Tritella pilimana Mayer, 1890

Common name(s): Skeleton Shrimp

Phylum Arthropoda
Subphylum Crustacea
Class Malacostraca
Subclass Peracarida
Family Aeginellidae 
Tritella pilimana found on eelgrass on March Point, Padilla Bay June 2007.  Total length not including antennae = 2.4 cm.
(Photo by: Dave Cowles July 2007)
Description:  As with all caprellid amphipods, the pereon has only 6 visible pereonites, some of which have only vestigialpereopods; the abdomen is vestigial; and the body is slender and sticklike, somewhat resembling a praying mantis. Tritella pilimana has gnathopods but no gills on pereonites 1 and 2 (photo).  It has flat, leaflike gills and vestigialpereopods on pereonites 3 and 4 (photo).    The vestigialpereopods on pereonites 3 and 4 have only 1 article (segment) (photo).  The mandible has a palp.  The second antennae have long setae on the longer articles, and the next to the last article of antenna 2 is about 6x as long as wide and has setae about 2x as long as the article is wide (photo).

How to Distinguish from Similar Species:Tritella laevis has a next-to-last article of antenna 2 only 4x as long as wide and its setae are not much longer than the article is wide.  Mayerella banksia has 2 articles on its vestigialpereopods on pereonites 3 and 4.

Geographical Range:

Depth Range:

Habitat:  Can be found on eelgrass

Biology/Natural History::  Caprellid amphipods such as this species appear to be fearsome predators for their size.  They hold onto substrates such as eelgrass or hydroids with their posterior appendages and wave their bodies around looking for prey to grab.  They can move from place to place by grabbing the new place with their anterior gnathopods, then loosening their posterior legs and moving them up to the new object to reattach..



Dichotomous Keys:
  Kozloff 1987, 1996
  Smith and Carlton, 1975

General References:

Scientific Articles:

Web sites:

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

This view shows the same individual from the dorsal aspect.

In this ventral view of the anterior half of the body, the gnathopods present at the anterior end of pereonite 1 and at the posterior end of pereonite 2 are visible.  It has no gills on either of these pereonites.

In this ventral view of the posterior half of the body (head is to right), the flat leaflike gills can be seen on midsections of pereonites 3 and 4 (part of the second gnathopods can be seen at the right on pereonite 2).  Ahead of each gill is a small bump which is the vestigial pereopod for that pereonite.  Pereonites 5-7 on the left have well-developed pereopods which act as claws to attach the animal to the eelgrass.

This view shows pereonites 3 and 4 closer up (the end of pereonite 2 with ghathopod 2 is visible to the right).  On each of pereonites 3 and 4 a small, 1-article vestigial pereopod can be seen projecting from near the front of the article and a leaflike gill projects from farther back.  Note the large dorsal, forward-directed spine on both pereonite 3 and 4.

In this lateral view of the head and antennae 2, the long setae on antennae 2 can be seen.  The next to last article of antenna 2 is about 6x as long as wide and has setae at least 2x as long as the article is wide.
Notice also the large, single dorsal spine on the head and the small first gnathopods at the anterior end of pereonite 1.  The large first antennae are extending upward out of the picture.

This dorsal view of the head shows more clearly the first and second antennae.
x x
These are the first gnathopods, directly behind the head.  Notice that they are subchelate and the carpus and propodus are enlarged. This is a view of the right second gnathopod.  Notice that it is also subchelate but the propodus is not particularly enlarged.

Gravid female

This gravid female is carrying a clutch of eggs enclosed within flap-like oostegites on the ventral side of her thorax.  Her total length is about 1 cm.  Found on Ulva in Padilla Bay, June 21, 2012.  Photo by Dave Cowles.

Authors and Editors of Page:
Dave Cowles (2007):  Created original page
Jonathan Cowles (2007):  Updated page with CSS