舌形动物类（学名：Pentastomida），又称五口动物类，是动物界的一个分类。这一种谜样的动物属于无脊椎动物，介乎于环节动物和节肢动物之间，均为寄生性动物。其特征是体软、扁而长，无色，透明，无足。身长从数毫米到十数厘米，体表分近百个清晰的节段，内部却并不分节。虫体前端口部突出，呈椭圆形，周围有钩2对,可伸缩，用以附着在寄主组织上。该门动物没有呼吸系统、排泄系统和循环系统，雌雄异体。

本物种的名称是因为从其部分物种的外型酷似脊椎动物的舌头，因而为名；而其学名及另一名称「五口动物」的来源，则是因为其口器的五个钩，好像有五个口一样，因而为名。这五个「钩」，其实只有一个为口器，其余四个只是颚足。过往由于对本分类物种的分类不明，单单从外形来判断，所以将其归类到门一层。后来到了2001年，研究证据显示五口动物实为退化了的寄生性节肢动物，本物种生物跟其他物种的关系得到确认，所以被降至归入成为颚足纲的一员，是为舌形动物亚纲。

Pentastomida are an enigmatic group of parasitic invertebrates commonly known as tongue worms due to the resemblance of the species of the genus Linguatula to a vertebrate tongue.

There are about 130 extant species of pentastomids; all are obligate parasites with correspondingly degenerate anatomy. Adult tongue worms vary from about 1 to 14 centimetres (0.4 to 5.5 in) in length, and parasitise the respiratory tracts of vertebrates. They have five anterior appendages. One is the mouth; the others are two pairs of hooks which they use to attach to the host. This arrangement led to their scientific name, meaning "five openings", but although the appendages are similar in some species, only one is a mouth.