The stock market finished lower on Monday, with initial enthusiasm giving way to concerns about valuations in the five-year-old bull market. Yet although most broad-based indexes escaped with only minimal losses, Netflix (NASDAQ:NFLX), Arrowhead Research (NASDAQ:ARWR), and Trina Solar (NYSE: TSL) took much more damage in the day's trading.

Netflix fell 7%. Many investors pointed to news that Apple (NASDAQ:AAPL) and Comcast (NASDAQ:CMCSA) could be in talks to create a television service that would potentially compete against the streaming giant, but Netflix investors should also bear in mind that Monday featured a general exodus away from quick-rising momentum stocks across all industries. Just as biotech stocks sold off heavily after seeing huge gains, Netflix has soared recently, and a pullback isn't worth of panic at this point -- especially given the difficulties that Apple and Comcast would have in completing a deal.

Arrowhead Research plunged 16% amid general carnage in the biotech arena, despite its having made a positive announcement this morning. The company said this morning that it started the dosing regimen in its phase 2a trial of its hepatitis-B candidate treatment ARC-520. The company hopes that it can follow in the footsteps of other successful players in the RNA-interference realm, generating potentially groundbreaking treatments that manipulate the body's own genetic code to assist in treatment. Yet with investors generally cooling on the prospects for speculative biotech companies, Arrowhead got caught in the crossfire after huge gains over the past year.

Trina Solar fell 9% on a bad day for solar stocks, as momentum investors also looked askance at the big gains in solar companies both in the U.S. and China. Yet positive news from rival ReneSola showed just how much improvement Chinese solar companies have seen lately, as big gains in demand for solar modules have pulled several players in the industry toward profitability. Pullbacks in fundamentally solid industries can be buying opportunities, and the prospects for solar still look bright on a long-term basis.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.