Cosmocephalus obvelatus (Creplin, 1825) Seurat 1919

Cosmocephalus obvelatus (Creplin, 1825) Seurat, 1919

Material studied: 12 males and 9 females; host: Larus argentatus Pontoppidan (Charadriiformes, Laridae); collected from Durankulak Lake, Bulgarian Black Sea coast (30 September 1990); site of infection: oesophagus.

Vouchers: ZMB Vermes Entozoa 7461 (3 males and 2 females); CLGE-BAS N000.011 (7 males and 5 females); CLGE-BAS N001.068 (2 males), SEM stub; CLGE-BAS N001.069 (2 females), SEM stub.

Description (Figs 5A–H; 6A–I)

General. Medium-sized acuariids. Anterior end with two triangular pseudolabia, each bearing single amphid and pair of prominent papillae (Fig. 6C). Pair of swellings situated dorsally and ventrally at bases of pseudolabia. Few pores situated posteriorly to apex of pseudolabium (Fig. 6D). Cordons arise dorsally and ventrally between pseudolabia (Figs 5A, B; 6A, B); each cordon forming loop adjacent to its base and then continuing its course along longitudinal body axis; at level of posterior end of buccal cavity, cordons recurrent in anterior direction and reach level of anterior quarter of buccal cavity where they anastomose laterally (Fig. 5A, B). Cordons consisting of a single row of cuticular plates (each plate c. 2 µm long) and longitudinal cuticular ridge along outer rims of plates; deep longitudinal groove between plates and longitudinal ridge. Plates of both descending and ascending cordon arms of unequal width, thus forming scalloped appearance. Deirids 13–20 long, bicuspid (Fig. 6E). Postdeirids c. 5 long, bifurcate (Fig. 6F). Lateral alae well-developed, extending from level just posterior of deirids to level about middle of body (Fig. 6A, B). Buccal cavity elongate. Excretory pore posterior to deirids (Fig. 5A, B). Nerve ring surrounding anterior portion of muscular oesophagus. Phasmids subterminal (Fig. 6I).

Male (from L. argentatus, n=10 except otherwise stated). Body length 9.8–11.3 mm (10.5 mm). Maximum body width 255–286 (271), about mid-body; width 98–136 (124) at level of cloaca. Tail 290–369 (325) long. Cordons 322–376 (350) long, recurrent in anterior direction to 97–170 (117) from anterior body end. Deirids and excretory pore at 384–434 (407) and 487–550 (506), respectively, from anterior body end. Left postdeirid and right postdeirid at 7.0– 8.1 mm (7.5 mm, n=7) and 6.1–7.1 mm (6.5 mm, n=7), respectively, from anterior body end. Buccal cavity 219–246 (231) long and 12–14 wide. Muscular oesophagus 848–940 (903) long and 61–72 (65) wide. Glandular oesophagus 2,927–3,640 (3,187) long and 104–120 (113) wide.

Nerve ring at 376–434 (407) from anterior body end. Cuticle 14–16 thick. Distance between cuticular striations 5–6 μm. Lateral alae extending to 6.4–7.1 mm (6.7 mm) from anterior body end, maximum width 44–50. Caudal alae 561–1,062 (839) long. Single ventral cuticular ridge extending between level at 2,036– 2,775 (2,243) from posterior end and caudal alae (Fig. 6G). Single median sessile precloacal papilla present. Nine pairs of pedunculate caudal papillae, 4 precloacal and 5 postcloacal; postcloacal pairs with almost equal distance between them, fifth pair at posterior part of tail (Figs 5D; 6G, H). Sixth pair of postcloacal papillae sessile, smaller, situated between bases of last pedunculate papillae. Left spicule 487–548 (515) long and 9–10 wide, with projection on its distal end (Fig. 5F). Right spicule 142–167 (156) long and 24–26 (25) wide (Fig. 5H). I CL/BL 0.029–0.036 (0.034); I mOE/gOE 0.246–0.317 (0.285); I OE/BL 0.370–0.421 (0.391); I CA/BL 0.056–0.095 (0.080); I LSP/RSP 3.109–3.859 (3.333).

Female (from L. argentatus, n=9 except otherwise stated). Body length 14.8–18.2 mm (16.6 mm). Maximum body width 402–456 (436), about mid-body; width 132–174 (150) at anus and 384–456 (414) at vulva. Cordons extending to 452–532 (490), recurrent in anterior direction to 97–122 (111) from anterior body end. Deirids and excretory pore at 474–590 (542) and 595–697 (639), respectively, from anterior body end. Left postdeirid and right postdeirid at 9.2–11.7 mm (10.6 mm) and 7.5–10.6 mm (9.3 mm) from anterior body end. Buccal cavity 456–519 (485) long, 14–17 (16) wide. Muscular oesophagus 1,055–1,284 (1,135) long, 70–89 (79) wide. Glandular oesophagus 3,922–4,375 (4,114) long, 147–182 (162) wide. Nerve ring at 469– 550 (515) from anterior body end. Cuticle 14–16 thick. Distance between striations 6–7 μm. Lateral alae extending to level of vulva, 43–48 wide. Vulva at 7.8–9.8 mm (9.0 mm) from anterior body end. Reproductive system didelphic. Vagina vera short, posteriorly directed, separated from vagina uterina by well-developed circular musculature (Fig. 5C). Vagina uterin а longer, with muscular walls. Posterior extremity of tail with button-like projection (Figs 5E; 6I). Eggs oval, 35–39 × 20–22 (37 × 21, n =20), containing first stage larva (Fig. 5G). I CL/BL 0.026–0.035 (0.030); I mOE/gOE 0.255–0.301 (0.276); I OE/BL 0.299–0.342 (0.316); I V/BL 0.520– 0.570 (0.543).

Remarks. Anderson & Wong (1981) redescribed Cosmocephalus obvelatus and listed C. diesingi Molin, 1858, Cosmocephalus obvelatus magnus Vasil’kova, 1926, C. firlottei Rao, 1951, C. tanakai Rodrigues & Vicente, 1963 and C. faridi Khalil, 1931 as its junior synonyms. We consider that the synonymy of C. faridi (described from Pelecanus onocrotalus from Egypt) with C. obvelatus is not well-founded (see below). C. obvelatus is parasitic in a wide range of aquatic birds (see below) and its distribution is cosmopolitan (summarised from Anderson & Wong 1981; Baruš et al. 1978; Azuma et al. 1988; Smogorzhevskaya 1990; Diaz et al. 2001).

The nematodes from Bulgaria identified here as C. obvelatus correspond with the known range of morphological variation of this species as presented in previous studies (e.g. Cram 1927; Rao 1951; Bowie 1981; Smogorzhevskaya 1990; Diaz et al. 2001). However, our specimens exhibit shorter spicules and tails compared with the material from Larus delawarensis from Canada (Table 1) described by Anderson & Wong (1981). An explanation of the differences in these characters requires further study.

Our SEM observations are in agreement with results published by previous authors (Baruš & Majumdar 1975; Bowie 1981; Diaz et al. 2001; Frantová 2002). In addition to them, we describe the presence of a single ventral cuticular ridge situated anteriorly to the cloaca in male specimens (Fig. 6G, H). This structure was not mentioned in the previous descriptions of C. obvelatus but was documented in the illustrations of two articles (Diaz et al. 2001; Frantová 2002).

We consider Cosmocephalus argentinensis Boero & Led, 1970 as a synonym of C. obvelatus. The former species was described on the basis of a single female nematode collected from Spheniscus magellanicus (Forster) (Spheniscidae) from La Plata Zoo, Argentina (Boero & Led, 1970). Its description, including the metrical data (Table 1), coincides with that of females of C. obvelatus. Recent studies have demonstrated high prevalence and intensities of infection of C. obvelatus in the same host species (Diaz et al. 2001; Pazos et al. 2003). Diaz et al. (2001) considered C. argentinensis as a species inquirenda.