Aspidogaster limacoides Diesing, 1834

Suthar, Jaydipbhai, Al-Jufaili, Sarah, Bray, Rodney A., Frank, Marcus, Theisen, Stefan & Palm, Harry W., 2021, Redescription of Aspidogaster limacoides Diesing, 1834 (Aspidogastrea: Aspidogastridae) from freshwater fishes of northern Germany, Parasitology Research (3405) 120 (10), pp. 3405-3416 : 3407-3410

Species: Aspidogaster limacoides Diesing, 1834

Synonym: A. donicum Popoff, 1926

Description and measurements (in µm, Figs. 1–4 ): Body elongated, bluntly rounded at the anterior and tapering towards the posterior end; widest at the level of the cirrus sac region ( Fig. 1A, B ). Body length (n = 13) 1,399 –3,069 and width (n = 13) 470–1,082. Oral and ventral suckers absent. Mouth at anterior extremity, aperture circular or elongate ( Fig. 1B ). Oral aperture muscular. Buccal funnel surrounds mouth. Mouth cup-shaped ( Fig. 2A, B ). A few papillae-like structure posterolateral to the mouth ( Fig. 2C, D ). Ventral disc oval, bears 4 longitudinal rows each with 13–14 alveoli; 4 alveoli on each transverse row with individual alveolus at the anterior and posterior extremities; alveoli in median the rows transversely elongate, other alveoli more or less square or oval ( Fig. 2B ). Alveoli number varies from 54 to 58. Median alveoli more regularly arranged than the peripheral alveoli especially on the extreme ends of the periphery of the disc. Ventral disc covers most of body, often including mouth. Ventral disc length (n = 13) 1,261 –1,923 and width (n = 13) 920–1,369. Marginal organs, as openings of exocrine, multicellular glands, pyriform, regular arranged on margins of both sides at junction of interalveolar septa of ventral adhesive disc ( Figs. 2E and F , 3A , 4D–F ). Opening of the terminal ducts of marginal organs at junction between transverse and longitudinal ridges on the rim of the ventral disc ( Figs. 2E and F , 3A , 4D–F ). Mouth connected to the pharynx via duct which gives funnel-shaped appearance to the mouth. Prepharynx length (n = 10) 183–367. Pharynx large, globular, strongly muscular. Pharynx length (n = 13) 203–320 and width (n = 13) 187–283. The intestine is simple, with single caecum, which reaches to the posterior end of the body ( Fig. 1A ). Caecum length (n = 1) 852. Presence of numerous pori (small openings) all over the body including inside and around the mouth, on neck, on fold between neck and ventral disc (including alveoli and on septa); dorsal, ventral, both lateral sides and posterior region ( Figs. 2D , 3 B-D). Excretory pore subterminal, towards more on the dorsal side ( Fig. 3E ).

Testis single, elongate, large and post-ovarian. Testis length (n = 5) 272–340 and width (n = 5) 170–239. Cirrus sac claviform, sinistral to pharynx, with doubled layered very thick muscular wall at proximal part, which becomes thinner at distal part. Cirrus sac length (n = 5) 402–537 and width (n = 5) 194–236. Internal seminal vesicle present, connected to pars prostatica, which opens into the ejaculatory duct. Genital pore not clearly visible, apparently opens at anterior level of pharynx.

Ovary single, globular and pretesticular. Ovary length (n = 2) 208–245 and width (n = 3) 141–170. The uterus is very long, fills posterior half of the body. Eggs are numerous, oval, often with opened operculum in distal part of the uterus. Egg length (n = 9) 72–93 and width (n = 9) 40–52.

Vitelline follicular, follicles globular, lateral fields beginning at equator, present on either side and confluent or nearly so at posterior end ( Fig. 1A, B ).

Histology of the ventral disc

The ventral disc consists of four longitudinal rows of alveoli. In cross-section, the ventral disc consists of longitudinal muscles, marginal gland cells interspersed with dorsoventral muscles and a layer with more tightly arranged nuclei of the marginal gland cells ( Fig. 4A–C ). The marginal organ consists of the duct connected with the marginal gland cells, the ampulla with the secretion, a muscular papilla and the terminal duct and opening ( Fig. 4D–F ).

Taxonomic summary

Type hosts: Not designated. First mentioned by Diesing. Squalius cephalus (L.) and Leuciscus idus (L.) ( Diesing, 1834 (short version), 1835 (extended version)).

Type locality: South of Vienna, Austria (see Reimer 2002).

Other hosts: Rutilus rutilus (L.), Scardinius erythrophthalmus (L.) and Abramis brama (L.)

Other locality: Lake Tollensesee , Mecklenburg-Western Pomerania, Germany (53°30′26″N 13°12′41″E).

Prevalence: Rutilus rutilus 61.7%, Scardinius erythrophthalmus 7.7%, Abramis brama 2.9%

Intensity (mean): Rutilus rutilus : 1–53 (9.3), Scardinius erythrophthalmus : 3 (3) and Abramis brama : 18 (18.0).

Site of infection: Mainly stomach and few specimens in intestine, post-mortem migration possible.

Deposition of voucher specimens: Natural History Museum Berlin (Museum für Naturkunde Berlin ( ZMB), Germany); E.7645-E7647 .

Phylogenetic analyses

Two contiguous sequences, 1,454 (accession number: MT951619) and 1,469 (accession number: MT951620) base pairs (bp) long, of the ITS1-5.8S-ITS2 region of rDNA were generated from adult worms isolated from Rutilus rutilus and Abramis brama . The newly obtained sequences varied by a single base. Our new sequence data showed 98.35% to 98.78% identity with ITS1-5.8S-ITS2 rDNA sequences of A. limacoides derived from R. rutilus sampled from Russia (accession codes: HE863971, HE863970, HE863969 and HE863966) using BLAST service. A. ijimai clade was subdivided according to geographical origin. This cluster formed a sister clade to A. chongqingensis with strong nodal support. Specimens of A. conchicola formed a distinct third clade. The fourth clade contained specimens of A. limacoides from German waters (present study) and the European part of Russia ( Fig. 5 ).

Figures

Fig. 1 Aspidogaster lima- coides line drawings from Rutilus rutilus from North Germany. A Dorsal view (scale bar=500 µm); B ventral view (scale bar=500 µm); C eggs (scale bar=50 µm); D cirrus sac (scale bar=200 µm)

Fig.2 Aspidogaster limcoides, SEM: A dorsal view (scale bar=100 µm); B ventral view with ventral disc (scale bar=100 µm); C neck region, arrow showing depression of neck (scale bar=20 µm), square D showing papillae-like structures posterior lateral to mouth; D posterior lateral papil- lae (arrow) (scale bar=2 µm); E ventral disc, arrow show- ing marginal organ (scale bar=20 µm); F ventral rim with marginal organ with terminal duct (arrow) (scale bar=10 µm)

Fig. 3 Aspidogaster limcoides, SEM: A marginal organ with terminal duct (scale bar=2 µm); B and B 2: Arrow showing pits inside the mouth (scale bar=20 µm); C Ventral disc showing pits on alveoli and septa (scale bar=10 µm); D dorsal view, posterior body with pits (scale bar=2 µm); E excretory pore (scale bar=20 µm)

Fig.4 Cross-section of Aspi- dogaster limacoides, histology, from the level of the anterior edge of the ventral disc: A and D arrows (black and blue) showing marginal organs on ventral disc; B, E and F dia- gram of marginal organ (black and red arrows); C dorsoventral and longitudinal muscles (green arrows). Note: A–C H&E staining and D–F Alcian blue staining

Fig. 5 Phylogenetic tree based on analyses of ITS1-5.8S-ITS2 sequences of species belong- ing to the genus Aspidogaster using the maximum likelihood method of phylogenetic recon- struction with TIM2+I model according to jModelTest soft- ware v 2.1.10. Nodal numbers give bootstrap statistical support for the analyses. AN, Amur River, Nikolaevsk-na-Amure; AK, Amur River, Khabarovsk; Kh, Khanka Lake; Chi, China; ER, European part of Russia; Ger, Germany; JPN, Japan. *Misidentified A. chongqin- gensis