Caprelloidea

Belongs within: Corophiida.
Contains: Cyamus, Caprella.

The Caprelloidea are a group of amphipods characterised by a modified head and more or less elongate body. Members include the Caprellidae, skeleton shrimp, which are small, elongate amphipods that are mostly found living among larger, camouflaging organisms such as bryozoans or seagrasses. Caprellinoididae resemble Caprellidae in body form but have the molars reduced or absent. The Podoceridae are less elongate than Caprellidae and vary in body form from broadly depressed to subcylindrical (Barnard 1969). The Cyamidae, whale lice, are specialised for living on the skin of cetaceans.

The skeleton of a shrimp

Published 24 February 2025

Historically, the classification of amphipods was seen as a challenge. A bewildering diversity of character combinations, with the attendant implication of regular homoplasy, impeded the recognition of evolutionary relationships. For a long time, the majority of amphipod lineages were lumped into a generalist suborder Gammaridea, with a small number of segregate suborders recognised for amphipod subgroups that were particularly distinctive. One such subgroup was the Caprellidea, the skeleton shrimps.

The skeleton shrimps are marine amphipods that are readily distinguished from other amphipods by their thin tubular bodies, much reduced abdomen, and a head that is strongly offset from the following segments (Barnard 1969). They are commonly found climbing on the surface of sessile animals such as cnidarians or bryozoans. Though their superficially mantis-like appearance has led to presumptions of carnivory, the majority of skeleton shrimps appear to be primarily detritivores (Guerra-García & Tierno de Figueroa 2009). An exception is members of the subfamily Phtisicinae which are predators on small crustaceans and worms. It has been suggested that the climbing habit of skeleton shrimp may have originally evolved to allow them to reach higher into the water column, from where they could use the antennae to capture floating food particles (Myers & Lowry 2003). However, this is by no means the universal lifestyle of modern forms, and many feed by scraping particles that have settled on their host. They may also be generalists, feeding on host tissues, faecal particles, or even each other as the need or opportunity arises.

Despite its extended history of use, amphipod specialists were long dissatisfied with the relegation of most taxa to the Gammaridea, recognising that the other suborders were likely specialised derivatives of this generalised base. Myers & Lowry (2003) reduced the ‘Caprellidea’ to a superfamily Caprelloidea within a broader suborder Corophiidea, the other members of which had previously been treated as gammarideans. They also included other ‘ex-gammaridean’ taxa in the Caprelloidea such as the family Podoceridae. These forms resembled skeleton shrimp in their more or less elongate body form and somewhat modified head but retained a well-developed abdomen following the walking legs. Myers & Lowry (2003) treated the true skeleton shrimp as a single family Caprellidae within the Caprelloidea but other authors have continued to divide them between multiple families.

One more group that has always been associated with the skeleton shrimp, whether in Caprellidea or Caprelloidea, is the whale lice of the family Cyamidae. Whale lice resemble skeleton shrimp in their lack of an abdomen but have a shorter, strongly flattened body form. As their common name indicates, they infest cetaceans, clinging to their skin. A single species, Sirenocyamus rhytinae, has been described from a non-cetacean host, the now-extinct Steller’s sea cow Hydrodamalis gigas. No cyamids have been recorded on other sirenians, and no specimens were definitively preserved. Potential preserved specimens of S. rhytinae later found in St Petersburg have been re-identified as belonging to Cyamus ovalis, typically a parasite of large whales (Carlton et al. 1999). Whether ‘Sirenocyamus’ represents a case of C. ovalis infesting an atypical host, lice specimens taken from a whale but attributed to the wrong host, or a fictive record unattached to the claimed specimens remains uncertain.

Despite feeding at least partially on said skin, whale lice do not typically appear to have a significant negative impact on their host. Indeed, the callosities on the heads of right whales seem to actively encourage the accumulation of lice populations. They may potentially benefit their host by cleaning away flaking skin or encrusting algae. Sometimes one must endure a little burn to maintain one’s complexion.

Systematics of Caprelloidea

Caprelloidea [Caprellida, Cystibranchia]
    |  i. s.: Protellopsis kergueleniL95
    |         Leptomera ventricosaG20
    |         Proto pedatusG20
    |--CaprogammaridaeLM13
    |--AeginellidaeB83
    |--Dulichia Krøyer 1845B69 [incl. Dyopedos Bate 1857B69; DulichiidaeLM13]
    |    |--*D. spinosissima Krøyer 1845B69
    |    |--D. monacanthaN00 [=Dyopedos monacanthusYS06]
    |    `--D. tuberculataN00
    |--ProtellidaeMD01
    |    |--Metaprotella sandalensis Mayer 1898L95
    |    |--Paraprotella prima Mayer 1903L95
    |    `--ProtellaL95
    |         |--P. gracilis Dana 1853L95
    |         `--P. similis Mayer 1903L95
    |--PariambidaeMD01
    |    |  i. s.: ‘Protella’ trilobata McCain & Gray 1971L95
    |    |--Pariambus typicus (Kröyer 1844)BD95 [=Podalirus typicusBK77]
    |    `--HemiaeginaL95
    |         |--H. costai de Qrujo Quitete 1972L95
    |         `--H. minutaL95
    |--Cyamidae [Cyamida, Cyamoidea]LM13
    |    |--Isocyamus delphiniW81
    |    |--Syncyamus pseudorcaeW81
    |    |--Neocyamus physeterisW81
    |    |--Platycyamus thompsoniW81
    |    `--CyamusW81
    |--CaprellinoididaeMD01
    |    |--Caprellinoides tristanensis Stebbing 1888L95
    |    |--ProliropusL95
    |    |--Verrucaprella Laubitz 1995L95
    |    |    `--*V. gracilispina Laubitz 1995L95
    |    |--Liropropus Laubitz 1995L95
    |    |    `--*L. segonzaci Laubitz 1995L95
    |    `--Pseudaeginella Mayer 1890 [incl. Fallotritella]L95
    |         |--P. antiguae Barnard 1932L95
    |         |--P. biscaynensis (McCain 1968)L95
    |         |--P. montoucheti (de Araujo Quitete 1971)L95
    |         |--P. polynesica (Müller 1990)L95
    |         |--P. sanctipauli Laubitz 1995L95
    |         `--P. tristanensis (Stebbing 1888)L95
    |--Caprellidae [Dodecadidae, Phtisicidae, Phtisicoidea]LM13
    |    |  i. s.: Liporus elongatus Mayer 1890BD95
    |    |         Pseudolirius kroyeri (Haller 1879)BD95
    |    |         Pseudoprotella phasma (Montagu 1804)BD95
    |    |--CaprellaLM13
    |    |--Paracercopinae [Paracercopidae]LM13
    |    |--PhtisicinaeLM13
    |    |    |--Phtisica marina Slabber 1769L95
    |    |    `--Quadrisegmentum triangulum Hirayama 1988L95
    |    `--DodecadinaeL95
    |         |--Dodecas elongata Stebbing 1883L95
    |         |--Pseudocaprellina pambanensis Sundara Raj 1927L95
    |         |--DodecasellaL95
    |         |--Semidodecas Laubitz 1995L95
    |         |    `--*S. beuroisi Laubitz 1995L95
    |         `--Symmetrella Laubitz 1995L95
    |              `--*S. arnaudi Laubitz 1995L95
    `--PodoceridaeLM13
         |--Cyrtophium Dana 1852B69
         |    `--*C. orientale Dana 1852B69
         |--Neoxenodice Schellenberg 1926B69
         |    `--*N. caprellinoides Schellenberg 1926B69
         |--Xenodice Boeck 1871B69
         |    `--*X. frauenfeldti Boeck 1871B69
         |--Laetmatophilus Bruzelius 1859B69
         |    `--*L. tuberculatus Bruzelius 1859B69
         |--Paradulichia Boeck 1871B69
         |    `--*P. typica Boeck 1871B69
         |--Leipsuropus Stebbing 1899B69
         |    `--*L. parasiticus (Haswell 1880) [=Cyrtophium parasiticum]B69
         `--Podocerus Leach 1814 [incl. Dexiocerella Haswell 1885, Platophium Dana 1852]B69
              |--*P. variegatus Leach 1814B69
              |--P. anguipesCS77
              |--P. capillimanus Nicholls 1938N38
              |--P. chelonophilus (Chevreux 1900)BD95
              |--P. herdmani Walker 1893N00
              |--P. isopus Walker 1889N00
              |--P. laevisN38
              |--P. minutusN00
              `--P. pulchellusM01

*Type species of generic name indicated

References

[BD95] Bakalem, A. & J.-C. Dauvin. 1995. Inventaire des crustacés amphipodes (Gammaridea, Caprellidea, Hyperiidea) des costes d’Algérie: essai de synthèse. Mésogée 54: 49–62.

[BK77] Barel, C. D. N., & P. G. N. Kramers. 1977. A survey of the echinoderm associates of the north-east Atlantic area. Zoologische Verhandelingen 156: 1–159.

[B69] Barnard, J. L. 1969. The families and genera of marine gammaridean Amphipoda. United States National Museum Bulletin 271: i–vi, 1–535.

[B83] Bousfield, E. L. 1983. An updated phyletic classification and palaeohistory of the Amphipoda. In: Schram, F. R. (ed.) Crustacean Phylogeny pp. 257–277. A. A. Balkema.

Carlton, J. T., J. B. Geller, M. L. Reaka-Kudla & E. A. Norse. 1999. Historical extinctions in the sea. Annual Review of Ecology and Systematics 30: 315–338.

[CS77] Cramp, S., & K. E. L. Simmons (eds) 1977. Handbook of the Birds of Europe, the Middle East and North Africa: The Birds of the Western Palaearctic vol. 1. Ostrich to Ducks. Oxford University Press: Oxford.

[G20] Goldfuss, G. A. 1820. Handbuch der Naturgeschichte vol. 3. Handbuch der Zoologie pt 1. Johann Leonhard Schrag: Nürnberg.

Guerra-García, J. M., & J. M. Tierno de Figueroa. 2009. What do caprellids (Crustacea: Amphipoda) feed on? Marine Biology 156: 1881–1890.

[L95] Laubitz, D. R. 1995. Caprellidea (Crustacea: Amphipoda) from the southern and western Indian Ocean. Mésogée 54: 81–100.

[LM13] Lowry, J. K., & A. A. Myers. 2013. A phylogeny and classification of the Senticaudata subord. nov. (Crustacea: Amphipoda). Zootaxa 3610: 1–80.

[MD01] Martin, J. W., & G. E. Davis. 2001. An updated classification of the Recent Crustacea. Natural History Museum Los Angeles County, Science Series 39: 1–124.

[M01] M’Intosh, W. C. 1901. The coloration of marine animals. Annals and Magazine of Natural History, series 7, 7: 221–240.

Myers, A. A., & J. K. Lowry. 2003. A phylogeny and a new classification of the Corophiidea Leach, 1814 (Amphipoda). Journal of Crustacean Biology 23 (2): 443–485.

[N38] Nicholls, G. E. 1938. Australasian Antarctic Expedition 1911–1914. Under the Leadership of Sir Douglas Mawson, O.B.E., B.E., D.Sc., F. R. S. Scientific Reports. Series C—Zoology and Botany vol. 2 pt 4. Amphipoda Gammaridea. David Harold Paisley, Government Printer: Sydney (Australia).

[N00] Norman, A. M. 1900. British Amphipoda: families Pontoporeidae to Ampeliscidae. Annals and Magazine of Natural History, series 7, 5: 326–346.

[W81] Watson, L. 1981. Sea Guide to Whales of the World. Hutchinson: London.

[YS06] Yu, O. H., & H.-L. Suh. 2006. Life history and reproduction of the amphipod Synchelidium trioostegitum (Crustacea, Oedicerotidae) on a sandy shore in Korea. Marine Biology 150: 141–148.