JapaneseJapaneseSociety Society of Systematic Zoology

Proc. Jap, Soc. Syst. Zool. No. 9 (1973)

A PRELIMINARY REPORT ON THE DEVELOPMENT OF THE SEA-STAR, LEIASTER LEACHll

B},

Mi6ko KoMATsu

(Department of Biology. Teyama University, Toyarna 930)

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While staying in Sabiura Marine Laboratory, the writer had an opportunity to find

spawning ef a specimen of Leiaster leachii (GRAy). Since the development of Leiaster

has not been reported, a brief note of normal development from the spawning to early ' bipinnaria will be described below.

The spawning was found at about 10:OO a. m. on August 11, 1972. The eggs were

continuously shed for about 1 hour from the dorso-lateral parts of the arms where

may be present gonopores. The spawning specimen was ca. 250mm in R, and attached

to the wall of an aquarium near the sea-water surface during the spawning. Germinal

vesicle was not observed in the eggs when they were collected from the aquarium. The

eggs seemed to be immediately after being fertilized because fertilization membrane

began to elevate at that time. Since several animals of this species were kept in the

same aquarium, the eggs may be fertilized by sperms from males, though sperm ejacula-

tion was not ascertained. The materials fer the sectioned preparation were fixed with BouiN's solution and sectioned in 10pt thick by routine parathne method. They were

stained with DELAFIELD's hematoxylin and eosin.

The fertilized egg of this species was translucent and 140Ft in average diameter. Thirty minutes after the fertilization the perivitelline space was 30 fi in height (Fig. 1). About1 anda quarter hours thereafter, the first cleavage began through animal and

vegetal poles at 25-28CC. At that time the height of the perivitelline space was 40ri. 'the The cleavage is of holoblastic, radiat type. Thirty minutes after beginning of the

lst cleavage, the 2nd cleavage occurred and 1 hour after the embryo was in 16-cell stage

(Fig. 2). Four hours after, the embryo developed into early coeloblastula which compris- ed blastomeres of approximately equal size (Fig. 3), Soon after, egression tracts appeared

on the surface ef the blastula and the embryo was into wrinkled blastula stage going 'that (Fig. 4). The histological observation of the wrinkled blastulae showed the egression tracts correspond to the invaginations of the blastoderm (Fig. 7). The egression tracts

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56 em de"nc\k nS.9(1 973)

increased gradually in number ancl size (Fig. 5). In sections the wrinkled blastula of

this stage had many invaginations reached to the center of the blastula (Fig. 8). At that

time, neighboring invaginations were in close contact with each other. Two and a half

hours after the commencement of wrinkling, the blastula showed the most progressecl

state in wrinkling. The egression tracts then began to decrease and the invaginations

shallowed again as revealed in Fig. 9. Five and a half hours after the beginning c)f wrin-

kling, the egressien tracts disappeared and the blasLula resumed smoeth surface

Examination of the sectioned material of the smooth blastulae in this stage showed that

the invaginations completely retreated from the blastocoel (Fig. 10). About 20 minutes thereafter the gastrulation took place at the vegetal pole, thus embryo becoming gastrula

(Fig. 11). The invagination for gastrulation is apparently independent of the invagina- tions for wrinkling. Rotation occurred about 20 minutes after the beginning of thc gas- trulation. Soon later the gastrula hatched out and swam about near the sea-water sur-

face. Nine hours after hatching out, the blind end of the archenteron became to be ex-

panded. In this stage thc mesenchymal cells began to set frec into blastoceel from the

top of the archenteron. The size of the gastrula in this stage was 210/t in length and

190It in width. Diameter of the archenteron was 70ft at the top and 35,tt at the neck.

Gastrula then became to grow along the archenteric axis. Twenty-five hours after the

ferLilization, the length and the width ot the embryo were 250 and 200,(t, respectively ,(t (Fig. 12). At that time, the archenteron reached more than half of the length of the

gastrula and tended slig'htly towards the future ventral side. Two rudiments of the

coelomic pouch appeared at the both sides of the top of the archenteren. Thirty-five

hours after the fertilization, the stomodaeum was formed. The gastrula ot this stage was 400p in length and 210,tt in width. Twelve hours thereafter, the differentiation of

the digestive system was completed. The blastopore has moved from the posterior end

to the ventral region of the gastrula. The hydropore was observed at the dorso-posterior

end of thc left coelomic pouch. The middle portion of the gastrula then began to expand

and at 50 hours after the fertilization the size of the expanded part attained 240!t in the widest part. At that time, the length of the gastrula was 380/.t and width of the poste- rior end of the gastrula was 150/i. Antcrior part of the gastrula, future preoral lobc,

was 190" in width and 160ft in length. A sac-like structure, 20pt in diameter, was

recognized at the posterior left portien between the stornach and intestine. Few hours

thereafter, the ciliary bands became apparent and the gastrula transformed inte bipinnaria.

Fifty-five hours aftor the fertMzation, the early bipinnaria was 480tt in length and 270ft

in width (Fig. 13). At that time, the left coelomic pouch was larger than the right one;

70st and 50!! in length, respectively. Seventy hours after the fertilization, the bipinnaria

was 5001t in length and 300ft in width (Figs. 14, 15). They had two separate coelomic

pouches, of which the length were 801! in left and 60st in right. Though about one

hundred bipinnariae were alive more than 20 days after the fertilization, they did not

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proc ， Jap． Soc． Syst． Zool． No ．9 （1973） 57

grow further and differentiation towards metamorphosis was not observed ． − In this study ， an oudine of the development from thc fertilized egg to early bipin

． eggs were small and naria was observed in Leiaster leacltiiThe ， 140 μ in dianleter，

embryos developed intQ bipinnariae through wrinklcd blastulae． The general process of

wrinkling in this species ｛s simnar to that reported in Asterina pectinifera（KoMATsu ， 1973 Astropecten scoparius 1972 Acant ゐaster ） and じ RO ， and ）， flanci （HAYAsllI，KoMATsli OG ）

（KOMATsu ， 1973 ）． − The developmcnt of thc sca ・stars belonging to the family Ophidiasteridae， which in ’ repc ）rted σ θ ata Linchia clude genus Jueiaster，has been in Linckia J 瞬 〜 （MoRTENsEN ， 1931），

MoRTENsEN 1938 Fro 〃 MoRTENsEN 1938 and Certonardoa mMltifora （ ， ）， zia gltarda4ana （ ， ）

semiregularis and egg of the two species （IIAYAsHI KoMATsu ， 1971）． Among them ，the

． the other thc egg of Lincki α is srnall in sizc ，and develops into bipinnaria On hand ， is

floating and large in size in Pbeomia ghardaqana and Certonardoα semireg ？tlaris ． They

have not bipinnaria stage ， Wrinkled blastula is known in Linckia lactvigatct， Fremia

devel （） of Leiaster ghardaqana and Certonardoa semiregularis ． In conclusion ， the pment ・ leachii resembles that of Linckia laevigata with respcct to the size of egg ， and in having

wrinkled blastula and bipinnaria stages ． ・ The writel wishes to thank Prof ． Tohru UclllDA and Prof。 Ryoji IIAYAsHI for their

． writcr also to Drs 。 Ken −Ichi HAYAsHI Takeshi unfailing guidance The is grateful ， ’ TATsuKI and Hiro omi UclllDA alld other nlembers of the Sabiura Marine Laboratory of

the Marine Parks Center of Japan for providing facilities and for their kindtless．

摘 要

ー い の 1972 年 8 月 11 口 に 串 本 海 中 公 園 セ ソ タ の 水 槽 Pectiniferaな ど の そ れ と 似 て る 。皺 胞 胚 期終 了

に が じ は の う胚 期 に 内 で オ オ ア カ ヒ ト デ Leiasterleachiiの 自然 放 卵 を 20分 後 は 植 物 極 よ り陥 入 生 ， 胚

． こ 確 認 し ，受精 卵 か ら 初 期 ビ ピ ン ナ リ ア 幼 生 ま で の 発 入 る （Fig，11）。孵 化 は 受 精 の 6 時 間 後 に お る n

140 の 25 の の う は 長 さ 幅 が そ れ ぞ れ 25 生 を観 察 し た v 受 精 卵 は 直 径 が μ の 透 明 卵 で ， 受 精 侍 間 後 胚 ，

− の の 第 1 卵 割 直 前 に は 高 さ 40 μ の 囲 卵 腔 を 有 す る 。25 μ ，200 μ で ，原 腸 の 先 端 の 両 側 方 に 体 腔 う ．原

Fig ．12 冂 28℃ に お い て 受精 の 1 時 間 45 分 後 に 第 1 卵 割 が 始 基 が 存 在 す る （ ）。受 精 の 35 時 間 後 に は 陥

・ で は に の に は ま り，卵 割 型 式 は 全 等 割 放 射 型 あ る n 胚 受 精 が 形 成 さ れ ，さ ら そ 12時 間 後 消 化 器 官 分 化

の 4 時 間 後 に は 初 期 中 空 胞 ．胚 に な る （Fig．3）。や が し て い る 。 ま た 後期 の う胚 に は 胃 と小 腸 の 間 の 左 側 て ，胚 表 は 皺 状 を 呈 す る よ う に な り ，胚 は 皺 胞 胚 期 後方 に 袋 状 の 構 造 が 認 め ら れ る 。 や が て 繊 毛 帯 が 現

ビ ピ ン ナ リ ア に る の 時 に 達 す る （Fig．4）。 こ の 皺 は 次 第 に 複雑 に な り，皺 わ れ ，胚 は 幼 生 な 。 受 精 70

ビ ビ ン リ ア が そ れ れ 胞 胚 形 成 開 始 の 2 時 間 半 後 に 胚 表 は 皺 に よ っ て 著 る 間 後 の 初 期 ナ 幼 生 は 長 さ ，幅 ぞ

Fig 5 500 300 で さ の な る 左 右 体 腔 の う し い 凹 凸 を 呈 す る （ ・ ）。 ま もな く 胚 表 の 皺 は 再 μ， μ あ り ，大 ぎ 異 ． び 単 純 に な り ，つ い に 皺 胞 胚 形 ．成 開 始 の 5 時 間 半 後 を 有す る （Figs．14，15）。

ア ヒ ト は の を に 皺 は 消 失 し ，胚 表 は 滑 ら か に な る 〔Fig，6）。切 片 こ の 観 察 に よ っ て オ オ カ デ 小型 卵 有

に い て の ビ ビ 標 本 に よ っ て 皺 胞 胚 期 と そ の 前 後 の 胞 胚 の 内 部 の 変 し ，そ の 発 生 お 皺 胞 胚 期 を 経 過 し た ち

化 を 観 察 し た が （Figs ．7，8，9，10），オ オ ア カ ヒ ト デ ン ナ リ ア 幼 生 に な る こ と が 明 ら か に な っ た 。

の 皺 胞 胚 形 成 過 程 の 概 略 は イ ト マ キ ヒ ト デ 滋 s齢 初 σ （第 9 回 動 物分類 学会 大 会 に て 講 演 ）

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58 thto-e>ta\ft--ts., 9 (1973)

References

HAyAs}{i, R. & M. Kopt{ATstJ, 1971. 0n the development of the sea-star, Cert'onardoa semiregularis (MULLEi{ et Ti{osciiEL) I. 1'roc. Itip. Soc. Syst. Zool., 7: 74-80.

HAyAsm, R,, M. Kontfvrsu & C, OquRo, 1973. Wrinkled blastula of the sea-star, .4canthaster Planci (LiNNaEus). Ibid., 9: 59-62. KoMA'rsu, M.. 1972. 0n the wrinkled blastula of the sea-star, Asterina pectini.fera. Zoel. bfZiE.IL, 81 : 227-231. (In Japanese with EngSish abstract) KopatA'rsu, M,, 1973, On the wrinkled blastula of the sea-star, AstptQPecten scoPariz{s. Ibid., 82: 204- 207. (In Japanese with English abstract) MoRTENsEN, Th., 1931. Contributions to the study of the development and !arval forms c}f echi-

noderms I-II. Kbngl. Danske Vid. Selsk. Skr,, Alat, Math. AITd,, (9), IV: 1-39. MoRi'ENsEN, Th., 1938. Contributions to the study ef the development and larval forms of echi-

nodcrms IV. Ibid., (9), VII: 1-59.

Explanation of Plate 1

Figs. 1-5 and .11-13 show living specimens. Figs. 7-10. Sections of fixed

specimens. Figs. 6, 14 and 15. Specimens kept in 7U% alcohol after fixed with B()uiN's solution.

Fig. 1. Fertilized egg with fertilization membrane.

Fig. 2. 16-cell stage.

Fig. 3. Early coeloblastuia.

Fig. 4. Early wrinkled blastula.

Fig. 5, Wrinkled blastula with developed egression tracts. Fig. 6. Later blastula just after resurning smooth surface. Fig. 7. Beginning of wrinkled blastula stage.

Fig. 8. Wrinkled blastula, same stage as shown in Fig. 5.

Fig. 9. Later wrinkled blastula.

Fig. 10. Later blastula, same stage as shown in Fig. 6. Fig. 11. Early gastrula just before hatching out. Fig. 12. Gastrula.

Fig. 13. Ventral view of early bipinnaria.

Fig. 14. Ventral view of bipinnaria, seventy hours after the fertilization.

Fig, 15. Left side view of bipinnaria, same stage as shown in Fig. 14.

(Magnification; ca. 150 × in Figs. 1--11. ca. 120xin Fig, 12, ca. 80 × in Figs, 13-15)

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