Abstract:
Ceratocorys armata, C. gourretii, and C. horrida have historically been treated
as distinct species based on morphology. Both field samples and cultured
strains, however, exhibit continuous morphological variation and intergradations between these taxa. Here, strains from Viet Nam, Japan (Pacific Ocean),
and France (Mediterranean Sea, Atlantic Ocean) were analyzed using integrated morphomolecular approaches. Cultured strains revealed morphological intergradations from C. horrida to C. armata and from C. armata to
C. gourretii. Phylogenetic analysis based on the ITS1-5.8S-ITS2 rDNA region
sequences and the SSU (18S) and LSU (28S) nuclear rDNA gene
sequences confirmed the genetic identity of these three taxa for these
markers. The ITS2 secondary structure comparisons—including C. malayensis
from Viet Nam and Malaysia—further supported their conspecificity, while validating
C.malayensis as a distinct species. Based on these data, we have proposed to
treat them as formae: C. horrida f. horrida, C. horrida f. armata, and C. horrida
f. gourretii. Furthermore, our results indicated that C. malayensis strains from
Viet Nam are non-toxic. We have also provided morphological descriptions and illustrations of C. bipes and C. magna, two species rarely reported in the AsiaPacific region, enhancing the taxonomic clarity of the genus.