nutritive polyp with variable number of tentacles all of equal length. They may be found in Bo (= both Acadian and Virginian provinces) usually associated with the hermit crab Pagurus longicarpus occupying smaller shells (e.g., Ilyanassa trivittatus, I. obsoletus, L. littorea, Urosalpinx cinerea)

H. symbiopollicaris Buss & Yund, 1989. Chitinous colony base does not exceed margin of host shell; nutritive polyps with dimorphic tentacles as in H. polyclina. Their distribution is Vi only, on larger shells (e.g., Neverita duplicata, Busycon, etc.) occupied by the hermit crab Pagurus pollicaris.

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