Pseudomonocelis paupercula Curini-Galletti, Casu & Lai
Creators: name: Casu, Marco
name: Cossu, Piero
name: Sanna, Daria
name: Lai, Tiziana
name: Scarpa, Fabio
name: Curini-Galletti, Marco
Publisher: name: Zenodo
Year: 2011
Subjects: Biodiversity
Taxonomy
Animalia
Platyhelminthes
Rhabditophora
Seriata
Monocelididae
Pseudomonocelis
Pseudomonocelis paupercula

description: Pseudomonocelis paupercula Curini-Galletti, Casu & Lai nov. sp.
(Figs 1, 2)
Material. Holotype: Italy, Sardinia, Porto Pozzo (41°11’20.22”N; 9°17’11.03”E), lower intertidal in brackish water; very silty mixed sand (May 2004); sagittally-sectioned (SMNH Type-8082). Paratypes: three specimens sagittally-sectioned (CZM 408 - 410); two whole mounts (in one slide) (CZM 411), same data as holotype. Additional material from the type locality: 10 specimens for karyology.
Greece, Gulf of Maliakòs, near Stylida (38°54’26.05”N; 22°37’22.25”E), lower intertidal in mixed, silty sand, near a fresh-water outlet (March 2004). 11 specimens, sagittally sectioned (CZM 412 - 422); 10 specimens for karyology.
Israel, Akko, Western Wall (32°55’29.94”N; 35°4’5.55”E), mixed sediment in rocky pools (October 1997). 10 specimens, sagittally sectioned (CZM 423 - 432); two specimens used for karyology.
Egypt, Alexandria, Montazah Palace (31°17’16.68” N; 30°0’35.16”E), mixed sediment at the mouth of a freshwater outlet (October 2003). 15 specimens, sagittally sectioned) (CZM 433 - 447); 10 specimens for karyology.
Etymology. From lat. pauper poor. Named for the small and poorly visible copulatory organ, the unusually small chromosomes for the genus, and its overall, non-descript appearance.
Note. The authorship of the species is limited to the three authors who most effectively contributed to the species description.
Diagnosis. Unpigmented Pseudomonocelis with copulatory organ provided with a stylet 15-29 μm long. With swollen female duct, and an unarmed accessory organ close to the female pore.
Description. Fixed mature specimens up to 2.8 mm long (holotype: 2.5 mm; paratype: 2.2 mm), elongate and cylindrical (Fig. 1 A). Living animals appear opaque due to gut content and internal organs, especially vitellaria. Without pigmented eyespots. Epithelium with insunk nuclei, ciliated. Cilia about 2.5 μm long ventrally, 2 μm dorsally. Ventral side entirely ciliated, apart from the area surrounding the female pore. Dorsally, the caudalmost area is unciliated. Frontal end with oily droplets. Ovoid rhabdoids 11-15 μm in length. 10-12 rhabdoid glands, particularly large and conspicuous, and easily noticeable in living specimens (Figs 1 A, 2E), are present caudally. These glands lie deeply imbedded in the parenchyma (Figs 1 D, 2D). Adhesive glands arranged radially at the posterior tip of the body. Animals can quickly modify the shape of the tail, from narrowly elongate to spatulate, and adhere strongly to the substrate.
Statocyst about 25 μm in diameter; containing one statolith about 15 μm long. The ovoid brain, 55 μm long and 50 μm wide in the holotype, abuts the statocyst. Body musculature formed by a very thin outer circular layer, and a thicker inner longitudinal layer. With a few transverse muscular fibres. Pharynx in mid-body, comparatively small, 150-200 μm long in mature specimens. Internally, it is ciliated in its distal half, with cilia 3-3.5 μm long; externally, it is uniformly ciliated (cilia 1–1.5 μm long), apart from the distal tip, where pharyngeal glands discharge. With a well developed oesophagus, about half the length of the pharynx. Musculature of pharynx inverted with respects to body musculature. The inner circular component is particularly strong distally, while it is not present below the oesophagus. Pharyngeal glands well developed, extending anteriorly in the body, and easily seen in living, squeezed specimens.
Male genital organs. With very few (5–10), ventral testes. Copulatory organ of the simplex-type (see Litvaitis et al., 1996), placed close to the ovaries. In some large, otherwise mature animals the copulatory organ was totally lacking (CZM 412, 422, 436, 439) or presumably non functional (CZM 435, 440). The copulatory organ is formed by a seminal vesicle lined by a muscular sheath and a penis papilla provided with a stylet (Fig. 1 C). Shape and size of the bulb strongly depend on contraction during fixation and amount of sperm content. It is 87 μm high, 81 μm wide in the holotype (Fig. 2 C); much smaller and regularly spherical (32 μm across) in the paratype, where sperm was not present. The bulb of specimens from Akko ranged from 40 μm high and 35 μm wide to 105 μm high and 93 μm wide. In specimens from Maliakos, the bulb ranged 28–40 μm high, and 34–53 μm wide (Figs 2 A, B). In specimens from Alexandria it ranged 24–43 μm and 20–64 μm respectively. The bulb is lined by an outer layer of circular musculature, and an inner layer of longitudinal musculature. The thickness of the muscular wall depends on its state of contraction. It is about 2 μm thick in the holotype, and ranges from up to 7.5 μm in specimens with a small, contracted bulb to less than 1 μm in diameter in the largest bulbs of specimens from Akko. The seminal vesicle is lined by a thin epithelium, which becomes high and glandular distally, where it is pierced by the outlet of prostatic glands, whose nuclei lie outside the bulb. The prostatic glands are few, and poorly developed. The penis papilla is small and conical, and is formed mostly by circular musculature. It is provided with a copulatory stylet. The stylet is pen nib-shaped, with a broader basis and a distal, gutter shaped pointed tip. The stylet is 26 μm long in the holotype (Fig. 2 C), and ranged 15–29 μm in the sample. The stylet is wrapped by the penis papilla, and its basis may protrude into the bulb. It has been observed in all the sectioned specimens from the type locality, which were large, mature animals. In the other populations, it has been detected in most specimens; it was absent in few specimens only, with the smallest copulatory bulbs. The stylet is thus presumably formed at full male maturity. Nonetheless, due to its small size and poor sclerification, the stylet can be detected in mature living specimens with great difficulty. On the contrary, it is easily noticeable in sectioned specimens, as it is intensely eosinophilous. The male antrum is small and unciliated, and opens to the outside through the male pore.
Female genital organs. With large, thick vitellaria, extending from behind the brain till the level of the copulatory organ. They are easily visible, due to their development, in living slightly squeezed specimens (Fig. 1 A). Ovaria post-pharyngeal. Up to 15 oocytes per ovary are discernible in sections, the largest (up to 33 μm in diameter) being the caudalmost. Shortly behind the ovaria, the two oviducts fuse into the female duct, which runs posteriorly and ventrally over the copulatory organ and opens to the outside through the female pore, just in front of the caudal end of the body (Fig. 1 B). At the joining of the two oviducts, a few specimens show a widening, up to about 20 μm across, which may be interpreted as a small bursa (Fig. 1 B). The entire female duct system is irregularly swollen along its course and is lined by a high, vacuolar epithelium (Fig. 2 G). The development of vacuoles is to such an extent that the entire female duct, in sections, appears as lacking a continuous lumen. This peculiar lining extends to the oviducts, which are surrounded by vacuoles. Duct and vacuoles are often filled with sperm. Vitelloducts consisting of several, independent ducts (Fig. 1 B). In some specimens, up to four vitelloducts could be traced, scattered along the length of the female duct, presumably connected to the overlying portion of the vitellaria. The most anterior vitelloducts join the oviducts, and are presumably connected to prepharyngean vitellaria. The female pore is surrounded by large, and numerous female glands (Fig. 1 D).
Accessory organ. It is an ovoid, muscular organ, 14-17 μm wide, 16-25 μm high, located just in front of the female pore (Figs 1 D, 2H). It is lined with a muscular sheath 2-2.5 μm thick, consisting mostly of longitudinal fibres, which are pierced by ducts of numerous glands, whose cell body lies outside the organ. The organ appears filled with the granular content produced by these glands, and opens to the outside through a short, narrow duct, very close to the female pore. Due to the reduced size of the organ, it is extremely difficult to discern in living specimens. In sections, it is easily detectable in large mature specimens only, and is absent in subadult specimens.
Karyotype. All populations showed karyotypes with haploid number n = 3, and F.N. = 6 (Fig. 2 F). Chromosomes small and slightly differing in size: Chromosome 3 is about 75% of the length of Chromosome 1. Chromosomes 1 and 2 are metacentric; Chromosome 3 is submetacentric, with high index value. Karyometrical data of the populations used for statistical analysis (PP, MA, AL) are reported in Table 2. A unifactorial ANOVA based on the relative length and centromeric index of each chromosome and the haploid genome length was not significant, for any variable, at P ≤ 0.01 (Table 2). Karyometrical data from two specimens from Akko closely corresponded to the other populations: Chrom. I = r.l.: 38.24 ± 3.32; c.i.: 46.33 ± 0.59; Chrom. II = r.l.: 32.45 ± 1.99; c.i.: 45.85 ± 1.45; Chrom. III = r.l.: 28.93 ± 5.74; c.i.: 35.65 ± 0.07;g.l.: 7.2 ± 0.8 μm.
PP MA AL F (2,27) P
r.l. 38.15 ± 0.48 39.13 ± 0.45 38.61 ± 0.48 2.58 0.0944 n.s.
Chromosome 1
c.i. 46.33 ± 0.65 47.18 ± 0.44 46.43 ± 0.27 0.93 0.408 n.s.
r.l. 32.96 ± 0.34 33.84 ± 0.22 32.43 ± 0.44 2.5 0.1009 n.s.
Chromosome 2
c.i. 45.73 ± 0.53 46.41 ± 0.35 46.32 ± 0.49 0.64 0.5349 n.s.
description: Published as part of Casu, Marco, Cossu, Piero, Sanna, Daria, Lai, Tiziana, Scarpa, Fabio & Curini-Galletti, Marco, 2011, A reappraisal of the monophyly of the genus Pseudomonocelis Meixner, 1943 (Platyhelminthes: Proseriata), with the description of a new species from the Mediterranean, pp. 59-68 in Zootaxa 3011 on pages 62-65, DOI: 10.5281/zenodo.202754