Pleionogaster horsti, Beddard, 1886

James, Samuel W., 2004, New Species Of Amynthas, Pheretima And Pleionogaster (Clitellata: Megascolecidae) Of The Mt. Kitanglad Range, Mindanao Island, Philippines, Raffles Bulletin of Zoology 52 (2), pp. 289-313 : 308-309

“ Pleionogaster horsti ”

Material examined. – 1 adult ( BMNH 1978 :41.49-55), Philippines, Ifugao Province, Lagawe municipality, R.D. Guerrero, coll. 4 Jul.1978, E.G. Easton det.

Description. – Unpigmented, body 150 mm x 4 mm. (vii), 4.5 mm (xv), 4.5 mm (xxv); first dorsal pore 12/13; spermathecal pores paired in 7/8, 8/9, surrounded by slight tumidity, female pores not seen, male pores crescentic openings paired in xviii on raised porophores, in 12 th setal line, 4-6 setae between male pores. Setae regularly distributed around segmental equators; estimated at 220 setae on vii, 210 on x, 126 setae on xxv. Clitellum annular 1/2xiii, xiv-1/2xvii; genital markings midventral broad pad presetal xvii, ends in line with male porophores, midventral short pad presetal xix. Nephridiopores not visible. Septa 5/6-8/9 thick, muscular, 9/ 10 thinner, remainder membranous. Weak gizzard in viii with very thin iridescent layer, intestinal origin xix, no caeca; thick intestinal gizzards xxvii-xxx.

Hearts x-xiii esophageal, commissural vessels v-ix lateral. Supra-esophageal vessel x-xvii, one pair efferent parietoesophageal vessels from body wall of xiv-xviii to ventral esophagus in xiv. Nephridia not discernible.

Ovaries and funnels free in xiii, spermathecae paired in viii, ix without nephridia on ducts; each spermatheca almost cylindrical, tapered towards ental end, ampulla not sharply demarked from duct; simple club-shaped diverticulum joins duct near body wall. Male sexual system holandric, testes and funnels enclosed in annular sacs in x, xi, these sacs encompass only testes and funnels, exclude hearts, seminal vesicles; seminal vesicles xi, xii small, acinous.

Remarks. – The syntype of Pl. sivickisi bears a strong resemblance to the figure representing Pl. horsti in Easton (1979: p. 115). The pattern of genital markings and shape of the spermathecae are virtually identical to that figured. Genital marking patterns of Pl. ternatae ( Michaelsen, 1896) and Pl. horsti s.s. are very similar to that of Pl. sivickisi , but the three species differ in the locations of the intestinal gizzards: xxv-xxvii, xxvi-xxviii, and xxviii-xxx respectively. Michaelsen (1896) gives the location of gizzards in Pl. ternatae as xxv, xxvii and xxix, which may be mistaken. The typical intestinal gizzard in this genus occupies the posterior half of the segment, the anterior half’s gut having the typical appearance of the intestine. This could lead one to believe that gizzards are in alternate segments, but Michaelsen’s difficulty in determining segmental location may have been due to poorly preserved material. The Lagawe worm has long, slender spermathecae whose duct and ampulla are not clearly differentiated, and a completely different pattern of genital markings (only midventral broad pads) more like that of Pl. samariensis ( Michaelsen, 1892) but differing from this species in the genital marking segmental locations. Pleionogaster sivickisi has only three intestinal gizzards, unlike the Lagawe material, which has four placed more posteriorly. The two worms are also unlike in general aspect, the length/width ratio of the Lagawe material being greater and more like other members of the genus (James unpub. data). The Lagawe worm’s testes sacs do not encompass the other contents of segment xi, whereas Pl. horsti is said to have testes sacs enclosing the seminal vesicles ( Easton, 1979). This worm from Lagawe probably represents a new species, not a range extension of Pl. horsti .

The other two species placed as synonyms of Pl. horsti , Pl. jagori ( Michaelsen, 1892) and Pl. samariensis , have far fewer genital markings, and differ from each other in number of micronephridia per segment (14 and 6-10 respectively, the uncertainty in the latter being Michaelsen’s) and number of intestinal gizzards (4 and 3).

The facts that so much variation was ignored in the synonymization of all previous Pleionogaster into Pl. horsti , and that the Lagawe worm was determined by Easton to be conspecific with a concept of Pl. horsti that includes Stephenson’s Pl. sivickisi cast doubt on the taxonomic decision in Easton (1979). This leads me to the conclusions that Pl. jagori and Pl. samariensis should be removed from the synonymy of Pl. horsti and that Pl. sivickisi and Pl. ternatae should be re-evaluated with reference to type material. Because I have not seen all the necessary types, and because I have further Philippine material collected close to the locations of the taxa in question, I will try to resolve these questions in a later paper. For the time being, I support retention of Pl. sivickisi and Pl. ternatae as junior synonyms of Pl. horsti .