Arhythmorhynchus sp.

Arhythmorhynchus sp.

Fig. 7 B View Figure 7

Host.

Mystus albolineatus Roberts ( Siluriformes , Bagridae ).

Locality.

Flood area of the Dan canal near Daeng Ban Non Du village , Udon Thani Province, Thailand (17°32.891'N, 103°03.831'E) GoogleMaps .

Site of infection.

Body cavity.

Infection rates.

Prevalence 1 / 1, intensity 6.

Molecular data.

Nuclear 18 S rRNA (1,703 bp), 28 S rRNA (1,132 bp), ITS (847 bp), and mitochondrial COI (603 bp) genes sequences of Arhythmorhynchus sp. were deposited in the GenBank database (Acc. nos. PQ 636382, PQ 636389, PQ 636392, PQ 631045).

Note.

Six cysthacanths of the genus Arhythmorhynchus were found in the body cavity of one bagrid catfish Mystus albolineatus Roberts. Five of them were in capsules with invaginated proboscis, one cysthacanth, female, had an evaginated proboscis, facilitating its morphological examination.

Morphology.

Trunk 1.27 mm long with maximum width at level of middle of proboscis receptacle 391. The front part of body with one field of spines. Its extent same ventrally and dorsally. Spines blades 21 long. Cylindrical proboscis with expansion in middle part. Proboscis 513 × 157 with 16 longitudinal rows of hooks, 22–23 hooks in each row. Sizes of hooks do not differ dorsally and ventrally. Hooks in anterior eight or nine rows large, with simple massive roots directed posteriorly. Hooks in next 13 rows spine-shaped, with short roots processes directed posteriorly. Length of hook blades: 33–40 (hook 2), 35–41 (3), 37–40 (4–7), 38–41 (8), 32–34 (9), 20–22 (10), 17–21 (11), 15–19 (12), 16–20 (13), 16–19 (14), 16–18 (15), 16–17 (16), 16 (17–23). Length of hook roots: 23–29 (2), 31 (3), 32–33 (4), 32 (5), 34–39 (6), 39–41 (7), 40–43 (8), 27–39 (9). Length of root processes of next hooks 8–12. Hooks in last one or two rows without roots. Neck retracted. Proboscis receptacle with double-layer muscular walls, 630 × 120 with oval cephalic ganglion in middle part. Lemnisci thin, ribbon-shaped, convoluted, 712 × 38, longer than proboscis receptacle. Vagina with two sphincters. Posterior body end slightly retracted. Genital pore terminal.

Remarks.

The definitive hosts of these acanthocephalans are gulls and waders ( Charadriiformes ), and fish are paratenic hosts. To date, 24 valid species have been described in the genus Arhythmorhynchus ( Amin 2013) . Only three species have more than 20 hooks in a longitudinal row on the proboscis: A. xeni Atrashkevich, 1978 described from Terek sandpiper Xenus cinereus (Güldenstädt, 1775) in Siberia, A. longicollis (Villot, 1875) Lühe, 1912 described from gulls in Europe, and A. limosae Edmonds, 1971 described from godwit Limosa lapponica in Townsville, Queensland, Australia ( Golvan 1956; Edmonds 1971; Atrashkevich 1978). The cystacanths of Arhythmorhynchus sp. from Thailand differs from all three species in the number of longitudinal rows of hooks (16 in Arhythmorhynchus sp. vs 19–20 in A. xeni and A. limosae , 22–24 in A. longicollis ), as well as in the ratio of large spine-shaped hooks (8–9 and 12–13 in Arhythmorhynchus sp. , 14–15 and 11–12 in A. xeni and A. limosae , respectively). The number of large hooks is similar in Arhythmorhynchus sp. and A. longicollis , 8–9 and 9–10 respectively; however, the length of the blades of the largest hooks in Arhythmorhynchus sp. is smaller than in A. longicollis (40–41 vs 48–50). Thus, morphological differences prevent us from classifying Arhythmorhynchus sp. as any of the known species of the genus.