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' flat animals ') [3] is a phylum of free-living (non-parasitic) marine invertebrates. [4] [5] They are blob-like animals composed of aggregations of cells. Moving in water by ciliary motion, eating food by engulfment, reproducing by fission or budding, placozoans are described as "the simplest animals on Earth."
The head capsule bears most of the sensory organs, including the antennae, ocelli, and compound eyes, along with the mouthparts. In the adult insect, the head capsule appears unsegmented, though embryological studies show it to consist of six segments that bear the paired head appendages, including the mouthparts, each pair on a specific ...
Two sets of muscles move the mandibles in the coronal plane of the mouth: abductor muscles move insects' mandibles apart ; adductor muscles bring them together . They do this mainly in opening and closing their jaws in feeding, but also in using the mandibles as tools, or possibly in fighting.
A proboscis (/ p r oʊ ˈ b ɒ s ɪ s,-k ɪ s /) is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elongated nose or snout.
A chordate (/ ˈ k ɔːr d eɪ t / KOR-dayt) is a deuterostomal bilaterian animal belonging to the phylum Chordata (/ k ɔːr ˈ d eɪ t ə / kor-DAY-tə).All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics (synapomorphies) that distinguish them from other taxa.
The head typically consists of two antennae, two compound eyes, two palpi, and a proboscis. [11] Lepidoptera have ocelli which may or may not be visible. They also have sensory structures called chaetosemata, the functions of which are largely unknown. The head is filled largely by the brain, the sucking pump, and its associated muscle bundles ...
Rather than being tooth-like, the mandibles of such insects are lengthened into stylets, which form the outer two parts of the feeding tube, or beak. The mandibles are therefore instrumental in piercing the plant or animal tissues upon which these insects feed, and in helping draw up fluids to the insect's mouth.
[citation needed] In particular, research is needed to determine how a group of cells that cannot be considered full-fledged epithelial tissue organizes itself, how locomotion and coordination occur in the absence of true muscle and nerve tissue, and how the absence of a concrete body axis affects the animal's biology.