Eisothistos macrurus Wägele, 1979

Knight-Jones, E. W. & Knight-Jones, Phyllis, 2002, Four new species of Eisothistos (Anthuridea: Isopoda) from tubes of Spirorbidae (Serpuloidea: Polychaeta), Journal of Natural History 36 (12), pp. 1397-1419 : 1400-1402

Eisothistos macrurus Wägele, 1979 (gure 1)

Material. Two post-partum females, one collected in Camp Bay , Gibraltar, 36ss07.2¾N, 5ss21.2¾W, depth <5 m, 17 February 1976, the other from Bodrum Harbour, 37ss02.2¾N, 27ss25.7¾E, depth ca 3 m, 19 July 1987. Camp Bay collection also included seven embryos, two juveniles and three mature females. Spirorbids invaded were mostly Pileolaria militaris Claparède .

Description. Both post-partum females have simpli ed antennules and antennae, lacking aesthetascs and with agellar setae restricted to terminal articles (gure 1A). Both have many large setae on head and anterior pereonite (gure 1B), which are characteristic of female E. macrurus at this stage in the succession of ecdyses ( Wägele, 1979). Figure 1A–F shows Bodrum female 3.2 mm long, which has an extra marginal seta on each side of telson. Wägele’s (1979) Abb. 5 shows a similar extra seta, but only on right side. In gure 1F the plumose setae are strongly exed, under pressure from the glass cover-slip. The post-partum female from Gibraltar (length 2.8 mm, but not gured here) has a telson which lacks one of the pair of plumose setae, but has both companion setae. It was accompanied by seven embryos free in the same tube, each like gure 1G. Another Gibraltar female 2.7 mm long (hind telson shown in gure 1J) has lost both plumose setae from the hind telson, leaving adcentral notches occupied only by companion setae. Another female 2.1 mm long seems to lack companion setae (gure 1K). One juvenile, length ca 1.3 mm, was seen in side view, so gure 1H was drawn to show a sagittal view of telson keel spines, with a uropodal exopod in another plane of focus. Figure 1H also shows, at its anterior edge, basis of pereopod 6 arising from last pereonite, for this was a manca stage, lacking pereonite 7.

As in most small Eisothistos (e.g. species lettered g, l, p and s in list above) each eye has about ve ocelli. Each antennule has a agellum with six articles, of which article 1 is smaller than its proximal and distal neighbours. In premating females antennule agellar articles 4 and 5 each bear an aesthetasc and article 6 bears three terminal setae (as shown in gure 2C). Each antennal agellum (as in gure 2D) has six articles, distinguished because they taper more regularly than the basal articles. Each of the six bears one or two curving setae.

Remarks. The hirsute anterior pereon shown here in gure 1B agrees well with those gured by Wägele (1979). Such bushy dorsal setae have not been described in any other Eisothistos . They were seen, however, only in females which had spawned (Wägele’s Abb. 4) or were about to do so (Abb. 7). Probably their function is to keep brooded embryos away from the mother’s mouth-parts, where they might be eaten. It must be admitted that the telson keels of two young females from Gibraltar (gures 1J, K) resemble those of Eisothistos pumilis Wägele , rather than E. macrurus , in having an extra row of small spines on each side of the mid-line row of larger spines. There were no post-partum females in Wägele’s material of E. pumilus , so more study of that species is needed.

Figures

FIG. 1. Eisothistos macrurus Wägele, dorso-lateral view of Bodrum female showing pereopods of right side with (A) antennules 1 and 2 atrophied, as in all brooding females; (B) clusters of setae on dorsum and sides of head and anterior pereonites; (C) pereopod 1 also unusually setose; (D, E) pereopods 2 and 3 with about seven pointed studs or warts on each ischium; (F) telson with about 12 keel spines, hind margin with six adcentral teeth separating two very long, curving plumose setae, each accompanied by small companion seta arising in same marginal notch; (G) embryo with well-developed limbs, brooded by similar female from Gibraltar; (H) side view of posterior end of manca from Gibraltar, showing uropodal exopod and keel spines in proŽle; (J) telson of mature Gibraltar female which lacks both plumose setae though companion setae remain; (K) tail-fan of young female, body length 2.1 mm. All scale bars: 0.2 mm.