Zoologica Scripta. Vol. 7, 179-186, 1978 zyxwvuts On the Fine Structure of zyxw Valvognathia pogonostoma gen. et sp.n. (Gnathostomulida, Onychognathiidae) with Special Reference to the Jaw Apparatus REINHARDT MOBJERG KRISTENSEN and ARNE NORREVANG Institute of Comparative Anatomy, University of Copenhagen, Copenhagen, Denmark zyxwvut Received 1978-01-20 Kristensen, R. Msbjerg zyxwvuts & Nmevang, A. 1978. On the fine structure of Valvognathia pogo- nostoma gen. et sp.n. (Gnathostomulida, Onychognathiidae) with special reference to the jaw apparatus.-Zool. Scr. 7: 179-186. Valvognathia pogonostoma gen. et sp.n. is described as belonging to the family Onychogna- thiidae Sterrer, 1972. An integrated picture zyxwv of the jaw apparatus is presented, based on inter- ference phase contrast (Nomarski) and electron microscopy. The teeth are shown to be con- tinuous with lamellae, apophyses, fibulae, and even jugum. These structures are all extra- cellular secretions covering the apical surfaces of the jaw apparatus epithelium. They con- stitute a single, interconnected, “cuticular” structure. Spiral-ciliary-organs and rhabditoid organelles are described in the epidermis. Reinhardt Msbjerg Kristensen, Arctic Station, DK-3953 Godhavn, Greenland. Arne Nsrrevang, Institute of Comparative Anatomy, University of Copenhagen, Universitets- parken 15, DK-2100 Copenhagen, Denmark. I zyx 1. Introduction The present paper is the second (see Kristensen & Nerre- vang 1977) in a series, the aim of which is to clarify the phylogenetic position of the Gnathostomulida by means of ultrastructural studies. Riedl & Rieger (1972) described many details, so far un- seen, in the jaw apparatus of the family Gnathostomulidae. While they used phase-contrast microscopy, we used inter; ference phase contrast (Nomarski) microscopy hereby ob- taining better resolution as well as optical sections of both live and fixed, mounted material. The drawings of the jaw apparatus are documented by Nomarski-micrographs. The aims of the present investigation are: 1) to contribute to the taxonomy of the Danish species of Gnathostomulida, 2) to study the detailed structure of the jaw apparatus by comparing light and electron microscopy, and 3) to make comparative studies of the jaw apparatus at the electron microscopical level. The species described here, Valvognathia pogonostoma, belongs to the family Onychognathiidae, which comprises Onychognafhia jilijera Riedl, 1971, from Florida, Onycho- gnafhia bractearotunda Ehlers & Ehlers, 1973, from the Galapagos Islands, and Nanognathia exigua Sterrer, 1973, from Florida. Furthermore, Sterrer’s genus XI (Sterrer 1972) belongs to Onychognathiidae. The range of the family is thus extended to temperate waters. 2. Material and methods Core samples were collected with a HAPS (Kanneworff & Nicolaisen 1973) at 10-12 meters depth, on DECCA-position H 11.0-D 73.2 south of Bakeme, near Helsingrar, Denmark. The sediment, which consists of coarse sand, ZoCrS60 pm grain size (Amphioxus sand) with high organic contents, was left in buckets for several days at Small samples were taken off the surface of the sedimented bucket I I-15°C. contents, and shaken vigorously with excess of water. The organic contents were poured into Petri dishes, and carefully inspected under the stereo microscope, using magnifications of 40-100 times. Our animals were the last to appear in the samplewften only after the buckets had been left for 3-4 weeks. Magnesium chloride was found to be less effective, as was the ice method of Uhlig. Live animals were studied and photographed in the interference fase contrast microscope (Nomarski). The jaw apparatus could be isolated after treatment with sodium hypochlorite (Figs. 5, 6). After identification using Nomarski, specimens were fixed for electron microscopy in trialdehyde with seawater, modified after Kalt & Tandler (1971), and embedded in Epon. 3. Description of Valvognathia pogonostoma gen. et sp.n. Type material. Holotype: Slide nr. GN 107. Date 19 March 1976. Two paratypes in polyvinyl lactophenol. Two specimens sectioned in Epon for LM and EM, alternately. All will be deposited at the Zoological Museum, University of Copenhagen. Type locality, see chapter 2. Efymology. Valvognathia is derived from valva (L., valve), re- femng to lobes of the basal plate, and gnarhos (Gk., jaws); pogo- nostoma from the words pogon (Gk., beard), and stoma (Gk., mouth). 3.1 External morphology The mature animals are about 400-475 pm long (Fig. 1). A distinct head, about 50 pm long, is followed by a short neck. The body is rather broad, about 4060 pm, tapering bluntly at the blind end. No annulation was noticed in the tail region. 3.2. Body zyxwvu wall and sense organs The epidermis is one-layered, each cell being provided with a single cilium, except for the spiral-ciliary organ, in which up to 8 cilia are found in each cell. In the head region, the apical parts of the epidermal cells contain very dark and. dense granules (Fig. 13, 16), which have been described as rhabditoid (Sterrer 1973). However, they are totally devoid of patterned substructures., Zoologico Scripto 7