BIOLOGY OF SEASTAR AND FEATHER STAR-1.pptx

Starfish are also referred to as sea stars because of their star-shaped appearance.
They are a part of the phylum Echinodermata and are related to sand dollars, sea urchins, and sea cucumbers.
Starfish belong to the class Asteroidea, derived from the Greek words “aster” (a star) and “eidos“ (form, likeness, appearance).
There are more than 1600 species of starfish alive today, and they have an important role in the community structure of the ocean floor.
All echinoderms share similar pentamerous radial symmetry and spiny skin characteristics, although sea stars differ slightly because they have five or more arms large enough to contain space for digestive and reproductive glands.

1. BIOLOGY OF SEASTAR AND FEATHER STAR Vinod Kumar FRM

2. SEA STAR Starfish are also referred to as sea stars because of their star-shaped appearance. They are a part of the phylum Echinodermata and are related to sand dollars, sea urchins, and sea cucumbers. Starfish belong to the class Asteroidea, derived from the Greek words “aster” (a star) and “eidos“ (form, likeness, appearance). There are more than 1600 species of starfish alive today, and they have an important role in the community structure of the ocean floor. All echinoderms share similar pentamerous radial symmetry and spiny skin characteristics, although sea stars differ slightly because they have five or more arms large enough to contain space for digestive and reproductive glands.

3. EVOLUTION AND SYSTEMATICS The class Asteroidea is a highly diverse group comprised of seven orders, 35 families, and an estimated 1,600 known living species, although their precise phylogenetic relationship and hence classification still proves challenging to taxonomists. Kingdom - Animalia Phylum - Echinodermata Class - Asteroidea Order - Brisingida , Forcipulatida , Notomyotida , Paxillosida , Spinulosida , Valvatida and Velatida and two extinct ones, Calliasterellidae and Trichasteropsida .

4. Pisaster brevispinus Pisaster giganteus Linckia laevigata Asterias rubens Pisaster ochraceus Astropecten articulatus

5. PHYSICAL CHARACTERISTICS Sea stars vary considerably in size, shape, and color, even within the same populations. Their diverse forms reflect evolutionary adaptation to the cosmopolitan habitats they occupy. Despite this diversity they all share similar physical characteristics. All are star-shaped (stellate) with a central body or disc that has symmetrically projecting arms with rows of tube feet running along the lower surface of a V-shaped furrow called the ambulacral groove.

6. Typically, the number of arms is five, but some species such as the coral-eating crown-of-thorns Acanthaster planci can have up to 30. Patiriella parvivipara , which gives the appearance of a nearly spherical body,

7. In most species, the arm tips carry an optic cushion of red-pigmented and light-sensitive cells that sense changes in the prevailing environment . The skeleton of a sea star consists of small calcium carbonate plates called ossicles. These are often studded and spiny, and provide a firm but flexible skeleton of connective tissue. Flexibility enables a variety of postures to be adopted without muscular effort, thus providing an effective means to capture and handle prey and allow individuals to closely follow irregular substrates in search of food.

8. DISTRIBUTION The greatest diversity of sea stars occur in coastal regions, although as a group, they are well represented globally from the Antarctic, Pacific, Atlantic, and Indian Oceans . They inhabit wave-exposed inter-tidal zones of coastal waters to the calm sandy pavements of the deepest oceans . The Benthopectinidae family of sea stars, for example, lives exclusively in the deep-sea of the Atlantic and Pacific Oceans, whereas the species Odontaster validus, which belongs to the family Ganeriidae, are found only in the Antarctic Ocean. P erhaps the most well-known and ubiquitous group of sea stars belongs to the order Forcipulatida. This group includes the genus Asterias, a veracious predator of mussels and oysters in many coastal waters around the world.

9. HABITAT As a group, sea stars live in virtually every habitat found in the sea, ranging from tidal pools, rocky shores, sea grass and kelp beds, beneath rock rubble, on coral reefs, sand, and mud. In some species a broad and flattened body may act as a snowshoe when foraging on very soft mud. In the upper shore, they are periodically exposed by the retreating tide, resulting in extended periods of desiccation.

10. FEEDING ECOLOGY AND DIET Sea stars are carnivorous, preying on sponges, shellfish, crabs, corals, worms, and even on other echinoderms. Most are generalists, feeding on anything that is too slow to escape, such as mussels and clams, whilst others are specialized feeders preying exclusively on sponges, corals, bivalves, or algae . Prey is located by the chemical odors emanating from its waste products .Or by small movements that betray its presence when detected by a sea sta r. Several species have specialized feeding behaviors including eversion of their stomachs. . T his means the starfish extends its stomach out of its mouth and over the digestible parts of its prey. The prey tissue is partially digested outside of the body, then the starfish brings its stomach back inside into its 10 digestive glands to finish feeding.

11. They have few predators as adults due to their armored spiny skeleton and rigid nature. In less heavily armored and juvenile sea stars, protection from predators comes from having a cryptic coloration. Other defensives include toxic spines or skin (e.g., Crossaster papposus and Acanthaster planci ) and predator avoidance by burrowing beneath the sediment surface (e.g., Astropecten irregularis and Anseropoda placenta ).

12. LOCOMOTION On their ventral side, starfish contain thousands of tube-like feet that contain cells that are specialized for adhesion . starfish can use these tube feet to move across a surface. Each foot has two sets of secretory cells that secrete compounds that allow the foot to first attach then detach to a surface. S ea stars have an unusual way of moving. Water is taken in through the madreportite, a small, perforated plate on the upper surface of the disc, and into the water vascular system, a canal of tubes connected to the tube feet. F ollowing muscular contraction water is directed under pressure to the tube feet, which then extend under its force. Movement is achieved through a coordinated stepping motion where, on muscle contraction, the feet adhere to the sediment surface, pushing the individual forward.

13. REPRODUCTION Most sea stars have separate sexes with no visible differences between them. I nternally , each arm contains a pair of gonads that become almost filled with eggs or sperm, depending on the sex, at the time of breeding . The majority of species are broadcast spawners where eggs and sperm are released into the water column to be fertilized. To increase the chances of fertilization, sea stars aggregate when they are ready to spawn . Asexual reproduction is another method of development that involves either fission or regeneration of entire animal from arm parts. A lmost a dozen species divide through their disc, producing clones with identical genetic makeup (e.g., Linckia laevigata ).

14. BEHAVIOUR Sea stars have a "central nervous system," or diffuse nerve net, but lack anything identified as a brain . Despite this, they are sophisticated enough to adapt to change based on previous experiences (conditioning), whereby behavior that is persistently unsuccessful, usually a feeding one, is stopped . They are not considered social animals, yet many species tend to aggregate or swarm in large numbers during certain times of the year.

15. RESPIRATION Sea stars don't use gills or lungs to breathe. T hey rely on diffusion across surfaces in their body. F or example, most oxygen is taken up from water that passes over their tube feet and papulae or skin gills.

16. EXCRETION Starfish have no distinct excretory organs; waste ammonia is removed by diffusion through the tube feet and papulae . The body fluid contains phagocytic cells called coelomocytes, which are also found within the hemal and water vascular systems.

17. WATER VASCULAR SYSTEM The water vascular system is a hydraulic system used by echinoderms, such as sea stars and sea urchins, for locomotion, food and waste transportation, and respiration . The system is composed of canals connecting numerous tube feet. The exact structure of the system varies somewhat between the five classes of echinoderm. The system is part of the coelomic cavities of echinoderms, together with the haemal coelom (or haemal system), perivisceral coelom, gonadal coelom and perihaemal coelom.

18. Threats and conservation status The biggest threats to starfish are a reduction of coral reef habitat, pollution, and marked changes in water temperature. T he iconic sunflower sea star has been listed as critically endangered by the International Union for Conservation of Nature following a groundbreaking population study led by Oregon State University and The Nature Conservancy.

19. FEATHER STAR feather star, any of the 550 living species of crinoid marine invertebrates (class Crinoidea) of the phylum Echinodermata lacking a stalk. The arms, which have feathery fringes and can be used for swimming, usually number five. Feather stars use their grasping “legs” (called cirri) to perch on sponges, corals, or other substrata and feed on drifting microorganisms, trapping them in the sticky arm grooves. A feather star is not the same as a starfish (also known as a sea star and sometimes misspelled as star fish). Close relatives of feather stars include sea stars, brittle stars, sea cucumbers and sea urchins.

20. HABITAT A feather star habitat is slightly different from a starfish habitat. Feather stars, also called crinoids, reside in the ocean, typically in shallow, warm waters. Some species do, however, exist in colder waters and deeper areas. A sea star or starfish habitat needs the right surface for the creature's feet to move across. Sea stars with tube feet reside among rocks, and sea stars with pointed tube feet tend to live on the seabed in sand or mud. Feather stars, however, live in areas with strong currents. They do not tend to live around silt, which can clog their feet. Living in areas with these currents ensures their survival, as they yield more opportunities to capture food. They may also swim through the water column if disturbed.

21. DISTRIBUTION They are most abundant from the Indian Ocean to Japan. where Tropiometra is the commonest genus. Antedon is the best known genus in the Atlantic.

22. SYSTEMATICS KINGDOM - ANIMALIA PHYLUM - ECHINODERMATA CLASS - CRINOIDEA ORDER - COMATULIDA Feather star species distributed among 150 genera and 17 families in one order .

23. Comaster nobilis Oxycomanthus bennetti Himerometra robestipinna Antedon mediterranea Leptometra celitica Nemaster grandis

24. LOCOMOTION These amazing creatures swim, float and “walk” through the sea. Feather stars swim by beating their arms up and down, or at times parachuting with their cirri out to grasp new substrate. When needed, however, feather stars can attach to rocks or other materials via their cirri. Feather stars previously were not considered fast movers.

25. FEEDING BIOLOGY They feed on small food particles, which they pick up by moving their feather-like arms. After they grab some food, they push it toward their mouth, which is in the center of their body. They usually inhabit shallow waters, and they prefer a reef with a bit of current so the food comes directly to them. Feather stars are usually nocturnal, but you can also observe them swimming or moving their tentacles during the day when they’re feeding or moving from one coral to another.

26. REPRODUCTIVE BIOLOGY Male or female feather stars reproduce via water fertilization. Eggs, produced in spring, hatch as larvae. The swimming larvae eventually attach to the sea bottom via stalks The fertilised eggs hatch to release free-swimming vitellaria larvae. The bilaterally symmetrical larva is barrel-shaped with rings of cilia running round the body, and a tuft of sensory hairs at the upper pole. Crinoids are not capable of clonal reproduction as are some starfish and brittle stars, but are capable of regenerating lost body parts.

27. WATER VASCULAR SYSTEM Like other echinoderms, crinoids possess a water vascular system that maintains hydraulic pressure in the tube feet. This is not connected to external sea water via a madreporite, as in other echinoderms, but only connected through a large number of pores to the coelom (body cavity). The main fluid reservoir is the muscular-walled ring canal which is connected to the coelom by stone canals lined with calcareous material.

28. NERVOUS SYSTEM The crinoid nervous system is divided into three parts, with numerous connections between them. The oral or uppermost portion is the only one homologous with the nervous systems of other echinoderms. It consists of a central nerve ring surrounding the mouth, and radial nerves branching into the arms and is sensory in function. Below this lies an intermediate nerve ring, giving off radial nerves supplying the arms and pinnules. These nerves are motor in nature, and control the musculature of the tube feet.

29. Threats and conservation status The main threats are recreational fishing, commercial fishing with gillnets, and habitat degradation. No species are listed by the IUCN.

30. CONCLUSION Sea stars are related to sand dollars, sea urchins, and sea cucumbers, all of which are echinoderms, meaning that they have five-point radial symmetry. However, this does not mean that all sea stars have five arms and species with 10, 20, or even 40 arms exist. Pycnopodia helianthoides, commonly nown as the sunflower sea star, is a large sea star found in the northeast Pacific.In 2020, the IUCN first assessed that the sunflower sea star was critically endangered. Feather stars are a type of marine invertebrate with featherlike arms that radiate from a central body. Feather stars are not considered threatened or endangered.

31. REFERENCES Lawrence, J. M. (Ed.). (2013). Starfish: biology and ecology of the Asteroidea. JHU Press. Garm, A. (2017). Sensory biology of starfish—with emphasis on recent discoveries in their visual ecology. Integrative and Comparative Biology, 57(5), 1082-1092. Vogler, C., Benzie, J., Lessios, H., Barber, P., & Wörheide, G. (2008). A threat to coral reefs multiplied? Four species of crown-of-thorns starfish. Biology letters, 4(6), 696-699. Holland, N. D. (2020). Cell cycle in regenerating feather star arms. In Echinoderms through time (pp. 217-220). CRC Press..

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