イリオモテミミズ

　フトミミズ科＞アズマフトミミズ属＞イリオモテミミズ Amynthas obtusus (Ohfuchi, 1957)

Pheretima obtusa Ohfuchi, 1957: 244; Ishizuka, 1999a: 63.

Amynthas obtusus Sims & Easton, 1972: 235.

Pheretima obutusa [sic] 上平, 1973a: 56.

タイプ標本

基産地：西表島祖納

タイプ標本所在地：不明（紛失？）(Reynolds & Cook, 1976)

形態

＜外部形態＞

　全長 49-54 mm、体幅 3.5-4.5 mm、体節数 70-110。

　体色は、フォルマリン液浸標本では背面は暗褐色で、腹面は明色。環帯は暗灰色。

　剛毛は第 7 体節で 33-37 本、第 20 体節で 43-50 本。第一背孔は第 11/12 体節間溝。

　環帯は、第 14-16 体節の 3 体節を占め、背孔や体節間溝、剛毛を欠く。受精囊孔は 4 対で、第 5/6/7/8/9 体節間溝。雄性孔は第 18 体節で、雄性孔の縁は体表からやや盛り上がる。雄性孔間剛毛は 9-11 本。性徴は第 17/18 体節間溝と第 18/19 体節間溝の雄性孔のすぐ内側にあり、直径は 0.8 x 1 mm の楕円形。

＜内部形態＞

　隔膜は、第 6/7/8/9 体節間では厚く、第 9/10 体節間で欠如し、第 10/11/12/13 体節間では厚い。

　腸管は第 16 体節から始まり、腸盲嚢は突起状型で鋸歯状の小突起を欠くが、隔膜によりくびれ、第 27 体節から第 24 体節まで伸びる。

　受精囊は 4 対で第 6-9 体節にあり、主嚢は三角形でやや平たく、長さ 1.5 mm、幅 1 mm。主嚢の導管は太短くて頑強。受精囊の副嚢は直線的で、先端は楕円形に膨らむ。貯精嚢は第 11-12 体節。摂護腺は大きく、5 体節分を占める。

＜原記載（クリックして展開）＞

Locality: Sonai of Iriomote. Collected by members, expedition to Riu-kiu Islands organized by Marquis Yamashina, on March 28, 1936.

External characters: The body length from 49-54 mm, the greatest diameters from 3.5-4.5 mm, the number of segments varies from 70-110. Apparently the segments comparatively short in length and around-shaped. Therefore, the body length is comparatively shorter than other species of this genus.

The colour in formalin, dorsally dark brown, light ventrally, clitellum dark grey, extends from XIV to XVI, dorsal pores, intersegmental furrows and setae are lacking. Prostomium epilobous. The setae begins on segment II, the setal numbers are as follows; 30-34/V, 31-35/VI, 33-37/VII, 36-40/VIII, 43-50/XX.

The first dorsal pore in XI/XII.

The spermathecal pores four pairs in V/VI, VI/VII, VII/VIII and VIII/IX, ventro-lateral in position. Two pairs of genital papillae are of oval-shaped, about 0.8 x 1 mm in transverse diameters, lie in ante-setal and post-setal line in XVIII just inside the position of the male pores, and each pair is close to the intersegmental furrows of XVII/XVIII and XVIII/XIX.

The male pores situated on setal line close to lateral border of XVIII separated by 9 or 11 setae. The margin of the porophore is slightly elevated over the body surface.

Internal characters: Septa VI/VII, VII/VIII and VIII/IX thickened IX/X absent, X/XI, XI/XII and XII/XIII thickened. But the septa in this species in general is rather delicate and not noticeably thickened.

Intestine begins in XVI, intestinal caeca simple, originated in XXVII and extending anterior into about XXIV without being serriformed and with rather distinct septal constrictions. The end bends to the ventral side.

Spermathecae, situated four pairs in VI, VII, VIII and IX. Ampulla is triangular in shape and smooth and slightly flattened about 1.5 mm in length 1mm in breadth, and continuous to the ampullary duct which is short and staut. The spermathecal diverticulum usually arises from the inner face of the spermathecal duct, straight and swallen in the end of the diverticulum and forms a round seminal chamber. The chamber is well developed and shinning like silver.

Ovaries, one pair of small tuft-shaped ovaries.

The prostate glands are very simple in shape, extended to five segments anterior and posterior.

The seminal vesicles lie in segments XI and XII.

Remarks: This species shows close resemblance to Pheretima micronaria (Goto and Hatai) in some external characters, for instance, the genital papillae in the male genital region, but many other characters especially presence of the diverticulum in the spermathecae in this species easily differentiate that species from the present one.

And this species shows a close resemblance to Pheretima minuta Gates, but easily distinguishable by the following facts; that in this new species, there are no genital papillae in the spermathecal region, but in the former species, the genital papillae are paired on one or more, or all, of segments VII, VIII, XIX, and XX, and are always located on the anterior border of the segment in the former. Unpaired median papillae of the same size and appearance are occasionally present on the anterior region of one or more of the segments just mentioned.

分布

　西表島でタイプ標本が採集された後、採集記録はない。

備考

　Easton (1981) は疑問符付きで、Blakemore (2003) は括弧と疑問符付きで、Blakemore (2012) は括弧や疑問符なしにヒナミミズのシノニムとした。ヒナミミズとの相違点は受精囊に副嚢を持つこと程度であり、本来ヒナミミズも副嚢を持っていたと考えられるため、別種と分けるには疑問が残る (南谷, 私見)。タイプ標本は紛失してしまっているため、西表島で新たに標本を採集し、分子系統学的手法を含めて再検討することが必要である。さらに、ヒナミミズの種内変異の検討も必要である。

シノニムリスト

Pheretima obtusa Ohfuchi, 1957a: 244. [形態記載]

Amynthas obtusus Sims & Easton, 1972: 235. [記述のみ]

Pheretima obutusa [sic] 上平, 1973a: 56 イリオモテミミズ. [同定形質のみ] (?, 1973)

Pheretima obtusa Ishizuka, 1999a: 63. [記述のみ]

引用文献

Blakemore, R.J., 2003. Japanese earthworms (Annelida: Oligochaeta): A review and checklist of species. Organisms Diversity and Evolution 11: 1-43.

Blakemore, R.J., 2012. Japanese earthworms revisited a decade on. Zoology in the Middle East 58 suppl 4: 15-22.

Easton, E.G., 1981. Japanese earthworms: A synopsis of the Megadrile species (Oligochaeta). Bulletin of the British Museum Natural History (Zoology) 40(2): 33-65.

Ishizuka, K., 1999a. A review of the genus Pheretima s. lat. (Megascolecidae) from Japan. Edaphologia (62): 55-80.

上平幸好, 1973a. 日本産陸棲貧毛類フトミミズ属(Genus Pheretima), 種の検索表. 函館大学論究 7: 53-69.

Ohfuchi, S., 1957a. On a collection of the terrestrial oligochaeta obtained from the various localities in Ryu-Kiu Islands, together with the consideration of their geographical distribution (Part 2). Journal of Agricultural Science, Tokyo Nogyo Daigaku 3(2): 243-261.

Reynolds, J.W., Cook, D.G., 1976. Nomenclatura Oligochaetologica: A Catalogue of Names, Descriptions and Type Specimens of the Oligochaeta. University of New Brunswick, Fredericton, Canada. 217 pp.

Sims, R.W., Easton, E.G., 1972. A numerical revision of the earthworm genus Pheretima auct. (Megascolecidae: Oligochaeta) with the recognition of new genera and an appendix on the earthworms collected by the Royal Society North Borneo Expeditions. Biological Journal of the Linnean Society 4: 169-268.