NAME : ANDI ALFINA ULANDARI

NIM : 121 444 1 015

CLASS : BIOLOGY ICP OF A

CRINOIDEA

A.INTRODUCTION OF CRINOIDEA

Although crinoids are the least understood of living echinoderms, their skeletal

remains are among the most abundant and important of fossils. They appeared during the

Lower Ordovician and underwent several major radiations during the Paleozoic Era.

Crinoids were major carbonate producing organisms during the Paleozoic and Mesozoic.

In fact, in many Paleozoic and Mesozoic settings entire carbonate shelves were composed

predominantly of crinoidal remains(Ausich 1997).

The examples, the enormous volume of skeletal material controlled the

sedimentary environment. Short stratigraphic ranges of many species make them important

as at least local biostratigraphic index taxa. The broad morphological diversity of crinoids

includes forms characteristic of specific habitats and oceanographic conditions. More than

5000 fossil species have been described.

A persistent, traditional view treats living crinoids as chiefly deep-sea organisms,

relicts of their opulent Paleozoic past, holding off final extinction in remote abyssal

habitats. This view is generally applied to stalked crinoids, or sea lilies, as typical of the

entire group, because they most closely resemble their fossil forebears. It is true that the

approximately 80 extant species of stalked crinoids are chiefly restricted to depths greater

than 200 m (the shallowest occurs in 100 m). However, 85% of extant crinoids

(approximately 540 named species) are unstalked feather stars, or comatulids, the products

of a continuing post-Paleozoic radiation (Meyer & Macurda 1977).

Comatulids are a monophyletic clade classified within the subclass Articulata

(Simms 1988). About 65% of living comatulids occur at shelf depths (<200 m). In the

tropical Indo-West Pacific, the richest region, single reefs may support as many as 50

species, almost as many as recorded for any individual fossil assemblage. Here, abundance

and diversity reach 115 specimens and 12 species per m2, respectively (Messing 1994).

Although far fewer comatulid species exist in cold waters, local abundance may

be much greater. All crinoids are passive suspension feeders. They produce no

feeding/respiratory current but, rather, rely on extrinsic, ambient water movement. In

extant crinoids, the food-gathering apparatus functions as follows: each featherlike arm

that radiates from the central body bears an open ambulacral groove bordered by triads of

fingerlike podia, or tube feet, which are terminal extensions of the water vascular system

(see figure below). The longest tube foot in each triad, 0.43-0.85 mm in length, is held out

at a right angle and flicks passing food particles into the groove. After a food particle is

captured by a crinoid, the shortest tube foot wraps it in mucous secretions; ciliary tracts on

the groove floor then transport it toward the mouth. In living crinoids, food particle size

ranges from about 50 to 400 µm. Diets include a variety of protists (e.g., diatoms and other

unicellular algae, foraminiferans, actinopods), invertebrate larvae, small crustaceans, and

detrital particles (Messing, 1987).

B.

CHARACTERISTICS

Crinoids are pentamerous, stalked echinoderms with a cuplike body bearing five

usually branched and commonly featherlike arms (see figure below). Most of a crinoid's

body consists of an endoskeleton composed of numerous calcareous pieces, called plates or

ossicles. The visceral mass of the crinoid animal is encased in the aboral cup that is

typically composed of 2-3 circlets of plates. The mouth and anus are on the upper or oral

surface of the animal. Additional circlets of fixed arm plates and fixed interradial plates

may occur above the aboral cup, making a larger calyx. Five radial plates (the uppermost

circlet of aboral cup plates) are aligned with the radial water vascular canals and give rise

to five arms on the oral side of the body. Each arm is an articulated series of ossicles

extending outward from the body. Arms contain extensions of coelomic, nervous, water

vascular, and reproductive systems and bear an ambulacral groove bordered by fingerlike

tube feet, or podia (terminal extensions of the water vascular system), used in suspension

feeding and respiration (see figure above). Arms may be nonbranching or branch in many

different ways. All living crinoids are pinnulate, that is, they bear a small side branch

(pinnule) on alternating sides of successive ossicles along the arm. In living crinoids, the

pinnules bear the food-gathering tube feet. Pinnules arose in several lineages during the

Paleozoic and are characteristic of all post-Palaeozoic crinoids (Bather,1990).

The crinoid stalk typically consists of numerous discoidal skeletal pieces called

columnals, held together by ligaments and penetrated by a central canal containing

coelomic and neural tissue. In most species, the stalk serves to anchor the animal

permanently to the substrate via one of a variety of terminal structures, e.g., a discoidal or

encrusting holdfast, rootlike radix, or grapnel. In others, such as the living isocrinids,

whorls of hooklike cirri (sing., cirrus) along the stalk allow the crinoid to release its hold

and crawl with its arms. Several crinoid groups, notably the comatulids, which include the

only living shallow-water crinoids, have lost the stalk. Comatulids anchor via numerous

cirri that arise from the retained topmost columnal (the centrodorsal) (Bather, 1990).

One

species of Crinoidea is Florometra serratissima

A. MORPHOLOGHY

Classification:

Kingdom : Animalia

Phylum : Echinodermata

Classis : Crinoidea

Order : Comatulida

Family : Antedonidae

Genus : Florometra

Species : Florometra serratissima

Crinoid tube feet occur in groups of three (podial triplets) that behave as

functionally integrated units for food particle collection. Scanning electron microscopy

shows that each triplet member has a distinctive morphology related to its behavioural role

in feeding. Particularly conspicuous features are papillar distribution, papillar processes,

ciliary tracts, and pores that are the openings of mucous glands. The primary podia serve

for initial particle capture. The secondaries, together with lappets, play a major role in

particle transfer from the primaries and may themselves also entrap particles. The tertiaries

manipulate particles within the food groove after their transfer from the other podia. The

tertiary podia use their papilla-free medial faces to compact mucusbound particles into

boluses. In pinnules, boluses are transferred to the food groove midline by tertiaries, then

propelled orally by paddling actions of these podia. Boluses are also transported by the

medial ciliary tracts of the pinnules and arms. Bolus transport by tertiary paddling is

probably more effective in the pinnular than the arm food groove. Short lateral ciliary

tracts at the base of each primary podium may guide boluses into the main ciliary stream or

may be cleansing currents. As the ultimate site of food particle collection, compaction and

transfer, podial triplets represent a third adaptive level of an intricate suspension feeding

system in which the first (arm postures) and second (pinnule orientations) adaptive levels

are related to increasing collecting efficiency in diverse ambient flow (Byrne and Fontaine,

1983).

B. ANATOMY

1. Anatomy of Arms

Arm loss through autotomy is common in west-coast Florometra serratissima,

but what causes it?  Reports on European species list wave action, moving debris

including seaweeds, high temperatures and other physiological stressors (including UV

light), and disturbance by animals. As Florometra is rarely found in waters shallower

than 20m, none of the physical factors listed are likely to influence them.  Potential

predators are more likely to be the cause.  The author describes attacks

on Florometra by predatory sea starsPycnopodia helianthoides resulting in arm loss,

and a single encounter with a spider crab Oregonia gracilis in the field that may have

resulted in arm loss (Mladenov, and 1983 Can J Zool, 61: 2873).

Autotomy in Florometra

serratissima can occur at several specific

breakage locations along the arms and cirri.  The arms and cirri are comprised of

skeletal ossicles joined by ligaments and other connective-tissue fastenings (see drawing

above Right). Each ligament consists of thousands of fibers running parallel to the long

axis of the cirrus.  Each fiber is a bundle of collagen fibrils along with associated

interfibrillar material including cells known as fibroblasts.  A large nerve travels the

length of each cirrus and arm, penetrating each ossicle at its centre and sending

branches into the ossicles. The special autotomy locations are characterised by ligament

fibers of collagen and nerve axons filled with presumed neurosecretory granules.  Fibers

vary in length depending upon the diameter at the autotomy site, but are in the range of

50-75µm.

Studies on specimens of Florometra indicate that the process of autotomy

involves a massive exocytosis of granules at the site stimulated by neural transmission

(see drawing below Right).  The released neurosecretions, which could contain

chelating agents, strong acids, and proteolytic enzymes or enzyme activators, is thought

to liquify the ligament fibers, fibroblasts, and other connective tissues, leading to loss of

the cirrus or arm.  The calcareous ossicles on either side of autotomy site show signs of

erosion. On stimulation of an arm tip in an intact specimen, such as by crushing or

cutting with scissors, the proximally closest autotomy site breaks after about 1sec

(Holland & Grimmer. 1981. 98: 169).

2. Anatomy of syzygial articulations before and after arm autotomy in Florometra

serratissima

About 1 s after appropriate stimulation, arms of Florometra serratissima break

at articulations called syzygies that are specialized for autotomy. The fine structure of

unreacted and of newly broken syzygies is described. The unreacted syzygy includes

(1) ligament fibers consisting of collagen fibrils interconnected by interfibrillar strands

and (2) axons filled with presumed neurosecretory granules. The newly broken syzygy

includes (1) ruptured ligament fibers consisting of swollen collagen fibrils associated

with interfibrillar globules and (2) axons containing few presumed neurosecretory

granules, some of which are fixed in the act of exocytosis; moreover, the calcareous

skeleton adjacent to the broken syzygy is partly eroded. The observations before and

after breaking suggest that the autotomy mechanism may comprise the following

sequence of events: rapid neural transmission from stimulation site to syzygy triggers

a massive exocytosis of granules from presumed neurosecretory axons; the released

neurosecretions (which could include chelating agents, strong acids, proteolytic

enzymes or enzyme activators) etch the skeleton and lower the tensile strength of the

ligament fibers by weakening the collagen fibrils and/or the interfibrillar material;

breakage of the ligament fibers, the major connective tissue of the articulation, is

quickly followed by rupture of all the other tissues at the syzygy ( Nicholas dkk,

1981).

3. Anatomy of crinoids that related to locomotion and swimming

Stalkless crinoids such as Florometra serratissima anchor to the substratum

using flexible cirri.  The cirri are jointed and can slowly bend and straighten. An

individual can slowly move about its habitat by crawling on its cirri. There are several

theories on how the cirri contract, including use of muscles, hydrostatics, ligament

elasticity, and ligament contractility. No muscle cells are visible with a light microscope

and there is no strong evidence to support the other ideas.  However, electron-

microscopical studies in southern California on Florometraand other stalkless species

(from Japan and Europe) suggest that the bending may owe to contraction of nano-

filaments in the cytoplasm of epidermal cells surrounding each cirrus.  The contraction

is thought to be antagonised by ligaments joining adjacent ossicles, and it is the elastic

energy in these that is thought to straighten the cirrus. The authors conjecture that cirrus

is able to be locked in a rigid state by neurosecretory changes in the protein rubber of

the ligaments.  Holland & Grimmer 1981 Cell Tissue Res 214: 207.

Florometra serratissima is the only swimming species of crinoid on the west

coast of North America.  It swims by graceful undulation of its arms in 2 sets of five,

each set moving alternately.  While half the arms effect the power stroke, the other half

are in recovery.  During the power stroke the arms extend out maximally for greatest

frictional resistance, while during the recovery stroke they bend inwards to minimise

resistance.

The only information on specific defenses in west-coast crinoid Florometra

serratissima s comes from anecdotal references to swimming on contact with sunflower

stars Pycnopodia helianthoides or crabs that wander through an aggregation. Contact

with Pycnopodia, for example, is followed by about a 5-sec delay, after which several

power strokes carry the stimulated individual 1-2m distance.  This cycle can be repeated

several times and capture by a sea star is actually thought to be rare (Mladenov 1983

Can J Zool, Lond 61: 2873).

C. REPRODUCTION

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 and Can J Zool, 64: 1642).

Embryonic development of the reproduction Pacific feather star Florometra

serratissima takes place within a ridged fertilization membrane. Cleavage is radial,

resulting in a coeloblastula, and gastrulations is by invagination. Cilia are swollen

terminally during ciliogenesis whereas fully grown cilia possess several swellings along

the length of their shafts. Young doliolaria larvae begin to hatch from the fertilization

membranes 35 h after fertilization (9.5° to 11.5°C); by 4 d the doliolaria has acquired

ciliated bands, a vestibular invagination and an antero-ventral adhesive pit. The surface of

the larva is covered with a delicate glycocalyx supported by microvilli. Larvae swim along

a vertical sinusoidal path just below the water surface; they begin to explore the substratum

at 4.5 d and settlement begins as early as 4.6 d, but can be delayed for up to 9 more days.

Larvae settle gregariously in culture and it is suggested that gregarious settlement plays a

role in the formation and maintenance of adult aggregations of F. serratissima.

Metamorphosis into a stalked cystidean following settlement is rapid. Major changes at

this period include: loss of cilia; withdrawal of ectoderm from the glycocalyx; covering

over of the vestibular invagination; and a 90 degree rotation of the vestibule to the former

posterior end of the doliolaria. Transformation from cystidean to pentacrinoid includes the

opening of the 5 oral plates, the extension of the 15 papillate tube feet and further

elongation of the stalk. The pentacrinoid is able to feed on small food particles. Rudiments

of all 10 adult arms are present by 4 months; at 6 months the pentacrinoid has an arm span

of 6.5 mm but cirri and pinnules are not yet present (Mladenov and Chia, 1983).

D. HABITAT

Look for F. serratissima  in the Demersal; depth range 11 - 1252 m

(Ref. 78719) environment. Specimens can be found in the Temperate zone.

They are distributed around the world in the Northeast Pacific:Alaska, USA

and Canada.

E. BENEFIT

The colour’s beauty of its body structure, so its included he marine biodiversity

that can beautify overlooked under the sea.