Bio 325 Lecture 7 Nematoda: roundworms have no circular muscles to antagonize their longitudinals; they locomote using helical crossed-fibre arrays of inextensible collagen. Echinodermata: starfish tube feet as an example of hydraulic skeletons; and they also use helical crossed-fibre arrays of collagen in the walls of their tube-feet. Mollusca: foot of burrowing bivalves as another example of hydraulic-based locomotion. Muscular hydrostats: when no cavity is needed: tongues, trunks, mantles. left over from last lecture Phylum Nematoda, roundworms • • Collagen cuticle, cylindrical to flat, “body cavity...is derived from the embryonic blastocoel and is called a pseudeocoel. Longitudinal muscles send extensions to the nerve cord rather than having motor nerves extending to the muscles. There are no circular muscles acting as antagonists in roundworms. Pseudocoelom from Barnes; transverse section incorporating pharynx. Classic paper on ‘crossed-fibre helical connective tissue arrays’ Shadwick assigned reading not Clark & Cowey • • • • Shadwick, R.E. 2008. Foundations of animal hyraulics: geodesic fibres control the shape of soft bodied animals. J. exp. Biol. 211: 289-291. “In 1958 R.B. Clark and J.B. Cowey published a paper in which they presented a simple geometric model, based on the idea of a fibrereinforced cylinder, to explain the mechanism underlying shape changes in ribbon worms and flatworms...” “the essential idea of this paper, [is] that a structure composed of inextensible fibres could accomodate large extensibility”, a paradox* Clark R.B., Cowey J.B. 1958. Factors controlling the change of shape of certain nemertean and turbellarian worms. J. exp. Biol. 35: 731-748. Fig. 4 of Kier is from Clark & Cowey (Fig. 3) 1958. The WORM VOLUME CURVE shows the way a helical fibre array angle will relate to the volume of a cylinder (a worm is modelled as a cylinder). If fibre angle increases above 75, volume must decrease: but the fluid in the a nematode’s pseudocoelom, is “incompressible and cannot escape”. So what changes, given the fixed volume, is the internal pressure within the fluid cavity. The increased pressure tends to return the longitudinals of one side to their precontracted state. Clark & Cowey model used to calculate this volume-fibre angle curve. nematodes Clark & Cowey model: “...a right circular cylinder wrapped with a single turn of an inextensible helical fibre ... is used to solve for the enclosed volume of the cylinder as the fibre angle varies from 90 deg to zero deg, with the maxiumum volume occurring at a fibre angle of 54 deg 44 min.” Nematodes - roundworms Roundness relates to adaptation for locomotion: so does high internal pressure WORM VOLUME CURVE What is the antagonist of nematode longitudinal muscle? Answer is the crossed-fibre helical array of collagen in the cuticle . NEMATODES OCCUPY THIS REGION OF THE VOLUME CURVE AND MAINTAIN A HIGH INTERNAL PRESSURE MAKING THEM ‘ROUND’ In Shadwick’s article see the paragraph p. 290, beginning “An interesting outcome...”. The idea here is that the antagonist to the longitudinals is elasticity stored and supplied by the fibre-reinforced cuticle with its helical array of collagen fibres. refer to Fig. 4: longitudinal muscle contracts increasing fibre angle; increase from 75 deg requires vol drop but this not possible so pressure increases Phylum Echinodermata radially rather than bilaterally symmetrical, with oral and aboral surfaces. Water vascular system is unique to these animals among phyla; it is a vessel system filled with coelomic fluid. ‘Arm vessels’ arise from a tubular ring canal. In an asteroid (starfish) five radial canals branch, one into each of the arms. Ambulacral groove on underside of each arm lined with tube feet also called podia. • • Asteroid echinoderms have an exoskeleton. In their dermis are embedded calcareous plates called ossicles (inorganic salt Calcium Carbonate is the material). The skin thus consists of stiff relatively shape-stable elements, in a matrix of flexible collageous fibres (i.e., connective tissue): tough, solid, thick yet flexible protective armour. Above each tube foot, within the arm, is a vesicle called an ampulla, encircled by ampullar muscles; contraction of ampullar muscles will displace fluid out of the ampulla into the tube foot because fluid is incompressible. There is a valve in the side branch to the radial canal – a one-way valve -- that closes to prevent backflow of the fluid into the water vascular system. So for each ampulla +tube foot as it operates the volume of fluid in the ampulla and tube foot lumen is fixed because the one-way valve closed. But this fixed volume of fluid moves back and forth from ampulla to tube-foot lumen; the system in the starfish is HYDRAULIC rather than hydrostatic as in earthworm segments. From Brown, Selected Invertebrate Types Circumferential stress in a pressurized cylindrical vessel (e.g., worm, tube foot) is exactly double the longitudinal stress ‘Kier’s Law’. Stress distribution in a fluid-filled cylinder is not uniform (as per annelid metameres): hoop stress [force acting to increase diameter] is twice as large as longitudinal stress. Imagine it as it isn’t: no helical array in the tube foot wall. When the ampulla pushes fluid into the podium lumen there will be an increase in diameter rather than a lengthening Rosette of ossicles with intrinsic musculature that pulls up the disc middle creating suction to substratum. End of extensible cylinder is the disc, larger in diameter than the stem. There is a central depression. Santos, R. et al. 2005. Adhesion of echinoderm tube feet to rough surfaces. J. exp. Biol. 208: 25552567. Fig. 6 External morphology of unattached pedal discs of Paracentrotus lividus (left) [sea urchin] and Asterias rubens [starfish] (right) . Temporary adhesion: the epidermis of the disc contains glands which produce two secretions: glue/bonder and de-bonder, i.e., adhesive secretions and de-adhesive secretions. The glue is delivered through the disc cuticle to the substratum where it forms a thin film bonding the foot. The debonding secretions act as enzymes, detaching the upper coat of the glue and leaving the rest of the adhesive material behind attached to the substratum as a footprint. Importance of tube foot in predation Virginia Living Museum ‘off the beaten path’ Pulling with tube feet adhering and starfish arm muscles to open the protective valves of shellfish Mollusca An interesting picture of razor clams packaged for sale in a chinatown market in Philadelphia Phylum Mollusca Razor clam burrowing Winter A.G. et al. 2012. Localized fluidization burrowing mechanics of Ensis directus. Journal of experimental Biology 215: 2072-2080. (See also Inside JEB, Kathryn Knight. 2012. Razor clams turn soil into quicksand to burrow.) Blood and foot sinuses serve as hydraulic burrowing mechanism. • • Cycle of burrowing movements Fig. from Winter: In stage A, adductor relaxed so shells braced on surrounding sand by ligaments; protractors start to contract (B) pushing blood into foot and the foot probes down, gaining ground into the mud; pushing force of foot makes body move up a little (C) (relative to dashed line). Stage D, adductors contract, pulling valves together, (red indicates the space they DID occupy), pushing blood into foot to make an anchor, simultaneously squirting seawater out around valves from mantle; this water* ‘puddles’ sand; foot swells with blood into this quicksand region– the localized fluidation; displaced blood is swelling the foot maximally into the bottom anchor of the TWO ANCHOR SYSTEM. Cycle renews (F). *Its not clear whether this involves ocean water drawn in by siphons; perhaps it does if the clam is burrowing near the surface and perhaps if lower down it oscillates (?) its valves to draw in pore water (Winter) Muscular hydrostats Kier p.1252 Tongues, tentacles, trunks: “lack the fluid-filled cavities and fibre-reinforced containers that characterize ... hydrostatic skeletal support systems” rather they are: “a densely packed, three-dimensional array of muscle and connective tissue fibres” Transverse sections showing the muscular arrangement of three examples of muscular hydrostats. A. Squid tentacle: T, transverse muscle fibres; L , longitudinal; transverse in the tentacle core, “and extend to interdigitate with bundles of longitudinal muscle fibres, notice the suckers. Kier W M J Exp Biol 2012;215:1247-1257 ©2012 by The Company of Biologists Ltd Transverse sections showing the muscular arrangement of three examples of muscular hydrostats. B. Elephant Trunk: R, radials ‘extend from centre of the trunk between bundles of longitudinal muscle that are more superficial, notice nasal passages. Kier W M J Exp Biol 2012;215:1247-1257 ©2012 by The Company of Biologists Ltd C. Monitor lizard tongue. Circular muscle fibres surround two large bundles of longitudinal fibres. • • • “The muscle fibers are typically arranged so that all three dimensions of the structure can be actively controlled, but in several cases such as the mantle of the squid [of which more later] and some frog tongues, one of the dimensions is constrained by connective tissue fibers.” “Because muscle tissue, like most animal tissues lacking gas spaces, has a high bulk modulus, selective muscle contraction that decreases one dimension of the structure must result in an increase in another dimension. This simple principle serves as the basis upon which diverse deformations and movement of the structure can be achieved” (Kier 2012). Read carefully all the section on muscular hydrostats by Kier: complex bending achieved by interplay of contracting muscles --more subtle than a passive uniform fluid in a chamber – i.e., some muscles by contracting can affect the bulk modulus presented to other muscles that are acting upon its incompressibility. *bulk modulus of a substance measures its resistance to uniform compression Wikki Muscular hydrostats (Kier contin.) • • • Selective contraction: “This simultaneous contractile activity is necessary to prevent the compressional forces generated by the longitudinal muscle from simply shortening the structure, rather than bending it, and can actually augment the bending by elongating the structure along the outside radius of the bend.” “The longitudinal muscle bundles are frequently located near the surface of the structure, as this placement away from the neutral plane increases the bending moment.” Helically arranged muscle fibres can be present and generate torsion. Bivalve: Pecten, scallop: water-jet swimming propulsion anterior adductor lost, posterior relocated more centrally Seawater exits from 2 openings near the hinge as the valves are adducted: this jets the scallop forward. An example of an antagonist to a muscle that is not another muscle; the Pecten adductor stores the energy of distortion that will later restore it to its precontracted state.