Pleionogaster Michaelsen, 1892

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 : 307-308

Pleionogaster Michaelsen

Perichaeta (part) Beddard, 1886:298.

Pleionogaster Michaelsen, 1892: 247 ; 1896: 198; Beddard, 1895: 433; Easton, 1979:114.

Plionogaster Michaelsen, 1900: 210 ; Stephenson, 1930:840; 1933: 923; Gates, 1943:105; Jamieson, 1971: 82.

Type species. – Pleionogaster jagori Michaelsen, 1892 ( Easton, 1979) .

Diagnosis. – Perichaetine Megascolecidae with larger

numbers of setae in the head segments than in post–clitellate segments, reduced esophageal gizzard in viii, intestinal gizzards in the region xxiv-xxxii, post-giceriate atyphlosolate section of intestine terminated by an intestinal constriction in region of xxxviii-lv; paired enteroic stomate meganephridia and regular ranks of exoic micronephridia in post-clitellate segments, and single pair of racemose prostates whose ducts are united with vasa deferentia near the middle of the duct.

Remarks. – So far as is known, the genus is restricted to the Philippines, since in all likelihood the record attributed to Ternate, Moluccas, Indonesia should be Ternate, Luzon, Philippines ( Easton, 1979). All known species have two pairs of spermathecae located in segments viii and ix, and superficial male pores of crescent shape with the concave side facing anteriorly. In light of the recent evaluation of infra-familial systematics of the Megascolecidae ( Jamieson et al 2002), I have expanded the diagnosis from that given in Easton (1979). For discussion of the proper spelling of the genus name and the designation of the type species, see Easton (1979).

Relationships with other megascolecine genera are not clear. Gastrodrilus ( Blakemore, 2000b) has numerous (7-10) intestinal gizzards in the same general region of the intestine, but has an esophageal gizzard in v, is lumbricine, has tubuloracemose prostates, no dorsal pores, has penial setae, and lacks meganephridia. Anisogaster ( Blakemore, 2000a) is perichaetine at least in the posterior regions, lacks penial setae, has racemose prostates, has dorsal pores, has intestinal gizzards in the same general region of the intestine as Pleionogaster , but lacks meganephridia and the esophageal gizzard is also in v. Blakemore (2000a, 2000b) describes the intestinal gizzards as moniliform, meaning like a string of beads. This condition is seen clearly in the Moniligastridae for example, but this is not the case in Pleionogaster , in which each intestinal gizzard is a thickened ring around the posterior half of the intestine in each giceriate segment. This leaves a non-giceriate interval between each gizzard. By simple similarity, Anisogaster among known taxa is morphologically closest to Pleionogaster .

Easton (1979) synonymized the five known Pleionogaster species as Pl. horsti Beddard, 1886 , an action with which I disagree. Examination of material seen by Easton supports my doubts, as will be seen below.