Pseudidothea miersii (Studer)

Poore And T, Gary C. B., 2004, Pseudidotheidae (Crustacea: Isopoda: Valvifera) reviewed with description of a new species, first from Australia, Memoirs of Museum Victoria 61 (1), pp. 75-83 : 81

Pseudidothea miersii (Studer)

Idothea Miersii Studer, 1884: 17 , pl. 1 fig. 5. (lapsus for Idotea )

Pseudidothea bonnieri Ohlin, 1901: 276–281 , fig. 6.— Nordenstam, 1933: 114, fig. 27.— Sheppard, 1957: 175–176.

Pseudidothea miersii .— Barnard, 1920: 380–381.— Nordenstam, 1933: 114.—Shepherd, 1957: 175–176, figs 1d, 14a–f.— Kussakin, 1967: 267–269, figs 28, 29.

Arcturides miersii . — Nierstrasz, 1941: 262.

Diagnosis. Head dorsally convex; pereon with irregular minute tubercles. Pleotelson with blunt anterolateral processes, dorsally smooth, tapering to broadly truncate and slighty upturned apex. Male antenna 1 flagellum with about 6 clusters of aesthetascs. Antennae and pereopods without tubercles. Antenna 2 peduncle with short setae on articles 3–5. Pereopods minutely setose and with tubercles. Male pleopod 1 endopod about 1.5 times as long as peduncle with marginal plumose setae; exopod longer, 16–17 spinules on lateral margin, tapering distally, to acute apex bent outwards, with oblique furrow opening at apex. Male pleopod 2 appendix masculina tapering to acute point, slightly longer than endopod. Uropodal exopod with strong apical setae, endopod with 1 short seta; exopod about two-thirds as long as endopod ( Ohlin, 1901). Oostegite absent from pereopod 5 ( Sheppard, 1957).

Distribution. East Patagonia, Falkland Islands, 115–500 m depth.

Remarks. Studer (1884) based his new species Idothea miersii on a specimen 9 mm long, collected by the Gazelle Expedition off the east coast of South America at 47°1'6''S, 63°29'6''W at 63 fathoms (110 m). In the same paper he redescribed his earlier named species, Arcturides cornutus . Ohlin (1901) based Pseudidothea bonnieri on two males, 9 mm long, in the Hamburg Museum. When Ohlin (1901) described P. bonnieri he was almost convinced that his specimens were identical with Idothea miersii (Studer) and in a footnote reported how he had tried to borrow Studer’s material from the Museum für Naturkunde in Berlin but “got the reply that, as there were only two of them, it would be against the regulations to send them away from the Museum.” Angelika Brandt compared material from the museums in Hamburg and Berlin on our behalf:

from Hamburg, a 4 mm manca and a 6.4 mm male (ZMH K-1877) labelled and catalogued “ Pseudidothea bonnieri, Pisagua , Chile, 19°27'S, 70°10'W, K. Kophamel 1877–1889”; and from Berlin, a 6.2 mm male (18804) labelled “Zool. Mus. Berlin 18804 Pseudidothea bonnieri (Syntype) Ohlin, 1901 Leg. Kap. Kophamel, 3.VI.1888, 43°6'S, 60°W ” and on another label “ Pseudidothea bonnieri Ohlin, 1901 ( Idothea miersi (Studer) ”, and catalogued in Berlin with further information, “Hamburger Museum ded. Pisagua”.

Brandt (pers. comm.) could find no differences between the specimens and concluded that one of Ohlin’s two males had been donated to the museum in Berlin. This seems certain. The locality recorded by the two museums, but not the coordinates and collecting date of the Berlin specimen, is at odds with the type locality and more recent records of the species and is clearly wrong. Ohlin must have included antennae in his total length of 9 mm while Brandt’s measurements of 6.2 and 6.4 mm do not. The manca was not mentioned by Ohlin. Studer’s material can not now be found although Ohlin’s footnote tells that it existed in 1901. It is tempting to speculate that, being unable to borrow Studer’s material and convinced of the synonymy of his species bonnieri with Studer’s miersii, Ohlin sent one of his syntypes to Berlin for comparison. This may explain why the Berlin male has two species names but whoever concluded this remains a mystery.

Sheppard (1957) examined many specimens from the Falklands region, reported them as Pseudidothea bonnieri but thought too that I. miersii was a synonym. Kussakin (1967) also illustrated a species using the older species name, as Pseudidothea miersii , and noted that P. bonnieri is probably a synonym. He observed that slight differences exist: in P. bonnieri the second article of the peduncle of antenna 1 bears a rounded tubercle with four setae (referring to Sheppard, 1957); in Kussakin’s specimens there is a slight swelling with five setae. The epipod of the maxilliped in Sheppard’s illustration of P. bonnieri has slightly concave lateral margins, while in Kussakin’s specimens it has a regular oval form with convex lateral margins. We consider that these minor differences can be attributed to intraspecific variation or mounting.

To add to the confusion, Nierstrasz (1941) synonymised Studer’s two species, Pseudidothea bonnieri and Arcturides cornutus , without explanation. It seems improbable that Studer could confuse his own two species in one paper and specimens of A. cornutus in our possession look nothing like a pseudidotheid; in fact, Poore (2001) placed the two species in different families.

We conclude, with Kussakin (1967), that P. bonnieri should be treated as a junior synonym of P. miersii . We treat as additional evidence the observation that all authors have reported only one species like this off eastern South America; the only other in the genus in the region, P. scutata Stephenson, 1947 is quite different.