Vol. 60, 2021
(update: 2021.04.14, 06.24)
Description of a New Species of the Marine Flatworm Prosthiostomum (Platyhelminthes: Polycladida) and its Three Known Congeners from Misaki, Japan, with Inference of Their Phylogenetic Positions within Prosthiostomidae
School of Science, Hokkaido University, N10W8, Sapporo, Hokkaido
060-0810, Japan. *Correspondence: E-mail: firstname.lastname@example.org
Received 22 September 2020 / Accepted
6 April 2021
The present study provides
morphological descriptions of four species of Prosthiostomum (Polycladida,
Kato, 1937; P. hibana sp. n.;
P. cf. ostreae Kato, 1937; and P. vulgare Kato, 1938—based on
specimens collected among branching coralline algae and kelp holdfasts
in Misaki, Japan. The new species P.
sp. n. is characterized by i) the dorsal surface of the body covered
with numerous orange maculae, some of which coalesce together to form
larger ones; ii) a pair of linear cerebral-eyespot clusters, each
consisting of relatively few (7–9) cerebral eyespots; iii) 3–4 pairs of
ventral eyespots embedded in parenchyma: iv) the inner wall of the male
atrium deeply ruffled; v) the lumen of the seminal vesicle being narrow
and elongated in shape; and vi) a large sucker situated in the center
of the body. We remark on some morphological characters that were not
mentioned in the original description of P. auratum.
We infer the phylogenetic positions of these four species within
Prosthiostomidae using the maximum-likelihood analysis based on partial
28S rRNA and COI gene
sequences determined de novo, in addition to those that are currently
available in public databases. In the resulting tree, the four species—P. auratum, P. hibana sp. n., P. cf. ostreae, and P. vulgare—were nested in a clade
that was composed of all the other Prosthiostomum
species included in the analysis.
Key words: Cotylea, Phylogeny, Species inquirenda, systematics, taxonomy.
Citation: Tsuyuki A, Kohtsuka H, Kajihara
H. 2021. Description of a new species of the marine flatworm Prosthiostomum
(Platyhelminthes: Polycladida) and its three known congeners from
Misaki, Japan, with inference of their phylogenetic positions within
Prosthiostomidae. Zool Stud 60:29.