Expanathura collaris Kensley, 1979

Annisaqois, Manikmayang & Wägele, J. Wolfgang, 2021, Morphology and Taxonomy of Isopoda Anthuroidea (Crustacea) from Sulawesi with description of six new species, European Journal of Taxonomy 768, pp. 1-52 : 27-34

Expanathura collaris Kensley, 1979

Figs 18–23

Panathura collaris Kensely, 1979: 823 , figs 7–9.

Panathura collaris – Müller 1993: 329, figs 172–202 (re-description).

Expanathura collaris – Wägele 1981b: 89 (new genus). — Negoescu 1999: 214, figs 9–11. — Negoescu & Brandt 2001: 121, figs 14–18. — Poore & Lew Ton 2002: 26 , figs 16–19, 20a.

Material examined

INDONESIA • ♀ (2.5 mm); Bangka Island (North Sulawesi), off Coral Eye Resort; 1°44′20.22″ N, 125°8′46.07″ E; 1–2 m depth; in coral rubble, dissected specimen; M. Annisaqois and J.W. Wägele leg.; Sep. 2019; MZB Iso 106 • 4 other specimen (2.0– 3.1 mm); same collection data as for preceding; MZB Iso 107 .

Description of female from Bangka Island

BODY. Slender, dorsal head pigmentation V-shaped.

ANTENNAE. Antenna 1 first article of peduncle 1.27 as long as wide, three flagellar articles, last article bearing 2 aesthetascs.Antenna 2 peduncle second article distally with distinct protrusion, with 5 short flagellar articles.

MANDIBLE PALP. With 3 articles, last article bearing 7 short setae, and - as is typical for the genus - the endite is slender and lacks a molar process, lamina dentata is present, the pars incisive small. Maxilla 1 distally with 5 spine-like teeth. Maxilliped palp with 5 articles, stout endite does not reach palp article 4.

PEREOPODS. Pereopod 1 propodus palm proximally with 1 protruding and apically rounded point, more distally a less protruding crenulated tooth and distal half of palm crenulated, carpus palm with protruding shorter rounded point distally. Pereopod 2 propodus palm proximally with 1 slender and curved protrusion, followed distally by edge with 1 shorter protrusion and some notches, distal half of edge irregularly crenulated. In other, smaller specimens the crenulations on P1 are weaker (see Fig. 21 ). Pereopod 7 propodus dorsal margin with 2 trifurcate setae.

PLEOPOD 1 ENDOPOD. Narrower and shorter than the broad exopod, distally narrower than proximally, with 3 apical feathered setae, exopod with 12 feathered setae. In other specimens (see Fig. 21 ) the number of setae on the pleopod 1 endopod varies between 2 and 5. Uropod exopod outer margin proximal half nearly straight, distal half with concavity, in between a rounded point.

TELSON. With convex margins, broadest nearly in the middle of its length, with a pair of lateral setae on broadest part, a pair of very short setae centrally on apex, rounded distal margin bearing 3 further pairs of long setae and 3 pairs of short setae; dorsally 2 pairs of short setae on telson. Shape and setation of uropod and telson vary a little in smaller specimens ( Fig. 21 ).

Remarks

Most characters useful to distinguish the species can be found in the shape of the palm of pereopod 1, pleopod 1 endopod, the uropod exopod, and the telson. The pereopod 1 palm generally has a proximal protrusion and often irregular crenulations on the upper half.

The species Expanathura amstelodami (Kensley, 1976) from Amsterdam Island and Madagaskar, E. ardea Poore & Kensley, 1981 from Queensland and E. mooreae Müller, 1993 from Moorea all have a pleopod 1 with a small, narrow endopod. In addition, these species have a lanceolate uropod exopod and a pereopod 1 propodus palm that lacks crenulations on its distal half. We call these species the amstelodami group.

Our material from Bangka Island is more similar to E. collaris ( Kensley, 1979) , originally described from Fiji and Rarotonga, E. haddae Kensley & Poore, 1982 from Houtman Abrolhos Islands, and E. macronesia ( Kensley, 1980) from Réunion, near Mauritius, and according to Kensley (1988) also found in the Aldabra Atoll. In these three species (the collaris-group) the uropod exopod is more rounded, with a concavity of the distal outer margin.

Our material from North Sulawesi clearly belongs to the collaris group and resembles most E. collaris as described by Kensley (1979). However, a difference is the shape of pleopod 1 endopod, which in Kensley’s material is wider and bears distally 8 swimming setae, while in our material pleopod 1 endopod is distally narrow, and the number of setae can vary from 2–5 (see Fig. 21 ). Expanathura haddae has been described with a flattened telson apex (Kensley & Poore 1982), less rounded than in E. collaris . Expanathura macronesia Kensley, 1980 has in the original description a P1 palm without crenulations on its distal half, however, these are present in Müller’s redescription ( Müller 1990). The proximal projection on the P1 palm is curved and more pointed than in the Bangka-Island material and the distal outer setae on P7 propodus are not trifurcate.

There are 6 publications with descriptions of Expanathura collaris from different places, with astonishing variations between populations (see Figs 22–23 ). Some of these differences can be attributed to the style and detail of illustrations, however, conspicuous differences in pereopod 1, uropod exopod shapes and of the endopod of pleopod 1 suggest that there is more than one species involved.

The material described by Chew et al. (2018) from Malaysia has a similar telson setation as the Bangka material, a uropod exopod with shorter setae, but further details are undescribed. Expanathura collaris as described by Negoescu & Brandt (2001) from Madang ( Papua New Guinea) looks more like E. macronesia Kensley (1980 , from the Madagaskar region); these animals have an acute and curved proximal projection on the propodus palm of pereopod 1 and a more acute point before the concave region of the uropod exopod margin. We propose to exclude this material from the species E. collaris s. str. Specimens from Fiji described by Negoescu (1999) share with our Bangka material the narrow pleopod 1 endopod with 3 distal swimming setae, however, the uropod exopod has a very different shape; the concave part of the outer margin is small and the exopod has a more rounded shape clearly different from Kensley’s original description. Specimens from Queensland described by Poore & Lew Ton (2002) have a pereopod 1 propodus palm with no crenulations on its upper half, the proximal protrusion is very small. This could also be a hitherto undescribed species. Specimens described by Müller (1993) also seem to lack the crenulation on the P1 propodus palm and there are no setae on the concave part of the uropod exopod margin.

For a better understanding of this species group new descriptions of material from several localities are needed. DNA data could help to clarify species delimitations.

Figures

Fig. 18. Expanathura collaris (Kensley, 1979). Ovigerous ♀ from Bangka Island, in dorsal and lateral view (2.5 mm) (MZB Iso 106). Abbreviations: A1 = antenna 1; A2 = antenna 2; Md = mandible; Mx = maxilla, Mxp = maxilliped.

Fig. 19. Expanathura collaris (Kensley, 1979) (MZB Iso 106). Ovigerous ♀ from Bangka Island. Abbreviations: P1–P7 = pereopods 1–7.

Fig. 20. Expanathura collaris (Kensley, 1979) (MZB Iso 106). Ovigerous ♀ from Bangka Island. Abbreviations: Plp 1–3 = pleopods 1–3; UEx = exopod of uropod; UEn = endopod of uropod; Tel = telson.

Fig. 21. Expanathura collaris (Kensley, 1979), immature specimens from Bangka Island showing variations (MZB Iso 107). Left: specimen of 2.5 mm; right: specimen of 2.2 mm. Abbreviations: P1 = pereopod 1; Plp1 = pleopod 1; UEx = exopod of uropod; Tel = telson.

Fig. 22. Expanathura collaris (Kensley, 1979), comparison of published descriptions. Pereopod 1, pleopod 1, telson and exopod of uropod. Populations from Fiji (after Kensley 1979), Queensland (after Poore 2002) and Moorea (after Müller 1993).

Fig. 23. Expanathura collaris (Kensley, 1979), comparison of published descriptions.pereopod 1, pleopod 1, telson and exopod of uropod. Populations from Fiji (after Negoescu 1999), Madang (after Negoescu and Brandt 2001) and Bangka Island (present publication).