Austrorhynchus artoisi, Willems, Wim R., Sandberg, Maria I. & Jondelius, Ulf, 2007

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 : 4-6

Austrorhynchus artoisi sp. nov.

( Fig. 1 A–C)

Localities. Loc. 2 and Loc. 4 (type locality).

Material. Three individuals studied alive. Two whole mounts (one from each locality), one of them designated holotype ( SMNH no. 7175). One serially-sectioned specimen (designated paratype; SMNH no. 7176).

Etymology. Species dedicated to Prof. Dr Tom Artois (Hasselt University) for his contributions on polycystidid taxonomy and systematics, and for being a close friend and colleague to Ulf Jondelius and Wim Willems.

Description. The animals are 0,9–1,4 mm long (measured on whole mounts), white to greyish, rather opaque and have no eyes. In all live individuals an almost round, bright yellow-orange egg ( Fig. 1 A: x) was present (dimensions: 304 x 342 µm). The general organisation in the live animals ( Fig. 1 A) is identical to that of other species of Austrorhynchus Karling, 1952 a. In one of the live individuals four pairs of proboscis retractors ( Fig. 1 A: pr) could clearly be seen, whereas testes were not visible in the studied specimens. The only serially-sectioned individual is in bad shape, because the presence of an egg caused rupture of the central part of all sections. Quality is however sufficient to study the general structure of the proboscis, pharynx and the genital system, which is comparable to that in other species of Austrorhynchus (see Karling 1952a; Artois & Schockaert 2003, 2005). The main differences with the other 16 known species of Austrorhynchus are found in the detailed structure of the two hard parts in the male genital system: prostate stylets type II and III (terminology of Artois & Schockaert 2003).

The double-walled prostate stylet type II ( Fig. 1 A: stII, 1B) is 61–63 µm (n = 2, as for all following measurements for this species) long and consists of a very short proximal funnel and a distal tube (4 µm wide), of which the tip is slightly bent. The funnel-shaped part is 20,5–24 µm wide and its length is approximately 1/7 of the total length. The inner stylet is not restricted to the distal part of the outer stylet and even bulges out of the funnel proximally. The outer stylet does not carry any spines or hooks, but the funnel-shaped part is ornamented with a ring, which gives the proximal part of the stylet the shape of a stirrup. It is 28–31 µm wide and 21–28 µm long. The prostate stylet type III ( Fig. 1 A: stIII, 1C; A-organ in Karling 1977) closely resembles that of A. hawaiiensis Karling, 1977 . The style and foot, which are 42–54 µm apart, are clearly recognisable, but unpronounced. They are interconnected by a narrow clasp (terminology of Willems et al., 2006b) and a thin, comb-bearing plate, which is 21 µm at its broadest point. The clasp is strongly bent and situated very close to the thickened, proximal edge of the plate, giving the whole the appearance of an eight-shaped ring. The inconspicuous foot is situated at the base of a thread-like flagellum, which is 86–90 µm long (measured from the proximal rim of the foot). This flagellum shows a strong curve at ± 65% of its length, but does not bear a comb nor is its distal end swollen. The most proximal third of the flagellum is not free, but connected to the plate.

B B-C 50 Μm

C pr

x

Diagnosis. Austrorhynchus artoisi sp. nov.: species of Austrorhynchus without eyes; double-walled stylet type II ca. 62 µm, consisting of a short proximal funnel, approximately 1/7 of the total length, and a distal tube with a bent tip; inner stylet is not restricted to distal part of outer stylet, which only carries a stirrup-shaped ornament proximally; stylet type III shows an unpronounced foot and stylet, ca. 48 µm apart; the foot tapers into a thread-like flagellum, which is ca. 88 µm long, bent and connected to a thin, comb-bearing plate.

Discussion. Within the taxon Austrorhynchus , the 16 hitherto known species mainly differ in the detailed structure of the two prostate stylets. In A. artoisi sp. nov. both stylets show a combination of features, not present in any other species of Austrorhynchus . The stylet type II of A. artoisi has a very short funnel-shaped part, approximately 1/7 of the total stylet length. Only in A. karlingi Brunet, 1965 and A. scoparius Brunet, 1965 the basal tube is similarly short. The total length of the stylet is significantly larger (100–110 µm in A. karlingi and 80–100 µm in A. scoparius ; see Brunet 1965). In most species of Austrorhynchus the stylet type II bears a hook, which is absent in A. artoisi and five more species ( A. antarcticus Artois et al., 2000 , A. galapagoensis Artois & Schockaert, 1999 , A. pacificus Karling, 1977 , A. pectatus Karling, 1952 a and A. scoparius ; see Karling 1952a, 1977; Brunet 1965; Artois & Schockaert 1999; Artois et al. 2000). Besides in A. artoisi , a distally bent stylet tube is only found in A. calcareus Karling, 1977 (see Karling 1952a, 1977). Two features regarding the stylet type II are clearly unique for A. artoisi : presence of a stirrup-shaped ornament and the inner stylet that is as long as the outer stylet. Whereas type II stylets are rather simple in structure, stylets of type III are more complex, and especially in species of Austrorhynchus they show a great variety in shape and size. Apart from the one present in A. artoisi , there are only four species of Austrorhynchus with an annular type III stylet: A. californicus Karling, 1977 , A galapagoensis , A. hawaiiensis and A. pacificus (see Karling 1977; Artois & Schockaert 1999; Willems et al. 2006). Of these A. galapagoensis clearly has an aberrant stylet, whereas in the other three the clasp (terminology of Willems et al. 2006) is not situated close to the plate, as is the case in A. artoisi . The reason for this is the presence of a more pronounced foot, in comparison with the situation in A. artoisi .

Apart from the hard structures in the male genital system, there is yet another interesting feature distinguishing A. artoisi from most other species of Austrorhynchus , namely the absence of eyes. Besides in A. artoisi , they are only lacking in four other species: A. antarcticus , A. karlingi Brunet, 1965 , A. magnificoides Artois et al., 2000 and A. magnificus Karling, 1952 a (see Karling 1952a, 1977; Brunet 1965; Artois et al. 2000).

This is the first record of a species of Austrorhynchus from the northern Atlantic region, and thus fills in the gap mentioned by Karling (1977: p. 159 and Fig. 9). Apart from the Mediterranean species ( A. bruneti Karling, 1977 , A. karlingi and A. scoparius ), this is the only species of the taxon occurring in European waters. Most species of Austrorhynchus have a very limited distribution, in most cases they are only known from one locality. An exception is A. hawaiiensis , found on Hawaii, the East-African coast and the eastern Australian coast ( Karling et al. 1972; Karling 1977; Willems et al. 2006b)

Figures

FIGURE 1. Austrorhynchus artoisi nov. sp. A, general organisation (from a live individual). B, prostate stylet type II (from the holotype). C, prostate stylet type III (from the holotype).