Neastacilla Tattersall, 1921

King, R. A., 2003, Neastacilla Tattersall, 1921 redefined, with eight new species from Australia (Crustacea: Isopoda: Arcturidae), Memoirs of Museum Victoria 60 (2), pp. 371-416 : 372-374

Neastacilla Tattersall, 1921

Neastacilla Tattersall, 1921 a: 243–244 .— Nordenstam, 1933: 118–119.— Kussakin, 1972: 178-189 -.— Kensley, 1978: 31.— Wägele, 1991: 91.

Type species. Astacilla falclandica Ohlin, 1901 , by plenary powers ( ICZN, 1987).

Diagnosis. Body cylindrical, slender and strongly geniculate between pereonites 4 and 5. Pereonite 1 fused to head, fusion indicated by groove, occasionally by lateral incision. Pereonite 4 elongate, 3–10 times length of all other pereonites. Pleon about same length as combined lengths of pereonites 5–7. Antenna 2 slender, flagellum of 2 or 3 articles with claw. Pereopod 1 included within margin of head, dactylus as long as wide; carpus and propodus of subequal length; dactylus without unguis, with distal setae. Pereopods 2–4 slender; with long, closely spaced setae; dactylus reduced and claw-like [lost entirely in a few Australian species]; flexion between carpus and propodus absent. Pereopods 5–7 progressively shorter posteriorly, dactylus with unguis and secondary unguis. Oostegites present on pereopods 1–4; oostegite 4 forming the major part of marsupium, thickened. Male pleopod 1 with lateral notch and setae on posterior face. Male pleopod 2 appendix masculina curved, with a ridge on posterior face, not extending much past endopod. Penial plate simple, tapering to apex, straight.

Composition. 38 species, excluding those inquirenda (see Table 1).

Remarks. Characters such as the morphology of pleopods 1 and 2 (including the short, curved appendix masculina), simple fused penial plate and the morphology of oostegite 4 in females are new characters used here to redefine Neastacilla . Importance has also been placed on the absence of flexion between the carpus and propodus in pereopods 2–4 (apparent in Astacilla ). Many existing description do not include these characters and so some species (especially those from the North-west Pacific) remain uncertainly placed within Neastacilla .

According to Kussakin’s criteria N. tzvetkowae belongs to Astacilla or possibly Arcturus because it possesses an antenna 2 with 3 or more flagellar articles and probably has an unguis on pereopod 1. N. tritaeniata was not thoroughly described but the flagellum of antenna 2 is composed of five articles and pereonite 4 is not elongate, suggesting a species of Arcturus . Similarly, N. sirenkoi has four antenna 2 flagellar articles and an unguis on the dactylus of pereopod 1 and should be placed in Arcturus . Further, these three species are all from the North-west Pacific where other species of Arcturus occur.

It is possible that Astacilla cymodocea Menzies and Glynn, 1968 from the Caribbean may yet be included in Neastacilla as it is described as lacking an unguis on pereopod 1 and lacking dactyli on pereopods 2–4. With no information available on the male sexual appendages (no specimens could be examined), it is not included here.

The morphology of arcturid oostegites is considered here to be taxonomically important, yet these characters have not often been included in species descriptions or illustrations. The morphology of oostegite 4, for example, was discovered to vary within Neastacilla . In some species of Neastacilla ( N. coonabooloo , N. deducta , N. monoseta and N. soelae ) there is a midlength suture in oostegite 4 that is not found in any other genus ( Figs 3A , 4E , 18C , 20B ). This suture is thought to be homologous to that separating the posterior lobe found on oostegite 4 in other species of Neastacilla ( Fig. 7C , 9E , 14E ) and in other genera. This condition is found in females where the pereonite 4 is extremely narrow and elongate. The smaller sutured posterior lobe may help aerate the marsupium while the female is brooding and it is possible that the suture found in elongate females performs a similar function.

Sexual characters are also argued here to be taxonomically important. Male pleopodal structure and female oostegites of the Australian and New Zealand species of Neastacilla differ from those in N. richardsonae , a north-western Pacific species. While it is the only species examined from this region, others from the north-western Pacific are figured similarly. Neastacilla richardsonae possesses a straight appendix masculina and a developed functional oostegite on pereopod 5. Both these character states are shared with Arcturus and not with Australian and New Zealand Neastacilla species. No information is available on the structure of the appendix masculina in other North-western Pacific species but the curved, ridged appendix masculina has so far only been found in Australian and New Zealand species of Neastacilla (and in Parastacilla , endemic to Australia ( King, 2000)). The North-western Pacific species remain in Neastacilla for the time being but they may belong to Arcturus , a new genus, or both.

Biogeographical evidence supports the view that the north-western Pacific species may belong to another genus. The majority of the species from around Australia and New Zealand are found in the Pacific Ocean, with four of the new Australian species described here ( Neastacilla lawadi , N. marrimarri , N. soelae and N. yuriel ) reported from the Indian Ocean (coast of Western Australia). The centre of diversity of Neastacilla is evidently Australia and New Zealand with undisputed species also reported from subantarctic islands. Clearly, the north-west Pacific species are geographically separated from this radiation and thus are only conditionally included within the genus until further work can make clear their position. Species from southern South America, South Africa and California, USA were unavailable for study and are similarly included in the genus until further clarification.

Figures

Figure 3. Neastacilla coonabooloo sp. nov., female holotype (NMV J1036): P1, P3, P4, P5, U; A, ventral view. Male (NMV J47323): Pe, PL1, PL2. Scales: a (P1, P3, P4) = 0.5 mm; b = (A) 1.0 mm; c (P5) = 0.5 mm; d (U, Pe, PL1, PL2) = 0.2 mm

Figure 4. Neastacilla deducta Hale, 1924, female (NMV J40673): A, lateral view; B, dorsal view; E, ventral view with oostegites. Male (NMV J40674): C, ventral view; D, dorsal view. Scale = 1.0 mm.

Figure 7. Neastacilla inaequispinosa (Guiler, 1949), female (NMV J39217): A, lateral view; B dorsal view; C, ventral view with oostegites; A1, A2. Male (NMV J40691): D, lateral view; E, ventral view. Scales: a (A, B) = 1 mm; b (C) = 1.0 mm; c (A2) = 1.0 mm; d (A1) = 0.5 mm.

Figure 9. Neastacilla kanowna sp. nov., female holotype (NMV J3418): A, lateral view; B, dorsal view; E, ventral view with oostegites. Male (NMV J40679): C, lateral view; D, dorsal view. Scales = a (A–D) = 1.0 mm; b (E) = 1.0 mm.

Figure 14. Neastacilla levis (Thomson and Anderson, 1921), female (NMV J4736): A, lateral view; B, dorsal view; E, ventral view with oostegites. Male (NMV J40675): C, ventral view; D, dorsal view. Scale: a (A–D) = 1.0 mm; b (E) = 1.0 mm.

Figure 18. Neastacilla monoseta (Guiler, 1949), female (NMV J1022): A, lateral view; B, dorsal view; C, ventral view with oostegites. Male (NMV J40641): D, ventral view; E, dorsal view. Scale: a (A, B, D, E) = 1.0 mm; b (C) = 1.0 mm.

Figure 20. Neastacilla soelae sp. nov., female holotype (NMV J16652): A, lateral view; B, dorsal view; C, ventral view with oostegites; A1, A2, left MXP, MX1, MX2, MD. Scale: a (A, C) = 1.0 mm; b (B) = 1.0 mm; c (A2) = 0.5 mm; d (A1) = 1.0 mm; e (MXP, MX1, MX2, MD) = 0.5 mm.