肉眼的特徴: 傘は径 8-15 mm, 半円形～貝殻形, 縁部は最初内側に巻き, 中丘を欠き, 周縁に向かって放射状に走る溝線を欠き, 乾性, 最初全体に絹糸状の毛に被われるがまもなく平滑になり, 最初一様に淡褐色のち次第に淡色になる. 肉は厚さ 0.3 mm以下, 傘表皮よりも淡色で, 強靱, 特別な味や臭いはない. 柄は 1-2×0.5-1 mm, 最初から著しく偏在するかまたはほぼ側生し, 中実, 表面は全体に絹糸状～繊維状, 傘より淡色, 根元に発達した菌糸体は見られない. ヒダは上生～直性し, 疎 (柄に到達するヒダは 8-13), 幅 2 mm以下, 1-4 の小ヒダを伴い, 傘より淡色; 縁部は平坦, 同色. 胞子紋は白色.
顕微鏡的特徴: 担子胞子は 10-12×5-6μm, 楕円形～長楕円形, 平坦, 無色, 非アミロイド, 薄壁. 担子器は未確認; 偽担子器は 17-26×5-7 μm, こん棒形. 縁シスチジアは 15-30×5-10 μm, 群生し, こん棒形～類こん棒形, 頂部に数本の短指状付属糸 (3-10×1-4 μm) を具え, 無色, 非アミロイド, 薄壁. 側シスチジアはない. 傘の表皮は毛状細胞に接続する円柱形の菌糸が層をなす; 菌糸細胞は 50-160×4-9 μm, 肥大せず, 薄壁またはやや厚壁 (0.5μm), 褐色の凝着色素に被われ, 非アミロイド, 時に隔壁にクランプを具える; 傘の毛状細胞は60-200 (-500)×4-10μm, 散生し, 匍匐性または直立し, 円柱形, 鈍頭の頂部に向かって細まり, 平坦, 無色, 偽アミロイド, 壁の厚さは 3μmに達し, まれに二次隔壁を持つ. 柄の表皮にも傘と同様の毛状細胞が散生する. 柄の実質は偽アミロイド, 厚壁 (1μm) になるが骨格菌糸は見られない (一菌糸型). 実質の菌糸にしばしばクランプが存在する.
コメント: アサリタケ節 （新称, Section Excentricinae) に属し, 子実体は半円形の傘と偏在性の短い柄からなり, 傘と柄の表面は最初無色の短毛に被われるが, まもなく平滑になる. 成熟した子実体は傘の表面が平滑になるため, ヒラタケ型の子実体を形成するシロホウライタケ属の仲間を想起させるが，表皮組織に偽アミロイドに染まる厚壁の毛状細胞を有する点で容易に区別できる．東京都高尾山のテイカカズラの枯枝上に発生. 本種の和名は子実体の形状が貝殻に類似していることによる.
最近本種をChaetocalathus 属と組み合わせる見解が提起されているが (Vizzini 2008), 本種の子実体の類型はヒラタケ型になり(Chaetocalathus はフウリンタケ型), 真正の柄を有する(Chaetocalathus は無柄または痕跡柄のみが存在する)点でChaetocalathus 属と明らかに異なる.
Crinipellis conchata Har.Takah., Mycoscience (2002) 43: 343-350 Figs. 1, 2
Pileus 8-15 mm in diameter, conchate to semiorbicular, at first with the incurved margin, not umbonate, not sulcate, dry, at first silky-pilose overall but soon glabrescent, when young evenly colored light brown, becoming paler in age. Flesh up to 0.3 mm thick, paler concolorous with the surface, tough, odor and taste not distinctive. Stipe 1-2×0.5-1 mm, strongly excentric or almost lateral from the first, terete, solid, silky-pilose to fibrillose overall, entirely paler concolorous with the pileus, insititious. Lamellae adnexed to adnate, distant (8-13 reach the stipe), with 1-4 series of lamellulae, up to 2 mm broad, paler concolorous with the pileus; edges even, concolorous.
Spore print pure white. Basidiospores 10-12×5-6 μm (Q = length/breadth: 2, n = 20 spores per two specimens), ellipsoid to elongate-ellipsoid, smooth, colorless, inamyloid, thin-walled. Basidia not observed; basidioles 17-26×5-7 μm, clavate. Cheilocystidia 15-30×5-10 μm, forming a compact sterile edge, clavate to subclavate, with several irregularly cylindric apical appendages 3-10×1-4 μm, colorless, inamyloid, thin-walled. Pleurocystidia none. Hymenophoral trama irregular; element hyphae similar to those of the pileitrama but often irregularly inflated (up to 17 μm wide). Pileipellis a hypotrichial layer of cylindric cells 50-160×4-9 μm, not inflated, with brownish incrustation, inamyloid, thin or slightly thick-walled (up to 0.5 μm thick), occasionally with clamped septa; hairs of pileus 60-200 (-500)×4-10 μm, arising directly from the hypotrichium, scattered, repent or erect, cylindrical, tapering to an obtuse apex or with a broadly rounded apex, smooth, hyaline, dextrinoid, with colorless walls up to 3 μm thick, rarely with a secondary septum. Hyphae of pileitrama 3-8 μm wide, irregularly arranged, cylindrical, not inflated, monomitic, smooth, hyaline, inamyloid, thin- or slightly thick-walled (up to 0.5 μm thick), occasionally with clamped septa. Stipitipellis of scattered hairs arising from cutis hyphae; hairs of stipe similar to those of the pileus. Stipe trama composed of longitudinally running, cylindrical hyphae 6-15 μm wide, monomitic, smooth, hyaline, dextrinoid, slightly thick-walled (up to 1 μm thick).
Distribution: Japan (Tokyo).
Habitat: Gregarious on dead twigs of Trachelopermum asiaticum (Siebold et Zucc.) Nakai, from June to July.
Notes: This species is characterized by its light brown, glabrescent, conchate pileus, the strongly excentric or almost lateral, short (up to 2 mm long) stipe, the relatively long
basidiospores (10-12 um in length), the clavate cheilocystidia with several digitate apical appendages, the dextrinoid, thick-walled hairs on the pileus and stipe surface, and the
basidiome formation on dead branches. The combination of these characteristics suggests that this species is closely related to the section Excentricinae (Singer) Singer of the genus Crinipellis Pat., as defined by Singer (Singer 1942, 1976, 1986). Crinipellis conchata, however, is distinct from all other described species in the section because of its pleurotoid basidiomata made up of a conchate pileus and a strongly excentric or almost lateral, poorly developed stipe and its longer basidiospores (usually less than 10.5 μm in length in the section). Its pleurotoid habit is also similar to the genus Chaeocalathus Singer (Singer 1943, 1976, 1986) which differs from the genus Crinipellis in forming a dorsally attached pileus with or without a rudimentary stipe never attached to the substratum and possessing either dextrinoid basidiospores or dextrinoid metuloid. Thus, C.conchata seems to be a phylogenetically intermediate taxon to connect Crinipellis with Chaeocalathus.
Its pleurotoid habit has superficial resemblance to the genus Marasmiellus, which differs in lacking dextrinoid hairs.
Aime, M.C. & Phillips-Mora, W. (2005) The causal agents of witches’ broom and frosty pod rot of cacao (chocolate, Theobroma cacao) form a new lineage of Marasmiaceae. Mycologia 97: 1012–1022.http://dx.doi.org/10.3852/mycologia.97.5.1012
Antonín V, Noordeloos ME (1997) A monograph of Marasmius, Collybia and related genera in Europe. Part 2: Collybia, Gymnopus, Rhodocollybia, Crinipellis, Chaetocalathus, and additions to Marasmiellus. Lib Bot 17:1–256
Antonín, V. et al. (2014) Three new species of Crinipellis and one new variety of Moniliophthora (Basidiomycota, Marasmiaceae) described from the Republic of Korea. Phytotaxa 170(2):86-102
Corner EJH (1996) The agaric genera Marasmius, Chaetocalathus, Crinipellis, Heimiomyces, Resupinatus, Xerula, and Xerulina in Malesia. Beih Nova Hedwigia 111:1–164
Singer R (1943) A monographic study of the genera “Crinipellis” and “Chaetocalathus.” Lilloa 8:441–534
Singer R (1976) Marasmieae (Basidiomycetes – Tricholomataceae). Flora Neotrop Monogr 17:1–347
Singer R (1986) The Agaricales in modern taxonomy, 4th edn. Koeltz, Koenigstein
Takahashi, H. 2002. Four new species of Crinipellis and Marasmius in eastern Honshu, Japan. Mycoscience. 43(4):343-350.
