Cercaria cattieni

Krupenko, Darya, Gonchar, Anna, Kremnev, Georgii, Efeykin, Boris, Krapivin, Vladimir & Methods, Materials And, 2020, New type of xiphidiocercariae (Digenea: Microphalloidea) from South Vietnam, Folia Parasitologica (033) 67, pp. 1-6 : 2-3

Cercaria cattieni 1 Fig. 1

F i r s t i n t e r m e d i a t e h o s t: Sulcospira dautzenbergiana (Morelet, 1884) (Caenogastropoda: Pachychilidae ).

L o c a l i t y: Stream in Cát Tiên National Park , Southern Vietnam (11.4305N, 107.4294E) .

P r e v a l e n c e: 2% (n = 41).

S i t e o f i n f e c t i o n: Digestive gland.

Vo u c h e r s p e c i m e n s: Five slides from one gastropod specimen were placed in the collection of the Department of Invertebrate Zoology of Saint Petersburg University under numbers V2018 F 01-1–V2018 F01-5

Daughter sporocysts (measurements based on six fixed specimens; Figs. 1 A , 2 A ): Sporocysts white, elongate, 799–1,628 × 291–369 (1,124 × 336), contain cercariae at different stages of development.

Cercariae (measurements based on 21 fixed s p e c i m e n s; F i g s. 1 B – E, 2 B – I): Body 481–758 (594) long, 285–460 (369) wide, pear-shaped, narrow at fore end. Hindbody wide, with folded margins. Tegument with simple spines, most densely arranged in forebody; largest spines in midbody. Tail simple, 603–841 (697) long, 69–101 (93) wide at base, with smooth tegument. Oral sucker subterminal, spherical, 69–103 × 66–102 (86 × 85). Its rim armed with simple spines thicker than body spines, their size reduces posteriorly ( Fig. 2D ). Stylet 43–52 (48) long, 5–8 (7) wide at base, single-pointed, with anterior thickening ( Figs. 1D,E , 2G ). Ventral sucker spherical, 142–196 × 140–204 (160 × 165); 4–5 irregular rows of spines (thicker than body spines) lie at sucker rim, around opening, surrounded by smooth zone with 6 large papillae (probably, sensory receptors) ( Fig. 2E ).

Prepharynx short; pharynx 28–47 × 20–41 (37 × 28); oesophagus very short. Caecal primordia composed of single row of cells ( Fig. 2F ), 3–6 (4) wide, extending nearly to level of excretory vesicle. Paired cephalic ganglia conspicuous, posterior to oral sucker, interconnected by dorsal commissure between pharynx and oral sucker. Dorsal and ventral pairs of longitudinal nerve chords visible along whole body. Penetration glands numerous, in forebody, anterolateral to ventral sucker ( Fig. 2F ). Ducts of penetration glands proceed along dorsal surface of oral sucker and open as two groups, lateral to stylet pouch ( Fig. 2G,H ).

Excretory vesicle I-shaped, 164–232 × 34–67 (189 × 47). Main collecting ducts starting from excretory vesicle anterolaterally ( Fig. 2I ). Flame-cell formula not determined. Primordia of testes symmetrical, 12–15 (13) in diameter, anterolateral to excretory vesicle. Cirrus sac primordium anterior to ventral sucker. Primordia of uterus, Laurer’s channel and ovary also visible ( Fig. 2I ). Cercariae swim with their body contracted, thus taking saucer-shape; elongated tail beats vigorously (Supplementary material).

Mucoid glands found in cercarial embryos as four pairs of cells, anterior, lateral and posterior to ventral sucker ( Fig. 1F , 3A ). Later these cells form numerous dendrites remaining close to ventral surface ( Fig. 3B, C ). At a certain stage, part of mucoid transferred into region of stylet pouch ( Fig. 3D ). Next, metachromatic staining disappears from stylet pouch, being found on cercarial surface ( Fig. 3E ). Mucoid from rest of glands transferred into body tegument, mostly in middle third of body ( Fig. 3F–H ).

We obtained sequences of three fragments of the rDNA and the mitochondrial COI gene for C. cattieni 1 ( Table 1 ). None of these sequences had any close BLAST hits. Preliminary 28S rDNA-based phylogenetic analysis (covering a broad range of taxa within the Xiphidiata) suggested focusing the dataset on the Microphalloidea and particularly the Renicolidae . The final alignment included 40 sequences and was 1,226 bp long, including 39 gaps. The resulting phylogenetic tree ( Fig. 4 ) featured two major clades corresponding to the Microphalloidea and Plagiorchioidea. One of the lineages within the Microphalloidea included the families Renicolidae , Eucotylidae , the unknown family with unidentified cercariae from Nigeria (KX022508 and KX022509, Awharitoma and Enabulele 2018), and also C. cattieni 1 forming a well-supported clade with Pachypsolus irroratus (Rudolphi, 1819) (family Pachypsolidae ) ( AY222274 ).

Figures

Fig. 1. Cercaria cattieni 1. A – sporocyst; B–F – cercariae; B – body structure; C – general view; D, E – stylet, ventral (D) and lateral (E) view;F – scheme of cercarial embryo with mucoid glands (grey).

Fig. 2. Microphotographs of Cercaria cattieni 1 stained with Erlich’s haematoxylin (A) and Heidenhain’s iron haematoxylin (B–I). A – daughter sporocyst; B – underdeveloped cercaria; C – cercaria at late stage of development (tail lost during fixation); oral (os) and ventral (vs) sucker, excretory bladder (ex), primordia of cirrus sac (cs) and uterus (ut) are visible; D, E – spination of the oral sucker (D) and ventral sucker (E) rim (DIC); note sensory papillae (se) on E; F – forebody of cercaria (DIC), caeca (c), cephalic ganglia (cg), oral sucker (os), penetration glands (pg) and pharynx (ph) are visible; G, H – ducts of penetration glands going along the oral sucker, opening near the stylet (st) tip (DIC); I – hindbody of the cercaria (DIC); primordia of ovary (ov) and Laurer’s channel (lc) are visible posterior to the ventral sucker (vs); main collecting duct (mcd) starts anterolaterally from the excretory bladder (ex) and goes around testis primordium (te).

Fig. 3. Toluidine blue staining of Cercaria cattieni 1. A – cercarial embryo, lateral view, early stage of mucoid glands (mg) formation; B – cercarial embryos at different stage, metachromatic staining shows mucoid glands; C – later cercarial embryo (tail lost during fixation), metachromatic staining of mucoid glands with numerous dendrites; D – mucoid staining of stylet pouch; E – mucoid on the surface of the fore region; F, G – mucoid in the midbody, beneath musculature and tegument; ventral nerve chords (vnc) are visible among mucoid; H – midbody, mucoid transferred to the tegument. os – oral sucker; vs – ventral sucker; t – tail. A, D, E, G, H – differential interference contrast.

Fig. 4. Phylogenetic position of Cercaria cattieni 1 within the Microphalloidea based on 28S rDNA sequence data analysis with Bayes- ian inference. Posterior probabilities are printed next to nodes; scale bar shows substitution rate.