TABLE 1.

Three main forms of shell disease affecting crustaceans.

Types	Type 1: erosion of cuticle	Type 2: Integumentary response to pathogen invasion usually without cuticle erosion	Type 3: changes in pigment but with no erosion of cuticle
Common names	Shell disease (including winter impoundment disease, endemic and epizootic shell disease	Burn spot disease	Rust spot disease
Main features	Progressive erosion of cuticle	Melanization reactions observed on the surface of the cuticle caused by microbial penetration of the cuticle, little or no cuticular erosion	Altered pigmentation but with no cuticular erosion
Microbial involvement	+ (changes in bacterial community structure)	+ (penetration of cuticle by fungi and/or oomycetes)	? (unknown aetiology—metal pollutant‐induced?)
Crustaceans affected	Wide range including lobsters, crabs	Crustaceans susceptible to fungal/oomycete penetration of cuticle including shrimp and crayfish	Narrow range including mud crabs (Scylla serrata) in Australia
Examples	Endemic shell disease in edible crabs (Cancer pagurus), winter impoundment shell disease and epizootic shell disease in American lobsters (Homarus americanus). See also Table 2	Penetration of shrimp and crayfish cuticles by Fusarium spp.	‘Rust spots’ in mud crabs
Key references	Vogan et al. (2008); Castro et al. (2012); Shields et al. (2012)	Makkonen et al. (2013); Rowley et al. (2022); Yao et al. (2022)	Andersen et al. (2000); Dennis et al. (2016)