Archimonocelis cygnicollis, Curini-Galletti, Marco, Delogu, Valentina, Campus, Paolo & Casu, Marco, 2007

Curini-Galletti, Marco, Delogu, Valentina, Campus, Paolo & Casu, Marco, 2007, New species of the genus Archimonocelis Meixner, 1938 (Proseriata, Archimonocelididae) from southern Apulia (Italy), Zootaxa 1557, pp. 47-58 : 52-54

Archimonocelis cygnicollis sp. n.

( Figs. 2 A, 3 D–F)

Holotype: one whole mount ( SMNH 6781).

Type locality: Apulia, Italy: Porto Cesareo (Lecce), in front of the harbour (lat. 40°14’59.44”N, long. 17°53’31.22”E), about 14 m deep, coarse silty sand, May 2005.

Paratype: a specimen from the type locality, whole mount ( SMNH 6782).

Additional material: a specimen from the type locality, whole mount (ZMC-60). A specimen from Torre Scianuli, about 7 m deep in pockets of sediments (mostly shell fragments) on a limestone cliff, May 2005; whole mount (ZMC-61). A specimen from the type locality processed for karyology.

Etymology: the specific epithet refers to the shape of the stylet, gracefully arched as the neck (lat: collus) of the mute swan Cygnus olor (Gmelin, 1789) .

Description. A small sized Archimonocelis : whole mounts range 3.2–4.7 mm in length. Similar in general morphology to the previous species. The specimen from Torre Scianuli had three types of heteroneme cnidocysts in each cnidosac: i) ovoid, about 8 µm long; ii) elongate, around 20 µm long; and iii) a few, very large ovoid cnidocysts, about 25 µm long. Specimens from the type locality showed a greater range of cnidocysts. All specimens contained predominantly large, elongate cnidocysts, 33–36 µm long; in addition, ovoid cnidocysts, of different size classes (around 5 µm; 8–10 µm; 15 µm; 25 µm) were also observed.

Male genital system. Ten to fifteen testes are located in one median row in front of the pharynx. The copulatory structures consist of one pair of seminal vesicles, a bulbus with the vesicula granulorum, a stylet surrounded by spines, and an accessory glandular organ provided with spines (figs 2A, 3D).

The stylet, 155–184 µm long (163 µm in the holotype), is a recurve tube, about 9 µm in diameter. The degree of the curvature appears variable in the sample, possibly as result of fixation. In squeezed mounts, it is possible to appreciate that the basal half of the stylet consists of two distinct layers ( Fig. 3 E). The inner layer has a straight, slightly inflated basis, provided with a proximal opening 21 µm wide in the holotype. The outer layer is gutter shaped, with a large, convex, obliquely truncated basis, provided with an opening 25–30 µm wide. Just above the basis, the outer layer is provided with a narrow, thickened ring. The two layers abut till approximately half the length of the stylet, where they gradually merge into a single layer. The stylet is provided with a small, concave distal tip, provided with an opening about 7 µm wide.

The two companion spines are needle-like, flexible and feebly sclerotized, up to 70 µm long.

The 30–32 copulatory spines are arranged into a girdle. The two first order copulatory spines are 98–110 mm long, with a stalk about 6.5 µm broad, and widen distally into a distinctly hooked, flattened apex, up to 15 µm broad, provided with an obtuse, obliquely sulcate, subterminal tooth. The second order copulatory spines are 75–115 µm long, with a very thin stalk, about 1.5 µm broad. Those closer to the two first order spines are longer, with a slender, slightly recurve apex and an obtuse subterminal tooth (maximum width of the subapical region around 5 µm). Farther from the stylet, the spines become progressively shorter, with a more flattened, larger and recurve apex, with a maximum width of about 7 µm.

The accessory glandular organ lies in a diverticle of the male antrum, surrounded by a muscular wall, and is provided with a girdle of 17–20 spines (18 in the holotype). Starting from the area closer to the male copulatory organ, the following, symmetrically arranged, groups of spines can be recognized:

A) 11–14 spines, similar in morphology to the copulatory spines of second order, 69–84 µm long, with a stalk about 3 µm wide, and with a slender, curved apex, 5 µm at its maximum width, provided with a weak subterminal tooth;

B) two pairs of knife-shaped spines, 67–80 µm long, with a stalk about 4 µm wide, and a maximum width of about 6 µm;

C) one pair of spines, similar to group B, 73–79 µm long, wider subterminally (to 8 µm broad), and with a narrowly pointed, recurve distal end.

Female genital system. With two ovaries, lying in front of the vitellaria, in the first third of the body. Vitellaria arranged in two lateral rows, from the ovaries to in front of the copulatory bulb. The oviducts fuse posterior to the vitellaria, widen into a bursa, connected posteriorly to the female common duct which opens into the female pore. A genito-intestinal duct is present just prior to the female pore.

Karyotype. Chromosome number: n = 4 ( Fig. 3 F); FN =5. The first chromosome pair is metacentric, and distinctly larger than the other pairs, which are acrocentric. Chrom. I = r.l.: 37.50 + 2.33; c.i.: 45.65 + 2.21 (m); Chrom. II = r.l.: 22.83 + 1.11; c.i.: 5.21 + 0.47 (t); Chrom. III = r.l.: 20.50 + 0.71; c.i.: 5.75 + 0.49 (t); Chrom. IV = r.l.: 19.20 + 0.56; c.i.: 6.01 + 0.32 (t) (based on the measurements of four spermatogonial plates).

Diagnosis. Archimonocelis species with two seminal vesicles and an accessory glandular organ. With a recurve, tubular stylet, 155–184 µm long, double walled in its proximal half, provided with a markedly oblique, large basis, formed by the outer layer, and small, spoon-shaped distal end. With two companion spines, and a girdle of 30–32 copulatory spines. With two falcate first order spines, 98–110 µm long, provided with an obtuse, obliquely sulcate proximal tooth. Second order spines 75–115 µm long, with a more flattened and curved apex distal to the stylet. With 17–20 accessory spines, 67–82 µm long; most are similar to the second order copulatory spines; the three pairs away from the copulatory organ are broader. With n=4; a large metacentric pair of chromosomes is present.

Remarks. A. cygnicollis n. sp. shares the presence of an accessory glandular organ, provided with spines with A. semicircularis Karling, 1966 ; A. oostendensis Martens & Schockaert, 1981 ; A. staresoi Martens & Curini-Galletti, 1993 ; A. meixneri Martens & Curini-Galletti, 1993 , and A. sabra Martens & Curini-Galletti, 1993 . However, none of these species has a double walled stylet. The small, cup-shaped distal end of the stylet of the new species is similarly unique: in all the species cited above, in fact, the stylet has a pointed tip, provided with a wide, oblique opening.

Among other differences: A. meixneri , from the Mediterranean, has one seminal vesicle, a small, straight stylet (61 µm long), with only 6 copulatory spines (37–52 µm), and 7 accessory spines, 25–35 µm long, all with the same shape ( Martens & Curini-Galletti, 1993);

A. semicircularis , from the west coast of North America, has a straight, slender stylet, about 60 µm long, with 70 copulatory spines, about 45 µm long, without first order spines, and an accessory organ with 3–4 spines only, of the same size and morphology of the copulatory spines ( Karling, 1966b);

A. sabra , from the Red sea, has a straight stylet, 77 µm long, 27–35 copulatory spines, 26–46 µm long, without first order spines, and 10 needle-shaped accessory spines, 21–24 µm long. Furthermore, its chromosome number is n=7 ( Martens & Curini-Galletti, 1993);

A. oostendensis , from the North Sea, is distinguished for its straight, shorter stylet, 49–53 µm long, much smaller copulatory and accessory spines (35–40 µm and 18–31 µm long respectively), differently shaped, and a karyotype with n=6 ( Martens & Schockaert, 1981; Martens & Curini-Galletti, 1993);

A. staresoi , from the Mediterranean, has a recurve stylet, similarly to the new species. However, it is smaller (about 100 µm long), with a less swollen basis; it is acutely pointed distally, with a large, oblique, distal opening. Furthermore, it lacks the narrow basal ring of A. cygnicollis n. sp. The species lacks companion spines; copulatory spines of first order are much smaller, 60 µm long, with a slender, straighter apex. Second order spines are similarly smaller, 40–50 µm long. A. staresoi has the same number (18–20) of accessory spines of the new species. These are however much shorter (20–33 µm), thin and needle-like close to copulatory organ; farther on, they progressively widen subterminally, and the two farthermost pairs are distinctly larger and broader ( Martens & Curini-Galletti, 1993). The general arrangement is thus comparable to the new species, where, however, the three farthermost pairs are knife-shaped, with one pair provided with a pointed, recurve apex. The karyotype of A. staresoi is known: it has n=5, with evenly sized markedly heterobrachial chromosomes ( Martens & Curini-Galletti, 1993).

Figures

FIGURE 2. Reconstruction (based on holotypes) of the sclerotized apparatus of A. cygnicollis sp. n. (A) and A. parastaresoi sp. n. (B). Scale = 50 µm.

FIGURE 3. Archimonocelis scopulicola sp. n. A, B: sclerotized apparatus (A: paratype; B: holotype); C: metaphasic plate from spermatogonia. Archimonocelis cygnicollis sp. n. D: sclerotized apparatus, holotype; E: detail of stylet, paratype; F: bivalents from male spermatocytes. Scale = A, B, E: 10 µm; C, F: 5 µm; D: 20 µm.