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Euastacus Morgani

Euastacus Morgani

 Kingdom:     Animalia
Phylum:     Arthropoda
Subphylum:     Crustacea
Class:     Malacostraca
Order:     Decapoda
Family:     Parastacidae
Genus:     Euastacus
Species:   Euastacus Morgani


 Euastacus morgani sp. n. is known only from the type locality, a highland (~600 m a.s.l.), rainforest site at the northern margin of Bindarri National Park, in a tributary to the Little Nymboida River (Figure 3). Two comparatively widespread species of Euastacus occur in the area, including a site in Little Nymboida River proximal to the type locality, Euastacus dangadi Morgan, 1997 and Euastacus neohirsutus Riek, 1956. We have surveyed numerous sites in the area, but our efforts yielded only these two more common species.

The species constructs a more or less horizontal burrow entrance from the water’s edge back into the stream banks. The specimens were collected by probing these bank burrow systems by hand until the crayfish attempted to exit via another entrance hole, typically located 1–2 m further back from the creek on the adjacent forest floor. The successful sampling was undertaken at night.

Although the precise locality is uncertain, Gary Morgan collected juvenile Euastacus specimens at a nearby site (‘Brimbin Creek’, near Lowanna) that were too small for taxonomic determination, although they appeared to be different to all local species (Morgan 1983). Morgan (1983) collected these specimens in sympatry with Euastacus neohirsutus, and observed differences to that species on the following taxonomic features: larger rostral carinae; larger antennal basipodite spine; better developed ventral lateral propodal spine row of the cheliped; lacking dorsal apical propodal spines; lacking spines above the cutting edge of the propodus. All of these characters are also true of Euastacus morgani, and thus it is likely that the small specimens observed by Gary Morgan were juveniles of this new species.

Euastacus morgani appears most similar in morphology to Euastacus simplex Riek, 1956. It can be distinguished among other characters by having: 3 instead of 2 mesial carpal spines on the cheliped; no spines above the propodal cutting edge of the cheliped; medium instead of barely discernible or small suborbital spines; poor development of the ventral lateral propodal spine row; a proportionally shorter interantennal scale; and a proportionally shorter exopodite and more pointed anterior terminus to the ischium of the third maxilliped. Systematically, the species thus fits within the ‘simplex’ complex (Morgan 1997), which includes Euastacus simplex, Euastacus clarkae Morgan, 1997, Euastacus maccai McCormack and Coughran, 2008, and Euastacus morgani. A key is provided below to distinguish Euastacus morgani from other species in the ‘simplex’ complex.

The description of Euastacus morgani increases the number of described species in this charismatic genus to 50 (Table 1). There are further taxa still awaiting formal description, and large areas of potentially suitable habitat that have yet to be surveyed. Unfortunately, 80% of Euastacus are considered to be threatened (Coughran and Furse 2010; Furse and Coughran in press a, b, c; IUCN 2010), and there is thus a sense of urgency for continued field surveys and taxonomic work on this genus. It would appear that Euastacus morgani has a severely restricted, highland distribution, and may be susceptible to similar threats facing other species in the genus, particularly those relating to over-collection, exotic species and climate change (Furse and Coughran in press a, b, c). Further research into its ecology is warranted.

Euastacus morgani sp. n. Dorsal view of body A and cheliped B, holotype specimen, AM P.84263. Dorsal view of antennal squame C, lateral view of third maxilliped D and ventral view of left hand side of cephalon showing interantennal scale E, specimen ACP 1103. Scale bars = 5 mm.

The maximum size of specimens collected was 39.9 mm OCL.

Description.

Rostrum. Rostrum short, usually reaching base of third antennal segment (occasionally not quite reaching base, and rarely extending as far as midlength of segment). Rostral sides slightly convergent to convergent, rostral bases divergent. Rostrum with 3 or 4 small marginal spines, extending to approximately rostral midlength, or beyond. Acumen similar in size to marginal spines. OCL/Carapace Length: 0.83–0.89. Rostrum Width/OCL: 0.16–0.19.

Cephalon. Numerous bumps and protrusions in cephalic region, with 1 (occasionally 2) on each side developed into more prominent, but small and blunt cephalic spine. First post-orbital ridge spine distinct but small. Second post-orbital ridge spine barely discernible to small; posterior to spine each ridge poorly developed initially, with large and swollen bump at posterior end. Suborbital spine medium in size, and acute.

Antenna. Basipodite spines small to medium. Coxopodite without distinct spines but with large, rounded development of coxopodal plate at mesial end. Interantennal spine of medium width and usually with slightly scalloped margins. Antennal squame lacking marginal spines, with near triangular inflation at midlength. Scale Length/OCL: 0.09–0.12.

Thorax. Thorax with 1–3 barely discernible to small cervical spines on each side, flattened and triangular in shape with moderate to sharp point. Dorsal thoracic spines present and numbering 10–20 on each side. Dorsal thoracic spines very small to small but distinct, and larger than general tubercles; spines highlighted against the carapace by profile (raised, but blunt) and/or colour (yellow-brown, grey-brown, grey or blue-grey). General tubercles small to medium in size (very small on specimens <25 mm OCL), and of moderate density. Areola Length/OCL: 0.35–0.39. Areola Width/OCL: 0.16–0.21. Carapace Width/OCL: 0.53–0.62. Carapace Depth/OCL: 0.44–0.50.

Sternal Keel. Lateral processes to first pereiopods (LPr1) slightly apart, slightly open to open in orientation, and with semi-abrupt posterior margins. LPr2 apart and with slightly open to open orientation. LPr3 narrow, and LPr4 of medium width. LPr2 to LPr4 all with distinctive, sharply defined margins, and sternal keel between both LPr2–LPr3 and LPr3–LPr4 entire and sharply developed.

Abdomen. Abdominal somite 1 lacking spines. Somite 2 with 3–5 tiny to small, moderately sharp to sharp Li spines. Somites 3–6 with 1 Li spine, decreasing in size posteriorly to be barely discernible on somite 6 (absent on some specimens <25 mm OCL). Frequently 1 or 2 small Lii spines on somites 3–6 of specimens > 20 mm OCL. Abdominal D-L spines present on somites 2–3 of one specimen, and on somites 2–6 of the largest specimen. Abdominal D spines also present on somites 2–3 of these two specimens only. Abdomen Width/OCL: 0.48–0.54 (male), 0.50–0.55 (female). OCL/Total Length: 0.39–0.43.

Tailfan. Standard tailfan spines small. Telson and uropods lacking surface and marginal spines. Telson Length/OCL: 0.33–0.37.

First Cheliped. Chelae usually intermediate in shape, occasionally elongate or stout.

Propodus. Dorsal lateral propodal spine row extending from apex to base of propodus. Ventral lateral propodal spine row less developed, with 1–6 (usually 4 or 5) more or less centrally located spines. Numerous bumps and protrusions lateral to dactylar base dorsally, of which 1 or 2 are usually distinctly larger. Bumps and protrusions also present on ventral surface of propodus lateral to dactylar base, often including 1–4 more prominently developed spines extending along propodal finger. Propodus with 5–7 mesial spines. Dorsal apical propodal spines absent. Two blunt spines at dactylar articulation. Propodal surface posterior to dactylar articulation lacking spines, with 2 or 3 distinctly deep punctuations. Pre-carpal area lacking spines, with occasional distinct punctuations. Spines above propodal cutting edge absent on both dorsal and ventral surfaces (2 barely discernible apical spines on dorsal surface of one specimen ACP1099). Prominent tooth near dactylar articulation. Propodus Length/OCL: 0.81–0.90 (male), 0.80–0.94 (female). Propodus Width/PropL:0.46–0.50. Propodus Depth/Propodus Length: 0.26–0.31.

Dactylus. Usually 1 or 2 barely discernible to small apical spines above dactylar cutting edge (absent on one specimen). Spines above cutting edge absent on ventral surface. Dactylus with 1 apical mesial spine and 1 dorsal mesial basal spine. All other dactylar spines absent (one regenerate chela with a small marginal dactylar basal spine). Dactylar groove distinct. Dactylus Length/Propodus Length: 0.55–0.61.

Carpus. Carpus with 3 mesial spines, decreasing in size posteriorly; generally produced to sharp point. Lateral margin of carpus with 2 spines. Ventral surface of carpus with large, sharp ventral spine and 1 or 2 tiny to medium, blunt ventromesial spines. Dorsal surface with deep groove; bearing 1–3 large, bluish-green, blunt bumps or spines (occasionally merging to effectively form raised ridge or boss) on dorsal surface mesial to groove.

Merus. Merus with 6 or 7 small to medium dorsal spines, and a barely discernible or small distolateral spine.

Third Maxilliped. Laterodistal corner of ischium produced to a distinct point. Exopodite shorter than or about as long as ischium (average 0.93 × ischium length).

Gastric Mill. Gastric mills were carefully extracted and examined for three specimens ranging in size from 29.94 to 39.87 mm OCL. Zygocardiac ossicle with 1.0–1.5 teeth anterior to ossicle ear (TAA), and 4.0–4.5 teeth anterior to posterior margin of ear (TAP), with tooth spread of 2.5–3.0. Urocardiac ossicle with 6 or 7 ridges.

Setation and Punctation. Setae sparse and short. Sparse to moderate and fine punctation on body. Chelae with occasional deep punctuations.

Colouration. Dorsally brown or green-brown with pale cream cephalic and cervical spines. Thoracic spines usually distinct from thorax background, and varying in colour (cream, grey, grey-brown or blue-grey). Abdominal somites marked heavily with blue laterally, with cream Li spines. First chelae mesially blue, with cream-tipped mesial propodal spines. Dorsal carpal bumps blue (often forming a raised, blue ridge). Walking legs blue-grey. Lateral propodal spines cream. Ventrally, a varying wash of pale blue-green, pink and orange, with a dull grey abdomen and tailfan. Merus of first cheliped and antennal bases vivid orange.
Sexes.

Males with cuticle partition. Female specimens without fully mature gonopores. All female specimens have calcified gonopores that lack marginal setation. Gonopores of four largest female specimens (29.9–39.9 mm OCL) with slightly incised rims, those of largest specimen appear to be in state of decalcification, being partially membranous on mesial margins. Thus, it would seem that female maturity occurs close to 40 mm OCL.
Etymology.

Named to honour Gary J. Morgan, whose landmark research on the Australian spiny crayfish genus Euastacus (Morgan 1983, 1986, 1988, 1989, 1991, 1997) has been pivotal to our understanding of these animals.