title used in learnabout sections of A SNAIL'S ODYSSEY
  Reproduction
   
 

photograph of parchment worm Chaetopterus sp. releasing sperm, courtesy Kevin Lee, Fullerton, CaliforniaPolychaetes as a group have a broad spectrum of reproductive modes. Within tubeworms there are species that broadcast gametes, considered here, and SPECIES THAT BROOD OUTSIDE OF TUBE, SPECIES THAT BROOD INSIDE OF TUBE, and SPECIES THAT ARE POECILOGONOUS, considered in other sections. There is also a general section on LARVAE. Photograph courtesy Kevin Lee, Fullerton, California diverKevin

 

 

 

 

Parchment worms Chaetopterus sp. spawning. At
least one of the worms is a male, emitting sperm 1X

 
  Species that broadcast gametes
  black dot
Research study 1
 

West-coast tubeworms Dodecaceria fewksii inhabit calcareous tubes and live in large, sprawling colonies.  Interestingly, the members of a colony consist of a single sex, likely a result of of cloning via autotomy and then regeneration of parts.  The pattern, described earlier for a European species Dodecaceria caulleryi, is thought by the authors perhaps also to apply to D. fewksii.  In this unique pattern, a portion of the middle part of the body separates into 2 individual segments plus the original head and tail.  Each of the 2 segments sprouts 2 buds, which grow to small adult-stage, then separate.  The segments repeat this process one more time, then die.  All 4 buds photograph of cirratulid worms Dodecaceria fewksii with other invertebratesbecome adults of the same sex as the original worm.  Additionally, the head and tail ends regenerate. Each  of these components has the potential to drift or swim off to form a new colony. The process was originally termed schizometamery but, possibly for reason of its rarity, the discriptor seems not to be in current use.  The present studies on D. fewksii from Vancouver Island, British Columbia reveal that individuals undergo sexual reproduction, with release of gametes, and development to a trochophore larval stage and to early segmentation (see drawings below).  Settlement and metamorphosis are not observed by the authors in their laboratory cultures.  A follow-up study would be justified to check if D. fewksii also reproduces asexually as described for D. caulleryi above. Berkeley & Berkeley 1954 J Fish Res Bd Can 11: 326.

NOTE Dehorne 1933 Bull Biol France Belgique 67: 298

A group of black-tentacled cirratulids Dodecaceria fewksii
partly overgrown by a colonial tunicate. Several solitary
tunicates Styela montereyensis appear to be gradually losing
out to the colonial species in the competition for space 0.5X

 

drawing of egg stage of development of the tubeworm Dodecaceria fewksii

Egg of D. fewksii. Scale bar is the same for all drawings

drawing of 24-h trochophore stage of development of the tubeworm Dodecaceria fewksii
24h trochophore stage
drawing of 48-h larval stage of development of the tubeworm Dodecaceria fewksii
48h larva
drawing of 72-h larval stage of development of the tubeworm Dodecaceria fewksii
72h larva
drawing of 100-h larval stage of development of the tubeworm Dodecaceria fewksii
100h larva
 
Research study 2
 

photograph of several colorful serpulid worms Serpula columbianaIntertidal tubeworms Serpula columbiana in San Juan Islands, Washington are reproductive in spring and summer, and freely spawn their eggs and sperm.  Spawning can be induced by disturbance, such as by blowing (with compressed air) the worm out of its tube into a fingerbowl.  The embryos hatch as trochophore larvae within a day of fertilisation and can be raised on cultured flagellates Dunaliella.  A single brilliant red eyespot or ocellus is present at this time.  By 26d at 12oC segmentation commences, 2 eyespots are prominent, and the larva is known as a metatrochophore. At 30d of age, setae appear on the nectochaete larva, and it settles to the bottom and begins crawling about. Metamorphosis occurs at 50d and the little worm now has a well-defined head with tentacle buds.  The larvae are photopositive up until about 25d, after which they become strongly photonegative.  Even the newly hatched trochophores swim upwards to the light but, as they lack eyespots, it is assumed that they are responding negatively to gravity.  The benthic nectochaete larvae appear to be indifferent to light, but at metamorphosis they orient the aperture of their tubes away from the light. The authors suggest that the eyespots in the swimming larvae may function in daily (diel) migrations - towards the surface at night and away during the day – possibly to avoid being eaten by visual predators.  These ideas, however, are based on laboratory observations, and it is not known whether the larvae behave in this way in the field.  Young & Chia 1982 Biol Bull 162: 457.




Several serpulid worms Serpula columbiana.
No research appears to have been done on the
variable colours in this species 0.7X




Developmental stages highlighted in black in the above account are shown in the photos below:

 
photograph of a 3-d trochophore larva of the serpulid worm Serpula columbiana courtesy Young & Chia 1982 Biol Biol 162: 457
3d trochophore larva
photograph of 26-d metatrochophore larva of a serpulid worm Serpula columbiana courtesy Young & Chia 1982 Biol Biol 162: 457
26d metatrochophore larva
photograph of a 30-d larva of a serpulid worm Serpula columbiana courtesy Young & Chia 1982 Biol Biol 162: 457
30d nectochaete larva
photograph of a 50-d larva of a sabellid worm Serpula columbiana courtesy Young & Chia 1982 Biol Biol 162: 457
50d larva at metamorphosis
 
Research study 3
 

graph showing percentage metamorphosis of polychaete worms Phragmatopoma californica in response to different concentrations of fatty acids in the sand on which the larvae are settlingSexes are separate in the southern California reef-building tube worm Phragmatopoma californica and gametes are freely spawned.  After several weeks or months feeding in the plankton, the larvae settle, often gregariously with adults. 

Experiments at the Scripps Institution of Oceanography, La Jolla, California show that several free fatty acids (FFA) present in the sand/organic-cement matrix of adut tubes actively stimulate the larvae to settle and metamorphose. Response of the larvae is dosage-dependent, as shown in the accompanying histogram for a known inducer fatty acid, palmitoleic acid (16:1).  Note that settlement is less for another fatty acid, eicosapentaenoic acid (20:5), and larvae develop abnormally in high concentrations of this substance. In a follow-up study, the research group determines that settlement of Phragmatopoma larvae is enhanced in higher current flows.  This is because the photograph of tubeworms Phragmatopoma californica courtesy Lovell & Libby Xlarvae tumble along the bottom and are brought into more intimate contact with inducer chemicals in the sand.  In slower flows, the larvae swim along in the water column and make less contact with the sand. This behaviour of larvae in different flow conditions may play an important role in their recruitment. Pawlik 1986 Mar Biol 91: 59; Pawlik et al 1991 Science 251: 421; Pawlik & Faulkner 1986 J Exp Mar Biol Ecol 102: 301; for a comparison of settling characteristics of P. californica with those of a European counterpart Sabellaria alveolata see Pawlik 1988 J Mar Biol Ass UK 68: 101. Photograph courtesy Lovell & Libby Langstroth, California and calphotos.edu.

NOTE  the researchers employ a racetrack-design flume tank with a 6-m straightaway containing an array of experimental sediments on its bottom.  Treatments include sands containing different concentrations of FFAs previously shown to be inductive (e.g., palmitoleic acid, 16:1) and non-inductive (e.g., palmitic acid, 16:0), sand from tubes of adult worms, and appropriate controls.  Larval-mimicking polystyrene spheres are also employed to monitor flow characteristics of the design


Part of a colony of tubeworms Phragmatopoma
californica.
Note the sand-grain type of
construction of the tubes 4X

 
Research study 4
 

A study at the Bamfield Marine Sciences Centre, British Columbia provides details of aging effects on reproduction in lecithotrophic tube-dwelling Capitella sp.  During their life-span of just a few months, females spawn an average of 3 times at monthly intervals with a total output of 2100 eggs.  For individuals that spawn up to 5 times, fecundity holds steady at about 700 eggs per spawning over the first 3 events, then declines rapidly over subsequent spawnings to levels of about 400 eggs per event.  Energy content of eggs likewise declines from the third spawning from 80µJ per egg to about 55µJ.  Older individuals thus produce fewer eggs of poorer quality than younger individuals. Interestingly, the individuals of this species when raised from juvenile stage in isolation behave hermaphroditically, and are able to produce fertilised eggs and viable larvae.  Qian & Chia 1992 J Exp Mar Biol Ecol 156: 23.

NOTE  at the time of publication this species was undescribed

 
Research study 5
 

photograph of sabellid worm Schizobranchia insignisdrawing of trochophore larva of a sabellid wormA researcher at Friday Harbor Laboratories, Washington provides the first detailed description of early development of the free-spawning sabellid Schizobranchia insignis.  Males spawn before females, and fertilisation occurs in the open water.  A trochophore larval stage is reached after 2d, and the first chaetiger (= setiger) stage after 4d (see photos below).  A larva is competent to settle after only 3d, but this may be delayed for several weeks if suitable substratum is not available.  The newly settled juvenile immediately constructs a tube, and feeding commences after about a week.  Interestingly, although the larva bears all of the requisite ciliary bands for capturing, concentrating, and transporting food particles to the mouth, the particles are rejected because a functional gut is absent (see drawing on Right).  Now, evolutionary loss of feeding in marine invertebrates, including several tubeworms, is often accompanied by loss of feeding structures.  Their persistence in S. insignis suggests that their evolutionary loss has been recent, that the ciliary bands are relatively inexpensive to construct and operate, or that some other function is being served by them.  The author remarks that the ability to feed tends to be lost in larvae of polychaetes following an evolutionary increase in egg size.  Because more energy provided in the egg would permit the larva to complete its development without particulate food, this logically seems the order followed in evolution.  Pernet 2003 Biol Bull 205: 295.

NOTE  the author includes descriptions of 3 other sabellid species Demonax medius, Myxicola aesthetica, and Pseudopotamilla occelata, the first being a brooding species, the last 2 also being broadcast spawners.  Most detail is provided for S. insignis, and it is the only one featured here

NOTE  these are commonly referred to as “opposed-band”, for the prototroch cilia, located anterior to the mouth, beat from anterior to posterior and are involved in swimming and feeding (in species that take food), while the metatroch cilia, located posterior to the mouth, beat from posterior to anterior, and area also involved in feeding.  Food particles caught between these bands are transported to the ventral mouth by cilia of the food groo

 
photograph of fertilised egg of the sabellid worm Schizobranchia insignis photograph of the trochophore larva of a sabellid Schizobranchia insignis photograph of a 14d larva of the sabellid tubeworm Schizobranchia insignis
Egg diameter is 155um before fertilisation and about 185um after 3d trochophore larva showing opposed ciliary bands and ventral (non-functional) mouth 14d larva bearing 3 segments known as chaetigers. The author does not follow development through to juvenile with functioning mouth and gut
 
Research study 6
 

photographs of a few developmental stages of the polychaete worm Owenia collaris, courtesy Smart & Dassow 2009 Biol Bull 217: 253A study on reproduction in the small, tube-dwelling polychaete Owenia collaris at the Oregon Institute of Marine Biology and Friday Harbor Laboratories, Washington provides information on early development and metamorphosis for Family Oweniidae.  Fertilisation after broadcast spawning leads within 12-24h to a free-swimming gastrula and then to a feeding mitraria larva within 48h (10-13oC, see photographs on Left). Metamorphic competence is attained after about 4wk in culture. 

photographs of a juvenile polychaete worm Owenia collaris, courtesy Smart & Dassow 2009 Biol Bull 217: 253By 3d after metamorphosis the juveniles, now about 1.2mm in length, are gathering sand grains to make their tubes (see photograph on Right). The authors note several unexpected features of development in common with deuterostomes, including the blastopore forming the anus, in contrast to it forming the mouth in other protostomes, suggesting that protostomial development may be more plastic than once thought.  Smart & Dassow 2009 Biol Bull 217: 253. Photographs courtesy the authors.

NOTE  larvae are fed in laboratory culture on 1:2 mixture of Rhodomenas lens  and Isochrysis galbana

 
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