Cystisoma spinosus (Fabricius)

Zeidler, Wolfgang, 2003, A review of the hyperiidean amphipod family Cystisomatidae Willemöes­Suhm, 1875 (Crustacea: Amphipoda: Hyperiidea), Zootaxa 141, pp. 1-43 : 37-38

Cystisoma spinosus (Fabricius)

Oniscus spinosus Fabricius, 1775: 298 .

The description of this species is based on a drawing by Sydney Parkinson, while on board the Endeavour, and it is unlikely that Fabricius actually saw any specimens ( Zeidler 1995).

Although the figures are relatively detailed and accurate, some critical, characteristic features such as the mandibular teeth and ventral spines are not illustrated, thus making it difficult to determine which species is depicted.

The name O. spinosus of Fabricius (1775) is listed by Fabricius (1781, 1787 & 1793) and by Gmelin (1789) but the species is not mentioned again in the literature until Stebbing (1888). Stebbing regarded C. neptunus ( Guérin­Méneville, 1842) and C. pellucida ( Willemöes­Suhm, 1873) as junior synonyms. He describes a number of specimens under that name of C. spinosum , some of which cannot be determined from the literature. These specimens have been examined. Specimen “A”, a male, is C. magna ( Woltereck, 1903) ; specimen “B” is typical of C. pellucida ; specimen “C” appears to be a juvenile C. fabricii ; specimen “CC” is unidentifiable; specimen “D” is a juvenile C. fabricii ; specimen “E” is a juvenile male C. magna ; specimen “F” the type of C. parkinsonii , is most likely C. latipes , and specimen “G” is the type of C. fabricii . Subsequent taxonomists have accepted the synonymy of C. neptunus and C. pellucida with C. spinosum , but recent workers have not recognised Fabricius’ species, and it has only been recorded four times this century. The records of Vosseler (1901) and Woltereck (1903) most likely refer to C. pellucida , that of Scott (1909) refers to a juvenile measuring only 20 mm and those of Tattersall (1906) and Yoo (1971) cannot be confirmed from the literature.

Mature, female specimens of C. pellucida are relatively easy to distinguish by examining the antennae and the urosome. The antennae end in a diamond­shaped glandular swelling and the exopodites of the uropods are distinctly longer than the endopodites. These characteristic features are clearly not evident in Parkinson’s drawings of Onidium spinosum (a mature female), and the above synonymy is not justified. Furthermore, Fabricius’s species differs from C. latipes ( Stephensen, 1918) by the head shape, antennal length and width of pereopod articles, and from C. fabricii by the antennal length. Also C. fabricii has a very large pair of anteroventral spines, which would have been noticed by Parkinson, and would most likely have been illustrated if present. So, by process of elimination, we are left with C. longipes and C. magna . These two species are very similar but are separated on the basis of the mandibular spines, one in C. magna and two or three in C. longipes . Unfortunately Parkinson does not illustrate the mandibles so it is difficult to determine the species depicted with certainty. However, by comparing measurements made on specimens, it would seem that the length of pereopod 4 relative to pereopod 6 is most similar to C. longipes .