Reproduction & development
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Research study 1
 

photograph of X-sections through pinnules of feather stars Florometra serratissima showing gonads courtesy Mladenov 1986 Can J Zool 64: 1642photograph showing general anatomy of feather star Florometra serratissimaStudies on feather stars Florometra serratissima at Bamfield Marine Sciences Centre, British Columbia mostly have separate sexes, but a small percentage is hermaphroditic.  Breeding is continuous throughout most of the year and “dribble” spawning is the norm.  Gonads appear as swellings on special pinnules of the arms, known as genital pinnules.  Genital pinnules occur on all 10 arms, but concentrate in the lower third of each arm.  Male individuals can be recognised by the creamy white colour of their genital pinnules, and females by pink or orange-coloured pinnules. A cross-sectional view through one of these pinnules in a female discloses oocytes residing within a germinal epithelium lining a central lumen (see photograph on Right).  In a given female about 24,000 oocytes each month are released from the ovarian epithelium into the lumens of the genital pinnules.  Within a few days they become mature eggs.  The mature eggs are spawned to the outside via nipple-like swellings that develop on each genital pinnule.  Maturation of spermatocytes occurs in a similar way in males, eventually leading to the entire lumen being filled with mature sperm (see photograph far Right).  Given a minimum 9-mo breeding season, a single female may spawn over 200,000 eggs.  The author notes that this is the first unequivocal documentation of continuous reproduction in a crinoid.  Mladenov 1986 Can J Zool, 64: 1642.

 

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Research study 2

 

Other research at the Bamfield Marine Sciences Centre, British Columbia provides details of early development of in Florometra serratissima.  After release, the eggs are fertilised and then develop a ridged coat (see photo on Left)photograph of doliolaria larva of feather star Florometra serratissima courtesy Mladenov & Chia 1983 Mar Biol 73: 309; Chia et al. 1986 J Morph 189: 99. The eggs hatch after 35h (at 10oC) and the embryos develop into non-feeding barrel-shaped doliolaria larvae after 4d (see photo above Right).  Four bands of cilia provide propulsion. An apical tuft of cilia at the anterior end is associated with an organ made up of at least 3 types of receptor cells.  Also at the front end is an adhesive pit containing cells that secrete an attachment cement at the time of settling.

drawing of sinusoidal swimming path of doliolaria larva of feather starThe larvae swim for a short time then begin to settle 4.5-10d after hatching.  The larvae swim in an unusual vertical sinusoidal path, rotating in a clockwise direction and oscillating in the dorso-ventral plane all the while (diagram on Left). Settlement occurs with the apical tuft first contacting the substratum. The larva spins around with each contact as though testing the chemical and physical features of the site with its apical organ. Mladenov & Chia 1983 Mar Biol 73: 309; Chia et al. 1986 J Morph 189: 99.

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Research study 3
 

schematic showing developmental schedule of feather star Florometra serratissima courtesy Lacalli & West 1986 J Embryol Exp Morph 96: 303

drawings of banding patterns in doliolaria larva of feather star Florometra serratissima courtesy Lacalli & West 1986 J Embryol Exp Morph 96: 303About 10h after fertilisation (at
10oC
), the doliolaria larva of Florometra serratissima is uniformly ciliated, and only at about 90h from fertilisation do the characteristic ciliated bands appear (see schematic on Left). 

Studies at Bamfield Marine Sciences Centre, British Columbia show that the final striped pattern arises secondarily from an initial pattern that has stripe-like elements (e.g., at 64h from fertilisation; see drawing upper Right) but is not, strictly speaking, striped (e.g, see 100h). The evolutionary implications of this are discussed by the authors.  Lacalli & West 1986 J Embryol Exp Morph 96: 303.

 

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Research study 4

 

drawing showing cut locations in doliolaria larvae of feather star Florometra serratissima courtesy Lacalli & West 1987 Development 99: 273Follow-up studies on ciliary-band formation in the doliolaria larva of Florometra serratissima at the Bamfield Marine Sciences Centre, British Columbia involve cutting the larva into 2 parts to test whether missing pattern elements are replaced in the offspring fragments or whether the pattern is mosaic, in other words, fixed, from an early age.  Results show that the complementary fragments from each cutting express parts of the total pattern without adding the missing pattern elements; thus, the pattern is a mosaic.  Typical results are shown in the accompanying schematic from cuts made at 42h and 46h, respectively.  Each pair of half-embryos has an apical tuft and pit, a vestibule, and 4 ciliary bands, with the positions of the last 2 features varying with age of the larva and position of the cut (this especially relates to which member of the pair receives the vestibule).  The authors conclude that the pattern in Florometra and perhaps other crinoids behaves as a mosaic from as early as the mid-gastrula stage, similar to what has been found in asteroids and holothuroids.  Lacalli & West 1987 Development 99: 273.

NOTE  cuttings are done in gastrula (20-28h from fertilisation) or early doliolaria (42-46h) stage, and the pieces are cultured for another 100h or so.  Band formation typically begins at about 56h

 

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Research study 5

 

photograph of juvenile (cystidea) of feather star Florometra serratissima courtesy McEdward et al. 1988 Int J Invert Reprod Dev 13: 9drawing of 4-mo feather star Florometra serratissima courtesy McEdward et al. 1988 Int J Invert Reprod Dev 13: 9Metamorphosis of the doliolaria larvae of Florometra serratissima occurs shortly after settlement, resulting in a tiny stalked juvenile known as a cystidea (see drawing on Right). The doliolarians settle gregariously and this leads to aggregations of adults (see photo below Left). The authors suggest that chemicals from the attachment cement of the cystidean may be the stimulus for settlement of neighbouring doliolaria larvae.  About 16d from settlement (21d from hatching), five cracks begin to open in the upper bladder part of the cystidean, and tube feet eventually appear from the cracks (see drawing lower Right). The stalked juvenile now begins to feed and is known as a pentacrinoid. About 27d after settlement the pentacrinoid is about 3mm in height.  By 6mo of age the pentacrinoid is 12mm in height, has an arm span of 6mm, and possesses 250, one-mm-long tubefeet for feeding (see drawing upper Left).  The pentacrinoid feeds for a time, after which the crown of tentacles breaks free and the juvenile feather star crawls down the stalk and adopts the adult mode of life. Mladenov & Chia 1983 Mar Biol 73: 309; Chia et al. 1986 J Morph 189: 99; some drawings of developmental stages modified from McEdward et al. 1988 Int J Invert Reprod Dev 13: 9. Photograph courtesy Dan Leus, Pacific Biological Station, Nanaimo.

NOTE
  lit. “bladder or bag” G., referring to the shape of the juvenile at this stage

NOTE  in this part of the overall study at Bamfield, British Columbia the larvae are settled in the laboratory in small plastic dishes, then placed out in the ocean at 25m depth for monitoring growthdrawing of aggregation of early pentacrinoid stages of feather star Florometra serratissima courtest McEdward et al. 1988 Int J Invert Reprod Dev 13: 9

photograph of aggregations of Florometra serratissima on a ship, the HMCS Chaudiere, sunk in SCUBA-depth water off the coast of British Columbia courtesy Dan Leus, PBS, Nanaimo
Aggregations of Florometra serratissima on a ship, the HMCS Chaudiere, sunk
in SCUBA-depth water off the coast of British Columbia 0.25X

 

 
Research study 6
 

schematic showing change in energy content of feather star Florometra serratissima during development courtesy In a study on energy contents of the different developmental stages of the feather star Florometra serratissima at the Bamfield Marine Sciences Centre, British Columbia researchers present data showing a decrease from 4.5 x 10-2 Joules in the egg to 0.9 x 10-2 Joules in the pentacrinoid stage. This represents an 80% reduction in energy content of the individual.  The startling aspect of these data is not the magnitude of reduction, which is reasonable; rather, it is the remarkably low energy content of the egg reported by the authors (4.5 x 10-2 Joules), which leads to what seems to be an unrealistically low estimate for energy content of the pentacrinoid stage (see graph on Right). In this scenario an egg of Florometra containing a little more than a microgram of carbon will develop into a pentacrinoid containing only 20% this amount. The authors note that other echinoderm eggs of comparable size contain 4-32 Joules, or about 90-700 times more energy than in a Florometra egg.  The authors remark that this is the first report of energy contents in the developmental stages of a crinoid.  McEdward et al. 1988 Int J Invert Reprod Dev 13: 9; see also McEdward & Carson 1987 Mar Ecol Progr Ser 37: 159

NOTE  conversion values for organic-carbon mass to energy quoted in the literature are variable: 1µg = 3.9-4.2 x 10-2 J.  In the present study organic carbon is measured by dichromate oxidation against a glucose standard with a reported resolution of 0.15 x 10-2 J, equivalent to about 0.03µg C.  This level of resolution is 2 orders of magnitude more accurate than the value of “≈ 5µg C” quoted by other authors as the level of resolution for what appears to be the same basic analytical method. This apparent discrepancy should be checked

NOTE if we assume that most of the soft tissues in Florometra are protein, then based on the energy values reported a pentacrinoid of 2cm in height would contain less than 2 millionths of a gram of live-mass protein with which to move its arms, line its coelomic cavities, articulate its skeletal ossicles, and form its gut. To say, as the authors do, that “a juvenile crinoid can be constructed with unusually little organic material” is an understatement, indeed 

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