38
3.4
Polydora aura (Fig. 1f )
3.4.1 Morphological Characteristics
Medium- to large-sized worms. The body and
palps are light orange but some worms without
conspicuous color. A short inconspicuous occipital tentacle is present. Special notochaetae are
present in the posterior chaetigers which exhibit
tight cylindrical bundles of short needles.
3.4.2 Biological and Ecological
Characteristics
All the larvae in the capsule developed simultaneously and revealed planktotrophic development. Little is currently known about other
characteristics, i.e., life history or reproductive
characteristics. As for P. haswelli , this species
was very large in size and common in South
Korean mollusk shells (Sato-Okoshi et al.
2012 ). The species caused severe infestations in
many commercially important shells, but again
appears limited to South Korea (Sato-Okoshi
et al. 2012 ).
4
Phylogenetic Analysis of 18S
rRNA Gene Sequences
Misidentifi cation and taxonomic confusion of
Polydora species often arise because of a lack
of effi cient morphological key characteristics
and a high degree of intraspecifi c variation.
In recent years, an increasing number of taxonomic studies are relying on molecular methods
for accurate species identifi cation. 18S rRNA
gene sequences of seven Polydora species
( P. onagawaensis , P. calcarea , P. brevipalpa ,
P. websteri , P. haswelli , P. aura , and P. uncinata )
have been analyzed (Sato-Okoshi and Abe 2012 ,
2013 ; Teramoto et al. 2013 ). The results of these
studies showed that the nucleotide sequence of
the 18S rRNA gene was completely identical
within a species even between separate populations and distinct between different species
(Fig. 3 ). Therefore, 18S rRNA gene analysis is
an effective tool for the identifi cation of these
Polydora species, including the four species
described above.
5
Discussion and Conclusion
As little data exists on the species characteristics
of Boccardia knoxi , a species reported to be a
severe shell-boring parasite of abalone shells by
Lleonart et al. ( 2003 ), it should be considered as
the focus of future studies. Additionally, discriminating between the morphologically identical
species P. hoplura and P. uncinata , for which
only P. uncinata has undergone molecular analysis (Sato-Okoshi and Abe 2012 ), remains problematic. As such, only data from P. uncinata will
be presented here. The key morphologically
identifying characteristics of these four species
are summarized in Table 2 .
The Polydora species differed according to
locality and in their host shells. The species considered to be the most damaging to East Asian and
Australian aquaculture were P. brevipalpa ,
P. uncinata , P. haswelli , and P. aura . It is now possible to speculate that some of these species have
been transported all over the world with commercially important host shells over a prolonged
period of time, making it diffi cult or impossible to
trace their origins. It has been demonstrated that
once invasive nonindigenous species successfully
are introduced to an area, it is very hard and costly
to eradicate them (Miura 2007 ). Although it is diffi cult to prevent polydorid infestation after they
succeed in boring into the shells, one of the most
effective ways to avoid their infl uences may be
preventing their early settlement on shells applying their life history traits. However, the harmful
species tended to be continuous breeders and have
high reproductive ability and possess long life
span, so as a result, they show long settling periods. Moreover, once P. uncinata is introduced to
the land-based tank- cultured system, the species
has the capacity to increase its population
rapidly according to its direct development.
W. Sato-Okoshi et al.
3.4
Polydora aura (Fig. 1f )
3.4.1 Morphological Characteristics
Medium- to large-sized worms. The body and
palps are light orange but some worms without
conspicuous color. A short inconspicuous occipital tentacle is present. Special notochaetae are
present in the posterior chaetigers which exhibit
tight cylindrical bundles of short needles.
3.4.2 Biological and Ecological
Characteristics
All the larvae in the capsule developed simultaneously and revealed planktotrophic development. Little is currently known about other
characteristics, i.e., life history or reproductive
characteristics. As for P. haswelli , this species
was very large in size and common in South
Korean mollusk shells (Sato-Okoshi et al.
2012 ). The species caused severe infestations in
many commercially important shells, but again
appears limited to South Korea (Sato-Okoshi
et al. 2012 ).
4
Phylogenetic Analysis of 18S
rRNA Gene Sequences
Misidentifi cation and taxonomic confusion of
Polydora species often arise because of a lack
of effi cient morphological key characteristics
and a high degree of intraspecifi c variation.
In recent years, an increasing number of taxonomic studies are relying on molecular methods
for accurate species identifi cation. 18S rRNA
gene sequences of seven Polydora species
( P. onagawaensis , P. calcarea , P. brevipalpa ,
P. websteri , P. haswelli , P. aura , and P. uncinata )
have been analyzed (Sato-Okoshi and Abe 2012 ,
2013 ; Teramoto et al. 2013 ). The results of these
studies showed that the nucleotide sequence of
the 18S rRNA gene was completely identical
within a species even between separate populations and distinct between different species
(Fig. 3 ). Therefore, 18S rRNA gene analysis is
an effective tool for the identifi cation of these
Polydora species, including the four species
described above.
5
Discussion and Conclusion
As little data exists on the species characteristics
of Boccardia knoxi , a species reported to be a
severe shell-boring parasite of abalone shells by
Lleonart et al. ( 2003 ), it should be considered as
the focus of future studies. Additionally, discriminating between the morphologically identical
species P. hoplura and P. uncinata , for which
only P. uncinata has undergone molecular analysis (Sato-Okoshi and Abe 2012 ), remains problematic. As such, only data from P. uncinata will
be presented here. The key morphologically
identifying characteristics of these four species
are summarized in Table 2 .
The Polydora species differed according to
locality and in their host shells. The species considered to be the most damaging to East Asian and
Australian aquaculture were P. brevipalpa ,
P. uncinata , P. haswelli , and P. aura . It is now possible to speculate that some of these species have
been transported all over the world with commercially important host shells over a prolonged
period of time, making it diffi cult or impossible to
trace their origins. It has been demonstrated that
once invasive nonindigenous species successfully
are introduced to an area, it is very hard and costly
to eradicate them (Miura 2007 ). Although it is diffi cult to prevent polydorid infestation after they
succeed in boring into the shells, one of the most
effective ways to avoid their infl uences may be
preventing their early settlement on shells applying their life history traits. However, the harmful
species tended to be continuous breeders and have
high reproductive ability and possess long life
span, so as a result, they show long settling periods. Moreover, once P. uncinata is introduced to
the land-based tank- cultured system, the species
has the capacity to increase its population
rapidly according to its direct development.
W. Sato-Okoshi et al.