Promesostoma baculum, Diez & Monnens & Wuyts & Brendonck & Reygel & Schmidt-Rhaesa & Artois, 2023

Diez, Yander L., Monnens, Marlies, Wuyts, Arlien, Brendonck, Luc, Reygel, Patrick, Schmidt-Rhaesa, Andreas & Artois, Tom, 2023, Taxonomy and phylogeny of Dalytyphloplanida Willems et al., 2006 (Platyhelminthes: Rhabdocoela), with the description of a new family, a new genus, and sixteen new species from Cuba and Panama, Organisms Diversity & Evolution (New York, N. Y.) 23 (4), pp. 631-681 : 654-656

Promesostoma Graff, 1882

Promesostoma baculum sp. n. Diez, Reygel & Artois ( Figs. 12a–c and 15a )

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Promesostoma sp. 2 in Diez et al. (2023)

Material and distribution. Cuba: Observations on one live animal, whole mounted afterwards, designated holotype ( ZMH, No. V13686 ), collected in Bueycabón (type locality) (February 21, 2018); sublittoral, on the alga Gelidiella acerosa , 0.5 m deep, salinity 33 ‰.

Etymology. Species named after the walking-stick-shaped stylet. Lat. Baculum: walking stick.

Diagnosis. Species of Promesostoma with eyes. Copulatory bursa present. Seminal vesicle, prostate vesicle and male atrium with stylet located latero-caudal to the pharynx. Slightly curved stylet 93 µm long, with the proximal funnel bent over about 90°. Tubular part of the stylet 2–3 µm wide, ending in a widened (5 µm) and oblique distal tip. Seminal vesicle oriented forward, surrounded by a strong sphincter at the connection to the prostate vesicle.

Description. The overall organisation is comparable to that of other species of Promesostoma (see Luther, 1943; Ax, 1951, 1952; Karling, 1967). The live animal is about 1 mm long, translucent, with two eyes ( Fig. 12a : e). Anterior adenal rhabdite tracts present ( Fig. 12a : ar). The pharynx ( Fig. 12a : ph) is located at 50%.

The testes ( Fig. 12a : t) are located anterior to the pharynx. The vasa deferentia fuse and form a single seminal vesicle. The seminal vesicle, the prostate vesicle and the stylet are located latero-caudal to the pharynx. On the whole mount it was impossible to infer whether or not the seminal vesicle is surrounded by a muscle layer. The seminal vesicle ( Fig. 12a, b : sv) is oriented forwards and opens into the prostate vesicle, running axially through it ( Fig. 12a, b : pv). A sphincter ( Fig. 12b : sph1) surrounds the connection between the seminal and the prostate vesicle. The slightly curved stylet ( Figs. 12a, b and 15a : st 12c) is 93 µm long, with the proximal funnel bent over ~ 90° relative to the tubular part. The funnel is 9 µm long, 6 µm wide proximally, and 3 µm wide distally. The base of the funnel is surrounded by a sphincter ( Fig. 12b : sph2). The tubular part of the stylet is 2–3 µm wide and ends in a widened (5 µm), oblique tip. At the location where the stylet bends, the male atrium ( Fig. 12b : cb) receives the male copulatory bursa ( Fig. 12a, b : mb; terminology of Karling, 1967).

The paired vitellaria ( Fig. 12a : vi) extend laterally, from the eyes to the caudal body end. The globular ovaries ( Fig. 12a : ov) are located caudal to the pharynx.

Promesostoma cubanum sp. n. Diez, Reygel & Artois ( Figs. 12d–f and 15b )

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Promesostoma sp. 1 in Diez et al. (2023)

Material and distribution. Cuba: Observations on live animals, whole mounted afterwards. Three whole mounts from Bueycabón (type locality) (6 February and 25 May 2018), one of which is designated holotype ( ZMH, No. V 13687) and the others paratypes (HU, No. 871–872), and one specimen used for molecular analyses; on leaves of T. testudinum and S. filiforme and the alga G. rugosa , 0.5 m deep, salinity 32‰. Two whole mounts from Sardinero (March 18, 2021), sublittoral, 0.5 m deep, on leaves of the turtlegrass Thalassia testudinum , salinity 32‰ (HU XIX.4.11– XIX.4.12).

Etymology. Species named after the island of Cuba.

Diagnosis. Species of Promesostoma with eyes. Copulatory bursa lacking. Seminal vesicles, prostate vesicle, and male atrium with stylet located caudal to the pharynx. Slightly curved stylet ~ 106 µm long, with a circular extension surrounding the stylet proximally and ending in a slightly swollen, rounded tip. A bipartite structure runs adjacent to the male atrium; consisting of a pronounced muscular part and a smaller, sperm-containing vesicle devoid of musculature.

Description. The overall organisation is comparable to that of other species of Promesostoma (see Luther, 1943; Ax, 1951, 1952; Karling, 1967). Measured on the whole mounts, animals are 0.5–1 mm long (x = 0.7 mm; n = 3), translucent, with a pair of kidney-shaped eyes ( Fig. 12d : e). Anterior adenal rhabdite tracts present ( Fig. 12d : ar), with the cell bodies caudal to the eyes, their necks in between the eyes and opening terminally at the anterior end of the body. The pharynx ( Fig. 12d : ph) is located at 50%, with a diameter of 68–114 µm (x = 94 µm; n = 3), measured on the whole mounts.

The testes ( Fig. 12d : t) are located anterior to the pharynx. The seminal vesicles, the prostate vesicle, and the male duct ( Fig. 12e : md) are located caudal to the pharynx. The seminal vesicles ( Figs. 12d–e and 15b : sv) are oriented backward and fuse just before entering the prostate vesicle ( Figs. 12d–e and 15b : pv), forming a seminal duct that runs axially through the prostate vesicle. It is not clear from the available material whether or not the seminal vesicles are surrounded by a muscle layer. The slightly curved stylet ( Figs. 12d–e and 15b : st, 12f) is 93–103 µm long (x = 106 µm; n = 5). Its proximal funnel is 7–10 µm long (x = 9 µm; n = 5), 11–18 µm wide proximally (x = 17 µm; n = 5), and 4–6 µm wide distally (x = 5 µm; n = 5). Its proximal rim is slightly folded backwards. Somewhat distally to the funnel, a circular extension surrounds the stylet. Distally to this extension, the stylet is tubular, 7–8 µm wide proximally (x = 7 µm, n = 5), 5–6 µm wide medially (x = 5 µm; n = 5), and 6–8 µm wide distally (x = 7 µm; n = 5). The distal tip of the stylet is a bit wider, with the opening exactly terminal.

A very muscular and cylindrical structure ( Figs. 12d–e and 15b : x) runs adjacent to the copulatory bulb. From the whole mounts, it is impossible to discern whether this structure is part of the male or the female system. Proximally, this structure continues in a non-muscular receptacle containing sperm ( Fig. 12e : sr). The paired vitellaria ( Fig. 12d : vi) extend along both sides of the body, from the eyes to the caudal body end. The oval ovaries ( Fig. 12d : ov) are located caudal to the copulatory bulb.

Figures

Fig. 12 a–c Promesostoma baculum sp. n. d, e Promesos- toma cubanum sp. n. a, d Body organisation. b, e Schematic reconstruction of the male genital structures. c, e Stylet (from the holotype). Structures oriented with the anterior end toward the top of the plate

Fig. 15 Male genital structures in the new species of Promesos- toma (from the holotype). a Promesostoma baculum sp. n. b Promesostoma cubanum sp. n. c Promesostoma cubitum sp. n. d Promesostoma panamaense sp. n. e Promesostoma roseaphar- ynx sp. n. f Promesostoma toryne sp. n. a, d–e Structures oriented with the anterior end toward the left side of the plate. b, c, f Structures oriented with the anterior end toward the top of the plate