SeaWorld, Mattress Firm Lead Thursday's After-Hours Movers

Prothena Corporation PLC PRTA jumped 37 percent to $40.16 in the extended session Thursday on news that the company's Phase I study of its treatment for Parkinson's disease met its primary end point for safety.

Mattress Firm Holding Corp MFRM picked up more than 5 percent in late trading to $64.03 on a favorable quarterly earnings report.

SeaWorld Entertainment Inc SEAS rose more than 2 percent to $19.50 in after-hours trading when the company named Joel Manby chief executive. The company canned former CEO James Atchison in January amid public relations woes concerning its treatment of whales.

Vascular Biogenics Ltd VBLT rose nearly 3 percent to $4.88 a share in late trading after the company posted fourth-quarter results.

Vectrus Inc VEC recouped some of its earlier losses in the extended session, gaining more than 3 percent to $25.98. The supplier of military base maintenance and operations services posted fourth-quarter results.

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Calpine Corporation CPN rose more than 2 percent to $22.33 in the extended session on no apparent news. Its shares had closed down 5 percent.

Rally Software Development Corp RALY gained more than 2 percent after hours Thursday to $11.35 when the company posted fourth-quarter revenue growth of 25 percent.

New York & Company, Inc. NWY gained 3 percent to $2.30 after the company forecast a wider first-quarter profit margin.

Magnachip Semiconductor Corp MX ticked down more than 1 percent to $5.41 in the extended session after closing up more than 4 percent. The South Korea-based semiconductor company hit a 52-week low of $5 Tuesday.