Mediorhynchus is a genus of small parasitic spiny-headed (or thorny-headed) worms. Phylogenetic analysis has been conducted on two known species of Mediorhynchus and confirmed the placement along with the related genus Gigantorhynchus in the family Gigantorhynchida. The distinguishing features of this order among archiacanthocephalans is a divided proboscis (specifically, the presence of a "teloboscis" which is the posterior third of a proboscis). This genus contains fifty-eight species that are distributed globally. These worms exclusively parasitize birds by attaching themselves around the cloaca using their hook-covered proboscis. The bird hosts are of different orders.
Taxonomy
Mediorhynchus is monophyletic based on phylogenetic analysis.Rodríguez, S. M., Amin, O. M., Heckmann, R. A., Sharifdini, M., & D’Elía, G. (2022). Phylogeny and life cycles of the Archiacanthocephala with a note on the validity of Mediorhynchus gallinarum. Acta Parasitologica, 1-11.
Description Species can be identified primarily morphologically by the arrangement of hooks of the proboscis. The presence of a divided proboscis (specifically, the presence of a "teloboscis" which is the posterior third of a proboscis) is an autapomorphy of Mediorhynchus. Males in some species possess eight cement glands which are used to temporarily close the posterior end of the female after copulation.
Species There are 59 species in the genus Mediorhynchus.
Name Taxonomy Host(s) and range Diagnostic featuresMediorhynchus africanusAmin, Evans, Heckmann and El-Naggar, 2013The species name africanus is named for the worm's distribution across sub-Saharan Africa. It is synonymous with Empodius segmentatus (de Marval, 1902) Southwell et MacFie, 1925 and Mediorhynchus selengensis Harris 1973. One mitochondrial and one nuclear gene sequence confirmed that M. africanus and M. gallinarum are allopatric sister species with 9.7% genetic sequence divergence. A dorsoventrally flattened, pseudo-segmented trunk bears numerous sensory pits. The proboscis is covered in 18–22 longitudinal rows of 4–6 hooks, and terminates in two conspicuous apical pores. In females, the posterior extremity is expanded and forms a dorsal, dome-shaped terminal projection situated opposite the subterminal gonopore. The eggs are comparatively large.
The trunk is pseudosegmented, flattened laterally, has many prevalent sensory pits, and measures 3.0 to 74.0 mm long by 0.5 to 2.80 mm wide in the male and measures between 4.00 and 110.00 mm long by 0.60 and 4.00 mm wide in the much larger female. There are up to 100 annuli (structures that permits shortening and lengthening of the body by telescoping) in females but fewer in the shorter males. The proboscis is divided by a prominent ridge into two parts: anterior and posterior. The anterior proboscis is pear or apple-shaped with a truncated bare apical end measuring 250 to 339 long by 278 to 478 wide in the male and 300 to 438 long by 330 to 510 wide in the female. The anterior proboscis has two prominent apical pores and 18 to 22 longitudinal rows of 4 to 6 hooks each. The hooks posteriorly directed and measure between 35 and 76 long with the smallest found anteriorly and the longest in the middle. The posterior proboscis is conically shaped and measures 291 to 332 long by 591 to 689 wide at junction with anterior trunk in the male, and 323 to 365 long by 99 to 745 wide at junction with anterior trunk in the female. Except for the posterior most end, the posterior proboscis is covered in very thin spines that are curved posteriorly or undulating with a total of 26 to 40 longitudinal rows of 2 to 6 spines each measuring 14 to 43 long with the longest spines found anteriorly. The Proboscis receptacle is single-walled with anterior portion encased in jacket of adjacent retractor fibers and measures 0.64 to 1.23 mm long by 0.11 to 0.44 mm wide in the male and 0.64 to 1.80 mm long by 0.11 to 0.55 mm wide in the female. The proboscis retractor muscles are prominent and attached to the proboscis receptacle near its posterior end dorsally. The lemnisci long, digitiform, unequal, and unattached. The shorter lemniscus measure between 1.60 and 3.38 mm long by 0.21 and 0.31 mm wide, with 5 or 6 giant nuclei in the male and measure 1.60 to 5.50 mm long by 0.19 to 0.33 mm wide, with 5 or 6 giant nuclei in the female. Longer lemniscus measures 2.15 to 3.47 mm long by 0.21 to 0.33 mm wide with 6, occasionally 7, giant nuclei in the male and measures 2.12 to 7.31 mm long by 0.19 to 0.62 mm wide with 6 giant nuclei in the female. The male reproductive system is located in the posterior third of trunk and consists of two oblong testes measuring Anterior testis measure 0.37 to 4.10 mm long by 0.30 to 1.10 mm wide and the posterior testis measure 0.32 to 3.15 mm wide. There are eight clustered cement glands larger anteriorly, each with one large central giant nucleus and with independent cement ducts emptying at posterior end of Saefftigen’s pouch, along with prominent common sperm duct. The male gonopore is terminal. The female reproductive system is short and located in the broad and flat posterior end of trunk. The uterine bell contains many large nucleated cells with its dorsal and ventral anterior ends connected to body wall with filaments. The gonopore is sub-ventral occasionally covered by a looping posterior trunk expansion. The eggs are ovoid being 65 to 86 long by 39 to 52 wide. Mediorhynchus alecturae(Johnston and Edmonds, 1947)Johnston & Edmonds, 1947 : Australian Acanthocephala n° 6. Records of the South Australian Museum, volume 8, pages 555–562 url=).Mediorhynchus alecturae was originally named Empodius alecturae by Johnston and Edmonds in 1947 and renamed by Golvan in 1962. It is considreded a junior synonym of M papillosus. The specific epithet derives from Alectura, the genus of the Australian brushturkey, which serves as the host for this species. Mediorhynchus cambellensisSoota, Srivastava and Ghosh, 1969Studies on the helminth fauna of the Great Nicobar Island The species name, cambellensis was named after the location the hosts were caught, Campbell Bay.M. cambellensis has been found infesting the intestine of an oriole and flycatcher on Great Nicobar Island. This worm closely resembles M. armenicum but differs from it in number of proboscis hooks and extent of lemnisci. The male is 9.13 mm long and 1.2 mm wide whereas the female is larger measuring 13 to 16 mm long and 2 mm wide. The proboscis is short and club shaped and 0.83 mm long in the male and 1.0 mm long in the female. The distal portion of the proboscis is truncated, the proximal portion is conical, and the proboscis receptacle 0.66 mm long. The proboscis hooks are anterior and in seven spiral rows each of 7–9 large hooks, posterior hooks are very numerous and small. The lemnisci are almost equal, measuring 3.15 by 0.25 mm. The testes are almost equal and measure 1.2 by 0.44 mm and the eggs measure 0.055 by 0.033 mm. There are four pairs of cement glands that are difficult to distinguish. Mediorhynchus centurorumNickol, 1969 M. centurorum was found in the egg and larval forms in Pennsylvania wood cockroach (Parcoblatta pensylvanica). In the laboratory setting, these worms were found to infect red-bellied woodpeckers (Melanerpes carolinus), red-headed woodpeckers (Melanerpes erythrocephalus), Northern flicker, (Colaptes auratus); and a hairy woodpecker, (Dendrocopos villosus) with a mean prepatent period of 35 days. Cystacanths fed to starlings (Sturnus vaulgaris), and red-winged blackbirds, Agelaius phoeniceus, did not produce infections. The eggs have 4 membranes, are 55 um long and have an elongation ratio of 1.53.Pfenning, A. C. (2017). Egg morphology, dispersal, and transmission in acanthocephalan parasites: integrating phylogenetic and ecological approaches.Url=https://via.library.depaul.edu/cgi/viewcontent.cgi?article=1273&context=csh_etd Mediorhynchus channapettaeGeorge and Nadakal, 1984 M. channapettae has been found birds of Kerala, India. Mediorhynchus cisticolaeSmales, 2011 The species name cisticolae is named after the host genus Cisticola. M. cisticolae has been found infesting the Red-faced cisticola (Cisticola erythrops) which is the type host, in the Cote D'Ivoire. Mediorhynchus colluricinclaeSmales, 2002 M. colluricinclae has been found parasitizing pomatostomatids in South Australian.The eggs are 51.5 um long and have an elongation ratio of 1.34. Mediorhynchus conirostrisWard, 1966 M. conirostris parasitizes rodents in Egypt.M. conirostris has a proboscis which contains 16 to 20 longitudinal rows of four to five hooks. Mediorhynchus corcoracisJohnston and Edmonds, 1950Johnston & Edmonds, 1950 : Australian Acanthocephala n° 8. Transactions of the Royal Society of South Australia, vol.74, p.1–5 url=https://www.biodiversitylibrary.org/item/128927#page/5/mode/1up. White-winged chough (Corcorax melanorhamphos)The little crow (Corvus bennetti)The Australian raven (Corvus coronoides)The little raven (Corvus mellori)Australian magpie lark (Grallina cyanolenca) New South Wales, Queensland, Victoria, and South AustraliaSouth AustraliaSouth AustraliaVictoria and South Australiasouth Australia and the northern territory It is named after the genus name of a host species Corcorax.M. corcoracis was found parasitising the white-winged chough (Corcorax melanorhamphos) in New South Wales, Queensland, Victoria, and South Australia, Australia. It is named after the genus name of the host species Corcorax. It is also found in several species of crow including the little crow Corvus bennetti from, the Australian raven Corvus coronoides, and the little raven Corvus mellori all from South Australia. It has also been found in the Australian Magpie-lark (Grallina cyanoleuca). Mediorhynchus edmondsiSchmidt and Kuntz, 1977 Mediorhynchus emberizae(Rudolphi, 1819) M. emberizae is found infesting the intestines of the red-cowled cardinal (Paroaria dominicana) in the State of Bahia, Brazil. Mediorhynchus empodius(Skrjabin, 1913) Mediorhynchus fatimaaeKhan, Bilqees and Muti-ur-Rehman, 2004 M. fatimaae has been found parasitizing the White-eyed buzzard (Burastur teesa) in Karachi, Pakistan. It is distinguished mainly by a unique proboscis