Hexangium saudii, Al-Jahdali & O, 2013

Al-Jahdali, O. & O, P., 2013, New Intestinal Trematodes From Siganid Fishes Off The Saudi Coast Of The Red Sea, Acta Zoologica Academiae Scientiarum Hungaricae 59 (1), pp. 3-12 : 6-7

Hexangium saudii sp. n.

( Fig. 1 )

Type- host: Siganusrivulatus ForsskåletNiebuhr (Teleostei, Siganidae ).

Site: Middleintestine.

Type- locality: RedSeaoffthecoastofRabigh (between 22°49′Nand 22°54′N), SaudiArabia. Prevalence: 8/40 fishesexamined; 20%.

Type- material: HolotypeandparatypesaredepositedintheNaturalHistoryMu-

seum, London, Reg. nos. 2011.8.2.1 and 2011.8.2.2–8.

Description (Basedon 10 fullygravidspecimens): Bodylanceolateorelongate- pyri- form, stout, somewhatdorso- ventrallyflattened, 2,261 –3,551 (2,906) inlength, 648–1,019 (834) inmaximumwidthinitsposteriorthird. Tegumentarmedwithfinesharpspines dorsallyandventrally (oftenlostduringfixation). Suckersabsent. Pharynxsub-terminal, globular, welldeveloped, directlysurroundsoralopening, 152–238 × 143–225 (195 × 184). Oesophaguslong, 529–831 (680), providedwithroundoesophagealbulbatitsposterior end; bulbsmall, 74–118 (96) indiameter. Intestinalbifurcationataboutjunctionoffirstand secondthirdsofbody; caecadistinctlyshort, wide, extendintomiddlethirdofbody. Testes 2, usuallyoval, sometimesround, situatedobliquelyinposteriorregionofbody, subequal, 260–408 × 232–366 (334 × 299). Cirrussacabsent. Seminalvesicleelongate, slender, extends anteriorlyfromshortdistanceposteriortointestinalbifurcationtonearthegenitalpore, 350–568 × 42–62 (429 × 52); distalendofvesiclejoinsthatoftheuterustoformrelatively shorthermaphroditicduct. Genitalporesituatedmid- waybetweenpharynxandintestinal bifurcation. Ovaryround, median, immediatelypost-testicular, neartoposteriorextremity, 119–183 (151) indiameter. SeminalreceptacleandLaurer’scanalabsent; uterineseminalre- ceptaclepresent. Uterusrelativelylong, coiledintesticularregionandbetweentestesand intestinalcaeca, thenpassesdirectlybetweencaecatogenitalpore. Eggsoval, yellowish, thick-shelled, moderatelylarge, 56–66 × 38–46 (61 × 42). Vitellinefolliclesmoderatelylarge, arrangedin 5–7 rosette- likegroupsoneachside, extendinglateraltocaecaforalmosttheir entirelength. ExcretoryvesicleV-shaped; excretoryarmsdividenearposteriorendofeach caecum, givingriseto 3 longcollectingductsextendinganteriorlytonearlevelofgenital pore. Excretoryporedorso- subterminal.

Comment – Hexangium GotoetOzaki, 1929 currentlyincludestwovalid species, H. sigani GotoetOzaki, 1929 and H. brayi HassanineetGibson, 2005 . Thefirstisthebestknown, sinceithasbeenrecordedinnumeroussiganid species (VELAsquEz 1961, FIscHtHAL & Kuntz 1964, 1965, AL-YAMAnI & NAH- HAs 1981, GEEts & OLLEvIEr 1996, KArDOusHA 2003, SEy etal. 2003, DzIkOwskI etal. 2003, EL-LAbADI etal. 2006), whereasthesecondisknownonlyfromits originaldescription.

Theabovedescriptionof H. saudii sp. n. agreeswiththeconceptof Hexangium GotoetOzaki, 1929 . However, itclearlydiffersfromthetwoknownspe- ciesofthegenus, beinguniqueinhavingthefollowingtwocharacters:

− Theintestinalcaecaaredistinctlyshort, extendingonlytothemiddle thirdofthebodyandaremoredistantfromthetestes (versuslongand extendingtoclosetothetestes).

− Thevitellinefolliclesarearrangedinrosette- likegroups (versusarranged singlywithoutacharacteristicappearance).

However, thenewspeciesdiffersfromeachoftheothertwospeciesof thegenusinseveralotherspecificcharacteristics: from H. sigani inhaving vitellinefolliclesonlydistributedlateraltothecaeca (versusdistributedlat- eralandmedialtothecaeca) andinhavingsmallereggs (56–66 × 38–46 μm) (versus 77–85 × 50–56 μm); andfrom H. brayi inhavingadistinctlysmaller oesophagealbulb, obliquelyarrangedtestes (versussymmetricallyarranged), vitellinefolliclesdistributedlateraltothecaeca (versusconfinedtotheintercaecalfield) andsmallereggs (56–66 × 38–46 μm) (versus 70–85 × 55–60 μm). Inviewofthesespecificdifferences, thepresentspeciesisconsideredtobe newtoscience.

Etymology: Thespecificname “ saudii ” ofthenewspeciesreferstothelocalityoffthe

coastofSaudiArabia.

Figures

Figs 1–2. Holotypes (whole-mount, ventral view): 1 = Hexangium saudii sp. n. from Siganus rivulatus, Red Sea. 2 = Progyliauchen magnacetabulum sp. n. from Siganus luridus, Red Sea. Scale bar= 500 μm.