Eisothistos adcentralis, Knight-Jones & Knight-Jones, 2002

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 : 1402-1406

Eisothistos adcentralis sp. nov.

(gures 2, 3)

Material. Mature female holotype, a larger post-partum female and a mature male from spirorbid tubes collected 20 October 1989 from shore rocks east of Lazareto, Funchal, Madeira, 32ss38.65¾N, 16ss53.2¾W. Two juveniles from old coaling jetty, 32ss38.1¾N, 16ss56.2¾W (NW of Ilheu Gorgulho), 29 October 1989. Nine females from shore collections at Sheraton Hotel, 32ss38.38¾N, 16ss55.3¾W, 24 January 1982 and 21 October 1989. Three females from a rock-pool collection at Baixa da Arrilhada, 32ss38.14¾N, 16ss55.6¾W, ca 500 m SW of Reids Hotel, 27 January 1982. Spirorbid species common at these locations were listed by Knight-Jones and Knight- Jones (1995). Five more of this species were from Dakar, Senegal, in tubes of Simplaria pseudomilitaris Thiriot-Quiévreux or Pileolaria dakarensis Knight-Jones (1978) , collected from shallow water and shore pools near Cape Verde, in Anse Soumb Dioum, 14ss40¾N, 17ss28¾W, 3 February 1976.

Description. HOLOTYPE. A mature female 1.2 mm long (gure 2A). Each eye with about ve ocelli (six or seven in larger specimens). Pereonites 3–6 somewhat swollen ventrally. Telson so transparent that marginal teeth cannot be distinguished in the glycerol mount, but higher magni cation (gure 2B, on left) shows that thin threads of tissue run longitudinally in the telson. These diverge as they approach posterior margin, where each thread connects with basal granule of a marginal seta. Since holotype telson is viewed so obliquely, from left side, gure 2B also includes (on right) the transparent telson of a paratype juvenile from Gorgulho jetty, which shows in dorsal view the three pairs of marginal setae found in this and the other species described here. Each adcentral plumose seta is accompanied by a small companion seta, which appears to arise from the same basal granule. Dorsal surface of telson bears a pair of small adcentral setae, anterior to the plumose setae, shown also here in telson of the female paratype (gure 2K). The telson of this larger female (total length 1.7 mm) was not too transparent in glycerol to show the usual six or seven pairs of incised teeth on hind and postero-lateral margins, with large adcentral plumose setae separated from each other by central pair of marginal teeth.

Antennules distal article with three thin distal setae, two adjacent articles each with one aesthetasc (gure 3J). Antennae with usual array of setae (gure 3K). Pereopods seven pairs, each with wheel-joint between propodus and dactylus, all except pereopod 1 with row of spines along ventral margin of propodus. Pereopods 2 and 3 (gure 3G) each with ca three very small conical studs on distal half of each ischium and four on merus.

PARATYPE. Female 1.9 mm long, from Lazareto beach, is post-partum or fertilized (see ‘Discussion’), for it has no aesthetascs, only a few small terminal setae on antennules 1 and 2, and no wheel-joints between propodus and dactylus of pereopods. Each pereopod 2 and 3 has about seven small pointed studs on ‘elbow’ surface of ischium and about three on merus (as in gure 2E). In pereopods 4–7 these articles each bear one such stud (as in gure 2F).

Dakar material (e.g. gure 2C, D) is like that at the same ecdysis stage from Madeira (gure 3J, K), with a few diVerences due to ‘variation’. Out of three Dakar females, two (1.7 and 2 mm long) have an extra seta on each side of the telson (e.g. gure 2H). These extra setae are small, and one of the largest females from Madeira has an extra small seta on left side, but not on right. A Dakar juvenile, 0.8 mm long, is a manca, lacking pereonite 7. Its telson lacks keel spines and has only four pairs of marginal teeth plus a central tooth; its main adcentral pair of marginal setae are not obviously plumose, lack companion setae and are separated from each other by three teeth (gure 2J). Anterior to hind margin, in positions characteristic of the species, is a pair of small dorsal setae. Two manca from Madeira are like that, except that both have companion setae and telsons so transparent that marginal teeth cannot be seen.

Male from type locality, length ca 12 mm (gure 3A), has large eyes, each with ca 10 ocelli; antennules with numerous aesthetascs, mostly arising from basal article 3 (gure 3B, C), but with one or two smaller aesthetascs from each of articles 1–6 of a seven-article agellum, article 7 very small, with ca two terminal setae. Antennae with three basal articles and agellum of six articles (gure 3C shows all except basis). Pereopods (gure 3D–F) longer than in female (gure 3G, H), with length/ breadth ratio of propus ca 4:1. Pereopod 1 propus lacks ventral fringe of spines usually seen in males of this genus (e.g. gure 7E) .

Etymology. Latin ad (towards or near) and centralis (centre), referring to pair of small dorsal setae anterior to the hind margin of the female telson, on either side of the sagittal line.

Remarks. No brooded eggs or embryos of this species were found, but largest female, 2 mm long from Dakar, had pereonites 2–6 swollen by about eight unspawned eggs. Another ovigerous female, 1.8 mm long, from Sheraton shore, Madeira, had about six eggs lling pereonites 3–5. The Dakar female still has her aesthetascs and pereopod wheel-joints, but the Sheraton one has lost them. Evidently this loss occurs before spawning the eggs, probably at an ecdysis associated with copulation. Moulting at mating is well-known in females of many Malacostraca (see e.g. Borowsky and Borowsky, 1987; Karnovsky et al., 1989), including some isopods ( Nair, 1984).

Earlier collections on Sheraton shore, 24 January 1987, yielded eight females, of which four lacked aesthetascs and wheel-joints. Only one of the four had a slender post-partum pereon. The others were plump, as though long past the brooding stage, and one had the three basal articles of each antennule very swollen (gure 9B). The ‘Discussion’ near gure 9 touches on the problem of senescent stages in this genus.