Kinorhyncha

Kinorhyncha is a phylum of microscopic marine invertebrates, commonly called mud dragons. Its members live in sediment and have segmented bodies covered by spines.

Scalids: Scalids are cuticular spines arranged in rings around the introvert of kinorhynchs and other scalidophorans. These retractable spines arm the head region used to probe sediment.
Kinorhynch locomotion: Kinorhynch locomotion is movement through sediment by extending the introvert and anchoring with spines. Alternating extension and anchoring lets the animal advance through narrow sediment spaces.
Scalidophora: Scalidophora is a group of ecdysozoan animals characterized by a retractable introvert bearing scalids. Kinorhynchs are grouped with priapulids and loriciferans in Scalidophora.
Echinoderes: Echinoderes is a genus of kinorhynchs with a spiny trunk and a retractable introvert. It is one of the most species-rich and frequently studied kinorhynch genera.
Introvert: The introvert is a retractable, spine-bearing anterior region found in scalidophoran animals. Kinorhynchs extend this head region to move through sediment and gather food.
Kinorhynch feeding: Kinorhynch feeding is the ingestion of organic material and microorganisms from marine sediment. The introvert and mouth bring sediment-associated food to the digestive tract.
Priapulida: Priapulida is a phylum of marine worms with a retractable, scalid-bearing introvert. Priapulids share the scalidophoran body plan but are generally larger and unsegmented.
Pycnophyes: Pycnophyes is a genus of kinorhynchs found in marine sediments. Its species exemplify kinorhynchs with a relatively robust, plated trunk.
Loric: A loric is a rigid outer covering formed from cuticle, often divided into plates or segments. Kinorhynch trunk segments bear cuticular plates that form a protective loric.
Kinorhynch nervous system: The kinorhynch nervous system includes a brain around the foregut and a ventral nerve cord with segmental ganglia. Its repeated ganglia correspond to the animal’s segmented body plan.

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GastrotrichRelated: Kinorhynchs are another meiofaunal animal group commonly found among marine sediment grains.