Jan. 25, Lecture 7 Squid mantle hydrostat Asterias tube feet; pulsate jet propulsion jellyfish Body waves: Nereis parapodia Snake locomotion Adhesive locomotion: gastropods The term test – short answer – scheduled for lecture time period on February 17, just before Reading Week

Last year’s two-way table re mantle function: there is an error: ’Volume decreases to 75% of relaxed volume’: should be 75% of relaxed diameter The essence of last lecture’s account of the squid mantle as muscular hydrostat: the collagen creates a tunic that prevents change in dimension in all longitudinal planes; this means that radial and circular muscles are now efficient antagonists, one able to stretch the other back to its precontracted state. ‘Imagine it as it isn’t’ to better understand the effect: imagine no collagen. Contract the radial muscles and normally the mantle thins. But without the longitudinal restriction imposed by collagen it is not as necessary to thin. The connective tissue collagen is a critical element in the design. ‘the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content. Collagen, in the form of elongated fibrils, is mostly found in fibrous tissues such as tendon, ligament and skin, and is also abundant in cornea, cartilage, bone, blood vessels, the gut, and intervertebral disc.’ [from Wikkipedia]

From Brown, Selected Invertebrate Types

A parallel to the squid mantle: spiral connective tissue limits response planes of structure and is essential for protraction

Santos, R. et al Adhesion of echinoderm tube feet to rough surfaces. J. exp. Biol. 208: Fig. 6 external morphology of unattached pedal discs of Paracentrotus lividus (left) [sea urchin] and Asterias rubens [starfish] (right). End of extensible cylinder is the disc, larger in diameter than the stem. There is a central depression. 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 are released within the cuticle [how?] and 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.

Pulsate jet swimming in jellyfish: pushes it in opposite direction of jet; cancellation parallel to destructive interference in sound production ? Polyp and medusa morphs Power and recovery strokes Incompressible fluid displaced: jetting seawater out from under umbrella Radial and circular fibres of myoepithelium; Antagonist MESOGLEA Stores elastic strain energy like ligament of scallop.

From Wikkimedia Commons pictures by Hans Hillewaert Nereis succinia epitoke of polychaete worm

Retrograde vs direct body waves Errant polychaetes, parapodia; aciculum [small pin] Circular oblique retractor (antagonist not another muscle: but coelomic fluidand longitudinal muscles, fenestrated septa Notopodium, neuropodium [noto = back] Nereis parapodia:

Body waves and parapodia interact complexly Parapodia, kept normal to the side of the segment and following the curve of the body wave, if they are on the outside of a body wave, move through a greater sweep of distance and develop more force against the water than those on the opposite – inside – of the wave. The propulsive forces produced are greater for parapodia on the outside of the curve. The worm accentuates the difference by parapodium retraction on the inside of the wave. BODY WAVE HEAD TO TAIL (like a fish): outside parapodia (on the outside of the curve and developing more force against the water are now sweeping forward toward the head which will tend to propel the worm backward. BODY WAVE TAIL TO HEAD: the more effective parapodia (on the outside of the curve now sweep backward toward the tail which will tend to propel the worm head-first. To make forward progress Nereis must use a direct body wave and not a retrograde one – the opposite of a fish.

sidewinder

Crotaline movement in snakes Only when certain portions of the body wave are in contact with the substratum

Pedal locomotion in Gastropoda From Wikimedia Commons Arion ater, black slug