Raosentis sp.

Raosentis sp.

Figs 6 View Figure 6 , 7 A View Figure 7

Host.

Mystus mysticetus 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.

Intestine.

Infection rates.

Prevalence 12.5 % (1 / 8), intensity 1.

Morphology

(based on one male with sperm). Quadrigyridae with characters of genus Raosentis : i) proboscis with four rows of hooks with an unequal number of hooks in anterior and posterior rows; ii) a large area without hooks between second and third rows of proboscis hooks.

Male. Small acanthocephalan, white, fusiform, 4.11 mm long, 471 maximum width in anterior quarter of body (Fig. 6 B View Figure 6 ). Anterior part of body with in 28 rings of small tegumental spines, 50–54 spines in each ring. Field of spines 1.16 mm long beyond level of posterior edges of lemniscus, do not reach level of anterior margin of anterior testis. Distance between anterior ring of spines and next rings 77. Distance between 2 nd and 17 th rings of spines 18–22, distance between rings of spines increases posteriorly to 55–61. Proboscis 186 × 206, with 27 hooks in 4 rows, 6 or 7 spines in each row (Fig. 6 A, C View Figure 6 ). Hooks of anterior row located irregularly, three slightly anteriorly, three slightly posteriorly. Hooks of two anterior rows large, with simple roots directed posteriorly (Fig. 4 A, C View Figure 4 ). Their blades and roots 2–3 × larger than blades and roots of two posterior rows. Hooks of third and basal rows separated from hooks of the two anterior rows by 35, their roots also simple and directed posteriorly. Hooks blades of anterior row 91, second 78–92, third 20–29, basal 17–21. Hook roots of anterior row 46, second 50–52, third 21–23, basal 17–20. The neck is pronounced, 74 long, width in anterior part 87, in posterior part 135. Proboscis receptacle 524 × 129, with single-layer muscular wall, with cephalic ganglion 79 × 47 at bottom. Lemnisci 796 × 67, extend beyond proboscis receptacle, not reaching level of anterior edge of anterior testis. Organs of reproductive system 2.45 mm long, occupying 60 % of body length, in its posterior part. Testes oval, tandem, anterior larger than posterior. Anterior testis 423 × 216, posterior 401 × 208. Cement gland elongated, 443 × 167, adjacent to posterior edge of posterior testis. Pear-shaped cement reservoir under cement gland, 190 × 72, branching posteгiorly into two vas deferens. Saefftigen’s pouch absent. Bursa in invaginated state 685 long. Gonopore terminal.

Remarks.

To date, all seven species of the genus Raosentis Datta, 1947 have been described from freshwater fishes in India ( Naidu 2012). Raosentis sp. from Thailand differs from all other species of the genus by a slender elongated body more than 4 mm in length in the male (the body length of the male of other species of the genus does not exceed 3.3 mm) ( Naidu 2012) as well as by the significant distance of the anterior rings of tegumental spines from the following rings of spines. Raosentis sp. morphologically resembles R. lucknowensis Saxena, Gupta, Johri, Ramakant, 2014 , described from Mystus vittatus (Bloch) in River Gomti (Lucknow, India) by the number of rings of tegumental spines (28 in Raosentis sp. , 28–30 in R. lucknowensis , in other species of the genus the number does not exceed 20) and by the length of the blades of the proboscis hooks of the two anterior rows (78–92 in our specimen, 70–90 in R. lucknowensis ) ( Saxena et al. 2014). However, these two species differ in the number of proboscis hooks (6, 7, 7, 7 in Raosentis sp. vs 8, 8, 8, 8 in R. lucknowensis ), the size of the blades of the third and fourth rows (20–29 and 17–21 in Raosentis sp. vs 30–40 and 30–40 in R. lucknowensis , respectively). We suppose that Raosentis sp. might be a new species of the genus Raosentis , however, we waive its formal description since only a single specimen was studied. At the same time, we consider it appropriate to present a key for identifying the species of the genus.