Abstract

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.