Segmented like an arthropod, the monster looks like a monkey, a crab, a whale, a squid, an eel. It can squat and be as wide as the city block it’s about to level. It can stand and tower the New York skyscrapers it’s about to topple. And that’s just the big one squeezing the Big Apple to its core.

Its street team is made up of spindly, spidery little buggers that have eyes on elongated lobster claws and chompers that … well, you’re better off getting stomped.

Speculative sketches of what the Cloverfield monsters might be — rampaging online since the film’s from-nowhere teaser last summer boosted the hype — are dead wrong. It’s every animal and no animal all at once, classifiable only as a behemoth that your brain might conjure in REM sleep.

A hard-to-shake story of a bone-crushing apocalyptic attack, Cloverfield taps into primal fears of twisting, shifting nightmares, down to how details of our lives can metaphorically inform them.

Using a handheld-camera structure to place us within the punishment, director Matt Reeves, writer Drew Goddard, producer J.J. Abrams and cinematographer Michael Bonvillain achieve realism without the burden of achieving reality. This creature has no mercy, motive or explanation for its existence, but it has full attention and new-media fascination from those it’s terrorizing.

Cloverfield jumps and jitters on one videotape covering two drastically different days: April 27, when longtime friends Rob (Michael Stahl-David, a Jim Caviezel lookalike) and Beth (Odette Yusman) enjoy the intimate afterglow of sleeping together; and May 22, a day before Rob takes a promotional transfer to Japan and one on which friends and family throw a farewell party.

Good times don’t last, and not just because of the monster. Rob knew he was leaving when he slept with Beth, and they argue at the party. Then roars, booms and thuds ring out, lights flicker and a rooftop view of what’s happening ends with Lady Liberty’s head rocketing down the street. (Check the crafty homage to the Escape From New York poster and the sly camera-phone joke.)

On the run with Rob are his brother Jason (Mike Vogel), Jason’s girlfriend Lily (Jessica Lucas), socially awkward impromptu cameraman Hud (T.J. Miller) and Marlena (Lizzy Caplan), a minor acquaintance whom Hud fancies.

Having left the party, Beth is pinned down in an apartment building that’s been trodden by the beast. Together, the five try to find her and escape from both the monster and the military response.

To appreciate its scope, Cloverfield must be seen as large and loud as possible. Handheld it is, YouTube it’s not. One creature clash in a subway tunnel echoes the dark, claustrophobic tension of Aliens. Near-seamless special effects blend with physical exertion during the apartment-building climb. The lack of a score heightens intensity and immediacy. And quick glimpses of the monster fall in with Hud’s stunned scrambles until the final, fully prolonged shots of its maw and sprawl.

Unlike The Blair Witch Project, there’s not a hope for confusion with actual events, although the 9/11-esque dusting of New York is as much a cheap tonal misstep here as in 2005’s War of the Worlds. Plus, an opening epigram threatens not to tip the movie’s hat, but remove it altogether.

Minor aftershocks can’t crumble this mammoth, rock-’em-sock-’em movie, though. It’s unapologetically B, what with its magnificent monster, melodramatic smooches, overly scripted comic relief and unsympathetic pecking order. Yet it’s also a thrilling, exhausting tale of an incomprehensibly horrible beast lovingly crafted in H.P. Lovecraft’s remorseless style.