Hyperia medusarum (Müller 1776)

Hyperia medusarum (O.F. Müller)

Cancer medusarum O. F. Müller, 1776:196.

Hyperia medusarum (O. F. Müller).–Murdock, 1885:143.–Bovallius, 1887b:16; 1889:147–159. pl. 9: figs. 1–21 [literature, synonymy].–Holmes, 1908:490.–Stephenson, 1923:15–17, chart 2 [synonymy, distribution]; 1924:80–81.–Dunbar, 1942:37; 1954:782–783; 1963:3 [distribution].–Bousfield, 1951:138–139; 1956:144.–Shoemaker, 1955:71–72.–Vinogradov, 1956:210–21 l.–Oldevig, 1959:125.

Hyperia latreillei H. Milne Edwards, 1830:388, pl. 11: figs. 1–7.–Bovallius, 1889:164–175, pl. 9: figs. 31–43, pl. 10: figs. 1–17.

Hyperia hystrix Bovallius, 1889:159–163, pl. 9: figs. 22–30.

Hyperia galba (Montagu).–Brusca, 1967a:388; 1967b:542–543 [misidentification].

DERIVATION OF NAME.–Not specifically stated, but presumably refers to association of species with scyphomedusae reported by Strøm (1762).

TYPE-LOCALITY.–Søndmør, Norway.

DIAGNOSIS.–Head length (lateral view) subequal to length of pereonites 1–2 combined. Interantennal lobe prominent (medusarum form) to moderate (hystrix form). Female Al flagellum falcate; A2 flagellum very slender. Relative length of segments of Md palp, 1:1.7:2.1; segment 2 gently arched; segment 3 nearly straight. Outer lobe of Mxp much longer than inner lobe; seta on anterior surface of inner lobe long, numerous, and dense. S6 of P1 and P2 with many spines on medial and lateral surfaces, more numerous and longer in older and larger specimens. In medusarum form (Figures 4c,d,f,g) some spines reach beyond apex of s7; in hystrix form (Figures 4a,b,e) spines are shorter and dactyl is relatively longer. Posterior margins of s6 and s7 serrate; serrations present in medusarum form but obscured by spines and twisting of segment, hence not readily apparent and margin appears notched. S4–s5 of P3–P4 with series of long and short spines on anterior margin, long spines about equal in length to width of segment; spines more numerous in medusarum form (Figure 3a), less numerous in ♂, where they may be limited to s5. S6 minutely serrate, anterior margin usually unarmed, but may bear a few spines. P5–P7 subequal in length in ♀; in ♂ P5>P6=P7, usually unarmed except for cluster of spines at anterodistal corner of s2 of P7. Additional setae occasionally present, especially in young of medusarum form; variation in setation shown in Figure 3. Posterolateral corners of pleonal epimera ending in points, most pronounced in pleonite 3.

VARIATIONS.–This species, the most common along the Pacific coast of North America, is rather variable. Specimens from Pt. Barrow, Alaska, are about 20 mm in length and closely resemble USNM specimens from Frenchman’s Bay, Maine. This is the typical H. medusarum described by Bovallius and Sars which occurs along the east coast of North America as far south as Connecticut and which is commonly found on scyphomedusae in Alaskan and Canadian Pacific waters. (Bowman, Meyers, and Hicks, 1963). Adults collected at Friday Harbor, Washington, in may cases from medusae, resemble those from Pt. Barrow, but are smaller and may have shorter spines on the gnathopods.

Specimens taken in plankton nets and midwater trawls between the latitudes of Vancouver Island and San Diego are smaller (9–15 mm), although fully mature, and the setal armature of the pereopods is less well developed. These specimens may belong to the form given specific status (Hyperia hystrix) by Bovallius (1889) and reduced to a synonym of H. medusarum by Stephensen (1924) after examining Bovallius’ syntypes. After studying carefully the material in the Smithsonian Institution I am inclined to accept Stephensen’s position, at least for the present. Although the majority of North Pacific specimens can be assigned with reasonable confidence to either H. medusarum (sensu stricto) or H. hystrix, the presence of seemingly intermediate specimens at Friday Harbor suggests the possibility of intergradation between the two forms. A definitive study based on more material than is available to me now is needed to resolve the question.

DISTRIBUTION.–The hystrix form was taken in limited numbers on the CalCOFI cruises, and Figure 6 shows its combined occurrences on Cruises 1, 5, and 9. Most of the positive stations were north of Point Conception, reflecting an affinity for cooler water. The medusarum form was not found in the CalCOFI samples, perhaps because of its closer association with scyphomedusae in coastal waters, or because it is limited to cooler water than that in the area of the CalCOFI cruises.

The distribution of H. medusarum in the Atlantic Ocean will be considered with the discussion of the distribution of H. galba.

Arctic to Gulf of Maine

pelagic and parasitic (host-eg. Cyanea)