Harpacticoida

Distinguished from other copepod orders by the presence of only a very short pair of first antennae. The biramous second antennae and the location of the major body joint between the fourth and fifth segments are additional diagnostic features. The wide abdomen and worm-like body form contrast with the more streamlined bodies of many planktonic copepods.

Body typically somewhat worm-like with a wide abdomen. First antennae very short, distinguishing them from other copepods. Second antennae biramous. Major body joint located between the fourth and fifth body segments.

Primarily benthic in marine environments worldwide. Freshwater habitats occupied by members of Ameiridae, Parastenocarididae, and Canthocamptidae. Found in marine sediments (meiofauna), sea ice in polar regions, algal holdfasts, phytal habitats on macroalgae, hyporheic zones of streams, and caves. Some species planktonic or living in association with other organisms.

Cosmopolitan distribution in marine environments worldwide. Freshwater representation in multiple families. Documented from Island Bay, New Zealand; Helgoland, North Sea; central Slovenia; Brazil; Bermuda; and polar seas.

Raptorial feeding has been observed in some species. Specific dietary habits vary; some phytal-dwelling species feed on algae associated with macroalgal substrates. Many species' diets remain undocumented.

• Laminaria hyperborea - holdfastsSubtidal North Sea, species Paramphiascella fulvofasciata
• Macro-algae - phytal habitatSix species studied at Island Bay, New Zealand; harpacticoids dominant in phytal meiofauna

Development includes naupliar and copepodite stages. In Paramphiascella fulvofasciata at 19°C: nauplii develop in 6-9 days, copepodites in 20-24 days, total development approximately 28 days. Females carry egg sacs; mean egg number around 27 per sac in studied species. Lifespan up to 193 days recorded in laboratory. Continuous or protracted breeding seasons observed in multiple species.

Nauplii of some species are non-swimming and perform stalking movements with antennal endopodites. Copepodites swim well, exhibit digging-in behavior, and show negative phototaxis. Substrate-specific preferences demonstrated for phytal-dwelling species. Some hyporheic species are stygobionts, living exclusively in groundwaters.

Second-largest meiofaunal group in marine sediments after nematodes. Dominant numerical component of phytal meiofauna on macroalgae. Important in food webs as prey for larger organisms and as consumers of microalgae and detritus. Density in phytal habitats comparable to sandy bottom sediment meiobenthos.

Indicator organisms for environmental conditions in aquatic ecosystems. Some species used in ecological studies of pollution impacts and habitat quality. Cave-dwelling species highlight conservation needs for fragile subterranean ecosystems.

• CalanoidaPlanktonic copepods with typically longer first antennae and more streamlined bodies; lack the short first antennae and worm-like form of Harpacticoida
• CyclopoidaDiffer in antennal structure and body proportions; typically have different habitat preferences and antennal segmentation

• copepod
• meiofauna
• benthic
• marine
• freshwater
• crustacean

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• New copepod species highlights fragile cave biodiversity
• Zoosystematics and Evolution | Blog - Part 5
• Zur Biologie vonParamphiascella fulvofasciata (Copepoda, Harpacticoida) On the biology ofParamphiascella fulvofasciata (Copepoda, Harpacticoida)
• Harpacticoid assemblages (Copepoda: Harpacticoida) in the hyporheic zone of four streams in central Slovenia Združbe harpaktikoidov (Copepoda: Harpacticoida) v hiporeiku štirih rečic v osrednji Sloveniji
• Ecological Studies on Marine Algal-Dwelling Copepoda (Harpacticoida) from Wellington, New Zealand