Allostoma matsueensis Omi 2026, sp. nov.

Allostoma matsueensis Omi sp. nov. Materials Type status: Holotype. Occurrence: catalogNumber: PL-6488; occurrenceRemarks: specimen represented by serial histological sections; recordNumber: Br- 6; recordedBy: Nao Omi; individualCount: 1; sex: hermaphrodite; lifeStage: adult; occurrenceStatus: present; occurrenceID: E457F203-E4C1-5ED4-B0C2-D1A4C7D76D69; Taxon: scientificName: Allostoma matsueensis; parentNameUsage: Prolecithophora, Pseudostomidae; kingdom: Animalia; phylum: Platyhelminthes; order: Prolecithophora; family: Pseudostomidae; genus: Allostoma; taxonRank: species; Location: continent: Asia; waterBody: Sea of Japan; islandGroup: the Japanese archipelago; country: Japan; countryCode: JP; stateProvince: Shimane; county: Matsue; municipality: Mihonoseki; locality: the coast of Matsue city, Shimane Prefecture, Japan; verbatimCoordinates: 35°33'29.0"N 133°18'31.9"E; decimalLatitude: 35.558056; decimalLongitude: 133.308867; georeferenceProtocol: GPS; Identification: identifiedBy: Nao Omi; Event: samplingProtocol: plankton net; eventDate: 6/20/2020; year: 2020; month: June; day: 20; habitat: marine; Record Level: type: PhysicalObject; language: en; institutionID: https://ror.org/04r8tsy16; institutionCode: NSMT; collectionCode: PL; ownerInstitutionCode: TNS; basisOfRecord: PreservedSpecimen; Material Entity: preparations: histological formalin-fixed, paraffin-embedded serial histological sections Type status: Paratype. Occurrence: catalogNumber: PL-6486; occurrenceRemarks: specimen represented by serial histological sections; recordNumber: Br- 2; recordedBy: Nao Omi; individualCount: 1; sex: hermaphrodite; lifeStage: adult; occurrenceStatus: present; occurrenceID: CBFD9733-74A1-5C97-9324-131D17A98C9B; Taxon: scientificName: Allostoma matsueensis; parentNameUsage: Prolecithophora, Pseudostomidae; kingdom: Animalia; phylum: Platyhelminthes; order: Prolecithophora; family: Pseudostomidae; genus: Allostoma; taxonRank: species; Location: continent: Asia; waterBody: Sea of Japan; islandGroup: the Japanese archipelago; country: Japan; countryCode: JP; stateProvince: Shimane; county: Matsue; municipality: Mihonoseki; locality: the coast of Matsue city, Shimane Prefecture, Japan; verbatimCoordinates: 35°33'29.0"N 133°18'31.9"E; decimalLatitude: 35.558056; decimalLongitude: 133.308867; georeferenceProtocol: GPS; Identification: identifiedBy: Nao Omi; Event: samplingProtocol: plankton net; eventDate: 6/20/2020; year: 2020; month: June; day: 20; habitat: marine; Record Level: type: PhysicalObject; language: en; institutionID: https://ror.org/04r8tsy16; institutionCode: NSMT; collectionCode: PL; ownerInstitutionCode: TNS; basisOfRecord: PreservedSpecimen; Material Entity: preparations: formalin-fixed, paraffin-embedded serial histological sections Type status: Paratype. Occurrence: catalogNumber: PL-6487; occurrenceRemarks: specimen represented by serial histological sections; recordNumber: Br- 4; recordedBy: Nao Omi; individualCount: 1; sex: hermaphrodite; lifeStage: adult; occurrenceStatus: present; occurrenceID: FB84E696-8515-54BF-85E1-EF51E9C8F239; Taxon: scientificName: Allostoma matsueensis; parentNameUsage: Prolecithophora, Pseudostomidae; kingdom: Animalia; phylum: Platyhelminthes; order: Prolecithophora; family: Pseudostomidae; genus: Allostoma; taxonRank: species; Location: continent: Asia; waterBody: Sea of Japan; islandGroup: the Japanese archipelago; country: Japan; countryCode: JP; stateProvince: Shimane; county: Matsue; municipality: Mihonoseki; locality: the coast of Matsue city, Shimane Prefecture, Japan; verbatimCoordinates: 35°33'29.0"N 133°18'31.9"E; decimalLatitude: 35.558056; decimalLongitude: 133.308867; georeferenceProtocol: GPS; Identification: identifiedBy: Nao Omi; Event: samplingProtocol: plankton net; eventDate: 6/20/2020; year: 2020; month: June; day: 20; habitat: marine; Record Level: type: PhysicalObject; language: en; institutionID: https://ror.org/04r8tsy16; institutionCode: NSMT; collectionCode: PL; ownerInstitutionCode: TNS; basisOfRecord: PreservedSpecimen; Material Entity: preparations: formalin-fixed, paraffin-embedded serial histological sections Type status: Paratype. Occurrence: catalogNumber: PL-6489; occurrenceRemarks: specimen represented by serial histological sections; recordNumber: Br- 8; recordedBy: Nao Omi; individualCount: 1; sex: hermaphrodite; lifeStage: adult; occurrenceStatus: present; occurrenceID: AA3FDB8C-2E6D-5371-9B22-F9A666EA3E0E; Taxon: scientificName: Allostoma matsueensis; parentNameUsage: Prolecithophora, Pseudostomidae; kingdom: Animalia; phylum: Platyhelminthes; order: Prolecithophora; family: Pseudostomidae; genus: Allostoma; taxonRank: species; Location: continent: Asia; waterBody: Sea of Japan; islandGroup: the Japanese archipelago; country: Japan; countryCode: JP; stateProvince: Shimane; county: Matsue; municipality: Mihonoseki; locality: the coast of Matsue city, Shimane Prefecture, Japan; verbatimCoordinates: 35°33'29.0"N 133°18'31.9"E; decimalLatitude: 35.558056; decimalLongitude: 133.308867; georeferenceProtocol: GPS; Identification: identifiedBy: Nao Omi; Event: samplingProtocol: plankton net; eventDate: 6/20/2020; year: 2020; month: June; day: 20; habitat: marine; Record Level: type: PhysicalObject; language: en; institutionID: https://ror.org/04r8tsy16; institutionCode: NSMT; collectionCode: PL; ownerInstitutionCode: TNS; basisOfRecord: PreservedSpecimen; Material Entity: preparations: formalin-fixed, paraffin-embedded serial histological sections Type status: Paratype. Occurrence: catalogNumber: PL-6490; occurrenceRemarks: specimen represented by serial histological sections; recordNumber: Br- 12; recordedBy: Nao Omi; individualCount: 1; sex: hermaphrodite; lifeStage: adult; occurrenceStatus: present; occurrenceID: 9A84CA47-00CC-5580-AFC4-A354FC1A4C12; Taxon: scientificName: Allostoma matsueensis; parentNameUsage: Prolecithophora, Pseudostomidae; kingdom: Animalia; phylum: Platyhelminthes; order: Prolecithophora; family: Pseudostomidae; genus: Allostoma; taxonRank: species; Location: continent: Asia; waterBody: Sea of Japan; islandGroup: the Japanese archipelago; country: Japan; countryCode: JP; stateProvince: Shimane; county: Matsue; municipality: Mihonoseki; locality: the coast of Matsue city, Shimane Prefecture, Japan; verbatimCoordinates: 35°33'29.0"N 133°18'31.9"E; decimalLatitude: 35.558056; decimalLongitude: 133.308867; georeferenceProtocol: GPS; Identification: identifiedBy: Nao Omi; Event: samplingProtocol: plankton net; eventDate: 6/20/2020; year: 2020; month: June; day: 20; habitat: marine; Record Level: type: PhysicalObject; language: en; institutionID: https://ror.org/04r8tsy16; institutionCode: NSMT; collectionCode: PL; ownerInstitutionCode: TNS; basisOfRecord: PreservedSpecimen; Material Entity: preparations: formalin-fixed, paraffin-embedded serial histological sections Description Allostoma matsueensis exhibits a short, cylindrical body form, measuring 884 ± 132.9 µm in length and 316 ± 62.9 µm in width (n = 9), based on measurements taken from fully extended live specimens (Fig. 1 c). The anterior end is rounded with a single ciliated groove near the brain, while the posterior end is slightly tapered. The species is characterized by a yellow to pale brown body with pigmentation present in the body parenchyma, and a brown intestine (Fig. 1 a, c). The frontal gland is present on the ventral side of the anterior end and both cyanophil and erythrophil (Fig. 2 b). Two pairs of black-pigmented eyes are located anteriorly, partially embedded in the brain capsule. The posterior eyes are heart-shaped (two lenses), and the anterior eyes are round (one lens) (Fig. 1 a, b, Fig. 2 a, Fig. 3 a). The brain is encapsulated, positioned posterior to the eyes and testis, with the nuclei layer directly underlying the extracellular-matrix (ECM) membrane (Fig. 1 b, Fig. 2 a, b, Fig. 3 a). The pharynx is positioned posterior to the intestine, near the posterior body end. The pharynx narrows and becomes folded proximally, and corresponds to a pharynx variabilis, consistent with other prolecithophorans. Two types of pharyngeal glands are present: (1) an erythrophil granular gland type and (2) a cyanophil smooth-textured gland type. The nuclei of both gland types are clustered around the proximal pharyngeal base, whereas their glandular extensions and secretory regions continue distally toward the distal end of the pharynx. It comprises circular, longitudinal, and radial muscles organized into inner and outer muscular layers (muscularis interna and externa) and is ciliated on both internal and external surfaces (Fig. 1, Fig. 2 b). The esophagus is short (Fig. 2 b). The pharynx and penis open into a common atrium. The atrium is lined with ciliated epithelial cells, the pharyngeal and genital regions of the atrium are partially delimited by a zone of dense extracellular-matrix (ECM) fibers continuous with the basement membrane, without forming a complete partition (Fig. 1 b, Fig. 2 a, b, Fig. 3 d, e). The thin ECM-membraned intestine lies posterior to the testis (Fig. 1, Fig. 2). The common oral – genital pore is surrounded by erythrophil granular glands and is circular muscle fibers forming a sphincter; these fibers are distributed along the length of the common pore and interdigitate with the basement membrane, rather than forming a single sharply delimited muscular ring in one plane of the section. In individual sections these fibers appear as discrete profiles embedded within the ECM (Fig. 1 b, Fig. 2 b, Fig. 3 h). Regarding the male system, the testis is located near the anterior end (Fig. 1 b, Fig. 2 a). Two vasa deferentia extend from the testis, passing laterally through the intestine to connect with the paired seminal vesicles (Fig. 1 a, Fig. 3 b). The seminal vesicles subsequently join the granular vesicle via a narrow tube (Fig. 1 a, b, Fig. 3 c). The male copulatory organ is located posterior to the pharynx and consists of a pear-shaped gr