Austrodecus bamberi Wang et al., 2013

Staples, David A., 2019, Pycnogonids (Arthropoda, Pycnogonida) from the Southwest Indian Ridge, Zootaxa 4567 (3), pp. 401-449 : 419

Austrodecus bamberi Wang et al., 2013

Figure 10 A–C; Plate 3 F–G

Austrodecus bamberi Wang et al., 2013: 73 –79.

Material examined. One male (NHMUK 2018.21), Southwest Indian Ocean, Coral Seamount, 41˚ 22.31'S, 42˚ 54.57'E, ROV, 732 m, specimen JC066-1298D, stn 4.38, mooring site, whale bone net, 20 November 2011. One male (dissected) ( NHMUK 2018.22 ). Southwest Indian Ocean, Coral Seamount, 41˚ 22.31'S, 42˚ 54.58'E, stn 4.38, ROV, 732 m, specimen JC 066-891, parent 1244, mooring site, on Mango wood, 20 November 2011 . Two males, four females, one subadult ( NHMUK 2018.23 ), Southwest Indian Ocean, Coral Seamount, 41˚ 22.31'S, 42˚ 54.58'E, ROV, 732 m, JC066-1296D, stn 4.38, mooring site, on Mango wood net, 20 November 2011 .

Remarks. Austrodecus bamberi was described from the SWIR based on a single male specimen ( Wang et al., 2013). This collection contains the first record of the female ( Plate 3 F, G ). Gonopores are not evident and apart from the presence or absence of femoral cement gland ducts there is seemingly no apparent means of distinguishing the sexes. The largest specimen in this collection is a female, but its size may be an indication of advanced maturity rather than sexual dimorphism. All other specimens, both male and female are of a similar size. In one male specimen, the cement gland is absent on two femora from opposite sides of the body and on different legs. Only a few comments are provided to complement the original description. The minor differences can possibly be attributed to interpretation of morphological characters and perhaps intraspecific variation.

I agree with Child’s (1994b) diagnosis of this family, in particular that the palps originate from anterolateral extensions of the cephalon. In this material the segmentation line shown at the base of the first palp segment by Wang et al. (2013, Fig. 1B, C ) is not present in which case the palps are five-segmented, not six-segmented. The first pair of legs is longer than legs 2–4 as evidenced in the measurements of first and third legs ( Wang et al. 2013). The dorsodistal spines on the femur and tibiae are over three-times the width of the corresponding segment. The ovigers are clearly four-segmented and are attached to a prominent extension on the ventral surface of the cephalon ( Fig. 10C ). A minor observation is the presence of one or two strong inwardly curved spines on the first palp segment in addition to the four similar spines on segment three. The distal-most spine is shortest.

One specimen was recovered on-board ship from Mango wood deployed as part of the moorings experiment however Austrodecus species are morphologically adapted to feeding on bryozoans and thecate hydroids, and it is most likely that this specimen was dislodged from its host substrate.

The ocular tubercle of the subadult specimen is more erect than that of adults and eyes are not evident.

Figures

FIGURE 1. Cruise track for JC66/67 from JC66 Cruise Report, (Rogers et al., 2012) showing the six Southwest Indian Ridge sites visited (the hydrothermal vent site studied during JC067 is indicated by the solid circle).

PLATE 3. Tanystylum tiara sp. nov., holotype male. A, trunk lateral; B, trunk, dorsal; C, trunk anterior view. Sericosura species indeterminate. D, trunk dorsal; E, trunk, lateral. Austrodecus bamberi. F, trunk dorsal; G, trunk, lateral. Austrodecus taylorae sp. nov., holotype, male. H, trunk dorsal.

FIGURE 10. Austrodecus bamberi. male A, dorsal process, third coxa; B, one of two dorsodistal tubercles on lateral process; C, oviger.