Sponges architecture by colour: new insights into the fibres morphogenesis, skeletal spatial layout and morpho-anatomical traits of a marine horny sponge species (Porifera)

This paper focuses on the skeletal architecture and morphotraits of the Mediterranean horny sponge Sarcotragus spinosulus (Demospongiae, Keratosa, Dictyoceratida, Irciniidae). This special endoskeletal system consists of a dense, variably complex connective architecture, which extends throughout the entire sponge body and is embedded in an abundant jelly-like extracellular matrix (ECM). To investigate the topographic arrangement and micro-morphotraits of these connective structures in detail and by colour, also during morphogenetic processes, histology techniques using light microscopy are essential. New information is provided on the coordinated morphogenetic processes that characterize the growth and assembly of collagenic prototype structures in the matrix of fibrous skeletal elements and drive skeleton remodelling. Our results also highlight some novelties and some remarkable peculiarities of fibrous, filamentous and fibrillar components at the levels of both composition and structure. The morphofunctional significance of skeletal architecture is suggested in the background of the anatomical complexity of S. spinosulus

Schmidtea mediterranea phylogeography: an old species surviving on a few Mediterranean islands?

Schmidtea mediterranea (Platyhelminthes, Tricladida, Continenticola) is found in scattered localities on a few islands and in coastal areas of the western Mediterranean. Although S. mediterranea is the object of many regeneration studies, little is known about its evolutionary history. Its present distribution has been proposed to stem from the fragmentation and migration of the Corsica-Sardinia microplate during the formation of the western Mediterranean basin, which implies an ancient origin for the species. To test this hypothesis, we obtained a large number of samples from across its distribution area. Using known and new molecular markers and, for the first time in planarians, a molecular clock, we analysed the genetic variability and demographic parameters within the species and between its sexual and asexual populations to estimate when they diverged. Results: A total of 2 kb from three markers (COI, CYB and a nuclear intron N13) was amplified from ~200 specimens. Molecular data clustered the studied populations into three groups that correspond to the west, central and southeastern geographical locations of the current distribution of S. mediterranea. Mitochondrial genes show low haplotype and nucleotide diversity within populations but demonstrate higher values when all individuals are considered. The nuclear marker shows higher values of genetic diversity than the mitochondrial genes at the population level, but asexual populations present lower variability than the sexual ones. Neutrality tests are significant for some populations. Phylogenetic and dating analyses show the three groups to be monophyletic, with the west group being the basal group. The time when the diversification of the species occurred is between ~20 and ~4 mya, although the asexual nature of the western populations could have affected the dating analyses. Conclusions: S. mediterranea is an old species that is sparsely distributed in a harsh habitat, which is probably the consequence of the migration of the Corsica-Sardinia block. This species probably adapted to temperate climates in the middle of a changing Mediterranean climate that eventually became dry and hot. These data also suggest that in the mainland localities of Europe and Africa, sexual individuals of S. mediterranea are being replaced by asexual individuals that are either conspecific or are from other species that are better adapted to the Mediterranean climate

<i>Schmidtea mediterranea</i> phylogeography: an old species surviving on a few Mediterranean islands?

Background: Schmidtea mediterranea (Platyhelminthes, Tricladida, Continenticola) is found in scattered localities on a few islands and in coastal areas of the western Mediterranean. Although S. mediterranea is the object of many regeneration studies, little is known about its evolutionary history. Its present distribution has been proposed to stem from the fragmentation and migration of the Corsica-Sardinia microplate during the formation of the western Mediterranean basin, which implies an ancient origin for the species. To test this hypothesis, we obtained a large number of samples from across its distribution area. Using known and new molecular markers and, for the first time in planarians, a molecular clock, we analysed the genetic variability and demographic parameters within the species and between its sexual and asexual populations to estimate when they diverged. Results: A total of 2 kb from three markers (COI, CYB and a nuclear intron N13) was amplified from ~200 specimens. Molecular data clustered the studied populations into three groups that correspond to the west, central and southeastern geographical locations of the current distribution of S. mediterranea. Mitochondrial genes show low haplotype and nucleotide diversity within populations but demonstrate higher values when all individuals are considered. The nuclear marker shows higher values of genetic diversity than the mitochondrial genes at the population level, but asexual populations present lower variability than the sexual ones. Neutrality tests are significant for some populations. Phylogenetic and dating analyses show the three groups to be monophyletic, with the west group being the basal group. The time when the diversification of the species occurred is between ~20 and ~4 mya, although the asexual nature of the western populations could have affected the dating analyses. Conclusions: S. mediterranea is an old species that is sparsely distributed in a harsh habitat, which is probably the consequence of the migration of the Corsica-Sardinia block. This species probably adapted to temperate climates in the middle of a changing Mediterranean climate that eventually became dry and hot. These data also suggest that in the mainland localities of Europe and Africa, sexual individuals of S. mediterranea are being replaced by asexual individuals that are either conspecific or are from other species that are better adapted to the Mediterranean climate

Overview of life cycles in model species of the <i>genus Dugesia</i> (Platyhelminthes: Tricladida)

An overview of the reproductive patterns of seven model species of triclads belonging to the genus Dugesia from circum-Mediterranean and Afrotropical freshwater is provided. Populations can reproduce exclusively sexually or exclusively asexually by fissiparity but the coexistence of both reproductive modes is displayed by some lineages. The comparison of data on the life cycles as documented in the literature with new data highlights a wide array of potentialities to shift from an asexual to a sexual state and vice versa in species with fissiparous populations. Life cycles are poorly diversified in species reproducing only sexually. Among fissiparous populations, planarians may sexualise, displaying various grades of reproductive functionality under laboratory conditions. Unexpectedly, asexual reproduction by fission occurred spontaneously in two species during the sexual state of ex-fissiparous individuals. The capacity to develop or reduce the reproductive apparatus during the life cycle either in sexual or in ex-fissiparous individuals illustrates the considerable morphogenetic plasticity in planarians. The Dugesia case contributes to the modelling of reproductive patterns and strategies in basal Metazoa as a continuum from sexual to asexual reproduction and vice versa, rather than a simple clear-cut alternative

Duplominona chicomendesi Curini-Galletti & Stocchino & Norenburg 2019, n. sp.

&lt;i&gt;Duplominona chicomendesi&lt;/i&gt; Curini-Galletti n. sp. &lt;p&gt;(Fig. 5 A&ndash;C)&lt;/p&gt; &lt;p&gt; &lt;i&gt;Holotype&lt;/i&gt;. Puerto Rico: Cayo Turrumote, off Isla Magueyes (Lat. 17.940478, long -67.043068), channels among &lt;i&gt;Montastrea&lt;/i&gt; outcrops, about 10 m deep, in silty medium sand, December 1988: original film and printed pictures of the copulatory structures (SMNH-Type 9179).&lt;/p&gt; &lt;p&gt; &lt;i&gt;Other material&lt;/i&gt;. Same data as holotype, two specimens observed alive, and used for karyology.&lt;/p&gt; &lt;p&gt; &lt;i&gt;Etymology&lt;/i&gt;. The species&rsquo; name honors Chico Mendes (December 15, 1944 &ndash; December 22, 1988), a Brazilian environmentalist, who fought to preserve the Amazon rainforest, and was killed on the very day the holotype of this species was being studied.&lt;/p&gt; &lt;p&gt; &lt;i&gt;Description and Diagnosis&lt;/i&gt;. Similar to &lt;i&gt;Duplominona dissimilispina&lt;/i&gt;, in habitus, arrangement of internal organs, number and position of genital pores (Fig. 5 A). Copulatory organ with a very small cirrus (Figs 5 B, C), with few spines arranged in 5&ndash;7 rows. Proximal spines are 3&ndash;5 &mu;m in length, strongly curved, with a wide, flattened basis, to 3 &mu;m in diameter. In the middle of cirrus, spines are longer, to 7.5 &mu;m, even more curved, with a very slender distal tip. Distalmost spines are smaller, to 2 &mu;m long, straighter, with a wide, flattened basis. Proximally, the cirrus lumen is surrounded by a furrowed pseudocuticula.&lt;/p&gt; &lt;p&gt;Prostatoid stylet about 20 &mu;m long.&lt;/p&gt; &lt;p&gt; &lt;i&gt; &lt;i&gt;Karyotype&lt;/i&gt;.&lt;/i&gt; With n=3, and basic karyotype for the Monocelididae (Curini-Galletti &amp; Martens, 1990); Chromosome pairs I and II markedly differing in length. Karyotype formula: FN=5; Chromosome I: 51.58 &plusmn; 2.81; 46.11 &plusmn; 1.29 (m); Chromosome II: 33.45 &plusmn; 1.53; 45.85 &plusmn; 1.34 (m); Chromosome III: 14.95 &plusmn; 2.46; 8.11 &plusmn; 3.9 (a) (based on 6 plates).&lt;/p&gt;Published as part of &lt;i&gt;Curini-Galletti, Marco, Stocchino, Giacinta A. &amp; Norenburg, Jon L., 2019, New species of Duplominona Karling, 1966 and Pseudominona Karling, 1978 (Platyhelminthes: Proseriata) from the Caribbean, pp. 127-147 in Zootaxa 4657 (1)&lt;/i&gt; on page 136, DOI: 10.11646/zootaxa.4657.1.5, &lt;a href="http://zenodo.org/record/3371005"&gt;http://zenodo.org/record/3371005&lt;/a&gt

Pseudominona cancan Curini-Galletti & Stocchino & Norenburg 2019, n. sp.

&lt;i&gt;Pseudominona cancan&lt;/i&gt; Curini-Galletti n. sp. &lt;p&gt;(Fig. 8)&lt;/p&gt; &lt;p&gt; &lt;i&gt;Holotype&lt;/i&gt;. Panama: Portobelo, Bahia Can Can (Lat. 9.517535, Lon. -79.687392), about 50 cm deep among seagrass, in mixed sediment, March 2016; one specimen sagittally sectioned (USNM 1569257).&lt;/p&gt; &lt;p&gt; &lt;i&gt;Paratype&lt;/i&gt;. Same data as holotype, two specimens sagittally sectioned (USNM 1569258&ndash;1569259).&lt;/p&gt; &lt;p&gt; &lt;b&gt; &lt;i&gt;Other material&lt;/i&gt;.&lt;/b&gt; Same data as holotype, three specimens studied karyologically.&lt;/p&gt; &lt;p&gt;Panama: Bocas del Toro (Lat. 9.352219, Lon. -82.255574). Sheltered beach in front of the Smithsonian Tropical Research Institute, intertidal in medium sand. June 2010; one specimen studied alive.&lt;/p&gt; &lt;p&gt; &lt;i&gt;Etymology&lt;/i&gt;. The species is named after the type locality&mdash; &lt;i&gt;cancan&lt;/i&gt; is a noun used in apposition.&lt;/p&gt; &lt;p&gt; &lt;i&gt;Description&lt;/i&gt;. Animals small, about 1.5 mm long, unpigmented, with the caudal region tripartite, provide with numerous adhesive glands (Fig. 8 A&ndash;C). Rhabdoids rod-shaped, about 5&ndash;7 &mu;m long. Statocyst surrounded by nuclei of the brain cells, and abutting the neuropil. With a short pharynx at about mid-body. Oesophagus less than 1/5 the total length of pharynx.&lt;/p&gt; &lt;p&gt; &lt;i&gt; &lt;i&gt;Male genital system&lt;/i&gt;.&lt;/i&gt; With about 20 testes in two more or less regular rows in front of pharynx (Fig. 8 A, B). With a copulatory organ about 50 &mu;m long and 40 &mu;m high in sections, provided with a thin outer muscular layer, about 1 &mu;m thick. With a nearly spherical seminal vesicle, separated by a muscular septum from a well-developed prostatic vesicle (Fig. 8 E, G). Cirrus short, 25&ndash;30 &mu;m long, provided with 10&ndash;15 rows of acutely triangular spines, 3&ndash;5 &mu;m long, progressively increasing in size distally (Fig. 8 D).&lt;/p&gt; &lt;p&gt;With an ovoid accessory organ, 20&ndash;25 &mu;m across, lined by a muscular coating 2.5 &mu;m thick, and provided with a slender stylet about 22 &mu;m long. The accessory organ opens to the outside through an own pore, just posterior to the male pore (Fig. 8 E, G).&lt;/p&gt; &lt;p&gt; &lt;i&gt; &lt;i&gt;Female genital system&lt;/i&gt;.&lt;/i&gt; Ovaria immediately postpharyngeal. The short oviducts enter a small roundish copulatory bursa (Fig. 8 F), connected to a vaginal duct that runs ventrally and opens close to mouth through the vagina. The female duct widens in front of the copulatory organ, and is surrounded by vacuoles containing sperm in various stages of degradation. The female duct opens to the outside posterior to the accessory organ pore (Fig. 8 G).&lt;/p&gt; &lt;p&gt; &lt;i&gt; &lt;i&gt;Diagnosis&lt;/i&gt;. Species of Pseudominona with tripartite tail. With a short cirrus, with 10&ndash;15 rows of acutely triangular spines, 3&ndash;5 &mu;m long. With a small bursa in front of the copulatory organ, and an external vagina close to mouth. With a prostatoid organ provided with a slender stylet 22 &mu;m long. Pore indices: a:b:c:d = 1: 14: 2: 4.&lt;/i&gt; &lt;/p&gt;Published as part of &lt;i&gt;Curini-Galletti, Marco, Stocchino, Giacinta A. &amp; Norenburg, Jon L., 2019, New species of Duplominona Karling, 1966 and Pseudominona Karling, 1978 (Platyhelminthes: Proseriata) from the Caribbean, pp. 127-147 in Zootaxa 4657 (1)&lt;/i&gt; on pages 141-142, DOI: 10.11646/zootaxa.4657.1.5, &lt;a href="http://zenodo.org/record/3371005"&gt;http://zenodo.org/record/3371005&lt;/a&gt

New species of Duplominona Karling, 1966 and Pseudominona Karling, 1978 (Platyhelminthes: Proseriata) from the Caribbean

Curini-Galletti, Marco, Stocchino, Giacinta A., Norenburg, Jon L. (2019): New species of Duplominona Karling, 1966 and Pseudominona Karling, 1978 (Platyhelminthes: Proseriata) from the Caribbean. Zootaxa 4657 (1): 127-147, DOI: https://doi.org/10.11646/zootaxa.4657.1.

Duplominona aduncospina Curini-Galletti & Stocchino & Norenburg 2019, n. sp.

&lt;i&gt;Duplominona aduncospina&lt;/i&gt; Curini-Galletti n. sp. &lt;p&gt;(Fig. 1)&lt;/p&gt; &lt;p&gt; &lt;i&gt;Holotype&lt;/i&gt;. Panama: Caribbean Sea: Bocas del Toro Is. (Lat. 9.364545, Lon. -82.238835), lower intertidal in coarse sand, sheltered by coral reef, June 2010: one whole mount (USNM-1569236).&lt;/p&gt; &lt;p&gt; &lt;i&gt;Paratypes&lt;/i&gt;. Same data as holotype, nine specimens sagittally sectioned (USNM 1569237&ndash;1569245).&lt;/p&gt; &lt;p&gt; &lt;i&gt;Other material&lt;/i&gt;. Same data as holotype, six specimens studied karyologically.&lt;/p&gt; &lt;p&gt; &lt;i&gt;Etymology&lt;/i&gt;. The name refers to the hook-shaped morphology of the cirrus spines of the new species (lat. &lt;i&gt;aduncus&lt;/i&gt;: hooked).&lt;/p&gt; &lt;p&gt; &lt;i&gt;Description&lt;/i&gt;. A slender, medium-sized monocelid (Fig. 1 A): fixed specimens up to 1.7 mm. Unpigmented. Anterior tip rounded, without sensory stereocilia. Caudal tip with numerous adhesive glands. Epidermis of the insunk type, ciliated all over the body, except for the caudal tip. Statocyst surrounded by nuclei of the brain cells, and abutting the neuropil. Subepidermal musculature weak. Pharynx in the second half of body, up to 175 &mu;m long in fixed specimens, ciliated except for small area at tip where glands discharge, and for a short, pre-oesophageal area, about 10 &mu;m long. Pharyngeal longitudinal and circular musculature poorly developed. The oesophagus is about 1/3 the length of pharynx.&lt;/p&gt; &lt;p&gt; &lt;i&gt; &lt;i&gt;Male genital system&lt;/i&gt;.&lt;/i&gt; With about 20 testes in one medio-ventral row (Fig. 1 A). With an ovoid copulatory organ of the duplex-type, with an outer and an inner muscular layer (Fig. 1 D). The outer muscular layer, about 3 &mu;m thick, wraps the entire copulatory bulb. With a small, nearly spherical seminal vesicle, separated by a weakly-muscular septum from a glandular area (the &lsquo;prostatic vesicle&rsquo;). Distally, a spiny cirrus is present, lined, as most of the prostatic vesicle, by the inner muscular layer. The cirrus, about 50 &mu;m long in squeezed conditions, is provided with a subterminal girdle of spines (Figs 1 B, C). The proximal and the distal portion of the everted cirrus are devoid of spines. The girdle is formed by about 30 spines, arranged in 3&ndash;4 parallel rows. The spines are 2&ndash;3 &mu;m high, with a broad basis (3&ndash;4 &mu;m wide), and a distinctly curved distal tip. In most specimens, proximal spines appear slightly larger than distal spines (Figs 1 B, C).&lt;/p&gt; &lt;p&gt;With a globular accessory organ, about 25 &mu;m across in sectioned specimens, lined by a muscular coating, about 3 &mu;m thick, and provided with a slender, pen-nib shaped stylet 20&ndash;25 &mu;m long. The prostatoid organ opens to the outside with its own pore just anteriorly to the female pore (Fig. 1 D).&lt;/p&gt; &lt;p&gt; &lt;i&gt;Female genital system&lt;/i&gt;. Ovaries ventro-lateral in front of the pharynx. Vitellaria dorso-lateral, extending from in front of testes to the copulatory organ. The narrow, elongate pre-penial bursa is lined by a high, vacuolated epithelium. With a short, wide vaginal duct, which opens to the outside through a vaginal pore, just in front of the male pore. The vaginal duct is surrounded by a thin inner layer of circular musculature and by a much stronger outer layer of short longitudinal fibres (Fig. 1 D). The female duct continues posteriorly to the bursa. It is lined by an irregular epithelium, and opens behind the prostatoid organ pore through the female pore. The distalmost portion of the female duct is surrounded by numerous female glands (Fig. 1 D).&lt;/p&gt; &lt;p&gt; &lt;i&gt;Karyotype&lt;/i&gt;. With n=3, and all chromosomes heterobrachial. Karyotype formula: FN=3; Chromosome I: 43.8 &plusmn; 5.42; 10.3 &plusmn; 4.57 (a); Chromosome II: 36.28 &plusmn; 2.9; 16.71 &plusmn; 2.49 (st); Chromosome III: 19.94 &plusmn; 4.07; 17.23 &plusmn; 2 (st) (based on three plates).&lt;/p&gt; &lt;p&gt; &lt;i&gt; &lt;i&gt;Diagnosis&lt;/i&gt;. Species of Duplominona with up to 20 testes in one row. Cirrus provided with a subterminal girdle of 3&ndash;4 rows of about 30 spines in total, 2&ndash;3 &mu;m high, with a basis 3&ndash;4 &mu;m wide, and markedly curved distal tip. With a long, narrow bursa in front of the copulatory organ. With an external vagina in front of male pore. With an accessory organ provided with a stylet 20&ndash;25 &mu;m long, opening with its own pore, in front of female pore. Karyotype with three pairs of heterobrachial chromosomes. Pore indices: a: b: c: d = &asymp;7: 1: 3.5: 1&lt;/i&gt; &lt;/p&gt;Published as part of &lt;i&gt;Curini-Galletti, Marco, Stocchino, Giacinta A. &amp; Norenburg, Jon L., 2019, New species of Duplominona Karling, 1966 and Pseudominona Karling, 1978 (Platyhelminthes: Proseriata) from the Caribbean, pp. 127-147 in Zootaxa 4657 (1)&lt;/i&gt; on pages 129-131, DOI: 10.11646/zootaxa.4657.1.5, &lt;a href="http://zenodo.org/record/3371005"&gt;http://zenodo.org/record/3371005&lt;/a&gt

Duplominona bocasana Curini-Galletti & Stocchino & Norenburg 2019, n. sp.

&lt;i&gt;Duplominona bocasana&lt;/i&gt; Curini-Galletti n. sp. &lt;p&gt;(Fig. 3 F&ndash;J)&lt;/p&gt; &lt;p&gt; &lt;i&gt;Holotype&lt;/i&gt;. Panama: Caribbean Sea: Bocas del Toro Is. (Lat. 9.364545, Lon. -82.238835), lower intertidal in coarse sand, sheltered by coral reef, June 2010: one whole mount (USNM 1569256).&lt;/p&gt; &lt;p&gt; &lt;b&gt; &lt;i&gt;Other material&lt;/i&gt;.&lt;/b&gt; Same data as holotype, three specimens studied karyologically.&lt;/p&gt; &lt;p&gt; &lt;i&gt;Etymology&lt;/i&gt;. The species is named after the type locality, Bocas del Toro.&lt;/p&gt; &lt;p&gt; &lt;i&gt;Description&lt;/i&gt;. A small species, similar to the previous species in general morphology (Fig. 3 F).&lt;/p&gt; &lt;p&gt; &lt;i&gt; &lt;i&gt;Male genital system&lt;/i&gt;.&lt;/i&gt; With 8&ndash;10 testes in one irregular row. Cirrus about 40&ndash;70 &mu;m long, provided with 8&ndash;15 rows of spines, with relatively few spines per row (Figs 3 G&ndash;J). Proximal spines larger, 5-6 &mu;m long, straight, with narrow bases, 2&ndash;2.5 &mu;m wide, with a somewhat obtuse distal tip. More distally, spines become more curved in shape, with proportionally wider bases. Distalmost spines become progressively smaller, to 2.5&ndash;3 &mu;m high, and 2.5&ndash;3 &mu;m wide. Near the top, spines are small, 1.5&ndash;2.5 &mu;m high, 1.5&ndash;2.5 &mu;m wide, only slightly curved.&lt;/p&gt; &lt;p&gt;Prostatoid organ just posterior to copulatory bulb, opening to the outside through it own pore. Prostatoid stylet about 20 &mu;m long.&lt;/p&gt; &lt;p&gt; &lt;i&gt; &lt;i&gt;Female genital system&lt;/i&gt;.&lt;/i&gt; Ovaria and vitellaria as in previous species. With a distinct bursa just in front of copulatory bulb, with external vagina (Fig. 3 F). Female pore posterior to prostatoid organ pore.&lt;/p&gt; &lt;p&gt; &lt;i&gt; &lt;i&gt;Karyotype&lt;/i&gt;.&lt;/i&gt; With n=3, and all chromosomes acrocentric, different in size. Karyotype formula: FN=3; Chromosome I: 57.8; 10.8 (a); Chromosome II: 25.14; 10 (a); Chromosome III: 17.08; 17.24 (st) (based on one plate).&lt;/p&gt; &lt;p&gt; &lt;i&gt; &lt;i&gt;Diagnosi&lt;/i&gt; s. Small Duplominona species with up to 10 testes in one row. Cirrus long and narrow, with 8&ndash;15 rows of narrowly triangular spines up to 6 &mu;m long proximally, becoming progressively more curved and with wider bases medially. Distal spines progressively smaller, to 1.5 &mu;m long. With a prostatoid organ provided with a stylet 20 &mu;m long. With a bursa and an external vagina opening close to male pore. Female duct and prostatoid organ open to the outside independently. Karyotype with three pairs of acrocentric chromosomes&lt;/i&gt; &lt;/p&gt;Published as part of &lt;i&gt;Curini-Galletti, Marco, Stocchino, Giacinta A. &amp; Norenburg, Jon L., 2019, New species of Duplominona Karling, 1966 and Pseudominona Karling, 1978 (Platyhelminthes: Proseriata) from the Caribbean, pp. 127-147 in Zootaxa 4657 (1)&lt;/i&gt; on page 134, DOI: 10.11646/zootaxa.4657.1.5, &lt;a href="http://zenodo.org/record/3371005"&gt;http://zenodo.org/record/3371005&lt;/a&gt

Duplominona pusilla Curini-Galletti & Stocchino & Norenburg 2019, n. sp.

&lt;i&gt;Duplominona pusilla&lt;/i&gt; Curini-Galletti n. sp. &lt;p&gt;(Fig. 3 A&ndash;E)&lt;/p&gt; &lt;p&gt; &lt;i&gt;Holotype&lt;/i&gt;. Panama: Caribbean Sea: Bastimento Is., off Wild Cane Key (Lat. 9.350423, Lon. -82.165980), mediumcoarse sand at - 7 m, in channels between coral heads, June 2010: one whole mount (USNM 1569253).&lt;/p&gt; &lt;p&gt; &lt;i&gt;Paratypes&lt;/i&gt;. Same data as holotype, two specimens sagittally sectioned (USNM 1569254&ndash;1569255); one specimen studied karyologically.&lt;/p&gt; &lt;p&gt; &lt;i&gt;Other material&lt;/i&gt;. Bastimento Is., off Wild Cane Key (Lat. 9.349746, Lon. -82.166838), medium sand at - 4.5 m, June 2010: two specimens studied karyologically.&lt;/p&gt; &lt;p&gt; &lt;i&gt;Etymology&lt;/i&gt;. The name refers to the diminutive size of the species (lat. &lt;i&gt;pusillus&lt;/i&gt;: small).&lt;/p&gt; &lt;p&gt; &lt;i&gt;Description&lt;/i&gt;. A slender, comparatively very small monocelid (Fig. 3 A); longest fixed specimen about 750 &mu;m long. Rod-shaped rhabdoids, about 2.5 &mu;m long. Statocyst inside brain, abutting its anterior edge. Subepidermal musculature strong. Small pharynx at about mid-body, about 60 &mu;m long. Oesophagus about 1/4 the total length of pharynx.&lt;/p&gt; &lt;p&gt; &lt;i&gt; &lt;i&gt;Male genital system&lt;/i&gt;.&lt;/i&gt; With 8&ndash;10 testes in one irregular row. With a copulatory organ (Figs 3 C, E) about 50 &mu;m long in sections. Outer muscular layer about 2 &mu;m thick. Prostatic tissue poorly developed. The cirrus is about 30 &mu;m in squeezed mounts, with at least 20 rows of densely and regularly packed spines (Figs 3 B, E). Proximal spines scale-like, about 2&ndash;3 &mu;m high and 2&ndash;3 &mu;m broad at basis, with a curved distal tip; medially, spines become progressively smaller, to 1.5 &mu;m in length; distalmost spines are slender, with straight apex, up to 2.5&ndash;3 &mu;m long (Fig. 3 B).&lt;/p&gt; &lt;p&gt;With an elongate accessory organ, about 30 &mu;m long in sections, lined by a strong muscular coating, up to 4 &mu;m thick, and provided with a comparatively broad stylet, about 18 &mu;m long (Figs 3 D, E).&lt;/p&gt; &lt;p&gt; &lt;i&gt; &lt;i&gt;Female genital system&lt;/i&gt;.&lt;/i&gt; Ovaria and vitellaria as in previous species. With a small bursa, about 20 &mu;m across, just in front of the copulatory organ. With a long vaginal duct, surrounded by heavily pigmented (glandular?) tissue; vaginal pore very close to male pore (Figs 3 C, E). Female duct running posteriorly to the bursa, lined by an irregular, vacuolated epithelium. The female duct opens to the outside very close to the pore of prostatoid organ. In living specimens, the two pores appear to be separated, very close to each other. In the sectioned, fully mature specimen, a single pore, where both female duct and prostatoid organ converge, was instead detected (Figs 3 D, E). However, the presence of a ciliated epithelium, similar to the outer body epithelium, between the two ducts, suggests the possibility that this pore fusion may be an artefact due to a strong contraction of the specimen sectioned.&lt;/p&gt; &lt;p&gt; &lt;i&gt; &lt;i&gt;Diagnosis&lt;/i&gt;. A small Duplominona species with up to 10 testes in one row. Cirrus cylindrical, with about 20 rows of scale-like spines proximally, up to 2.5 &ndash;3 &mu;m long and broad, with curved apex; medially, spines are similar but smaller, about 1.5 &mu;m long; distal spines are longer, to 3 &mu;m, straight, and more slender. With a small bursa and an external vagina opening very close to male pore. With a prostatoid organ provided with a broad stylet 18 &mu;m long. Female duct and prostatoid organ open to the outside in close proximity&mdash;may be fused. Pore indices: a:b:c: d =&lt;/i&gt; &asymp;12: &lt;i&gt;1: 4: (?).&lt;/i&gt;&lt;/p&gt;Published as part of &lt;i&gt;Curini-Galletti, Marco, Stocchino, Giacinta A. &amp; Norenburg, Jon L., 2019, New species of Duplominona Karling, 1966 and Pseudominona Karling, 1978 (Platyhelminthes: Proseriata) from the Caribbean, pp. 127-147 in Zootaxa 4657 (1)&lt;/i&gt; on pages 132-134, DOI: 10.11646/zootaxa.4657.1.5, &lt;a href="http://zenodo.org/record/3371005"&gt;http://zenodo.org/record/3371005&lt;/a&gt