Dictymetra gerganae, Mariaux & Georgiev, 2018

Mariaux, Jean & Georgiev, Boyko B., 2018, Seven new species of cestode parasites (Neodermata, Platyhelminthes) from Australian birds, European Journal of Taxonomy 440, pp. 1-42 : 17-22

Dictymetra gerganae sp. nov.

urn:lsid:zoobank.org:act:B01CE7CD-9AB5-4861-9938-9C39350875BB

Figs 17–22 , Table 4

Etymology

The species is dedicated to our friend and colleague, Dr. Gergana Vasileva (Sofia, Bulgaria), a recognized specialist of avian cestodes taxonomy.

Material examined

Holotype

AUSTRALIA: Tasmania, 16 Oct. 1981, David Obendorf (?) leg. (AHC 36489).

Paratypes

AUSTRALIA: about 14 specs, same data as for holotype (AHC 36490–36494).

Other material

AUSTRALIA: about 20 very fragmented specs, previously identified as “ Choanotoania sp. nov.” by R. Wilcox, Victoria, Healesville, 37°41′ S, 145°32′ E, 20 Mar. 1997, P. Holz leg., 21 Oct. 1997 (AHC 36495).

Host

Podargus strigoides (Latham, 1802) (Caprimulgiformes, Podargidae ).

Site of infection

Intestine.

Intensity

About 15 specimens in a single host.

Description

Body of medium size, with length 65–73 mm and maximum width 1.88–2.3 mm (2.03 mm, n = 5) at level of gravid proglottides. Most complete specimens consisting of 79–92 proglottides. Proglottides craspedote, wider than long, progressively becoming longer than wide and up to over twice as long as wide when gravid. Osmoregulatory canals mostly indistinct due to the slight maceration of the specimens.

Scolex rounded ( Fig. 17 ), with diameter 305–360 (n = 2). Suckers rounded, 145–175 (158, n = 8) in diameter, smooth. Rostellar apparatus musculo-glandular ( Fig. 17 ). Rostellar sac well-delineated, but weakly muscular, extending beyond level of posterior margin of suckers, 230–292 × 118–145 (n = 4). Rostellum heavily muscular with expanded anterior part bearing rostellar hooks, bulb-shaped behind hooks, 195–212 × 98–132 (n = 2). Rostellar hooks in two regular rows, 24 in number, robust, slightly curved overall, with long blade and handle. Anterior hooks 46–53 when measured on complete scolex (49.5, n = 6) long (see also other material below); posterior hooks, slightly larger and more curved than

those of anterior row ( Fig. 18 ) (see also other material below). Neck short and weakly marked, 200–250 (n = 2) wide; proglottization distinct at 230–325 (268, n = 3) from posterior margin of suckers. Genital pores anterior, situated at border of anterior 20% of lateral proglottis margin, irregularly alternating in short series; up to seven consecutive pores observed on one side. Position of genital ducts in relation to excretory canals not observed. Genital atrium small, barely marked. No genital papilla.

Testes 60–77 (70, n = 16) in number, in single layer with occasional overlaps, in one continuous large field, filling posterior two thirds of median field, extending in anterior direction up to level of vitellarium both porally and antiporally, often more anteriorly, up to level of ovary on antiporal side ( Fig. 19 ). External vas deferens 20–27 in diameter highly convoluted and making compact mass adjacent to cirrussac at level of antiporal wing of ovary; sometimes partially overlapping cirrus-sac and (or) seminal receptacle. Cirrus-sac small, ovoid to pyriform, 100–132 × 65–83 (115 × 74, n = 42), opening into ductus masculinus surrounded with thin setae (26–36 long), forming a dense terminal tuft ( Figs 20–21 ). Internal vas deferens forming several coils. Cirrus cylindrical, terminally ornate, with long thin setae, mostly difficult to distinguish from those of ductus masculinus.

Vitellarium slightly posterior to level of cirrus-sac, poral to proglottis’ midline, antiporal to seminal receptacle, compact and weakly lobate. Ovary small, anterior, slightly poral, bi-alate and lightly lobulate: antiporal wing larger and more anterior than poral wing, at level of vas deferens; poral wing smaller and at level of vitellarium; ovarial wings on both sides of vitellarium. Seminal receptacle elongate, poral to or partially overlapping poral wing of ovary. Vagina opening posteriorly to male pore, most often straight, sometimes slightly bent, rather wide (18–30 in diameter) and short. Vaginal walls regular, bordered externally by loose small cells.

Uterus starts its development in late mature proglottides as reticulum situated ventrally to testes and female gonads and occupying entire median field, crossing osmoregulatory canals and lateral parts of it situated in lateral fields. Outer shell of eggs with irregular shape, sometimes not distinct ( Fig. 22 ). Embryophore oval, 50–65 (57, n = 20) in diameter, thick. Oncosphere round to slightly oval, 28–40 (33, n = 17) in diameter. Central embryonic hooks 20–21.5 (20.5, n = 12) long, lateral ones 16.5–19.5 (18, n = 18).

Observations on additional specimens

Although there is no doubt that this material is conspecific with the one described above, we do not include it in the type series due to its poor preservation state. Its observable general characteristics fit the above description with the exception of the occasional presence of well-marked genital papillae. Three hook preparations allowed for more precise observations and measurements of the rostellar armament. We counted 24 hooks on two complete sets, and 20 on an incomplete one. Hooks measuring 48–52 (49.2, n = 23) and 50–56 (52.8, n = 26) in the anterior and posterior crowns, respectively.

Remarks

Helminth parasites of frogmouths are virtually unknown. As for tapeworms, the single reported taxon from these birds is Proparuterina aruensis Fuhrmann, 1911 from the Aru Islands in Podargus papuensis ( Fuhrmann 1911; Georgiev & Vaucher 2003). Unidentified cestodes were however more recently reported in P. strigoides in Queensland by Gelis et al. (2011).

Some confusion exists around the systematic organization of dilepidids with cirrus bearing a terminal tuft of long fine spines. According to Bona (1994), they should be distributed in 12 distinct genera and this author provided diagnoses for each of them. By presenting medium-sized strobila, rostellar hooks in two rows, irregularly alternating pores and a reticulate uterus, our material should be placed in Dictymetra Clark, 1952 that has Charadriiformes as ‘typical hosts’ ( Bona 1994). Egg polar processes that are typical of worms with aquatic life-cycles are found in these taxa. It should be noted that other (including terrestrial) birds are also considered by Bona as hosts of members of Dictymetra . They include Passeriformes (for D. belopolskajae Spasskaya & Spasskii, 1973 ) and Trogoniformes, although the latter are unpublished. This obviously casts some doubts about the monophyly of the genus.

The genus Dictymetra has been erected by Clark (1952) for cestodes found in North American curlews and has been considered very variably by different authors since then, including as a synonym of Krimi Burt, 1944 (see Matevosyan 1963) or Anomotaenia Cohn, 1900 (see Bona 1975; Schmidt 1986). In the review of the Dilepididae that we follow here, Bona (1994) gives a detailed diagnosis of the genus, which is significantly different from the original one from Clark (1952). In accordance with Spasskaya & Spasskii (1978), and contrary to Schmidt (1972), he also considers D. radiaspinosa Matevosyan, 1953 (syn. D. numenii Clark, 1952 , nec Owen 1949) as its type species.

Liga Weinland, 1857 , which is found in terrestrial birds, mostly Piciformes , is another genus with characters close to those of Dictymetra but normally with a small strobila and dorsal genital ducts. Several members of this genus, however, have a longer strobila reaching the size of the present material. For this reason, we compared our material to the presently recognized species of Dictymetra as well as to the “long” Liga spp. ( Table 4 ).

As for Australia, D. adelaidae ( Schmidt, 1972) from the spur-winged plover ( Lobibyx novaehollandiae Stephens, 1819 now Vanellus miles novaehollandiae ) in Queensland was described by Schmidt (1972) as a member of Lapwingia Singh, 1952 , which is now considered a synonym of Dictymetra (see Bona 1994). This species does not fit to the diagnosis of Dictymetra and should be place in another genus. Spasskaya & Spasskii (1978) transferred it to the genus Anomotaenia Cohn, 1900 . It is in any case very different from the present material for most usual characters, including the length of hooks (shorter) and number of testes (less numerous).

Our material clearly differs from all recognized species in the genus ( Table 4 ) by several characters, the most obvious being the high number of testes, which is only approached but not matched by D. volvulus (von Linstow, 1906) . The latter species has however slightly smaller rostellar hooks and a much shorter cirrus-sac. In consequence, we consider our specimens as belonging to a new species that we name Dictymetra gerganae sp. nov. Even though we are confident that this taxon is new, we should notice that the whole taxonomic organization of this group of genera remains quite uncertain due to the scarcity of reliable information for many species. This will probably lead to their complete revision and the definition of new genera, in which our material may need to be placed in the future.

Figures

Figs 17–22. Dictymetra gerganae sp. nov. 17. Scolex. 18. Hooks. 19. Mature proglottis. 20. Terminal genitalia. 21. Terminal genitalia tuft. 22. Egg. Scale bars: 17 = 100 µm; 18, 20, 21 = 50 µm; 19 = 500 µm; 22 = 20 µm.