Sclerocollum saudii Al-Jahdali, 2010, sp. nov.
Creators: name: Al-Jahdali, Mohammed O.
Publisher: name: Zenodo
Year: 2010
Subjects: Biodiversity
Taxonomy
Animalia
Acanthocephala
Palaeacanthocephala
Echinorhynchida
Rhadinorhynchidae
Sclerocollum
Sclerocollum saudii

description: Sclerocollum saudii sp. nov.
(Fig. 2 A–H)
Description. Based on 30 whole-mounts of each stage:
Cystacanths (Fig. 2 A)
Elongate, cylindrical, usually curved at one end, 1,125–3,512 (2,318) × 300–659 (479), and contains a single active juvenile measuring 516–910 in length; Excystment of juvenile is through a tubular portion released from the cyst, and is preceded by squirts of a foamy material.
Newly excysted juvenile (Fig. 2B)
Trunk 953–1,340 (1,164) in length, differentiated into an anterior frustum-shaped part (contains proboscis receptacle and lemnisci) and a posterior tubular part (contains anlagen of reproductive system). Frustumshaped part 491–855 (673) in length, 450–748 (599) in greatest width near its base. Tubular part 448–690 × 195–221 (569 × 208). Proboscis relatively short, cylindrical, 294–362 × 82–130 (328 × 106), armed with 10 alternating longitudinal rows of sharp recurved hooks; each row includes 8–9 hooks of variable length; basal hooks alternate with each other (not forming ring). Proboscis hooks: first 3 hooks, 27–32 (29); next 3, 29–35 (32); and the remaining 2 or 3, 21–25 (23) in length. Neck short, 41–63 (52) in length. Proboscis receptacle cylindrical, 290–394 × 118–146 (342 × 132). Lemnisci claviform, 372–468 × 96–144 (420 × 120). Anlagen of reproductive system hardly seen; sex of a newly excysted juvenile not evident.
Immature worms (Fig. 2 C, D)
Immature males (Fig. 2 C): Trunk elongate-fusiform, 2,311–5,370 (3,840) in length, 396–688 (542) in greatest width at its anterior region. Proboscis 308–364 × 75–93 (336 × 84). Proboscis hooks: first 3 hooks, 30–34 (32); next 3, 32–38 (35); and the remaining 2 or 3, 23–28 (25) in length. Neck 64–76 (70) in length. Proboscis receptacle 348–470 × 78–102 (427 × 90). Lemnisci 877–1,043 × 73–111 (960 × 92). Testes 2, elongate-oval, tandem, contiguous, nearly in middle of trunk; anterior testis 205–390 × 98–196 (297 × 147), posterior testis 210–412 × 84–164 (311 × 124). Cement glands 4, tubular, shriveled, in two tandem pairs; anterior pair 311–681 (496) in length; posterior pair 275–615 (445) in length. Seminal vesicle irregularly tubular, shriveled. Genital pore terminal.
Immature females (Fig. 2 D): Trunk elongate, 2,910–6,013 (4,461) in length, 671–1,102 (886) in greatest width at level of lemnisci. Proboscis 355–376 × 91–129 (365 × 110). Proboscis hooks closely similar to those of males in size. Neck 65–81 (73) in length. Proboscis receptacle 378–602 × 106–156 (490 × 131). Lemnisci 811–1,060 × 75–117 (935 × 96). Uterine bell 113–153 × 65–97 (133 × 81), its base 534–1,128 (831) from posterior end. Uterus tubular, short, 417–765 (591) long. Vagina short, guarded by sphincter muscle on each side. Genital pore terminal.
Mature worms (Fig. 2 E–H)
General: Body moderate in size. Females larger than males. Trunk thick-walled, uspined; conspicuous sclerotised plaques embedded in the tegument at the anterior region of the trunk. Proboscis relatively short (Fig. 2 H), cylindrical, armed with 10 alternating longitudinal rows of sharp recurved hooks; each row includes 8–9 hooks of variable length; basal hooks alternate with each other (not forming ring). Neck short. Proboscis receptacle double-walled, relatively short, claviform. Ganglion near middle of proboscis receptacle. Lemnisci claviform, equal in length, distinctly longer than proboscis receptacle.
Mature males (Fig. 2 E): Trunk elongate-fusiform, 5,624–11,350 (8,487) in length, 881–1,378 (1,129) in greatest width at its anterior region. Proboscis 323–387 × 95–140 (355 × 117). Proboscis hooks: first 3 hooks, 34–38 (36); next 3, 36–40 (38); and the remaining 2 or 3, 24–30 (27) in length. Neck 65–91 (78) in length. Proboscis receptacle 522–829 × 124–176 (675 × 150). Lemnisci 1,161–1,944 × 98–178 (1,332 × 138); lemnisci length/ Proboscis receptacle length is about 2.3. Testes 2, elongate-oval, tandem, contiguous, in middle of trunk or slightly anterior; anterior testis 513–875 × 240–400 (694 × 320); posterior testis 525–1,053 × 209–425 (789 × 317). Cement glands 4, tubular, in two tandem pairs; anterior pair 755–2,310 × 90–205 (1,532 × 147); posterior pair 690–1,960 × 81–165 (1,325 × 123). Seminal vesicle claviform, relatively large. Copulatory bursa well developed, hemispherical, 371–637 (504) in diameter. Genital pore terminal. In copulating male, the extrusion of the bursa appears to induce a slight displacement of the sexual organs toward the posterior end.
Mature females (Fig. 2 F): Trunk elongate, 6,595–15,421 (11,008) in length, 695–1,421 (1,058) in greatest width at its anterior region. Proboscis 335–391 × 90–138 (363 × 114). Proboscis hooks closely similar to those of males in size. Neck 71–107 (89) in length. Proboscis receptacle 483–725 × 121–185 (604 × 153). Lemnisci 1,032–1,735 × 91–157 (1,383 × 124); lemnisci length/ Proboscis receptacle length is about 2.25. Uterine bell well developed, 166–198 × 85–154 (182 × 119), its base 1,480–3,081 (2,280) from posterior end. Selector apparatus 210–394 × 65–113 (238 × 89). Uterus tubular, relatively short, 1,357–2,841 (2,099) long. Vagina short, guarded by sphincter muscle. Genital pore terminal. Eggs elongate (Fig. 2 G), small, with polar swelling of middle membrane; uterine eggs 20–28 × 6–10 (24 × 8).
Type host. Siganus rivulatus Forsskål (Teleostei, Siganidae).
Site. Anterior 80% of intestine.
Type locality. Red Sea off the coast of Rabigh, Saudi Arabia.
Prevalence. 24/30 fishes examined; 80%.
Type material. Holotype and paratypes are deposited in the Natural History Museum, London, Reg. no. male-holotype-2009.11.13.6, female-allotype-2009.11.13.7, male and female paratypes-2009.11.13. 8–10.
Etymology. The specific name saudii refers to the locality (Saudi Arabia).
Remarks. As mentioned above, 2 species of Sclerocollum are currently recognized, i.e. S. rubrimaris Schmidt et Paprena, 1978 (type species) and S. robustus (Edmonds, 1964) Schmidt et Paprena, 1978. The first is the best known, since it has been recorded in many siganid species (Siganus argenteus, S. canaliculatus, S. luridus, S. oramin, S. rivulatus, S. rostratus and S. sutor) from the Red Sea, Arabian Gulf and Kenyan coast (see Amin et al. 1984; Diamant 1989, El-Naffar et al. 1992; Martens and Moens 1995; Geets and Ollevier 1996; Hassanine 2006; Hassanine and Al-Jahdali 2007), while the second is still known only from its original description. In both species, the proboscis is armed with 14 alternating longitudinal rows of sharp hooks; in the former, each row includes 8–10 hooks and the lemnisci are slightly longer than the proboscis receptacle, while in the second, each row includes 24–25 hooks and the lemnisci are slightly shorter than the proboscis receptacle. Sclerocollum saudii sp. nov. is similar to S. rubrimaris, but significantly differs in having a proboscis only armed with 10 rows of hooks (8–9 hooks in each row), smaller proboscis hooks (anterior hooks 34–38, intermediate hooks 36–40, posterior hooks 24–30 vs. 34–44, 44–50 and 30–38μ in length), lemnisci much longer than proboscis receptacle (about 2.3 as proboscis receptacle length vs. slightly longer than the proboscis receptacle) and in having much smaller eggs (20–28 × 6–10 vs. 55–72 × 14–16μ). These differences in proboscis hooks, lemnisci length and egg dimensions are specific, and usually considered as key characteristics to differentiate species of acanthocephala (see Amin 1985); their combination is sufficient to consider the present species as a new one.
Excystation and activation of acanthocephalan cystacanths has been examined in only three species: Moniliformis dubius Meyer, 1933 (see Graff and Kitzman 1965), Echinorhynchus truttae Schrank, 1788 (see Awachie 1966) and Polymorphus minutus Goeze, 1782 (see Lackie 1974). Activation is thought to be mainly stimulated superficially by the bile of the host or by the osmotic pressure of the surrounding medium. The exact role of the bile is not fully understood (Khanna 2004). In S. saudii sp. nov., excystment of the active juvenile is through a tubular portion released from the cyst, and is preceded by squirts of a foamy material. Thus, juvenile growth may lead to an increasing pressure on the inside of the cyst which could be instrumental in impelling the tubular portion through which the juvenile escapes from the cyst.
description: Published as part of Al-Jahdali, Mohammed O., 2010, Helminth parasites from Red Sea fishes: Neowardula brayi gen. nov., sp. nov. (Trematoda: Mesometridae Poche, 1926) and Sclerocollum saudii sp. nov. (Acanthocephala: Cavisomidae Meyer, 1932), pp. 57-65 in Zootaxa 2681 on pages 61-64, DOI: 10.5281/zenodo.199330