title used in an account of west-coast marine invertebrates entitled A Snail's Odyssey
  Reproduction
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  Attachment
 

Reproductive events include attachment considered in this section, and
COPULATION & LARVAL DEVELOPMENT
LARVAL BIOLOGY,
SELECTION OF SUBSTRATUM,
SETTLEMENT CUES,,
SETTLEMENT COUPLED WITH OCEANIC PROCESSES, and
POST-RECRUITMENT EFFECTS ON COMMUNITY STRUCTURE, considered in other sections.

 
Research study 0
 

An early study at the University of Washington, Seattle describes initial stages of settlement and attachment in the subtidal barnacle Balanus crenatus.  The cyprid larva at the time of settlement is about 0.1mm in length.  After testing the substratum for a suitable spot the cypris attaches momentarily by its probing antennules and then twists onto its dorsal side using its antennules as a lever.  The ventral side is now uppermost.  Three successive rings of gelatinous tubules are now secreted, forming a suctorial film that serves in initial attachment prior to cementation The final observation made by the author is that the 2 valves of the cyprid develop into the opercular valves of the juvenile barnacle.  Bohart 1929 The Am Nat 63 (687): 353.

  drawings of stages in initial settlement of a cypris larva of barnacle Balanus crenatus
 
Research study 1
 

There are 4 main attachments or “adhesions” during the life of a barnacle: 1) temporary attaching by the antennules as the cyprid “walks” and tests the substratum, 2) cementing of the antennules to the substratum surface, 3) cementing of the “pinhead” barnacle juvenile to the substratum at about 1wk of age, and 4) cementing of the adult during its growth.  Each process but the third one is fairly well known in terms of its adhesive mechanics. Barnacles are among the commonest fouling organisms in the marine environment, and it is in relation to them that most anti-fouling research and development have been dedicated. Marine biochemists have extracted and purified barnacle adhesive proteins for use in dental and other medical purposes, such as repair of teeth, bone, and blood vessels.  The advantage of barnacle and other cements is they are non-toxic, set in an aqueous environment, and have low immunogenicity in humans.  They are also exceedingly strong.  Measured forces of attachment of barnacles at different stage are shown below. Crisp et al. 1985 J Colloid Interface Sci 104: 40; Crisp et al.1985 J Colloid Interface Sci 104: 40.

 
STAGE TYPE OF ATTACHMENT FORCE TO DETACH  
exploring cyprid 
cyprid cemented 
pinhead  
juvenile 2mo 
adult 5-10mo  
temporary attachment  
larval cement 
not known
secondary cement
secondary cement 
20-50mg
1.5g
6g
600g
5-20kg
 
   
 

NOTE  these data are for the European barnacle Balanus balanoides, which has a membranous base. Hoever data for other species of adult barnacles, including ones with calcareous bases, have similar attachment strengths.  This suggests that the base has little effect on overall adhesion to the substratum. Little research on attachment has been done on west-coast species 

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Research study 2
 

drawing of longitudinal view of barnacle Balanus nubilis showing cement glands, ducts, and cement layersIn Balanus nubilis the cement glands are intermixed with ovarian follicles in connective tissue. This species has a membraneous base and so the soft tissues are cemented directly to the substratum. Lacombe 1970 Biol Bull 139: 164.photograph of giant barnacle Balanus nubilis surrounded by corallimorpharians Corynactis californica

 
Research study 3
 

drawing of cyprid larva of barnale Balanus glandula showing cement gland and ductThe second type of “adhesion” noted in the introductory part above occurs when the cyprid identifies a suitable spot to settle and metamorphose.  At this time, large paired cement glands within its body release their secretions from openings on the attachment or adhesive organs, cementing the antennules firmly to the substratum.  The glue is a complex insoluble protein that is arguably the most durable and toughest in marine organisms.  The adhesive secretion has low-viscosity at first, but soon hardens.  In species such as Balanus glandula that have a basal plate, calcium secretion and cementing solidifies the photograph of barnacles Balanus glandula showing basal platesbasal plate on which the rest of the body sits.  Metamorphosis involves thickening of this plate by formation of calcified cuticle, migration of the cement glands into the lower lateral portions of the body, and moulting of the larval carapace and exoskeleton In the meantime, the outer test plates begin to be secreted by the cuticle.  As the barnacle grows and its need for cement increases, new cement glands develop and form clusters on either side of the body.  Khandeparker & Anil 2007 Intern J Adhesion Adhesives 27: 165.

NOTE  further details on barnacle growth are available elsewhere in this section of the ODYSSEY: LEARN ABOUT ACORN BARNACLES: FOODS, FEEDING, & GROWTH: GROWTH & ENERGY BUDGETING


Barnacles Balanus glandula showing basal plates remaining after
detachment of several individuals. The body-wall plates attach to the
bases by membranous joinings, and it is the connective tissue in
these joinings that secretes the shell plates for growth 0.33X

 
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