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Nyctiphanes australis G. O. Sars, 1883

Etymology: Nyctiphanes - night visible/shining; australis - of Australia

Eye: The eye is round, large in size, and tends to remain black under preservation (N. australis eye & rostrum). The eye diameter : carapace length is about 0.20.

Peduncle of 1st Antenna: The dorsal surface of the 1st segment carries a short broadly based, triangular lappet with the narrow apex pointing upward and forward. The 2nd segment in the male bears a short rounded keel extending upward from the distal inner margin. In the female, a very small forwardly directed spine is present at the inner side of the distal upper margin of the 2nd segment and another is at the distal upper margin of the 3rd segment. The 3rd segment is shorter than the 2nd and its outer lateral margin is convex (N. australis,) (N. australis, ).

Rostrum: A rostrum is lacking; the frontal plate is short, has upturned margins and forms an obtuse triangle (N. australis dorsal head) (N. australis eye & rostrum).

Carapace: There are no lateral carapace denticles. In large specimens, >13 mm, there is an acute triangular forward-directed spine (post-ocular spine) behind each eye at the base of the frontal plate (N. australis photo) (N. australis post-ocular spine).

Thoracic legs: Legs 1-6 (endopods) are similarly developed, the 7th is nearly as long but consists of only 2 segments. Exopods present on legs 1-7 in males; in females 1-5, sometimes 1-6. The 8th is rudimentary. In the female, paired eggs sacs are secreted adhering to the two posterior thoracic endopods (6th and 7th).

Abdomen: The 6th segment has a small mid-dorsal posterior spine.

Length: Adults are10-17 mm.

Petasma: The curved spine-shaped process is strong. Proximal and terminal processes are lacking. The median lobe reaches to the end of the lateral process and nearly to the end of the inner lobe which is serrate along its outer margin (N. australis petasma).

Thelycum: Described by Guglielmo and Costanzo, 1983.

Comments: The leaflet on the 1st segment of the peduncle of the first antenna is broader than long and smaller than in N. simplex and N. capensis (Nyctiphanes,). Characteristics of N. australis are the rounded keel-like plate on the 2nd segment of the 1st antenna of the male and the post-ocular spine, in both sexes, on specimens >13 mm.

N. australis is a coastal species. It is a food source for squid, birds (e.g. the short-tailed shearwater, the mutton-bird Puffinus tenuirostris, and various terns), and fishes, notably the barracuda, southern bluefin and skipjack tunas, and the shelf's bottom living tiger flat-head. Sheard (1953) cited evidence that N. australis feeds both in the water column and upon near-bottom detritus.

N. australis occurs in the coastal waters of south-east Australia south of ~30°S and along the southern coast of Australia, westward from Tasmania to about 132°E. In New Zealand waters it occurs around both North and South Islands, and as far south as the Snares Islands (48°S) (N. australis distribution).

The principal population of N. australis is in shelf waters, to ~100 m depth, and swarms have been seen near the surface in the daytime (N. australis aggregation). It remains near the bottom in the daytime and in summer when the surface layer is warmest.

See the development summary (N. australis Table) for the stage descriptors and length in stage.

Metanauplius - (2 forms), only metanauplius illustrated (N. australis A)

Shape - The carapace is smoothly rounded.
Marginal spines - absent

Calyptopis - (3 stages) (N. australis B)

Shape - The carapace is smoothly rounded.
Marginal spines - absent
Postero-dorsal spine - absent
Lateral denticles - absent

Postero-lateral spines - PL3 is longer than PL2.

Furcilia - (7 stages) (N. australis C), (N. australis D)

Eye: The eye is large and round.

Frontal plate/rostrum - The frontal plate is truncated, in early stages it may be slightly indented medially.
Marginal spines - absent
Postero-dorsal spines - absent
Lateral denticles - A pair of denticles is present.

Thoracic legs: There is sequential development without elongate leg(s).

Mid-dorsal spines - absent

Pleopods: There is a variety of forms in F1 and F2 with different levels of pleopod development. The developmental pathway varies, for example 0 - 4' - 4"1’'- 5" and 2' - 2"3' - 5".

Postero-lateral spines - PL3 is longer than PL2.
Lateral spines - One pair of lateral spines is present.

Comments: Sheard (1953) gives an extensive discussion of the geographical variation in the frequency of forms in the furcilia phase of N. australis .

In life there are two red chromatophores on the telson of N . australis ; they are close together in C1 but distinct in later stages.

The calyptopis stages of N. australis resemble those of P. latifrons. In living larvae the species may be separated by the presence of the red chromatophores on the telson of N. australis and lack of chromatophores in P. latifrons . In the calyptopis 3 of P. latifrons the carapace projects posteriorly extending beyond the lateral margins in a hood-like manner over the first abdominal segment. In N. australis the posterior margin appears about equal in length to the lateral margins of the carapace. In the furcilia phase, the anterior margin of the carapace frontal plate inP. latifrons is deeply emarginate with prominent antero-lateral projections while in N. australis these features are less exaggerated.

N. australis is separated geographically from the other three species in the genus, N. capensis , N. couchi , and N. simplex . In two of the species, N. capensis and N. simplex , the carapace frontal plate is truncated, the anterior margin is concave, and the antero-lateral angles may be acute. In N. australis and N. couchi the anterior margin appears usually to be flat, it may be slightly indented in F1.

(N. australis Table), development summary for the stage descriptors and length in stage.

N. australis, selected stages
N. australis A [metanauplius]
N. australis B [calyptopis 1-3]
N. australis C [furcilia 1-3]
N. australis D [furcilia 5-6]
key to larval illustrations

Nyctiphanes australis