Argathona aff. macronema ( Bleeker, 1857 )

Bruce, Niel L., Wong, Helen P. - S. & Merrin, Kelly L., 2022, The genus Argathona Stebbing, 1905 (Crustacea: Isopoda: Corallanidae) in Singapore marine waters, with description of two new species, Raffles Bulletin of Zoology 70, pp. 492-510 : 506-508

Argathona aff. macronema ( Bleeker, 1857)

Aega macronema Bleeker, 1857: 23 , pl. 1 figs. 1–lc. Monod, 1975: 1003.

Corallana macronema .— Miers, 1880: 469.

Brotherus longicornis Budde-Lund, 1908: 307 .— Stebbing, 1911: 179; Monod, 1975: 1003.

Argathona similis Richardson, 1910: 11 , fig. 10.— Hale, 1925: 162, fig. 16; 1929: 251, figs. 244–245; Nierstrasz, 1931: 175; Monod, 1933: 177; 1975: 1003.

Alcirona macronema .— Nierstrasz, 1917: 97, pl. 14 figs. 29–35; 1931: 168; Monod, 1924: 99; 1975: 1003.

Orcilana hanseni Nierstrasz, 1931: 170 , figs. 48–57, pl. 40 figs. 19–20.— Monod, 1975: 1003.

Argathona longicornis .— Monod, 1933: 179, 182.

Argathona macronema .— Monod, 1933: 174, 182, figs. 4–11; 1975: 1003, figs. 1–20; Nordenstam, 1946: 14; Shiino, 1961: 98; Bruce, 1982b: 13; 1997: 200; 1999: 306; 2002: 210; Grutter & Lester, 2002: 250; Trilles, 2008: 27; Justine, 2010: 170; Anil et al. 2018: 298, figs 5, 6, 4.

Material examined: Female (non-ovig. 13.7 mm), Kusu Island, 01°13.314′N, 103°51.640′E, 04 Jun 2013, SCUBA , depth, 16.3 m, stn. SD 177, SS-4249, coll. Heok Hui Tan & party ( ZRC.2022.0017). Manca (5.4 mm), taken along with an A. rhinoceros , SS-0828, same data as ZRC.2022.0017 ( ZRC.2022.0018) .

Remarks: Bleeker’s (1857) description and figures are minimal and provide few clues to identity other than the long antennal flagellum. The perceived long antennal flagellum has been critically influential in subsequent species identifications (e.g. Monod, 1933, 1975; Bruce, 1982b). The presence of a long antennal flagellum, among some other characters, has also influenced the placing of several notional species into junior synonymy with A. macronema .

Bleeker (1857: figs. 1, 1a–c) gave four small figures, and while there is barely enough detail to characterise the species, it can be seen that the ‘long antennae’ are in fact considerably shorter than that of many the records and synonyms subsequently reported under the name A. macronema , extending at most to the anterior of pereonite 5 rather than posterior of pereonites 6 and 7 (or longer) for most subsequent records. Interpreting Bleeker’s figures suggests that there is a short pentagonal frontal lamina, and that the pleotelson is relatively broadly rounded with a distinct median longitudinal carina; it is not possible to determine if the dorsal surfaces are setose or smooth.

Several species have been placed in synonymy, but to date there has been no type-based redescription of A. macronema . Bleeker’s material is held at the Naturalis Museum, Leiden, so probable type specimens are available. Unfortunately, at the time of writing, the probable type material of Argathona macronema ( Bleeker, 1857) was not available for examination or loan as the collection was in the process of being relocated (Karen van Dorp, pers. comm.). Monod (1933, 1975) described specimens as this species but his two records are clearly of two different species. Australian specimens (as A. similis Hale, 1925 ) have a long antennal flagellum extending to nearly to the pleon and a long anteriorly rounded or truncate frontal lamina—not the same as Monod’s (1933, 1975) descriptions. Specimens from the Great Barrier Reef, Queensland (held at the Queensland Museum: QM W10817–W10828, W15486, W15489) have a long antennal flagellum extending to at least pereonite 6 and occasionally to the anterior of the pleon; the frontal lamina is elongate pentagonal, with rounded angles that can appear rounded if viewed slightly from the posterior. These specimens agree well with the material from Singapore.

It is highly probably that several species have been and are being recorded under the name of A. macronema . Some species names may need to be brought out of synonymy. Establishing the identity of both named and potential new species is not possible without a detailed type-based species redescription against which all subsequent records can be assessed, and to confirm identity of the synonymised taxa to make sure that they are or are not the same species. Below are comments on the records of A. macronema with an assessment of their status.

Our conclusion is that the current usage of Argathona macronema includes a number of similar species and a full revision, based on the type material for the species, is needed; the material for all records and synonyms needs to be reexamined and the identification confirmed or rejected. For completeness the presented synonymy includes all uses of the name Argathona macronema (in different combinations) as well as the names that have been placed into junior synonymy. It is clear that most subsequent records are misidentifications.

Most host records under this species name are from Serranidae .

Argathona macronema ( Bleeker, 1857) . Bleeker’s (1857) figures (figures 1, 1a-c) show the antenna flagellum (described by Bleeker as “plus longue que la moitié de la longuer du corps.”) extends only to the posterior of pereonite 4. If interpreted correctly, the frontal lamina is pentagonal, 2.1 times longer than wide ( Bleeker, 1857, figure 1a) and, if interpreted correctly, the pereonites may be setose, but that is not clear, and there is no mention of nodules on the pereonites or pleonites.

Locality: Java Sea (as ‘mer du Batavia’) .

Brotherus longicornis Budde-Lund, 1908 . While briefly described by Budde-Lund (1908), there are a number of precise figures that permit some characterisation. Notably the pentagonal frontal lamina has concave lateral margins that clearly diverge towards the anterior, with the straight anterior margins strongly convergent. The pleon and pleotelson both appear setose but there is insufficient detail to allow interpretive comparison to other species. The length of the antennal flagellum was not described or figured. The shape of the frontal lamina excludes this species from both Argathona macronema of Bleeker (1857) and from the Singapore-Australian group of species documented here.

Locality. Majunga Bay, northwestern Madagascar; from eels (“Meeraales”).

Argathona macronema of Bruce (1982b). This species is common on the Great Barrier Reef and is conspecific with specimens collected in Singapore. It differs from A. macronema (of Bleeker, 1857) in having a longer antennal flagellum that extends to at least the posterior of pereonite 6, sometimes longer if not broken, and an elongate frontal lamina (3.8 times as long as posterior width) with a rounded or ‘rounded pentagonal’ anterior margin. A colour photo of this species was given by Bruce (1999: 306). Referred to below as the ‘ Singapore –Australian species’, this species is possibly the same as Argathona similis Richardson, 1910 .

Locality: Great Barrier Reef ( Bruce, 1982b; Bruce et al., 2002) and Singapore (present study); also, Papua New Guinea and probably Indonesia ( Richardson, 1910; Nierstrasz, 1931) and New Caledonia ( Justine, 2010); possibly Andaman Islands ( Anil et al., 2018).

Orcilana hanseni Nierstrasz, 1931 . As far as can be seen, this species corresponds to the Singapore –Australian species rather than to Bleeker’s figures, with the antennal flagellum extending to pereonite 7.

Locality: Atjatuning, western New Guinea

Argathona similis Richardson, 1910 . Figured by Hale (1925). This species agrees well with the SingaporeAustralian species, with long to very long antenna extending to the pleon, relatively large eyes, a narrowly rounded pleotelson apex and uropodal rami that extend beyond the posterior margin of the pleotelson. The name has priority over most other species names except Brotherus longicornis Budde-Lund, 1908 , but that species is clearly a distinct species (see above).

Locality: Lembeh Strait, North Sulawesi, Indonesia; South Australia and Western Australia ( Hale, 1925).

Argathona macronema of Monod (1933). This species is not the same as the Singapore –Australian species: the antenna flagellum is shorter, extending only to pereonite 5 (vs to posterior of pereonite 6 or 7); it is far more setose dorsally (vs setose only on pleotelson and weakly on pleon, not setose on the pereon); the uropods do not or not significantly extend beyond the pleotelson apex (vs clearly beyond); and the frontal lamina has a rounded anterior margin but is much shorter.

Locality: Egypt.

Argathona macronema of Monod (1975). The identity of this record is uncertain. It is not the Singapore –Australian species, nor does it appear to be the same as the species from Egypt. The frontal lamina was not described or figured; while the uropods extend well beyond the pleotelson apex, the endopod is drawn as rounded and quite unlike the Singapore –Australian species which has an acute or subacute apex.

Locality: Kenya.

Alcirona macronema of Nierstrasz (1917). Nierstrasz’s photograph of the dorsal view (plate XIV, fig. 29) shows a posteriorly acute pleotelson apex, with strongly convergent and nearly straight lateral margins; both the uropodal exopod and endopod have acute apices. These characters agree neither with Bleeker’s (1857) original description and figures, nor with the later accounts of Monod (1933, 1975) but correspond to the Singapore –Australian species, based on material examined here from Singapore and the Great Barrier Reef.

Locality: Java, Indonesia.

Argathona macronema of Anil et al. (2018). As figured, the frontal lamina is elongate–pentagonal, the pleotelson has a notably acute apex and straight lateral margins, the uropodal endopod has an acute apex, and the antennal flagellum is described as extending to pereonite 6. This record does not agree with Bleeker’s (1857) description; it is perhaps most similar to the Singapore –Australian species although the frontal lamina shape differs from that species.

Locality: Andaman Islands.

Corallana macronema of Miers, 1880. Miers (1880) considered this to be a species of Corallana as it had a “narrow linear interantennulary process (frontal lamina)”; this character would exclude the species from Argathona . Identity not known.

Locality: Miers (1880) had no locality data, other than ‘Malaysia’ in the broadest sense.