Duplominona aduncospina Curini-Galletti, 2019

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), pp. 127-147 : 129-131

Duplominona aduncospina Curini-Galletti n. sp.

( Fig. 1 )

Holotype. 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).

Paratypes. Same data as holotype, nine specimens sagittally sectioned ( USNM 1569237–1569245 ) .

Other material. Same data as holotype, six specimens studied karyologically.

Etymology. The name refers to the hook-shaped morphology of the cirrus spines of the new species (lat. aduncus: hooked).

Description. 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 μm long in fixed specimens, ciliated except for small area at tip where glands discharge, and for a short, pre-oesophageal area, about 10 μm long. Pharyngeal longitudinal and circular musculature poorly developed. The oesophagus is about 1/3 the length of pharynx.

Male genital system. 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 μm thick, wraps the entire copulatory bulb. With a small , nearly spherical seminal vesicle, separated by a weakly-muscular septum from a glandular area (the ‘prostatic vesicle’). Distally, a spiny cirrus is present, lined, as most of the prostatic vesicle, by the inner muscular layer. The cirrus, about 50 μm 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 3–4 parallel rows. The spines are 2–3 μm high, with a broad basis (3–4 μm wide), and a distinctly curved distal tip. In most specimens, proximal spines appear slightly larger than distal spines ( Figs 1 B, C ).

With a globular accessory organ, about 25 μm across in sectioned specimens, lined by a muscular coating, about 3 μm thick, and provided with a slender, pen-nib shaped stylet 20–25 μm long. The prostatoid organ opens to the outside with its own pore just anteriorly to the female pore ( Fig. 1 D ).

Female genital system. 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 ).

Karyotype. With n=3, and all chromosomes heterobrachial. Karyotype formula: FN=3; Chromosome I: 43.8 ± 5.42; 10.3 ± 4.57 (a); Chromosome II: 36.28 ± 2.9; 16.71 ± 2.49 (st); Chromosome III: 19.94 ± 4.07; 17.23 ± 2 (st) (based on three plates).

Diagnosis. Species of Duplominona with up to 20 testes in one row. Cirrus provided with a subterminal girdle of 3–4 rows of about 30 spines in total, 2–3 μm high, with a basis 3–4 μm 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 20–25 μm long, opening with its own pore, in front of female pore. Karyotype with three pairs of heterobrachial chromosomes. Pore indices: a: b: c: d = ≈7: 1: 3.5: 1

Figures

FIGURE 1. Duplominona aduncospina n. sp. (A) Habitus of a living animal. (B, C) Reconstructions of the copulatory cirrus (B: everted; C: inverted) showing the sclerotised copulatory structures. (D) Reconstruction of the genital organs from sagittal sections. (E) Micrograph of a sagittal section of the genital organs. (F) Micrograph of the genital area of a living animal. (Scale bars: B, C = 5 m; E = 20 m).