Velvet crab

Lore & Background

Linnaeus gave it the name Cancer puber; at the time, all crabs were classified indiscriminately into the genus Cancer. Linnaeus provided a very brief Latin description – 'vague and unsatisfactory', according to Lipke Holthuis. In fact, the identity of the crab Linnaeus described is unclear, as no type material was assigned and the description was simply too vague to be certain. This classification still stands. The genus name Necora is derived from the Galician word 'necoras', not from Greek.

Reader's Guide

The velvet crab is a species of commercial importance, particularly in the British Isles, France, and Spain. In the United Kingdom, velvet crabs were once regarded as pests but became commercially important after the collapse of Spanish fisheries in the 1980s. Phylogenetic studies have placed Necora in various clades, with recent work in 2022 placing it in a monophyletic Carcinidae clade, though earlier studies using nuclear and mitochondrial DNA have suggested different relationships. The species is described as 'very common' in conservation terms.

Did You Know?

• The species has been reclassified four times and is now the only member of the genus Necora.
• In the Scottish fishing industry, velvet crabs are sometimes known just as 'velvets'.

Taxonomic Placement and the Invertebrate Question

The Velvet crab occupies a position within the overwhelmingly dominant group of animals that lack a vertebral column. As a crustacean and arthropod, it falls squarely within the monophyletic clade Protostomia, which encompasses the vast majority of invertebrate life. Yet the label "invertebrate" itself carries a peculiar taxonomic awkwardness: it is not a formal taxon in the way that Arthropoda or Vertebrata are, but rather a term of convenience that groups together every animal that is not a chordate vertebrate. This makes the category paraphyletic, meaning it excludes some lineages that are actually more closely related to vertebrates than to other members of the group. The very word traces back to the Latin vertebra, a joint or spinal segment, rooted in verto, meaning to turn, with the prefix in- signaling absence. Despite its lack of formal circumscriptional power, the concept has endured for well over a century in both popular and scientific discourse, and the Velvet crab sits comfortably within this sprawling, if loosely defined, assemblage.

Body Architecture and the Exoskeleton

Like all crustaceans, the Velvet crab is armored in a hard outer shell rather than relying on an internal bony framework. This exoskeleton represents one of the two principal structural strategies among invertebrates, the other being fluid-filled hydrostatic support seen in organisms like jellyfish and worms. The crab's body is composed of differentiated tissues, and as a heterotroph it must consume other organisms to sustain itself, processing food through a digestive chamber that opens to the exterior at one or two points. In terms of symmetry, most multicellular invertebrates display either radial, bilateral, or spherical arrangements, and the Velvet crab, as an arthropod, falls into the bilateral camp. Yet asymmetry is no stranger to the crab world: fiddler crabs and hermit crabs routinely display one claw dramatically larger than the other, and a male fiddler that loses its oversized pincer will regenerate a replacement on the opposite side after its next moult. The Velvet crab shares this broader arthropod capacity for structural variation and regrowth.

Neural Wiring and Sensory Response

The Velvet crab's nervous system, like those of arthropods broadly, operates through neurons that fire in response to stimuli remarkably similar to those that trigger mammalian nerve cells: tissue trauma, elevated temperature, and shifts in pH all register as signals. While the first invertebrate neuron ever identified belonged to the medicinal leech, subsequent research has mapped neural activity across a wide spectrum of invertebrate species, including annelids, molluscs, nematodes, and arthropods. The capacity for learning and memory has been documented in molluscs such as the sea hare Aplysia, where nociceptors play a role in sensory processing, and mollusk neurons have been shown to detect both increasing pressures and physical tissue damage. Though the specific neural architecture of the Velvet crab has not been the focus of the same landmark studies, its placement among arthropods means it shares the fundamental principle of stimulus-responsive neuronal firing. These cells do not merely react; they encode, process, and in some invertebrate lineages, retain information about past encounters with their environment.

Ecological Context and Species Diversity

The Velvet crab is one member of an animal kingdom in which invertebrates constitute the overwhelming majority. One widely cited estimate places the figure at roughly 97 percent of all animal species, and the IUCN Red List data from 2014 suggests that of all described animal species, more than 95 percent belong to invertebrate groups. By contrast, only about 66,178 extant vertebrate species have been formally described, a tiny fraction of the total. Among invertebrates, insects account for the largest number of described species by a wide margin, but the broader arthropod phylum—which includes the crustaceans to which the Velvet crab belongs—also harbors extraordinary diversity. The invertebrate world spans an astonishing range of body sizes, from myxozoans measuring just 10 micrometers to the colossal squid reaching nine to ten meters in length. Within this vast assemblage, the Velvet crab occupies a niche defined by its hard shell, its bilateral symmetry, and its role as a heterotrophic consumer in marine ecosystems, contributing to the intricate web of interactions that characterizes the animal kingdom.