Marine Invertebrates

Amphipod (Amphipoda): biology, diversity and ecological roles Amphipod Amphipods are a diverse order of mostly small, carapace-less crustaceans found in marine, freshwater, cave and terrestrial habitats; many are scavengers or detritivores and importa…

Bivalve (Bivalvia): two‑valved molluscs — overview, anatomy, ecology, uses Bivalve Bivalves are aquatic molluscs with two hinged shells. This article summarizes their anatomy, feeding, habitats, reproduction, evolution, ecological roles and human uses.

Brachiopod (lampshell): anatomy, fossil record, ecology and modern status Brachiopod Brachiopods are a phylum of marine, shelled animals with a long fossil record. This article covers their anatomy, ecological roles, major groups, evolutionary history and how they…

Cephalopod (Cephalopoda): biology, evolution, behavior and human uses Cephalopod Cephalopods are a diverse class of marine molluscs—octopus, squid, cuttlefish and nautilus—known for intelligence, camouflage, jet propulsion and a rich fossil record including amm…

Chelicerata: anatomy, evolution, diversity and ecological roles Chelicerata Chelicerata are a major arthropod subphylum including arachnids and horseshoe crabs, defined by chelicerae and a two-part body; they have a long fossil record and play key ecologic…

Chondrophore (Porpitidae): colonial, surface‑dwelling hydrozoans Chondrophore Chondrophores (family Porpitidae) are small colonial hydrozoans that float at the ocean surface. Known members include Porpita porpita and Velella velella; they resemble jellyfish…

Coleoidea — the modern shell‑less cephalopods Coleoidea Coleoidea is the cephalopod subgroup that includes octopuses, squids and cuttlefish, distinguished by reduced or internal shells, advanced nervous systems, and diverse marine ecolo…

Echinoderm Echinoderms are a phylum of exclusively marine invertebrates—sea stars, sea urchins and relatives—characterized by calcitic plates, a water‑vascular system and usually fivefold sym…