Caprella kennerlyi (Stimpson, 1864)

Common name(s): Skeleton shrimp

Synonyms: Metacaprella kennerlyi Caprella kennerlyi
Phylum Arthropoda 
Subphylum Crustacea 
Class Malacostraca 
Subclass Eumalacostraca 
Superorder Peracarida 
Family Caprellidae 
Caprella kennerlyi, apparently a male, found on Fidalgo Bay Marina dock.  Total length 3.5 cm.
(Photo by:  Dave Cowles, July 2014)

Description:  Family Caprellidae ("skeleton shrimp") are distinctive-looking. Their long, stick-like bodies are composed of a cephalon (head), pereon (thorax), and a tiny abdomen. The vast majority of the body is the pereon. Caprellids have two pairs of antennae, and the first pair is usually the longest (photo). The first two segments (pereonites) of the pereon have large legs (pereopods) called gnathopods (photo). The gnathopods are large, usually subchelate claws, and are used to capture prey and to grasp the substrate as they move around. Pereopods 3 and 4 are usually reduced or absent, but pereonites 3 & 4 (and 2 on some species) have pairs of leaf-like gills. Females also have a marsupium (pouch) on pereonites 3 & 4 in which they carry the eggs or young (photo). Pereonites 5-7 have a set of 3 smaller pereopod pairs at the posterior end of the body that are smaller than the gnathopods and are used to grasp the substrate (photo). The abdomen is tiny and attached to the dorsal end of pereonite 7 (photo). This species (Caprella kennerlyi) has two forward-projecting spines on the back of its cephalon (head) (photo) (photo).  The articles of the peduncle of antenna 1 are much longer than wide (photo) (photo), and the flagellum of the first antenna is shorter than the peduncle (see photo above and below).  On males, the peduncle of antenna 1 is stout and setose (photo) and the flagellum has less than 20 articles.  The  mandible of this species has a molar process but does not have a palp.  Usually the cephalon is fused to the first segment (pereonite) of the pereon. The merus of gnathopod 2 has a sharp, spiny anteroventral projection or a stout, spinelike seta (photo).  The propodus of gnathopod 2 is less than 2/3 as wide as long (photo), and the second pereonite does not have a  ventral spine between the two gnathopods (photo).  Pereonites 1 and 2 of males are more than twice as long as wide (photo).  It has gills only on pereonites 3 and 4 (See photos above and below).  Pereonites 3 and 4 also have several pairs of spines and have oostegites on mature females, but not even rudimentary legs on either sex.  Pereopods 5-7 (the legs near the back) have a single grasping spine or tooth on their propodus (photo  photo).  Females have a rough texture, with spines on all segments.  Often has pink spots and bands.

How to Distinguish from Similar Species:  This is an unusually large skeleton shrimp species. Metacaprella anomala has the flagellum of antenna 1 longer than the peduncle and pereonites 1 and 2 of males are not more than twice as long as wide.

Geographical Range:  All along the N American Pacific coast

Depth Range:  Intertidal and subtidal

Habitat:  Many different substrates and fouling communities (first described from a fouling community on a ship in Port Townsend).  Often in Abietenaria hydroid colonies.

Biology/Natural History:  May be especially well-camouflaged on Plumularia lagenifera hydroids.  The setae on the antennae are apparently used to scrape algae off the body.  Filter feeders and detritus eaters such as this species scrape their body clean.  Carnivorous predator and scavenger species allow algae to grow on them, presumably to increase their camouflage.



Dichotomous Keys:
  Carlton, 2007
  Kozloff, 1987, 1996 (as Metacaprella kennerlyi)

General References:
  Johnson and Snook, 1955
  Ricketts et al., 1985

Scientific Articles:

Caine, E.A., 1980.  Ecology of two littoral species of caprellids (Crustacea) from Washington, USA.  Marine Biology 56: pp 327-335

Jensen, M.P., 1969.  The ecology and taxonomy of the Caprellidae (Order: Amphipoda; Suborder: Caprellidea) of the Coos Bay, Oregon, area.  Ph.D. dissertation, Department of Entomology, University of Minnesota

Martin, D.M., 1977.  A survey of the family Caprellidae (Crustacea, Amphipoda) from selected sites along the northern California coast.  Bulletin of the Southern California Academy of Sciences 76: pp 146-167

Web sites:

General Notes and Observations: Locations, abundances, unusual behaviors:

Ventral view
This ventral view shows the gills but no legs on pereonites 4 and 5. On the second gnathopods, the merus has an anteroventral spine, the propodus of the second gnathopod is less than 2/3 as wide as long, and the ventral region of the second pereonite between the bases of the second gnathopods is smooth instead of having a tubercle or spine.

First antennae
On males such as this one, the peduncles of the first antennae are robust with many setae, and the antennal  flagellum is shorter than the peduncle.

Head spines
This dorsal view of the head shows the forward-pointing head spines.  The middle spine is lower than the others and may be a piece of debris.

Ventral head view
This ventral view of the head gives a clear view of the mouth, antennae, gnathopods 1 and 2, and pereonites 1-5. 

Head of a 3 cm-long individual male found on Padilla Bay eelgrass in 2018. Note the long peduncle with elongated, setose articles and the small flagellae on the first antennae, the much smaller 2nd antennae with the curled flagellum, one of the head spines which is visible, and the first and 2nd gnathopods. Pereonites 1 & 2 are more than twice as long as wide. Notice that gnathopod 2 (bottom right) has an anterior projection on the short merus, and that the propodus (base part of the claw) is quite long and less than 2/3 as wide as long. Photo by Dave Cowles, August 2018.

head enlarged
This closeup of the head shows the sessile eye and the two head spines. Note also the fusing of the head with the first pereonite. On the lower left the first gnathopods can be seen attached to the front of the first pereonite. Above them are the mouth parts, and the bases of the two antennae are above that. Photo by Dave Cowles, August 2018.

Note that this species has leaf-like gills only on pereonites 3 & 4 (behind the 2nd gnathopod but anterior to the grasping legs on pereonites 5-7), and no legs (pereopods) on those 2 segments. Photo by Dave Cowles, August 2018

Pereopods 5-7
This close-up of pereopods 5-7 shows that the propodus of these pereopods has several setae but only one basal spine. Note also the tiny, nubbin-like abdomen on the dorsal base of pereonite 7. Photo by Dave Cowles, August 2018

This even closer view of one of  the posterior grasping pereopods (pereopod 5 or 6) clearly shows the single spine at the base of the propodus. Photo by Dave Cowles, August 2018

Authors and Editors of Page:
Dave Cowles (2014):  Created original page
CSS coding for page developed by Jonathan Cowles (2007)

Salish Sea Invertebrates web site provided courtesy of Walla Walla University