Caprella ferrea

Caprellid, “Ghost” or “Skeleton” shrimps, so called for their skeletal appearance. Amphipod crustaceans, easily distinguished by the elongate stick-like body form and reduction of the abdominal appendages. Head is generally fused with pereonite 1. Pereopods on first 2 segments (pereonites) are most flexible and called gnathopods; gnathopods 2 being the largest, used in defense, feeding and substrate attachment. In many species pereopods 3 and 4 may also be reduced or absent. Gills on pereonites 3 + 4, rarely on pereonite 2. Pereopods 5 - 7 much smaller than 1 + 2, used for clinging to the substratum. In females, brood plates (öostegites) develop on pereonites 3 + 4. Much remains to be learnt about their biology, ecology and in many cases changing distributions.

California, British Columbia, Alaska

National Museum of Natural History, Washington DC: (NMNH) 25909; Off Humboldt Bar; CA; -land Stanford Jr Univ; Acc no. 28,797

Most easily distinguished from Metacaprella anomala and M. kennerlyi (it was previously grouped in Metacaprella) by paired spines postero-dorsally on pereonite 5 (unpaired in other 2 species). Martin 1977 described Californian specimens to differ "in that peduncle segments 2 and 3 of antenna 1 were heavily setose". C. ferrea and C. alaskana are extremely difficult to differentiate as juveniles. As adults, C. alaskana is number more slender and C. ferrea has a rougher body surface, always has head spines and frequently small tubercles laterally on anterior pereonites. Pereonite 5 in C. alaskana is usually longer than 6 plus 7 and shorter in C. ferrea.

Length: 9.4+mm. Body spination as follows: dorsally one pair small blunt spines on head; pereonite 2 with large pair plus variable number of pairs; pereonite 3 one pair medially plus other pairs; pereonite 4 median and posterior pairs; pereonite 5 three pairs; pereonites 6 and 7 two pairs each; laterally anterior projections over the gills. Antenna 1 longer than cephalon plus pereonites 2 and 3, peduncle lightly setose. Antenna 2 shorter than two basal articles of antenna 1, flagellum with long swimming setae. Gnathopod 1 with serrate grasping margin to propodus and dactylus. Gnathopod 2 propodus length more than twice width; palm with proximal grasping spine and accessory spine, small distal poison spine and triangular projection. Basis attached posteriorly on pereonite 2, stout with large antero-lateral ridge. Gills oval. Pereopods 5 to 7 short, propodus with proximal medial grasping spines. Female differs in having smaller head and body spines; gnathopod 2 arises anteriorly.

Intertidal on algae, hydroids, bryozoans, sabellid tubes, and other substrates.