Duplominona trimera Curini-Galletti n. sp.

(Fig. 5)

Holotype. Gulf of Panama, Playa Venado (Veracruz, Panama)(Lat. 8°53’27.07”N; Lon. 79°35’44.16”W), intertidal in silty coarse sand, December 2011: one specimen sagittally sectioned (USNM 1622585)

Paratypes. Same data as holotype, five specimens sagittally sectioned (USNM 1622586; USNM 1622587; USNM 1622588; USNM 1622589; USNM 1622590) .

Other material. Same data as holotype, three specimens observed alive, and prepared as semi-permanent mounts. Gulf of Panama: Iguana Island (Lat. 7°37’45.33”N; Lon. 79°59’51.05”W), lower intertidal in coarse sand, February 2016, one whole mount (USNM 1622591), two specimens sagittally sectioned (USNM 1622592; USNM 1622593); two specimens observed alive, and prepared as semi-permanent mounts .

Etymology. The name derives from the greek trimeros (three parts) and refers to the to trichotomous tail of the new species.

Description. A rather large and sturdy Duplominona, about 2.5 mm long. With both dot-like and rod-like rhabdoids. Caudal end tripartite, with numerous adhesive glands all along its length (Fig. 5 A). Morphology of the three ‘tails’ highly variable, according to movement and adhesion, from short and stubby to narrowly elongate (Fig. 5 F, G). Short pharynx at midbody.

Male genital system. With 6–10 testes in two symmetrical rows. With an elongate copulatory organ, up to 85 μm long, lined by a thin muscular layer. With a large spiny cirrus, up to 65 μm long, provided with numerous spines and a tubular stylet (Fig. 5 B, I–K). The stylet is formed by the distal part of the ductus ejaculatorius, which is everted within the cirrus. On the outer side of this duct the epithelium is absent, and the basal lamina is thickened, producing a hard-tube-like structure, 40–55 μm long, and 13–20 μm wide at its basis (Fig 5 M: s). The distalmost part of the everted ductus ejaculatorius is provided with numerous, densely packed small, scale-like spines, 1.5 –3 μm in length, arranged in about 8 rows (Fig. 5 B–D, I–K: ds). Numerous, larger spines are present proximally, surrounding the stylet in its inverted conditions (Fig. 5 B, I, K, M: ps). These are arranged in 15–20 rows of densely packed, acutely triangular spines, 6.5–10 μm long, with a basis up to 2.5 μm wide (Fig. 5 E). Proximally, smaller spines, 3–4 μm long, may be present.

Accessory organ 35–50 μm across, lined by a thin muscular layer. Its position varied in the specimens studied, from lateral to the copulatory organ to just posterior to it (Fig. 5 G, I: ao). The stylet is acutely pointed, 24–32 μm long. The accessory organ opens to the outside with its own pore, almost midway between male and female pores.

Female genital system. Ovaries and vitellaria as previous species. With a spherical bursa nearly halfway between pharynx and copulatory organ, lined with high, vacuolated epithelium. Vaginal duct long and broad, caudally oriented in most sectioned specimens, and surrounded by a thick muscle layer (Fig. 5 C, L: vd). The female duct continues posteriorly and opens through the female pore.

Karyotype. With n=3. Karyotype formula: FN=5; Chromosome I: 44.86 ± 1.03; 45.62 ± 2.01 (m); Chromosome II: 36.03 ± 1.5; 46.95 ± 1.16 (m); Chromosome III: 19.1 ± 2.47; 7.81 ± 2.51 (a) (based on four plates, from two specimens from Playa Venado)(Fig 5 H).

Diagnosis. Species of Duplominona with tripartite tail. With up to 10 testes arranged into two rows. With a large cirrus provided with a tubular stylet 40–55 μm, surrounded by 15–20 rows of acutely triangular spines, 6.5–10 μm long. With few rows of small, densely packed spines on top of stylet. With a spherical bursa in front of the copulatory organ and external vagina; vaginal duct long, wide, and muscular. Accessory organ stylet 24–32 μm long. Karyotype with two large metacentric pairs and one pair of heterobrachial chromosomes. Pore index: a: b: c: d = =3: 2.5: 1: 1.