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Mesopsammic polyclad members in the family Boniniidae have attracted attention in terms of their evolutionary shifts of microhabitat and their unique morphology such as a pair of pointed tentacles extending from the anterolateral margins and prostatoid organs harbouring stylets. Here, we establish a new species of this family as Boninia panamensis sp. nov. from the Pacific coasts of Panama, based on its morphological characteristics of (i) four cerebral and 61-80 marginal eyespots, (ii) two prostatoid organs located anterior and posterior to the penis papilla, and (iii) two uterine canals departing from the anterior part of the Lang's vesicle. We also report Boninia cf. uru from Hawai'i, USA, based on its morphological identity with B. uru from Okinawa, Japan, along with their genetic distances for the partial cytochrome c oxidase subunit I (COI ) sequences, which were beyond the range of intraspecific differences observed in congeners in this study. Boninia oaxaquensis is also reported from Panama as a new locality for the species. Involving the above-mentioned three species sequenced herein, we reconstructed molecular phylogenetic trees of Boninia based on the four gene markers (18S rDNA, 28S rDNA, 16S rDNA and COI ). Our phylogenetic trees indicated the synapomorphy within the genus Boninia of the small numbers of stylets (2-4) and the connection route of the uterine canals to the Lang's vesicle. The results also showed a characteristic distribution pattern in which pairs of species in distinct lineages occurred sympatrically with different microhabitats, as observed in Boninia uru and Boninia yambarensis in Okinawa and B. panamensis sp. nov. and B. oaxaquensis in Panama. In addition, we discuss possible speciation pathways in this genus based on the tree topology. ZooBank: urn:lsid:zoobank.org:pub:D414BACD-C14A-4B34-8AF9-7ACBA28F46D0.

Eight new species of Duplominona (Platyhelminthes, Proseriata, Monocelididae) are described from the Pacific coast of Panama. They differ from their congeners in the detailed morphology of hard structures associated with the copulatory organ. Duplominona basidilatata n. sp. has a cirrus provided with 5-6 rows of triangular spines, 3-8 μm long, with a large, flat, poorly sclerotized basis. D. hystricina n. sp. has 10-12 rows of needle-shaped spines, 3.5-15 μm long, with a swollen basis. The cirrus of D. hyperhystricina n. sp. is provided with 20-25 rows of slender spines 1.5-9 μm long, with a recurved distal tip. In D. veracruzensis n. sp., cirrus spines increase abruptly in size, from 1.5-2 μm to 6-7 μm. D. uniserta n. sp. has a very long seminal vesicle and a small cirrus, provided with one girdle of hook-shaped spines, 3-5 μm long. D. macrodon n. sp. has one girdle of large, triangular spines, 8-18 μm long. Both D. trimera n. sp. and D. pseudotrimera n. sp. have a tripartite tail, and their cirrus is provided with a stylet. In D. trimera n. sp., the stylet is surrounded by 15-20 rows of spines, 6.5-10 μm long, while D. pseudotrimera n. sp. has 6-8 rows of large spines, 7-22 μm long. D. uniserta n. sp. and D. aduncospina Curini-Galletti, 2019 from the Caribbean coast of Panama have few rows of morphologically nearly identical spines, and are possible candidates as trans-isthmian geminate species. The presence of species with a tripartite tail on both sides of the Isthmus of Panama suggests the possibility of further geminate species pairs; however, no support could be obtained on the basis of the morphology of their hard structures. Five of the eight new species of Duplominona have been found in a single locality, and the diversity of genus along the Pacific coast of Panama may be far higher than present contribution suggests.

Nine new species of Duplominona and one new Pseudominona (Platyhelminthes, Proseriata, Monocelididae) are described from the Caribbean coast of Panama and from Puerto Rico.                Duplominona aduncospina n. sp.; D. terdigitata n. sp.; D. pusilla n. sp.; D. bocasana n. sp. (from Panama) and D. dissimilispina n. sp.; D. chicomendesi n. sp.; D. macrocirrus n. sp.; D. diademata n. sp.; D. puertoricana n. sp. (from Puerto Rico) can be distinguished from the numerous congeneric species based on fine details of the sclerotized structures of the copulatory organ. Duplominona aduncospina n. sp. is characterised by a cirrus provided with 3-4 rows of recurve spines, 2-3 μm long. D. terdigitata n. sp. shows a tripartite tail, and needle-shaped cirrus spines, 1.5-9 μm long. Cirrus spines of D. pusilla n. sp. are scale-like, 1.5-3 μm long. D. bocasana n. sp. has triangular spines, 1.5-6 μm long. D. dissimilispina n. sp. has needle-shaped spines, 3.5-15 μm long. D. chicomendesi n. sp. has a small cirrus, with few, strongly curved spines, 2-7.5 μm long. D. macrocirrus n. sp. has a large cirrus, provided with spines 3-9 μm long, with the longest spines placed medially. D. diademata n. sp. has a cirrus with two separate spiny areas, with spines 7-13 μm long. D. puertoricana n. sp. has a very long cirrus, with poorly sclerotised proximal spines, and distal spines to 6 μm long. A taxonomic key of the genus Duplominona is provided. Pseudominona cancan n. sp. from Panama differs from P. dactylifera from Bermuda, the only species known in the genus so far, for its shorter cirrus and fewer, triangular spines 3-5 μm long, and for the position of the vagina, close to mouth. A specimen attributed to P. dactylifera collected in Puerto Rico is described. Distribution of the new species suggests a complete separation of Panamanian and Puerto Rican proseriate fauna, confirming previous reports of restricted ranges and high endemicity of mesopsammic Platyhelminthes.