Espegrendia norvegica Westblad, 1954

Willems, Wim R., Sandberg, Maria I. & Jondelius, Ulf, 2007, First report on Rhabdocoela (Rhabditophora) from deep parts of Skagerrak, with the description of four new species, Zootaxa 1616, pp. 1-21 : 12-14

Espegrendia norvegica Westblad, 1954

( Fig. 5 A–B)

Localities. Loc. 1, Loc. 4 and Loc. 5.

Known distribution. Northern Atlantic, Norway ( Westblad 1954).

Material. A few individuals from Skagerrak studied alive, three of them serially-sectioned. Three serially-sectioned individuals from a depth between 50 and 100 m at Skipelle near Drøbak, Norway (18/08/1955; coll. Westblad, SMNH nos 32853–32855).

Description and remarks. Up till now this species is only known from one cross-sectioned specimen (designated holotype), described by Westblad (1954). As already pointed out by Ehlers (1972), the original description is unsatisfactory and especially the detailed organisation of the male system as described and depicted by Westblad (1954) is highly doubtful. This is probably caused by the nature of the holotype as the interpretation of cross-sections is often very hard, especially regarding long and winding structures as a cirrus. A redescription is therefore deemed necessary.

The following redescription is based on the newly collected material from Skaggerak and sectioned specimens collected by Westblad in Norway (August 1955), which were never reported upon.

The Skagerrak specimens are rather small and colourless and lack eyes. They have a drop-shaped, slightly elongated body if swimming freely, but are oval-shaped or almost round when immobilized. The syncytial epidermis is 3–4 µm thick, contains small rod-shaped rhabdites, equally distributed over the entire epidermis, and is covered with short cilia that are of equal length over the whole body. The outer circular muscles of the subepidermal body wall musculature ( Fig. 5 A: cm) are exceptionally thick, whereas the inner longitudinal muscles ( Fig. 5 A: lm) are rather weak.

The pharynx ( Fig. 5 A) is situated in the first body half. It is oriented caudally and can be fairly long (maximally half of the total body length), almost snake-like, altough it can strongly vary in length, depending on the degree of contraction. A separate mouth is lacking, as the prepharyngeal cavity is connected to the genital atrium through a short duct, which is lined with a low, nucleated epithelium and surrounded by longitudinal muscles. The prepharyngeal cavity proper ( Fig. 5 A–B: pc) is very deep, lined with a low, anucleated epithelium and surrounded by longitudinal muscles ( Fig. 5 A: ep1). The distal pharyngeal rim bears short cilia ( Fig. 5 A: cil) and the pharynx bulb, bulging out into the prepharyngeal cavity is covered with the remains of a degenerated epithelium ( Fig. 5 A: ep2). The pharynx lumen ( Fig. 5 A: pl) is almost completely filled by a degenerated epithelium (= pseudociliation; Fig. 5 A: ep3). The pharynx is surrounded by an outer longitudinal (= continuation of layer surrounding the prepharyngeal cavity; Fig. 5 A: elm) and an inner circular muscle layer ( Fig. 5 A: ecm). The internal muscles consist of rather weak radial muscles ( Fig. 5 A: rm), a circular ( Fig. 5 A: icm) and two longitudinal ( Fig. 5 A: ilm1–2) muscles layers. The longitudinal layer immediately surrounding the pharynx lumen ( Fig. 5 A: ilm1) consists of eight thick muscle fibers, whereas the second layer (( Fig. 5 A: ilm2), situated more peripherically consists of at least 30 weaker fibers. Two types of glands enter the pharynx proximally ( Fig. 5 A: pg1–2). One type of glands is rather small and contains a fine-grained eosinophilic secretion ( Fig. 5 A: pg1), whereas the second type consists of very large gland cells, containing a basophilic rod-shaped secretion ( Fig. 5 A: pg2). A few glands of the latter type are also present intracapsulary ( Fig. 5 A: pg3). The exact location where these glands open into the lumen could not be determined.

The common genital pore, which is combined with the mouth ( Fig. 5 A–B: m + gp), is situated in the most distal part of the body. Close to this combined opening, the prepharyngeal cavity ( Fig. 5 A–B: pc) opens into the common genital atrium ( Fig. 5 A–B: cga) from the rostral side. The genital atrium is lined with a high nucleated epithelium and surrounded by inner circular and outer longitudinal muscles. The former are clearly thicker around the distal part of the genital atrium. The presence of nuclei is restricted to the most proximal part of the atrium. A small, bean-shaped bursa ( Fig. 5 B: bu), which contains resorbed sperm, opens into the genital atrium from the dorsal side.

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Dorsally from the prepharyngeal cavity the male atrium ( Fig. 5 A–B: ma) opens into the genital atrium from the rostral side. The male atrium is a wide cavity proximally, distally narrowing to a duct. It is lined with a nuclated epithelium and surrounded by circular muscles. Proximally the male atrium is connected to the oval-shaped copulatory organ, which is surrounded by a very strong circular muscle layer and divided into two compartments. The most proximal part contains an internal seminal vesicle ( Fig. 5 B: ivs), which receives sperm directly from the swollen vasa deferentia ( Fig. 5 B: vd). The distal part of the copulatory organ contains a long, winding cirrus ( Fig. 5 B: ci), which is surrounded by a strong longitudinal muscle layer. Proximally the unarmed cirrus is filled with sperm, wheras the middle part is lined with a thick, glandular epithelium (eosinophilic). The distal part of the cirrus, approximately half of its total length, is lined with a low, anucleated epithelium.

The female genital system is rather simple and only consists of two kidney-shaped ovaries ( Fig. 5 B: ov), situated dorsally to the genital atrium, to which they are connected through two short oviducts ( Fig. 5 B: od). They open into the atrium separately and are distally surrounded by a circular muscle layer, which forms a very thick and distinct sphincter ( Fig. 5 B: sph) half way the oviducts. A uterus is lacking.

Apart from the detailed organisation of the copulatory organ, the overall structure of the genital system is identical to that described by Westblad (1954). The male copulatory organ in the holotype is decribed as consisting of “two twisted chitinous filaments or tubes” ( Westblad 1954: p. 17). However, careful re-examination of the holotype shows only a single, but strongly winding cirrus, which is not lined with a pseudocuticularised epithelium, but with a low anucleated epithelium.

Diagnosis. Espegrendia Westblad, 1954 : Lenopharynginae with combined mouth and gonopore; resorbing bursa opening into common genital atrium; copulatory organ an oval-shaped, muscular bulb containing a seminal vesicle proximally and a long, winding and unarmed cirrus distally; oviducts with distinct sphincter.

Type species: Espegrendia norvegica Westblad, 1954 : Provisionally with the same diagnosis as the genus.

Figures

FIGURE 5. Espegrendia norvegica Westblad, 1954. A, reconstruction of the pharynx from the right side. B, reconstruction of the atrial organs from the right side. (A – B, from a Skagerrak-specimen).