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The caprellid amphipod Caprella penantis, male in side-view. Modified from Diaz et al. 2005.

Species Name: Caprella penantis Leach, 1814
Common Name: None
Synonymy: None

    Kingdom Phylum/Division Class: Order: Family: Genus:
    Animalia Arthropoda Malacostraca Amphipoda Caprellidae Caprella

    Species Description

    Caprella penantis is a common, cosmopolitan caprellid amphipod. Members of the genus Caprella, commonly referred to as skeleton shrimps, typically have a slender, cylindrical body and three rear pairs of morphologically specialized periopods (walking legs) that allow them to cling to various substrata such as algae, hydroids, and seagrasses (Aoki 1997). The animal possesses large hooked gnathopods and setose antennae, and their abdominal segments are greatly reduced.

    Caprella penantis is relatively robust-bodied and has a small, sharp rostrum on the front of the head that is useful for distinguishing it from other caprellids (Rupert and Fox 1988), although identification to species is generally difficult. Bynum (1900) and Caine (1989) report morphological variation between C. penantis collected from exposed versus protected habitats, with animals from exposed sites being relatively more robust than those from protected sites.

    McCain (1968) describes morphological adaptations suiting the species to gorgonian host substrata, namely, a reduction in periopod setae and a reduction in the size and number of grasping spines. Typically drab in coloration, C. penantis may gain color camouflage by incorporating the pigments of the biotic substrata on which it feeds (Caine 1998).

    Potentially Misidentified Species

    A number of other caprellid amphipods belonging to genus Caprella and Paracaprella co-occur in the IRL with C. penantis. Differentiation of these animals is generally beyond the scope of amateur naturalists and typically involves morphometric analysis of a number of body parts. Caine (1989) has demonstrated a high degree of environment-mediated morphological plasticity (e.g., body and appendage robustness), and questions the reliability of using body and appendage proportions for taxonomic purposes.

    Caprella equilibra, the most common congener in the southeastern US, is typically larger than C. penantis (around 2 cm, versus 1.3 cm) and has no rostrum. Paracaprella tenuis, another common caprellid, typically reaches only 1 cm and lacks a rostrum as well as regularly arrayed setae on the antennae (Rupert and Fox 1988).


    Regional Occurrence

    Caprella penantis is a cosmopolitan species, widespread in tropical, subtropical, and temperate waters of the world's oceans (Vassilenko 1991). Along the east coast of the US, Caprella penantis occurs from Florida (both coasts) northward to north of Cape Cod, MA (Fox and Bynum 1975).

    IRL Distribution

    The reported Florida distribution of Caprella penantis includes the entire IRL system.


    Age, Size, Lifespan

    Caprella penantis is fairly large, around 1.3 cm in length.

    Bynum (1978) suggests that female C. penantis from North Carolina live for approximately one year.


    Caprella penantis can be encountered in abundance. Bartholomew (2002) lists it as the fourth most abundant mobile invertebrate colonizing artificial seagrass plots in experiments conducted in York River, VA, Zostera beds. More than 5,000 individuals were collected from the plots during two one-week sampling periods.

    Marsh (1973) reported C. penantis as the 12th most abundant epifaunal species in the York River. In the Zostera beds he examined, C. penantis occurred in 37 of 48 collected samples and represented more than 2% of the total fauna collected.

    Fox and Bynum (1975) list C. penantis as common and widespread in NC estuaries, and very abundant on pilings and exposed open beaches. Marsh (1973) noted that Caprella penantis was common in the York River, VA, Zostera beds only during the colder months of the season. Williams and Bynum (1972) indicate that C. penantis was present in North Carolina samples from all months except October, and was most abundant in May-June.


    Bynum (1978) studied aspects of the reproduction of Caprella penantis in North Carolina. Males grasp females with the posterior periopods, in contrast to male gammaridean amphipods which employ the first gnathopods for this purpose. Males defend grasped females from competing males.

    Breeding occurred year-round with a peak in the spring and a lesser peak in the late summer and early fall. Females probably live for one year and produce several broods during their life (Bynum 1978).

    Vassilenko (1991) reports that female C. penantis in his studies from Japan had broods of approximately 16-21 eggs and that they ranged between 0.25-0.30 mm in diameter. Egg-bearing females ranged between approximately 15-30 mg in weight.


    Embryology is typical of peracarid crustaceans, with fertilized eggs carried in the brood pouch of the female and direct-developing young emerging as crawl-away juveniles with no free-living planktonic larval stage (Aoki 1997).

    Although prolonged co-habitation of mother and young emerged from the brood pouch has been observed in some caprellid amphipods (Lim and Alexander 1986, Aoki and Kikuchi 1991), Aoki (1997) reports that C. penantis shows no such interaction between mother and emerged young in experimental trials. Instead, newly emerged juveniles immediately dispersed onto the experimental substratum (algal thalli or hydroid branches).



    Broad distribution along the east coast of the US from Florida to north of Cape Cod indicates a broad thermal tolerance for this species.


    Widespread distribution in coastal ocean habitats as well as inshore estuarine habitats demonstrates that Caprella penantis can persist within a relatively broad salinity range.

    Dissolved Oxygen

    Sagasti et al. (2000) indicate that Caprella penantis persists in the face of frequent summer hypoxic stress (O2 concentrations as low as 0.5 ppm) in the shallow epifaunal community of the York River, VA. Vassilenko (1991) calculated weight-based oxygen consumption rates for several Japan Sea caprellids (including C. penantis) and demonstrated that the metabolic rate of caprellids is 1.5 times lower than that of gamarideans.


    Trophic Mode

    Feeding is accomplished both by scraping and by filter feeding (Caine 1974). Gnathopods are used to scrape encrusting diatoms, epiphytes, and detritus from the surfaces of the host substratum, while entrapment of suspended particles occurs via the setose antennae (Caine 1978). Luczkovich et al. (2002) confirmed epiphyte-grazing as the primary feeding strategy.

    Duffy (1990) reports that C. penantis significantly reduced the growth of epiphytes (primarily diatoms and the filamentous brown alga Ectocarpus siliculosus) on the brown macroalga Sargassum filipendula in experimental mesocosms, but left the macroalgal substratum unaffected.

    Caine (1979, 1983) notes a particular instance in which the efficiency of C. penantis particle capture by direct interception was modified by the use of an adherent substance on the filtering structures. The adherent substance was mucus from the associated sea whip Leptogorgia virgulata. Its presence on the filtering antennae of C. penantis resulted in improved filtering efficiency and retention of materials finer than the setal spacing. Laboratory studies by Morgan (1989) indicate that C. penantis is also at least capable of facultatively feeding on planktonic crab zoeae.


    Intraspecific competition between male Caprella penantis for mates has been described. Males aggressively defend grasped females from competing males and often may employ a poison tooth on the second gnathopods to inflict mortal injury on competitors (Bynum 1978, Caine 1991).

    The dual ability to scrape food from host substrata and to filter food from the water column likely minimizes the need to compete for dietary resources.


    Phytal amphipods are an important component in the diet of several fish species associated with macrophytes. Orth and Heck (1980) observed C. penantis remains in the guts of juvenile (140-165 mm) black sea bass, Centropristis striata. Teixeira and Musick (1995) record that C. penantis was among the top three amphipod species consumed by northern pipefish, Syngnathus fuscus, in Zostera beds of the lower York River, VA. Caine (1983) lists a number of fish species, including pinfish, blennies, gobies, and pipefish, observed feeding on the C. penantis-dominated Leptogorgia virgulata epibiont community in the Thallassia seagrass beds of northwest Florida. Analysis of pinfish gut contents revealed that C. penantis was the only Leptogorgia epibiont consumed.

    Predatory invertebrates such as nemertean worms are also capable of preying on C. penantis (McDermott 1976). Thiel and Kruse (2001) also list C. penantis as among the amphipod prey of the nemertean Tetrastemma elegans.

    Associated Species

    Caprella penantis is strongly associated with a variety of macrophyte substrata including seagrasses and macroalgae. The conspicuous presence of C. penentis within the Florida Gulf Leptogorgia virgulata epibiont community has been noted previously. Frick et al (2004) list C. penantis as one of 12 new records of species encountered as epibionts on loggerhead sea turtles (Caretta caretta).


    Caprella penantis is described by Boesch et al (1976) as an opportunistic species with demonstrated capacity to quickly colonize habitats after a disturbance in response to relaxed biotic pressure. It is a common inhabitant of seagrass habitats, and in particular has been observed as the primary epibiont of the sea whip Leptogorgia virgulata within northwest Florida Thalassia testudinum beds (Caine 1983).

    This amphipod can be found in association with several species of macroalgae (e.g., Sanchez-Moyano and Garcia-Gomez 1998) in exposed and protected sites, and has also been recorded as a minor component of the sand-beach amphipod assemblage on the east coast of Florida (Charvat et al 1990). The stout, short segmented body and periopods of C. penantis are well-suited for clinging to macroalgae in exposed environments (Hirayama and Kikuchi 1980).


    Special Status


    Economic/Ecological Importance

    The species has no direct economic value, but it is an ecologically important community component, both as a prey resource to other species and as a potential mediator of the health of phytal substrata. Duffy (1990) states that the species composition of a phytal amphipod community determines whether the amphipods increase or decrease the fitness of the phytal habitat components. Whereas the amphipod Ampithoe marcuzii consumed host Sargassum Caprella penantis significantly reduced algel epiphytes without negatively affecting the Sargassum macroalgal substratum.


    Aoki M and T Kikuchi. 1991. Two types of maternal care for juveniles observed in Caprella monoceros Mayer, 1890 and Caprella decipiens Mayer, 1890 (Amphipoda: Caprellidae). Hydrobiologia 223:229-237.

    Aoki M. 1997. Comparative study of mother-young association in caprellid amphipods: Is maternal care effective? Journal of Crustacean Biology 17:447-458.

    Bartholomew A. 2002. Faunal colonization of artificial seagrass plots: The importance of surface area versus space size relative to body size. Estuaries 1045-1052.

    Boesch DF, Diaz RJ, and RW Virnstein. 1976. Effects of Tropical Storm Agnes on soft-bottom macrobenthic communities of the James and York Estuaries and the Lower Chesapeake Bay. Chesapeake Science 17:246-259.

    Bynum KH. 1978. Reproductive biology of Caprella penantis Leach, 1814 (Amphipoda: Caprellidae) in North Carolina, U.S.A. Estuarine and Coastal Marine Science 7:473-485.

    Bynum KH. 1980. Multivariate assessment of morphological variation in Caprella penantis Leach, 1814 (Amphipoda: Caprellidae). Estuarine and Coastal Marine Science 10:225-237.

    Caine AE. 1974. Comparative functional morphology of feeding in three species of caprellids (crustacea, amphipoda) from the northwestern Florida gulf coast. Journal of Experimental Marine Biology and Ecology 15:81-96.

    Caine EA. 1978. Habitat adaptations of North American caprellid amphipoda (Crustacea). Biological Bulletin 155:288-296.

    Caine EA. 1979. Functions of swimming setae within caprellid amphipods (Crustacea). Biological Bulletin 156:169-178.

    Caine EA. 1983. Community interactions of Caprella penantis Leach (Crustacea: Amphipoda) on sea whips. Journal of Crustacean Biology 3:497-504.

    Caine EA. 1989. Relationship between wave activity and robustness of caprellid amphipods. Journal of Crustacean Biology 9:425-431.

    Caine EA. 1998. First case of caprellid amphipod-hydrozoan mutualism. Journal of Crustacean Biology 18:317-320.

    Charvat DL, Nelson WG, and TA Allenbaugh. 1990. Composition and seasonality of sand-beach amphipod assemblages of the east coast of Florida. Journal of Crustacean Biology 10:446-454.

    Diaz YJ, Guerra-garcia JM, and A Martin. Caprellids (Crustacea: Amphipoda: Caprellidae) from shallow waters of the Caribbean coast of Venezuela. Organisms, Diversity and Evolution 5:249-251.

    Duffy JE. 1990. Amphipods on seaweeds: partners or pests? Oecologia 83:267-276.

    Frick MG, Williams KL, Markesteyn EJ, Pfaller JB, and RE Frick. 2004. New records and observations of epibionts from sea turtles. Southeastern Naturalist 3:613-620.

    Fox RS and KH Bynum. 1975. The amphipod crustaceans of North Carolina estuarine waters. Chesapeake Science 16:223-237.

    Hirayama, A., and T. Kikuchi. 1980. Caprellid fauna associated with subtidal algal beds along the coast of the Oshika Peninsula, Tohoku District.-Publications from the Amakusa Marine Bio- logical Laboratory 5: 171-188.

    Lim STA and CG Alexander. 1986. Reproductive behavior of the caprellid amphipod, Caprella scaura typical Mayer, 1890. Marine Behaviour and Physiology 12:217-230.

    Luczkovich JJ, Ward GP, Johnson JC, Baird D, Neckles H, and WM Rizzo. 2002. Determining the trophic guilds of fishes and macroinvertebrates. Estuaries 25:1143-1163.

    Marsh GA. 1973. The Zostera epifaunal community in the York River, Virginia. Chesapeake Science 14:87-97.

    McCain JC. 1968. The Caprellidae (Crustacea: Amphipoda) of the Western North Atlantic. United States National Museum Bulletin 278:1-147.

    McDermott JJ. 1976. Observations on the food and feeding behavior of estuarine nemertean worms belonging to the Order Hoplonemertea. Biological Bulletin 150:57-68.

    Morgan SG. 1989. Adaptive significance of spination in estuarine crab zoeae. Ecology 70:464-482.

    Orth RJ and KL Heck, Jr. 1980. Structural components of eelgrass (Zostera marina) meadows in the Lower Chesapeake Bay: Fishes. Estuaries 3:278-288.

    Rupert EE and RS Fox. 1988. Seashore Animals of the Southeast. A Guide to Common Shallow-Water Invertebrates of the Southeastern Atlantic Coast. University of South Carolina Press. 429 p.

    Sagasti A, Schaffner LC, and JE Duffy. 2000. Epifaunal communities thrive in an estuary with hypoxic episodes. Estuaries 23:474-487.

    Sanchez-Moyano JE and JC Garcia-Gomez. 1998. The arthropod community, especially crustacea, as a bioindicator in Algeciras Bay (Southern Spain) based on a spatial distribution. Journal of Coastal Research 14:1119-1133.

    Teixeira RL and JA Musick. 1995. Trophic ecology of two congeneric pipefishes (Syngnathidae) of the lower York River, Virginia. Environmental Biology of Fishes 43:295-309.

    Thiel M and I Kruse. 2001. Status of the Nemertea as predators in marine ecosystems. Hydrobiologia 456:21-32.

    Vassilenko SV. 1991. Eco-physiological characteristic of some common caprellid species in the Possjet Bay (the Japan Sea). Hydrobiologia 223:181-187.

    Williams AB and KH Bynum. 1972. A ten-year study of meroplankton in North Carolina Estuaries: Amphipods. Chesapeake Science 13:175-192.

Report by: J. Masterson, Smithsonian Marine Station
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Page last updated: October 1, 2008

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