Physocephalata

Specimen of Phronima sedentaria inside the hollowed-out salp test it uses as a home. Photo from here.

Belongs within: Amphipoda.

The Physocephalata are a group of planktonic marine amphipods. The name means 'swollen head' and refers to the conspicuously enlarged head of many (but not all) members of the group.

See also: Another case of mistaken identity.

Characters (from Bowman & Gruner 1973): Head large, longer than pereonite 1. Eyes large (small to moderately large in Vibilia), occupying most of head surface (excluding rostrum in Oxycephalidae). Maxilla 1 without inner lobe. Maxilliped with inner lobes completely fused. Pereopods 1 and 2 usually chelate or subchelate, less commonly simple.

<==Physocephalata
    |--Lycaeopsidae [Lycaeopsoidea] MD01
    |--Vibilioidea MD01
    |    |--Cystisomatidae MD01
    |    |--Paraphronimidae MD01
    |    `--Vibilia B26 [Vibiliidae MD01]
    |--Platysceloidea MD01
    |    |--Anapronoidae MD01
    |    |--Lycaeidae MD01
    |    |--Oxycephalus B26 [Oxycephalidae MD01]
    |    |--Parascelidae MD01
    |    |--Platyscelidae MD01
    |    `--Pronoidae MD01
    `--Phronimoidea
         |--Dairellidae MD01
         |--Phronima B26 [Phronimidae MD01]
         |    `--P. sedentaria B26
         |--Phrosina Risso 1822 H01 [incl. Megallecto Gotto 1986 H01; Phrosinidae MD01]
         |    `--*P. semilunata Risso 1822 [incl. *Megallecto thirioti Gotto 1986] H01
         `--Hyperia B26 [Hyperiidae MD01]
              |--H. galba B26
              |--H. latissima Bovallius 1889 BD95
              `--H. medusarum B26

*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.

[B26] Bigelow, H. B. 1926. Plankton of the offshore waters of the Gulf of Maine. Bulletin of the Bureau of Fisheries 40 (2): 1-509.

Bowman, T. E., & H.-E. Gruner. 1973. The families and genera of Hyperiidea (Crustacea: Amphipoda). Smithsonian Contributions to Zoology 146: 1-64.

[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.