Learn About Feather Stars: Feeding & growth

Feeding in west-coast crinoids Florometra serratissima is quite well covered in the research literature, but foods are not. In the laboratory F. serratissima can be fed on mixed diatoms, but field diets are poorly known. Perhaps food boluses from animals feeding in the field could be collected and analysed for content. Growth, other than regeneration, appears not to have been studied in detail in any west-coast crinoid.

Research study 1

photograph of several feather stars Florometra serratissima with arms raised in cone shapes courtesy Dan Leus, Pacific Biological Station, Nanaimo, BCphotograph of feather star Florometra serratissima with arms extended in fan formTextbook descriptions of feeding in crinoids state generally that diatoms and small planktonic animals are captured by being flicked into the food grooves of the pinnules by the tube feet, with the particles then being conveyed by cilia along the food grooves to the mouth. Studies on feeding of Florometra serratissima at Bamfield Marine Sciences Centre and Galiano Island, British Columbia include in situ SCUBA observations and add detail to this description. Florometra inhabits areas of still water or slow-velocity water currents.

diagram of water flow through feather star Florometra serratissima showing orientation of armsphotograph of feather star Florometra serratissima showing different pinnule patternsIn slow-velocity water currents the arms are extended in a fan (see photo above Right), while in still water the arms are positioned in a cone (see photo above Left). In the fan position some arms have their food grooves facing the current, while most are turned against it (see Left part of drawing on Left). In the cone position the arms tend to have their food grooves facing inwards. The fan shape apparently creates a baffle effect that reduces current flow within the pinnules and therefore increases feeding efficiency. The pinnules are arranged either in planar or angled pattern, perhaps in response to current magnitude and direction (see photo on Right).

drawing of tube-foot triplet of feather star courtesy Byrne & Fontaine 1981 Can J Zool 59: 11The tube feet are arranged in triplets, with the longest, or primary, tubefoot of each triplet being extended (see drawing lower Right). Together, the primaries form a filtering net. Each primary tube foot secretes fine mucous threads that hang down and waft in the current. Prey items caught up by the primaries are moved into the food groove. There, the secondary tube feet, attached for much of their length to moveable lappets lining the food groove, scoop the particles and mucus from the primary tube feet, and scrape and compact the particles in the food groove to form boluses. The food boluses are manipulated by the tertiary tube feet and are then moved moutwards by ciliary action. Byrne & Fontaine 1981 Can J Zool 59: 11; photo above Left courtesy Dan Leus, PBS, Nanaimo.

Research study 2

drawing of tube-foot triplet of feather star courtesy Byrne & Fontaine 1982 Zoomorph 101: 175photograph of tube-foot triplet of feather star courtesy Byrne & Fontaine 1982 Zoomorph 101: 175

As noted in Research Study 1 above the tube feet of crinoids occur in functional groups of 3, and each member of the triplet is morphologically adapted to its particular role in the feeding process. The largest, or primary, tube feet (1100µm in length) are involved in initial food-particle capture; the secondaries (360µm length) along with their associated lappets transfer food from the primaries and may capture food particles themselves; finally, the tertiaries (230µm) pack the particles together into mucous-bound balls or boluses.

Each tube foot or podium bears numerous papillae (40µm), with mucous glands at their bases. Secretion from these glands gives the podia their sticky surfaces. At rest the tertiary podia are typically held curved in towards the midline of the food groove and, in this position, intercept and propel boluses onward by a paddling action as the boluses pass down the groove (see drawing on Left). Both paddling and ciliary beating contribute to movement of the boluses. The lappets alternate with one another along the food groove and give a scalloped appearance to the food-groove margins (see photo on Right). When the podia retract during feeding, the lappets form a roof over the groove and help contain the boluses as they are moved along. The podial triplets represent the third adaptive level of a 3-tiered feeding system, in which arm posture and pinnule orientations are the first and second levels, respectively. Byrne & Fontaine 1982 Zoomorph 102: 175.