Hysterothylacium cornutum
Creators: name: Moravec, F.
name: Nagasawa, Kazuya
Publisher: name: Zenodo
Year: 2000
Subjects: Biodiversity
Taxonomy
Animalia
Nematoda
Secernentea
Ascaridida
Ascarididae
Hysterothylacium
Hysterothylacium cornutum

description: Hysterothylacium cornutum (Stossich, 1904)   
(Figure 4)  
 Ascaris cornuta Stossich, 1904; Thynnascaris legendrei Dollfus, 1933.   
 Description   
Medium sized, whitish to yellowish nematodes; cuticle with ®ne dense transverse striation. Body broadest at its middle or posterior part, this being conspicuous particularly in large gravid females; anterior end of body relatively narrow, elongate. Very narrow cervical alae present. Anterior end with three pentagonal lips; dorsal lip somewhat smaller than subventral lips; lips broadest at middle, provided with relatively narrow ¯anges. Dorsal lip with two lateral double papillae; subventral lips with amphid, adjacent mediolateral double papilla and single lateral papilla. Interlabia well developed, nearly one half length of lips. Oesophagus long, almost cylindrical. Nerve ring encircling oesophagus approximately at border of ®rst and second sixths of its length. Ventriculus spherical, narrower than oesophagus; ventricular appendix much longer than intestinal caecum. Excretory pore slightly posterior to level of nerve ring. Caecum wide, short, approximately twice as long as ventriculus. Rectum a hyaline tube surrounded by three small, unicellular rectal glands. Tail conical, its tip without cuticular spines.  
 Male (four specimens). Body 11,701 ±29,149 long, maximum width 206±989. Length of lips 48±92, of interlabia 16±32. Oesophagus 1540±2688 long and 78±148 wide, forming 9±13% of body length. Nerve ring and excretory pore 313±426 and 352±513, respectively, from anterior extremity. Ventriculus 40±87 Ö 52±96; ventricular appendix 556±1009 long. Intestinal caecum 100±235 long. Length ratio of caecum and ventricular appendix 1: 4.5±10.1. Spicules equal, alate, slightly sclerotized, 988± 1832 (in juvenile male only 520) long, representing 4.4±6.3% of body length; their proximal ends blunt, distal ends pointed. Preanal papillae: 22±24 pairs of which about ten pairs closer to cloaca very small; adanal papillae: one pair; postanal papillae: seven to ten pairs of minute papillae. Pair of small lateral papillae present slightly anterior to level of last pair of caudal papillae. Ventral precloacal region with numerous longitudinal minute crests. Tail conical, broad at anterior part, 128± 168 long; its distal part posterior to region with caudal papillae narrowed to form a kind of sharply pointed spike 64±68 long; this spike indistinct in juvenile male (®gure 4E).   
 Female (three gravid specimens). Length of body 37,162 ±53,519, maximum width 1030±1936. Length of lips 104±160, of interlabia 36±60. Length of oesophagus 3729±3785 long and 148±157 wide, forming 7±10% of body length. Nerve ring and excretory pore 479±609 and 574±687, respectively, from anterior extremity. Ventriculus 104±157 Ö 131±174; ventricular appendix 183±348 long, markedly narrow, in largest female its maximum width 87 and minimum width at its anterior end 17. Length of intestinal caecum 131±174. Length ratio of caecum and ventricular appendix 1:4.2±10.7. Vulva in anterior part of body, situated anterior to anterior ovary, 8322±9785 from anterior end of body (at 16±26% of its length); vulva somewhat depressed, without elevated lips. Vagina muscular, directed posteriorly from vulva. Uteri opposed. Eggs almost spherical, unembryonated, 64±76 in diameter. Tail conical, narrow, elongate, 1453±1975 long; its tip lacking cuticular spines.   
 Host. Thunnus alalunga (Bonnaterre) (Scombridae, Perciformes).   
 Site of infection. Stomach.   
 Locality. Eastern North Paci®c Ocean (29 ss 28 ¾ N, 158 ss 07 ¾ W; 30 ss 33 ¾ N, 158 ss 24 ¾ W) (11 ± 12 February 1992).   
 Prevalence. 51% (25 ®shes infected/49 ®shes examined).   
 Comments   
 Specimens of the present material correspond, more or less, to the descriptions of H. cornutum given by Hartwich (1975), DeardorOE and Overstreet (1982) and Bruce and Cannon (1989). The last named authors reported the length of spicules to be 137±175 m m long, but this is an evident error and, apparently, it should be 1.37±1.75 mm. Baylis (1923) reported the length of spicules of H. cornutum to be 1.9 mm, Hartwich (1975) 1.23±2.40 mm; the present material shows that the spicules may be markedly short (520 m m) in juvenile males. Bruce and Cannon (1989) observed a considerable variability in the numbers of male caudal papillae (both preanal and postanal) in this species, which is con®rmed in the present paper; they found more numerous (38±47 pairs) caudal papillae than recorded in this study (30 ±35 pairs), with the exception of one male in which only 28 pairs were found; Hartwich (1975) reported 35±50 pairs of preanals and 11 pairs of postanals; we consider these diOEerences to be within the intraspeci®c variability of this species.   
 This nematode species was originally described from the Atlantic blue®n tuna, Thunnus thynnus (L.) oOE Trieste, Italy. According to Bruce and Cannon (1989), H. cornutum is apparently speci®c to the genus Thunnus (Thunnidae), being reported from T. thynnus (type host), T. alalunga (Bonnaterre), T. albacares (Bonnaterre) and T. maccoyii Castelnau from the Mediterranean, Bay of Biscay, eastern North Atlantic, North and Baltic Seas, North Paci®c, Hawaii, and oOE eastern Australia (see also Petter et al.,1995).   
 From the Paci®c Ocean oOE Japan, this species has already been reported, under the synonym Contracaecum legendrei (Dollfus, 1933), by Yamaguti (1941), who obtained three mature females from the stomach of the same host species (T. alalunga). Present data indicate that H. cornutum is a common parasite of T. alalunga in the eastern North Paci®c.
description: Published as part of Moravec, F. & Nagasawa, Kazuya, 2000, Some anisakid nematodes from marine ® shes of Japan and the North Paci ® c Ocean, pp. 1555-1574 in Journal of Natural History 34 (8) on pages 1563-1566, DOI: 10.1080/00222930050117486, http://zenodo.org/record/5279801