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  Research study 1

Members of the Order Pennatulacea are colonies of polyps. The primary polyp of the sea pen after metamorphosis asexually buds off feeding (autozooid) and respiratory (siphonozooid) polyps that ultimately make up the colony.  The feeding polyps, located on the distal portions of the leaves, have tentacles for catching food, and the digestive cavities of all polyps are interconnected. The respiratory polyps are located on the rachis and these lack tentacles.  The seawater pumped into the colony by the respiratory polyps is probably less for gas exchange than for inflating and deflating the entire colony, a process that can happen quite quickly. A slender internal support or style composed likely of flexible protein/chitin runs up the centre of the colony, drawing of style within a sea pen Ptilosarcus gurneyipresumably for support.

NOTE  lit. “tube or pipe animal” G., referring to its function of moving water into and out of the colony

photograph of sea pen Ptilosarcus gurneyi showing makeup of cologyNOTE  if you have ever wondered what happens to the style when a large colony contracts to about one-quarter its original length (see photo), consider this. A large colony of 75cm expanded length has a style of about 12cm in length, or just a bit shorter than the same colony fully contracted (est. 16-19cm L), so the style would be accommodated without having to bend. An unpublished thesis account of the morphology of P. gurneyi notes that the style does not extend upwards much beyond the length of the peduncle (see drawing), so it must be positioned quite loosely so that the tissues can slide by during retraction. Interestingly, the author finds that style length squared correlates almost perfectly (R-squared = 0.968) with colony dry mass and this, in turn, would be expected to correlate equally well with colony live mass - if, that is, it could be reliably measured. Batie 1971 MSc Thesis, University of Oregon. 97pp.

Two individual colonies of Ptilosarcus
, one expanded and the other
pulled down into the soil 0.33X

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Research study 2

Colonies of sea pansies Renilla amethystina (koellikeri)are similar to sea pens in that they are made up of siphonozooids for water flow and autozooids for catching and ingesting food, but in this case the 2 types of polyps are scattered over the surface of the rachis.  There are many hundreds of inhalent siphonozooids, but only a single large exhalent one located on the midline of the rachis. A peduncle or holdfast support extends down into the sand from the under-surface of the rachis. The colonly undergoes periodic deflations and expansions. photograph of feeding polyps of a sea pansy Renilla amethystina courtesy Anderson & Case 1975 Biol Bull 149: 80Anderson & Case 1975 Biol Bull 149: 80.

Close view of autozooids (feeding polyps) of R. amethystina 5X



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