Dairella Bovallius, 1887

Zeidler, Wolfgang, 2004, A review of the families and genera of the hyperiidean amphipod superfamily Phronimoidea Bowman & Gruner, 1973 (Crustacea: Amphipoda: Hyperiidea), Zootaxa 567, pp. 1-66 : 48-49

Genus Dairella Bovallius, 1887

Dairella Bovallius, 1887: 24 . – Stebbing 1888: 1342–1343. Bovallius 1889: 332. Vosseler 1901: 51. Schellenberg 1927: 637. Pirlot 1929: 107. Bowman & Gruner 1973: 36–37. Vinogradov et al. 1982: 331. Vinogradov 1990: 65. Vinogradov 1999a: 1181.

Type species

Paraphronima californica Bovallius, 1885 . Type material could not be found at the SMNH, ZMUC or in Uppsala and is considered lost. However, Dairella is a very distinctive genus, adequately characterised by Bovallius (1887, 1889).

Diagnosis

The characters of the family are also those of the genus.

Monotypic.

Sexual dimorphism

The sexes are very similar, but the filiform, multi­articulate antennae readily distinguish males. Mature males also tend to have uropod 3 with relatively broader exopods and endopods, and the apex of the telson is often concave medially in females but is usually convex in males. Females also have a much broader pereon ( Fig. 7A ), especially in mature specimens.

Remarks

Dairella is a very distinctive genus, readily distinguished by the relatively broad, dorsoventrally compressed pereon, and the simple gnathopods and pereopods. The genus seems to be uncommon, and very little is known about the biology.

Following an examination of over 200 specimens I have found it impossible to distinguish between the two nominal species, D. californica ( Bovallius, 1885) and D. lattisima Bovallius, 1887 , and consider them synonymous. The material examined confirms that the characters used to distinguishing between the two species fall into the range of variation resulting from sex and age. Bovallius (1889), followed by Vinogradov et al. (1982), separate them as follows. In D. californica , pereopod 5 is only slightly longer than pereopod 4; the basis of pereopod 5 is slightly longer than the carpus, and uropod 3 has narrowly lanceolate exopods and endopods. In D. latissima , pereopod 5 is distinctly longer than pereopod 4; the basis of pereopod 5 is subequal in length to the carpus, and uropod 3 has broadly lanceolate exopods and endopods. These characters are subjective and have proved to be unreliable. In the material examined, which included numerous examples of both sexes, pereopod 5 was always only slightly longer than pereopod 4 (1.1–1.2x) and the basis of pereopod 5 was mostly subequal in length to the carpus in mature specimens (about 1.2x), but slightly longer in immature specimens (1.3–1.6x). The endopods and exopods of uropod 3 vary considerably amongst females, usually being broader in larger and ovigerous specimens ( Fig. 8 ). Juvenile males are more like females, although the rami of uropod 3 maybe slightly broader ( Fig. 7D ), becoming even broader in mature specimens ( Fig. 7E ). In males pereopod 5 is also marginally longer than in females.

Figures

FIGURE 7. Dairella californica. A, dorsal view of ovigerous female, 7.2 mm, tropical SE Atlantic (Dana stn. 3996iii). B, lateral view of male, 8.1 mm, central South Pacific (Dana stn. 3620v). C, D, uropod 3 of male and female, 6.6 mm, central South Pacific (Dana stn. 3620v). E, uropod 3 of B. Scale bars = 1.0 mm (A, B), 0.5 mm (C–E).

FIGURE 8. Dairella californica, ovigerous female, 7.2 mm, tropical SE Atlantic (Dana stn. 3996iii). Scale bar = 0.5 mm.