Scientific Name and Authority

Caprella mutica   Schurin, 1935


Caprellid amphipods have a greatly modified body form, when compared to more familiar gammarid amphipods. The body is elongated (giving rise to the name 'skeleton shrimp'), though the abdomen is compressed. The head is partly fused with the first thoracic segment (called Pereonite 1 in amphipods). The head bears a pair of long antennae 1, somewhat shorter antennae. The 1st antennae (A1) have a 3-segmented peduncle, tipped by a flagellum with multiple segments. The 2nd antennae (A2) may be fringed with long setae, and have 3-4 segments in the peduncle, and a shorter flagellum, usually of 2 segments. A mandibular palp of several segments is present in some genera, arising between the antennae, but this is absent in Caprella. There is a small pair of gnathopods, with small grasping claws, with a movable finger (Gnathopod 1) on Pereonite 1. Pereonite 2 bears a much larger pair of gnathopods (Gnathopod 2), which may have conspicuous spines or setae. Pereonites 3 and 4 usually have round or club-shaped gills, while in most species, including Caprella, pereiopods are absent. Pereopods 5, 6, and 7 are roughly equal and hook-like, for climbing and attachment, with 6 segments. Females develop oostegites, plates which form a brood pouch. Males are usually larger than females of the same species. Females and immature males can be hard to identify to species level. (Description from: Barnes 1983; Watling and Carlton, in Carlton 2007).  

Caprella mutica males can grow up to 35 mm, while females grow up to 15 mm (MarLin 2006). Paired dorsal and lateral spines on pereonites 3 to 7 increase in number and size with maturity. Mature males can often be distinguished from other caprellids by naked eye. Immature specimens may only have small paired dorsal spines on pereonite 5. Live specimens of both sexes are bright orange to red in color, with the brood pouch of the female being pale white with dark red dots (Platvoet et al. 1995). There are a number of morphological differences between male and females. Females have no setation on the first and second pereopods, but do have dorsal and lateral spines on pereonites 3 to 7. The pereonites and Gnathopod 2 of females are greatly shortened compared with those of the males. Mature females are distinguished by the developing oostegites and brood pouch. (See further descriptions from: Platvoet et al. 1995; Ashton 2006; MarLin 2006; and Watling and Carlton, in Carlton 2007)

Taxonomic Classification:

Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Subclass: Eumalacostraca
Superorder: Peracarida
Order: Amphipoda
Suborder: Caprellidea
Infraorder: Caprellida
Superfamily: Caprelloidea
Family: Caprellidae
Genus: Caprella
Species: mutica


Caprella acanthogaster humboldtiensis (Martin, 1977)

Caprella macho (Platvoet, De Bruyne and Gmelig-Meyling, 1995)

Potentially Misidentified Species:

Caprella acanthogaster

Carlton (1979) and Marelli (1981) mistakenly applied this name to Caprella mutica in California. Caprella acanthogaster is also native to the northwest Pacific, and has been introduced to Tasmania (Guerra-Garcia and Takeuchi 2004), but is not known from North American or European waters.

Caprella alaskana

NE Pacific native, California to Alaska

Caprella kennerlyi

NE Pacific native, California to Alaska

Caprella laeviuscula

NE Pacific native, California to Alaska

Caprella linearis

N Atlantic native, New England-Labrador, Arctic Russia-Spain, Alaska