How does a sea louse look? - briefly
The sea louse is a minute, oval‑shaped crustacean, usually 2–5 mm long, featuring a semi‑transparent, segmented exoskeleton and a hardened dorsal plate. It possesses three pairs of swimming legs and two pairs of clawed appendages for attaching to fish.
How does a sea louse look? - in detail
Sea lice are small, marine crustaceans belonging to the order Caligidae. Adults typically measure 2–6 mm in length, with a laterally compressed, oval body that tapers toward the posterior. The exoskeleton is hardened and semi‑transparent, allowing internal organs to be faintly visible. The dorsal surface features a pair of short, stout antennae equipped with sensory setae, while the ventral side bears four pairs of walking legs ending in hooked claws that secure the parasite to its fish host.
Key morphological elements include:
- Cephalothorax: a fused head and thorax region covered by a smooth carapace; houses the mouthparts and two prominent antennae.
- Mandibles and maxillipeds: robust, serrated structures used to rasp skin and feed on mucus and blood.
- Abdomen: segmented, flexible, ending in a short, pointed telson with a small pair of caudal rami.
- Legs: each of the four thoracic appendages possesses a series of spines and hooks, providing strong attachment; the fourth leg is often the largest and most developed.
- Coloration: generally pale gray to translucent, sometimes tinged with brown or pink depending on the host’s blood content.
Developmental stages present distinct visual differences:
- Nauplius: free‑swimming, spherical, 0.2–0.4 mm, with three pairs of simple, whip‑like antennae and no visible segmentation.
- Copepodid: elongated, 0.5–1 mm, six pairs of legs, distinct cephalothorax, and a more defined dorsal shield.
- Chalimus: attached by a filament, exhibiting a rounded body and reduced mobility; coloration matches the adult form.
- Adult: fully sclerotized, larger, with fully developed claws and a flattened silhouette adapted for permanent attachment.
Overall, the organism’s compact, armored shape, paired antennae, clawed legs, and transparent exoskeleton constitute its defining visual profile.