Stenomesotrema nomen novum

Dronen, Norman O. & Blend, Charles K., 2008, Observations on the Parorchis acanthus complex (Philophthalmidae: Parorchiinae) with the description of three new species of Parorchis Nicoll, 1907 and the replacement of the preoccupied junior homonym Paratrema Dronen & Badley, 1979 with Stenomesotrema nomen novum, Zootaxa 1843 (1), pp. 1-23 : 4

Stenomesotrema nomen novum

(syns. Parorchis Nicoll, 1907 ; Paratrema Dronen & Badley, 1979 , preoccupied)

( Figs 1–3)

Type species: Stenomesotrema numenii n. comb. (syn. Paratrema numenii ).

Etymology: The genus designation comes from the Latin “steno”, meaning slender; “meso”, meaning middle and “trema”, referring to Trematoda; the slender middle trematodes.

Rediagnosis: Body spinose, barbell-like or hourglass shaped, midbody thin forming an isthmus-like region, forebody wider than hindbody. Oral sucker wider than long, surrounded by reduced, rudimentary head collar, restricted to area immediately around oral sucker; head collar armed with fine spines in single continuous dorsal row, ventral corner spines usually in 2 rows; acetabulum, large with definite pre-midbody placement, hindbody much longer than forebody. Mouth subterminal; prepharynx short to absent; pharynx longer than wide; esophagus moderately long, typically with short lateral diverticula; cecal bifurcation immediately anterior to acetabulum; ceca long, extending to near posterior extremity. Testes near posterior end of body, side by side to tandem, irregular to deeply lobed. Ovary spherical to oval, immediately pretesticular on midline of body. Genital pore opening between level of cecal bifurcation and anterior margin of acetabulum, cirrus sac short, enclosing cirrus and prostate gland cells; seminal vesicle external to cirrus sac, overreaching acetabulum posteriorly, extending some distance into the hindbody. Vitellaria variable, extending from anterior end of hindbody or level of midbody to level of anterior testis. Excretory vesicle essentially Y-shaped, arms of vesicle diverticulate. Excretory pore nearly terminal. Intestinal parasite of curlews and other charadriiform birds.

Remarks: Of the 11 species of Parorchis that have been described from charadriiform birds (primarily scolopacid wading birds) other than gulls ( Laridae ), Parorchis asiaticus was originally described from the gull-billed tern ( Shtrom 1927) from Turkestan. According to Yamaguti (1971) this species has also been reported from the eastern curlew, Numenius madasgascariensis (Linnaeus) , from the Amur basin of Russia. This species is unusual among known species of Parorchis in having a barbell-like body shape rather than the pyriform body shape typical of members of the genus, and would be assigned to body type 1 above. It also has a reduced head collar (confined to the region immediately around the oral sucker), as compared to the more well developed, shoulder-like head collars of the remaining species of Parorchis . Dronen & Badley (1979) erected the genus Paratrema with the description of P. numenii from the long-billed curlew from Texas, U.S.A., separating it from Parorchis based on its having an unusual barbell-like, almost hourglass body shape rather than the pear-shaped body form characteristic of species of Parorchis , the presence of a reduced head collar with 2 rows of corner spines on the ventrad instead of having the more extensive, shoulder-like collar with 1 row of corner spines typical of Parorchis , and the testes in P. numenii were diagonal to tandem rather than being side by side. Parorchis asiaticus is similar in general appearance to P. numenii in having a barbelllike body shape and a reduced head collar. Shtrom (1927) did not give a detailed account of the spines that were presumably on the head collar of P. asiaticus ; however, unlike P. numenii , it has the testes arranged side by side as is typical of species of Parorchis . Kanev et al. (2005) apparently felt that the similarities in the body shapes of these 2 species (“its specimens are similar to P. asiaticus ”) was justification to synonymize Paratrema with Parorchis , although these authors gave no details of the reasons for the synonymy.

Paratrema , as erected by Dronen & Badley (1979), is preoccupied and represents a junior homonym, as this genus designation was previously assigned to a genus of Echinodermata by Koehler (1927). Based on Article 60.3, replacement of junior homonyms without synonyms (ICZN, 1999), we propose the nomen novum Stenomesotrema as a replacement, as redefined herein, to accommodate Stenomesotrema numenii n. comb. as the type species. The unusual barbell-like or hourglass body shape where the midbody is thin forming an isthmus-like region, and the forebody that is wider than the hindbody; the definite pre-midbody placement of the acetabulum and the resulting more extensive hindbody length; and the reduced, rudimentary, less laterally extensive head collar that is restricted to the area immediately around the oral sucker shared by Stenomesotrema numenii n. comb. and P. asiaticus , suggests that these species may belong together in Stenomesotrema . The side by side rather than diagonal to tandem arrangement of the testes seen in the latter may indicate that the general body morphology seen in these two species represents a case of convergent evolution, and that P. asiaticus may represent a genus separate from either Parorchis or Stenomesotrema ; however, until additional specimens of P. asiaticus are available we tentatively assign this species to Stenomesotrema , as Stenomesotrema asiaticus n. comb. Parorchis asiaticus magnus described from the eastern curlew, Numenius madagascariensis (Linnaeus) , by Bolopol’skaja (1963) does not have this distinctive body form and can not be assigned as a subspecies of S. asiaticus n. comb. We recommend that P. a. magnus be elevated to the species level as Parorchis magnus n. comb.