Eisothistos macquariensis, Poore, Gary C. B., Lew, Helen M. & Ton, 2002

Poore, Gary C. B., Lew, Helen M. & Ton, 2002, Expanathuridae (Crustacea: Isopoda) from the Australian region, Zootaxa 82, pp. 1-60 : 12-18

Eisothistos macquariensis n. sp. ( Figs 7–11 )

Material examined.– Holotype. Australia, Macquarie I., Aerial Cove (54° 29.5 S, 158° 57.2 E), in serpulid tube in tunicates under sheltered rock overhang, J.K. Lowry, 9 Dec 1977 (stn MA­99), NMV J27646 (female, 7.2 mm, with 1 slide). Paratype. Collected with holotype, NMV J27647 (male, 2.9 mm).

Description of female holotype: Body with short well­defined pereonite 1, fringed by dorsolateral rows of 8–9 long setae; peronite 2 longer with dorsolateral rows of 4–6 long setae; pereonite 3 with 1 dorsolateral seta; pereonites 4 and 5 elongate and flaccid; 6 and 7 shorter, with dorsolateral rows of up to 9 long setae; each pereonite with lateral coxal lobes. Pleonites 1–5 very short, each with lateral long setae; pleon and pleotelson 0.27 body length.

Head without visible ommatidia produced well beyond bases of antennae. Antenna 1 with article 1 shorter than wide, article 2 longer than wide and with 1 long seta, article 3 shorter than second and with 2 short distal setae; flagellum with short first article, second much longer, 3–6 progressively shorter, only last with distal setae. Antenna 2 with article 2 produced distomedially, with 2 long setae on lobe and 2 laterally, articles 3 and 4 shorter and with medial setae, article 5 longer than 3 and 4 together; flagellum of 6 articles. Mandible and maxilla not dissected. Maxilliped with proximal articles poorly defined, with 2 long setae, distal short article with 4 distal setae.

Pereopod 1 not subchelate; basis twice as long as broad, with c. 10 long lateral setae; ischium with 2 long posterior setae; merus and carpus progressively shorter, setose; propodus twice as long as broad, with long lateral seta, other shorter setae, and small distal spiniform seta; dactylus two­thirds length of propodus, curved, with unguis quarter its length. Pereopods 2 and 3 longer and stronger than pereopod 1; basis with anterior and posterior long setae; ischium with tubercles along posterior margin; merus with 1 tubercle, long setae; carpus with row of pectinate setae and longer simple seta on posterior margin; propodus little more than twice as long as broad, with row of pectinate setae and small distal spiniform seta along posterior margin; dactylus 0.4 length of propodus and half its width, with unguis 0.2 its length. Pereopod 4 sparsely setose; carpus and propodus with posterior row of pectinate setae, propodus with distoposterior spiniform seta; dactylus with very short curved unquis. (Pereopod 5 similar to 4 but broken on both sides.) Pereopod 6 basis with row of 8 long setae; ischium with shorter setae; merus with short and long setae; carpus and propodus with row of pectinate setae and posterodistal flattened spiniform seta; dactylus with very short curved unguis. Pereopod 7 similar but with fewer long setae.

Pleopod 1 with rami fused, with 21 marginal plumose setae and 6 on anterior surface. Pleopods 2–5 (not figured) with exopod smaller than endopod, marginally setose.

Uropodal peduncle with distomedial seta; endopod attached obliquely, distolateral oblique margin irregularly straight, with short denticulate spiniform setae on posterior angle and longer finer setae on dorsal surface; exopod with inner distal lobe narrowly rounded and setose, a central short projection, and more rounded dorsal lobe, upper surface minutely spinose. Telson narrowest anteriorly, broadest near posterior end, truncate, margin obscurely dentate posterolaterally, with dorsal and near­posterior setae and irregular middorsal row of denticles.

Description of male paratype: Shorter than female (40% of length). Body cylindrical, pereonites well­defined, pereonites 1–4 of similar lengths, 5–7 progressively shorter, 7 about half length of 6. Pleon and pleotelson 0.28 total length; pleonites 1–3 of similar length, 4 and 5 each half as long.

Head with lateral ommatidia, produced beyond bases of antennae. Antenna 1 peduncle articles with pappose setae; flagellum with short proximal article, second article long and with rows of aesthetascs; flagellar articles 3 and 4 together as long as first, with distal aesthetascs; articles 5–8 progressively shorter, 5 and 8 with simple setae. Antenna 2 articles 2–4 short, article 5 elongate, all with pappose setae; flagellum of 6 articles, each with few setae.

Pereopod 1 with elongate articles, propodus to carpus with few setae; propodus 4 times as long as wide, with row of pectinate setae and 1 distal spiniform seta along posterior margin; dactylus two­thirds as long as propodus, its unguis about 0.4 its length. Pereopods 2 and 3 longer and more robust than pereopod 1; carpus and propodus with pectinate setae; propodus with distal spiniform seta. Pereopod 4 shorter than pereopods 2 and 3, sparsely setose; carpus and propodus each with posterodistal denticulate spiniform seta and row of pectinate setae. Pereopods 5 and 6 similar to pereopod 4. Pereopod 7 with more elongate propodus and dactylus.

Pleopod 1 with elongate rami, endopod with 5 and exopod with 6 long distal plumose setae. Pleopod 2 endopod with 3 distal plumose setae; appendix masculina as long as endopod and ending in sharp denticulate apex; exopod broader than other rami, with 6 distal plumose setae. Pleopod 3 with elongate rami, endopod with 5 and exopod with 6 distal plumose setae. Pleopod 4 endopod narrow, with 4 distal plumose setae; exopod broadened, with 6 distal setae. Pleopod 5 shorter than others; endopod with 2 distal setae; exopod smaller and with 3 setae.

Uropodal peduncle with dentate inner margin; endopod about 2.5 times as long as wide, lateral margin strongly dentate, inner margin less so; endopod with cluster of pappose setae proximally, other simple surficial setae and distal spiniform seta; exopod with narrow dorsal spike bearing distal spiniform seta, and irregularly lobed ventral lobe. Telson almost parallel­sided over middle region, apex rounded with dentate margin; with 3 pairs of submarginal setae posteriorly, others along median longitudinal ridge, and denticles on dorsal surface distally.

Distribution: Known only from Macquarie I., Australian subantarctic; subtidal. Etymology: For Macquarie Island, type locality.

Remarks: Two other species of Eisothistos have been described from subantarctic islands. Illustrations of two juveniles, less than 1 mm long, of E. minutus Sivertsen & Holthuis, 1980 from Tristan da Cunha suggest some similarities with the new species (bifid uropodal exopod) and differences in the uropodal endopod and telson but are not sufficient to discuss in detail. The unique specimen of E. crateris Kensley, 1976 from St Paul is a male with a much narrower uropodal exopod and longer appendix masculinis than the present species. There is a dense cluster of aesthetascs on the end of the peduncle of antenna 1, replaced in E. macquariensis n. sp. by scattered aesthetascs along the flagellum.

Figures

FIGURE 7. Eisothistos macquariensis n. sp. Holotype female, NMV J 27646. Scale bar = 1 mm.

FIGURE 8. Eisothistos macquariensis n. sp. Holotype female, NMV J 27646.

FIGURE 9. Eisothistos macquariensis n. sp. Paratype male, NMV J 27647. Scale bar = 1 mm.

FIGURE 10. Eisothistos macquariensis n. sp. Paratype male, NMV J 27647.

FIGURE 11. Eisothistos macquariensis n. sp. Paratype male, NMV J 27647.