イシカワミミズ

　フトミミズ科＞アズマフトミミズ属＞ イシカワミミズ Amynthas ishikawai (Ohfuchi, 1941)

Pheretima ishikawai Ohfuchi, 1941b: 248; 小林, 1941c: 260; 大淵・山口, 1947: 1356, 1965: 550; 上平, 1973a: 60; Ishizuka, 1999a: 61.

Amynthas ishikawai Sims & Easton, 1972: 236.

タイプ標本

基産地：高知県三宝山の龍河洞　（現：高知県香美市土佐山田町逆川龍河洞）

タイプ標本所在地：不明

形態

＜外部形態＞

　全長 47-65 mm、体幅 2.3-2.8 mm、体節数 60-72。第一背孔は第 12/13 体節間溝に始まる。

　体色は淡色で沈着がなく、背面と腹面は同色。皮膚が薄いため、外皮を通じて背行血管や貯精嚢が透けて見える。

　剛毛は第 7 体節で 40 本、第 20 本で 44-45 本。

　受精囊孔は 1 対で第 5/6 体節間溝にある。環帯は第 14-16 体節の 3 体節分を占め、剛毛や体節間溝、背孔を欠く。雄性孔は第 18 体節の体側にあり、楕円形で体表からやや盛り上がる。雄性孔の縁は体表から明らかに盛り上がり、雄性孔間剛毛は 1-2 本。性徴は全くない。

＜内部形態＞

　隔膜は第 6/7/8 体節間は厚く、第 8/9/10 体節間では欠き、第 10/11/12/13/14/15/16 体節間では厚い。

　腸管は第 16 体節から始まる。腸盲嚢は単純状型で第 27 体節に開口し、第 24 体節まで達する。腸盲嚢の腹側・背側とも隔膜で締め付けられてくびれる。

　受精囊は 1 対で、第 6 体節にあり、受精囊の主嚢はやや平たい卵型で、長さ 1.7 mm、幅 1.3 mm で導管は主嚢嚢状部の 1/2 程度。受精囊の副嚢は細く、主嚢と同長で 2.3 mm ほどで、ネジ曲がらずまっすぐ。副嚢の先端は丸い袋状に膨らむ。精巣は第 10-11 体節にある。貯精嚢はよく発達し、第 11-12 体節を占め、前側の嚢は背面・腹面とも完全につながり、ドーナツ型。卵巣は 1 対で小さく、第 12/13 体節間隔膜の背面に付着する。摂護腺は長さ 2.3 mm で、第 15-21 体節の 7 体節分を占め、導管は外部からは見えない。

＜原記載（クリックして展開）＞

External characters:

　　The measurements of the body and number of the segments of three individuals from Ryugado are as follows:

　　The body length varies between 47-65 mm (56 in average) the width at the male genital region of XVIII varies from 2.3 to 2.8 mm (2.5 mm in average), the number of segments varies from 60 to 72 (64 in average).

　　The colour is pale and unpigmented, and no difference was noticed between the dorsal and ventral surfaces. The skin is rather thin so that the dorsal blood-vessels in this species can be seen very easily through the semitransparent integument, especially in the very well developed seminal vesicles. This character is worthy of specific value.

　　The spermathecal openings consist of one pair in the intersegmental furrow V/VI, and are situated in the ventro-lateral. The pores are small.

　　Clitellum occupies 3 segments, XIV, XV and XVI without setae, intersegmental furrows and dorsal pores.

　　Setae beginning on segment II. Setal numbers of the earthworms are tabulated below (Table 2). 40 in VII, 44-45 in XX.

　　The openings of the male pores are in segment XVIII and are situated close to the lateral border on the slightly elevated oblong area. The margins of the pores are considerably elevated over the body surface, and are separated by 1 or 2 setae.

　　The first functional dorsal pore is found in XII/XIII.

　　The seminal vesicles are very well developed, on account of this character the segments X, XI, XII are much distended on the outside.

　　Genital papillae are not found in either the spermathecal and male pore regions.

Internal characters:

　　One pair of spermathecae are situated in segment VI. The ampulla is ovoid and is a little flattened dorso-ventrally; about 1.7 mm long, 1.3 mm broad in the widest part and continuous to the spermathecal duct which is about 1/2 the length of the ampulla. The diverticulum is slender and nearly equal to the combined length of the duct and ampulla, being about 2.3 mm long, not coiled or looped; it is swollen at the end and forms a round chamber.

　　Ovisac, one pair, it is small and hangs behind the septum XII/XIII.

　　Prostate gland about 2.3 mm long, and extends through XV-XXI (about 7 segments occupied). The muscular duct does not bend as is usually seen in the other species, open to segment XVIII, straight from the prostate gland, in this way, the muscular duct hides itself under the gland.

　　The saccular intestine originates in XVI and a pair of the intestinal caeca originates in XXVII and extends to XXIV anteriorly. The caeca is a single, conical projection, serriformed in both ventral and dorsal margins, and with slight septal constrictions. Septum VI/VII and VII/VIII more or less thickened, VIII/IX and IX/X absent, X/XI, XI/XII, XII/XIII, XIII/XIV and XIV/XV thickened, XV/XVI more or less thickened.

　　The seminal vesicles are well developed and are situated in XI and XII, very large, each anterior vesicle of this species is completely combined at both the dorsal and ventral sides and forms a doughnut-shape with the vesicle. Testis sacs in X and XI, anterior pair rounded, and projecting into X, connected in ventral medially with its opposite by a bridge; testis round in shape situated at the anterior inner wall of each sac. Spermduct united in XII.

Remarks:

　　It is of considerable interest to find that the present species possesses one pair of spermathecae. Beddard (1895), recorded in his monograph nine species which possess only one pair of spermathecae in the genus Pheretima. Among them only one species, Pheretima pusilla (Ude) collected from Buitenzorg and Java, has the one pair situated in segment VI, while the others all possess one pair of spermathecae in each of the segments V, VII, VIII and IX.

　　Michaelsen (1900) recorded 26 species of worms in his "Das Tierreich". and particularly five species, viz. Pheretima phacellotheca (Michaelsen), Pheretima biserialis (E. Perrier), Pheretima lompobatangensis (Michaelsen), Pheretima pusilla (Ude) and Pheretima urceolata (Horst) which are said to possess one pair of spermathecae in segment VI.

　　Only one species, Pheretima schizopora reported by Goto and Hatai (1898) from Tokyo, Japan, has the spermathecae situated in segment VIII, that of the left side is said to have three diverticula,and that of the right side only one. This species appears to differ in the position of the spermatheca, which is one of the most important characters of the species.

　　The spermathecae in the former are situated in VIII, instead of in VI as in present one. Such a species with one pair of spermathecae in segment VI has hitherto been unrecorded in Japan. It was collected from the Ryugado acve and is pale in colour and unpigmented, showing no difference between the dorsal and ventral surfaces; such characters are not found in the common species living in outer ordinary conditions, as for instance in those uncavernicolous Oligochaeta as Pheretima divergens (Michaelsen) and Pheretima masatakae (Beddard) which have never been collected from the Ryugado cave.

　　Undoubtedly the present new species here recorded can be regarded as a true cavernicolous earthworm.

Pheretima ishikawai (=Amynthas ishikawai) の形態 (原記載図) (Ohfuchi, 1941b p. 249, fig. 5 より)

生息環境

　龍河洞は、全長 4 km の石灰岩鍾乳洞で、主洞は 1 km の深さがある。3 つの入り口がある内の東側洞窟の入口から 160 m のところで、キクガシラコウモリ Rhinolophus ferrumequinum の糞が堆積した場所に生息している (Ohfuchi, 1941b)。

　Ohfuchi (1941b) は本種は完全な洞窟生活者であるとしている。

備考

　大淵・山口 (1947) は和名をイシカワミミズとしている。

　Gates (1972) はシバミミズと形態学的に識別できないことを指摘し、Easton (1981) により本種はシバミミズのシノニムとされた。その後も、シバミミズのシノニムとされることが多い。一方で、シンガポールで採集された minimus の形態を検討した Shen & Yeo (2005) は、体サイズが大きく、剛毛数が少ないものの体後部に向かうに連れて徐々に多くなり、貯精嚢がよく発達すること、摂護腺も大きく、その導管は太く直線的であることから、本種は独立種であるとした。

　今後、新たな標本を得て、分子系統学的手法を含めた再検討することが必要である。

シノニムリスト

Pheretima ishikawai Ohfuchi, 1941b: 248. [形態記載]

Pheretima ishikawai 小林, 1941c: 260. [記述のみ]

Pheretima ishikawai 大淵・山口, 1947: 1356. [同定形質のみ]

Pheretima ishikawai 大淵・山口, 1965: 550. [同定形質のみ]

Amynthas ishikawai Sims & Easton, 1972: 236. [記述のみ] (Sep ?, 1972)

Pheretima ishikawai 上平, 1973a: 60 イシカワミミズ. [同定形質のみ] (?, 1973)

Pheretima ishikawai Ishizuka, 1999a: 61. [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., 2008d. A review of Japanese earthworms after Blakemore (2003). In: Ito MT, Kaneko N, (eds.), A Series of Searchable Texts on Earthworm Biodiversity, Ecology and Systematics from Various Regions of the World, 2nd Edition (2006) and Supplemental. COE soil Ecology Research Group, Yokohama National University, Japan. CD-ROM Publication.

Blakemore, R.J., 2012b. 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.

小林新二郎, 1941c. 四国、中国、近畿及中部諸地方の陸棲貧毛類に就て. 動物学雑誌 53(5): 258-266.

Ohfuchi, S., 1941b. The cavernicolous oligochaeta of Japan. I. The Science Reports of the Tohoku Imperial University, 4th series (Biology) 16: 243-256.

大淵眞龍, 山口英二, 1947. 環形動物貧毛綱. In: 内田清之助 (ed.), 新日本動物図鑑. 北隆館, 東京. pp. 1352-1371.

大淵真龍, 山口英二, 1965. 環形動物貧毛綱. In: 内田亨 (編), 新日本動物図鑑上. 北隆館、東京 p.533-563.

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.