Simplexcystis asymmetrica Diez, Reygel & Artois, 2021

Diez, Yander L., Monnens, Marlies, Aguirre, Rosa Isabel, Yurduseven, Rana, Jouk, Philippe, Van Steenkiste, Niels W. L., Leander, Brian S., Schockaert, Ernest, Reygel, Patrick, Smeets, Karen & Artois, Tom, 2021, Taxonomy and phylogeny of Koinocystididae (Platyhelminthes, Kalyptorhynchia) with the description of three new genera and twelve new species, Zootaxa 4948 (4), pp. 451-500 : 489-492

Simplexcystis asymmetrica Diez, Reygel & Artois gen. n. sp. n.

( Fig. 21–23 )

urn:lsid:zoobank.org:act:BB2226F6-C526-47E4-8B49-F5CF45AB242E

Material and distribution. Observations on one live specimen, serially sectioned afterwards, designated holotype ( FMNH https://id.luomus.fi/ KV.655), collected in Playa Chica (28°55’05”N, 13°40’07”W) (Type Locality), Puerto del Carmen , Lanzarote, Canary Islands (October 10, 2011), fine sand accumulated at the end of the rocky reef, 18 m deep, salinity 35 ‰.

Etymology. The genus name refers to the fact that the construction of the atrial organs in the new genus is relatively simple compared to that of other koinocystidids. The species name refers to the fact that the copulatory bulb is asymmetric due to the seminal duct entering laterally.

Diagnosis of Simplexcystis gen. n. Representative of Koinocystididae with strong juncture sphincter in between proboscis bulb and cone. Male duct running eccentrically through the copulatory bulb, the latter also enclos-

ing the prostate vesicle. Copulatory organ devoid of any hard structure. Without bursa. Epithelium of the female, the male, and part of the common atrium lined by a brush border. All these structures surrounded by a sheath of muscles in different orientations.

Type species: S. asymmetrica sp. n. (by monotypy). Provisionally with the same diagnosis as the genus.

Description. Live specimen about 1.5 mm long, translucent, with pinkish parenchymal glands and a pair of eyes ( Fig. 21A : e). The brain ( Fig. 21A : br) is located caudally from the proboscis. The syncytial and fully ciliated epidermis is 5–7 µm thick, with cilia 3–4 µm long. The epidermis shows many vacuoles some of which are empty, others filled with a dark, granular secretion. The epidermis shows many rhabdites ( Fig. 21B–C , 22 & 23C–E : rh) all over the body, except for the part anterior to the proboscis. Rhabdites are also lacking around the mouth and gonopore. The rhabdites situated near the apical surface of the epithelium are globular, 1–2 µm in diameter, while those more to the basal part of the epithelium are more elongated (3–4 µm long).

The proboscis ( Fig. 21A : pr, 21B, 23A) is of the typical koinocystidid construction (see Brunet 1972; Karling 1980), with well-developed cone retractors ( Fig. 21B & 23A : cret) and nuclei in the parenchyma of the proboscis bulb. In between the bulb and the cone there is a strong juncture sphincter ( Fig. 21A–B & 23A : js). In the live specimen, the proboscis is about 15% of the body length. Several types of glands enter the proboscis through its caudal wall: dorsally coarse-grained basophilic ones ( Fig. 21B : prg1), more centrally larger, fine-grained eosinophilic glands (stained pinkish) ( Fig. 21B : prg2), and ventrally small fine-grained eosinophilic glands (stained yellowish) ( Fig. 21B : prg3). There are three pairs of proboscis retractors ( Fig. 21B : pret). The exact number of fixators ( Fig. 21B & 23A : pfix) and dilatators ( Fig. 21B : dil) could not be determined. There is one pair of ventral and one pair of dorsal integument retractors ( Fig. 21B : iret). The proboscis sheath is lined by a high, nucleated epithelium and is surrounded by an external longitudinal muscle layer. The sheath epithelium is continuous with the epithelium of the proboscis cone, which is very low and devoid of nuclei. The most proximal part of the sheath epithelium contains some oval to circular-shaped eosinophilic gland cells ( Fig. 21B & 23A : egl). The epithelium surrounding the cone is lined by a brush border ( Fig. 23A : bb). The proboscis pore ( Fig. 21B : prp) is surrounded by a sphincter ( Fig. 21B : sph).

The pharynx ( Fig. 21A : ph, 21C, 23B) is located at 40%. In the live specimen, it has a diameter of 10% of the body length. The prepharyngeal cavity ( Fig. 21C : ppc) is lined by a nucleated epithelium, and is surrounded by an internal circular and an outer longitudinal muscle layer. The mouth ( Fig. 21C : m) can be closed by a sphincter ( Fig. 21C : sph). Three types of glands open into the pharynx lumen: coarse-grained eosinophilic ones (stained reddish) opening most distally ( Fig. 21C & 23B : phg1), and, opening more proximally coarse-grained eosinophilic ones (stained dark pinkish) ( Fig. 21C & 23B : phg2) and coarse-grained basophilic ones (stained greenish) ( Fig. 21C & 23B : phg3). The oesophagus ( Fig. 21A, 21C & 23B : oe) is lined by a nucleated epithelium. A bundle of glands ( Fig. 23B : oeg) opens into the oesophagus. It consists of coarse-grained basophilic glands ( Fig. 21C : oeg1), fine-grained basophilic ones ( Fig. 21C : oeg2), and fine-grained eosinophilic ones ( Fig. 21C : oeg3). The pharynx lumen is surrounded by a low, nucleated epithelium. The musculature of the pharynx consists of a layer of longitudinal muscles outside of the septum ( Fig. 21C : lm), which is continuous with the longitudinal muscles surrounding the prepharyngeal cavity, and a circular one just inside of the septum ( Fig. 21C : cm1). The distal opening of the pharynx is lined by a thick layer of longitudinal muscles, which in sagittal section, gives the impression of forming a lip-like structure ( Fig. 21C & 23B : slm). The pharynx lumen is surrounded by a circular muscle layer ( Fig. 21C : cm2). Radial muscles run ( Fig. 21C & 23B : rm) between the wall of the pharynx lumen and the outer septum.

The two elongated testes ( Fig. 21A : t) are located rostrally from the pharynx. They seem to be divided into three follicles that are closely packed together. However, this could also be an optic effect caused by the testes being heavily folded. The vasa deferentia run towards the caudal body end, and distally form the elongated seminal vesicles ( Fig. 21A & 22 : sv). The seminal vesicles are lined by a low, nucleated epithelium, and are surrounded by longitudinal muscles. The copulatory bulb is oviform, and lies in the caudal body third ( Fig. 21A & 23C : cb). It is surrounded by a longitudinal muscle layer. Distally from the seminal vesicles, the vasa deferentia enter the ejaculatory duct separately ( Fig. 21A , 22 & 23C–E : ed). The ejaculatory duct is elongated, with its distal half situated eccentrically within the copulatory bulb ( Fig. 21A & 23C : cb). Distally the seminal duct opens into the male atrium, surrounded by the prostate vesicle ( Fig. 22 & 23C–E : pv), which also opens in the male atrium. The seminal duct is lined by a low nucleated epithelium, and is surrounded by longitudinal muscles. The prostate glands ( Fig. 22 : pg) are extracapsular, without clearly separated gland necks in the prostate vesicle. The latter contains a coarsegrained eosinophilic secretion in its proximal half and a fine-grained one in its distal half. The male atrium ( Fig. 22 & 23D–F : ma) is divided into a short, broad proximal part, and a tubiform distal part, which ends in the common genital atrium ( Fig. 22 & 23C : ca). The male atrium, the female atrium, and the common genital atrium are lined by a nucleated epithelium and are surrounded by longitudinal muscles. Outside of this longitudinal muscle layer, a thick layer of muscles with different orientations (probably circular and oblique ones) and connective tissue occurs ( Fig. 22 & 23C–F : tl). At its apical side the epithelium is lined by a brush border ( Fig. 22 & 23D–F : bb), which is lacking in the most distal part of the common genital atrium.

In the live specimen, we only observed a single, poorly differentiated ovary ( Fig. 21A & 22 : ov), located at the level of the seminal vesicles. In the serially-sectioned specimen, we observed two weakly developed oviducts, suggesting that the female system in full maturity has two ovaries. The very long oviducts ( Fig. 22 : od) are lined by a nucleated epithelium; muscles were not observed. They open proximally into the female duct ( Fig. 21A , 22 & 23D–F : fd). The female duct is lined by a nucleated epithelium and contains sperm. It opens into the female atrium ( Fig. 22 , 23D & 23F : fa) through a strong sphincter ( Fig. 21A & 23E–F : sph, 22: sph1). The female atrium enters the common genital atrium dorsally. There is no bursa. The uterus ( Fig. 21A , 22 , 23C : ut) is lined by a nucleated epithelium and surrounded by longitudinal muscles. Coarse-grained eosinophilic uterine glands ( Fig. 22 : ueg) open into the uterus somewhat proximally from the entry point into the common genital atrium. Just distally from the entry point of the uterus, some fine-grained eosinophilic atrial glands ( Fig. 22 : ag) enter the common genital atrium. The common gonopore lies ventrally, at about 95% ( Fig. 21A , 22 & 23C : cg), and can be closed by a sphincter ( Fig. 22 : sph2, 23C: sph).

Figures

FIGURE 21. Simplexcystis asymmetrica gen. n. sp. n. A, general organisation (from a live animal). B, sagittal reconstruction of the proboscis from the right hand side. C, sagittal reconstruction of the pharynx from the right hand side.

FIGURE 22. Simplexcystis asymmetrica gen. n. sp. n. Sagittal reconstruction of the genital system from the right hand side.

FIGURE 23. Simplexcystis asymmetrica gen. n. sp. n. A, sagittal section through the proboscis. B, sagittal section through the pharynx. C–F, sagittal sections through the atrial organs.