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Embryogenesis of Sea Squirts (Boltenia villosa) Bio 120 Developmental Biology BITANGCOR, Cindy B., CAYASAN, Roxanne D., MANAN, Almera O., SILOS, Rose-Ann C., SILVA, Maria Daylara B. Section T45 3/20/2012

Embryogenesis of Sea Squirt

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Page 1: Embryogenesis of Sea Squirt

Embryogenesis of Sea Squirts

(Boltenia villosa) Bio 120 Developmental Biology BITANGCOR, Cindy B., CAYASAN, Roxanne D., MANAN, Almera O., SILOS, Rose-Ann C., SILVA, Maria Daylara B.

Section T45 3/20/2012

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I. Background Information

Scientific Classification:

Kingdom: Animalia Phylum: Chordata Subphylum: Tunicata Class: Ascidiacea Order: Pleurogona Suborder: Stolidobranchia Family: Pyuridae Genus: Boltenia Species Name: Boltenia villosa

Common name(s): Spiny-headed tunicate, hairy sea

squirt, stalked hairy sea squirt, bristly tunicate

Description:

It is a solitary ascidian with an opaque, leathery tunic that is covered with spinelike projections or large, bristly hairs. Attached to the substrate by a stalk, which may be short or long. The tunic is reddish-orange or tan, with orange to red siphons. The siphons can be hard to see and are short. Tunic bristles bear many secondary bristles that are irregularly distributed, or may be smooth.

Size:

The globular or heart shaped body is 1 to 3cm across, and borne on distinct stalk that is 1 to 4cm

long. It can be up to 10 cm tall, especially if on a long stalk, and a diameter that is about 2.5 cm.

Geographical Range: Southern Alaska to San Diego, CA. It is most common on outer coasts.

Depth Range: Low intertidal to 100 m

Habitat: Attached to hard substrates in water with good circulation

How to Distinguish from Similar Species:

The only other solitary ascidians with an opaque tunic and with spinelike projections have no distinct stalk and the projections have side branches arranged in circles.

Biology/Natural History:

This species concentrates vanadium in its body tissues (500-750 ppm by dry weight, excluding the tunic). These are some of the highest levels of vanadium concentration seen in tunicates. Diet includes crustacean nauplii, mollusc veligers, and eggs. Predators include the seastars Dermasterias

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imbricata and Orthasterias koehleri, and the predatory Oregon triton snail Fusitriton oregonesis . Sometimes contains the symbiotic crab Pinnotheres pugettensis or the several species of copepods. Gametes are ripe year-round, but mainly in the summer. Fertilization is external. Settle 6 hours to 5 days after hatching.

LIST OF REFERENCES

Marine Biodiversity of British Columbia. 2012. Sea Squirts. Retrieved March 13, 2012 from

http://bcbiodiversity.lifedesks.org/pages/20590

Gary McDonald. 2010. Boltenia villosa. Retrieved March 13, 2012 from http://www2.ucsc.edu/

seymourcenter/ Inverts/Ascidiacea/Boltenia_villosa/Boltenia_villosa.html

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II. Stages of Embryonic Development of Spiny-headed tunicate (Boltenia villosa)

A. Unfertilized Egg

B. Fertilized Egg, Zygote

C. Cleavage , 2-cell Stage

The orange myoplasm is seen throughout the cortex of the egg. The test cells (T) float around the egg inside of the thick chorion. Attached to the chorion are a number of follicle cells (F). Most ascidian eggs have both test cells and follicle cells.

T F

After fertilization, the myoplasm contracts toward the vegetal pole which will become the dorsa side of the embryo. The myoplasm marks where gastrulation will begin at the vegetal pole.

2-cell stage embryonic development of Boltenia villosa

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D. Cleavage: 4-Cell Stage

E. Cleavage, 8-cell Stage

F. Cleavage, 16-cell Stage

At the 4-cell stage, the polarity of the embryos is visible by the bright orange myoplasm at the posterior.

8 cell stage embryonic development of Boltenia villosa

A 16-cell embryo shows the distinct bilateral cleavage in an ascidian embryo. The plane of the bilateral symmetry is in the center, anterior is up. At this stage, there are 4 myoplasm containing cells.

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G. Cleavage, 32-cell Stage

H. Cleavage, 64-cell Stage

a) Animal hemisphere b) Vegetal hemisphere

32-cell stage of Boltenia villosa

64-cell stage of Boltenia villosa; (a) animal hemisphere and (c) vegetal hemisphere. The entire endoderm lines of cells are derived from only 10 precursor cells beginning at this stage.

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I. Cleavage, 110-cell Stage

a) Animal hemisphere b) Vegetal hemisphere

J. Gastrula Stage

K. Early Tail Bud Formation

110-Cell stage of Boltenia villosa; (e) animal hemisphere contains the ectoderm cells and (g) vegetal hemisphere contains the endoderm cells.

Gastrulation begins. The cells dive in (invagination) towards the interior of the embryo.

After gastrulation, an early tail bud forms. The tail bud embryo has a white head and the orange muscle cells surround the notochord in the posterior.

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L. (A) Late Tail Bud Formation and (B) Tail Formation

M. Tadpole

a) Head b) Tail

(A) Late formation of tail bud. (B) The tadpole larva just before hatching has undergone extensive convergence and extension, so now the tail wraps around the head and the white notochord cells are visible in the center of the tail.

Tadpole finally develops. (a) Head portion and (b) tail portion of the tadpole. Palps (adhesive papillae) are found in the anterior portion of the tadpole.

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N. Juvenile Stage O. Siphon

LIST OF REFERENCES

Cell Dynamics. 2004. Embryogenesis in the Sea Squirt Boltenia. Retrieved March 13, 2012 from http://celldynamics.org/embryos/boltenia.html

Dassow, G. von. . 2004. Sea Squirts. Retrieved March 13, 2012 from http://celldynamics.org/celldynamics/courses/archive/2003gndcb/squirtweb/index.html

Spring 2001 Undergraduate Apprenticeship at FHL. 2012. Boltenia villosa. Retrieved March 13, 2012 from

http://faculty.washington.edu/bjswalla/fhl_sp01/boltenia.html

After the larva swims for a period of time, the tail retracts during the process of metamorphosis. The metamorphosing juvenile flattens down and makes a number of ectodermal ampullae that radiate out from the larva.

Siphon of Boltenia villosa where water will enter.

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