Austrochiltonia australis (Sayce, 1901)

King, Rachael A., 2009, Redescription of the freshwater amphipod Austrochiltonia australis (Sayce) (Crustacea: Amphipoda, Chiltoniidae), Memoirs of Museum Victoria 66 (1), pp. 85-93 : 86-92

publication ID	https://doi.org/ 10.24199/j.mmv.2009.66.11
persistent identifier	https://treatment.plazi.org/id/451A87FB-FF91-FF80-FF59-6B54FEA7F9C9
treatment provided by	Felipe
scientific name	Austrochiltonia australis
status

Treatment

Austrochiltonia australis View in CoL

Figures 1–4 View Figure 1 View Figure 2 View Figure 3 View Figure 4

Synonymy.

Hyalella australis Sayce, 1901: 226–30 , pl. xxxvi.

Chiltonia australis Sayce, 1902: 47–48 View in CoL .—? Smith 1909: 70.—? Chilton, 1923: 95.

Austrochiltonia australis Hurley, 1959: 765-767 View in CoL .— Williams, 1962: 202-208, figs. 1A-I, 3A-O.— Lowry and Stoddart, 2003: 127.

Material Examined. Lectotype, NMV J11248 View Materials , male, 8.1mm, Yarra Lagoon, East Kew , Victoria, coll. O.A. Sayce. Paralectotype, NMV J11247 View Materials , female, 6.2mm, collection information same as for J11248 . Paralectotype, NMV J11249 View Materials , 8 males (11.4mm, 10.5mm 10mm, 9.5mm, 8.1mm, 7.7mm, 4.7mm, 3.3mm), 4 females (8.6mm (ovigerous), 6.1mm, 5.6mm (ovigerous), 3.9mm). NMV J46778 View Materials , male, 7.3mm, collection information same as for NMV J11249 View Materials . NMV J46779 View Materials , male, 6.8mm, collection information same as for NMV J11249 View Materials . NMV J46780 View Materials , female (ovigerous), 8.2mm, collection information same as for NMV J11249 View Materials .

Distribution. Yarra River and tributaries, Victoria, Australia (Type Locality: Kew Billabong, Melbourne, Victoria (previously called the Yarra Lagoon, East Kew)).

Description. Male (based on large male NMV J46778), length: 7.3mm. Head about as long as deep (fig. 1A). Antenna 1 (fig. 1C) peduncular article 1 1.8 times as long as broad, inner lateral margin with three robust setae, ventral-distal margin with single robust seta; peduncular article 2 shorter than article 1 (0.8 times as long), 2.5 times as long as broad; peduncular article 3 similar length to article 2, 2.8 times as long as broad; flagellum slightly longer than peduncle, of 11 articles, with ventral aesthetascs on the proximal margins of the seven distal articles. Antenna 2 (fig. 1D) about 0.6 times length of antenna 1; peduncular article 3 broader than long, inner-distal margin with two robust setae; peduncular article 4 longer than article 3, 2 times longer than broad, inner lateral margin with three robust setae, distal margin with two robust setae; peduncular article 5 longer than article 4, 3.7 times as long as broad; flagellum slightly shorter than peduncle, of eight articles.

Upper lip (fig. 1I) broader than long, apically bluntly rounded, with numerous short setae along apical margin. Lower lip (fig 1J) with bluntly rounded lateral lobes, apical margins rounded, apical and inner margins with numerous short setae. Left mandible (fig. 1H) with incisor of six teeth, lacinia mobilis of five teeth, spine row of three plumose setae and triturative molar. Right mandible (fig. 1G) with incisor of six teeth, lacinia mobilis of three teeth, spine row of two plumose setae and triturative molar with a long plumose seta. Maxilla 1 (fig. 1B) outer plate with nine setulate robust setae; inner plate with two long apical plumose setae. Maxilla 2 (fig. 1F) outer plate with two apical rows of 12 simple setae; inner plate with two apical rows of 17 simple setae, with a plumose seta on the inner lateral margin. Maxilliped (fig. 1E) inner plate apical margin with two short spine-like robust setae, with plumose seta along apical and inner lateral margins; outer plate with numerous simple setae along apical and inner lateral margins; palp articles 1 and 2 similar width, palp article 2 with numerous simple setae on inner lateral margin; palp article 3 not as broad as articles 1 and 2, with numerous simple setae on inner lateral and distal margins, with three long settulate setae on outer distal margin; palp article 4 short, about 0.3 times as broad as article 3, with unguis and simple setae on distal and outer margins.

Gnathopod 1 (fig. 2A) coxa distally almost as broad as long, distal margin with 33 short simple setae; basis dorsal and ventral margins with scattered long simple setae, ventral distal corner with cluster of simple setae; ischium, and merus ventral distal corners with clusters of setae; carpus with ventral-lateral lobe and row of 13 setulate setae becoming longer distally, dorsal-distal margin with long settulate setae; propodus triangular in shape, 1.7 times as long as broad, ventral-distal corner with one robust seta (near where tip of dactylus touches), ventral-distal margin (adjacent to dactylus length) with short robust and long simple setae, dorsal-distal margin with long simple setae, inner face with 11 robust plumose setae; dactylus curved, fitting against ventral-distal corner of propodus, with dorsal plumose seta. Gnathopod 2 (fig. 2B) coxa short, 1.1 times as long as broad, distal margin with 14 short simple setae; basis dorsal and ventral margins with scattered simple setae; ischium and merus with scattered setae on ventral margins; propodus 1.6 times as long as broad, with proximal lobe covering distal margin of carpus, ventral-distal corner marked with two distinct carina-like lobes and a ventral-distal groove present on inner face to accommodate the tip of the dactylus, ventral distal margin with numerous apically bifid robust setae. Pereopod 3 (fig. 2C) coxa distal margin with 21 short simple setae; basis dorsal and ventral margins with scattered simple setae, ventral distal corners with clusters of setae; ischium ventral distal corners with clusters of setae; merus with distinct dorsal-distal lobe, dorsal margin with three clusters of simple setae, ventral margin with scattered simple setae, ventral distal corner with cluster of setae; carpus ventral margin with robust setae and scattered simple setae; propodus dorsal margin with three clusters of simple setae; ventral margin with nine clusters of robust and simple setae; dactylus dorsal margin with plumose seta, ventral margin with simple seta, unguis present. Pereopod 4 (fig. 2D) coxa with distinct proximal excavated corner, distal margin with 39 short simple setae; basis dorsal and ventral margins with scattered simple setae, ventral distal corner with cluster of simple setae; ischium ventral distal corner with cluster of setae; merus with distinct dorsal-distal lobe, dorsal margin with three clusters of simple setae, ventral margin with scattered simple setae, ventral distal corner with cluster of setae; carpus dorsal margin with three clusters of simple setae, ventral margin with scattered robust and simple setae; propodus ventral margin with eight clusters of robust and simple setae; dactylus dorsal margin with plumose seta, ventral margin with simple seta, unguis present. Pereopod 5 (fig. 2F) coxa anterior lobe with one short seta, posterior lobe with three long plumose setae and 9 short setae along margin; basis 1.2 times as long as broad, dorsal margin with 11 robust setae along length, dorsal-distal margin with seven robust setae, ventral margin subtly crenulated and with 24 short simple setae along length; ischium dorsal-distal margin with distal robust setae; merus with strong postero-distal lobe, dorsal margin with robust setae in four clusters, ventral margin with robust setae in three clusters; carpus as long as merus, dorsal margin with robust setae in four clusters, ventral margin with robust setae in three clusters; propodus longer than merus, dorsal margin with eight clusters of robust setae, ventral margin with three clusters of simple setae, ventral distal corner with cluster of simple setae; dactylus with plumose seta on ventral margin, unguis present. Pereopod 6 (fig. 2G) coxa posterior lobe with seven robust setae and seven short setae along margin; basis slightly longer than broad, dorsal margin with 12 robust setae along length, distal end of dorsal margin with cluster of robust setae, ventral margin subtly crenulated and with 23 short simple setae along length; ischium dorsal margin with distal robust setae; merus with strong postero-distal lobe, dorsal margin with robust setae in four clusters, ventral margin with robust setae in four clusters; carpus as long as merus, dorsal margin with robust setae in four clusters, ventral margin with robust setae in five distal clusters; propodus longer than merus, dorsal margin with nine clusters of robust setae, ventral margin with five clusters of simple setae; dactylus with plumose seta on ventral margin, unguis present. Pereopod 7 (fig. 2E) coxa ventral margin with five short simple setae; basis longer than broad, dorsal margin with 15 robust setae along length, distal end of dorsal margin with four robust setae, ventral margin subtly crenulated and with 18 short simple setae along length; ischium dorsal margin with distal cluster of robust setae; merus with strong postero-distal lobe, dorsal margin with robust setae in four clusters, ventral margin with robust setae in five clusters; carpus as long as merus, dorsal margin with robust setae in five clusters, ventral margin with robust setae in four distal clusters; propodus longer than merus, dorsal margin with six clusters of robust setae, ventral margin with six clusters of simple setae; dactylus with plumose seta on ventral margin, unguis present.

Pleopods 1-3 similar (fig. 2K), unmodified (as in Chiltonia ), peduncle inner margins with two distal retinacula (coupling hooks).

Uropod 1 (fig. 2L) peduncle distinctly longer than rami, dorsal margin with five robust setae along the length of the outer margin and five along the inner margin; outer ramous with distal cluster of four robust setae and two rows of robust setae along length, outer margin with four robust setae, inner margin with two robust setae; inner ramous with distal cluster of six robust setae and two rows of robust setae along length, outer margin with two robust setae, inner margin with three robust setae. Uropod 2 (fig. 2J) peduncle similar length to rami, dorsal margin with three long robust setae; outer ramous slightly smaller than inner ramous, with distal cluster of four robust setae, with one row of eight robust setae along length; inner ramous with two rows of robust setae along length, outer margin with fourteen robust setae, inner margin with eighteen robust setae (distal cluster of setae obscured by rows of setae). Uropod 3 (fig. 2I) with two articles; first article 2.8 times longer than second article; second article distal margin with one short robust seta, and one to three long robust seta apically and one long seta subapically.

Telson (fig. 2I) slightly longer than broad, apically slightly concave with pairs of two long and two short plumose setae around each distal corner.

Small male (based on small male NMV J46779). Length: 6.8mm. Similar to large male except for the following: Antenna 1 (fig. 3A) flagellum of 14 articles, with ventral aesthetascs on the proximal margins of the eight distal articles. Antenna 2 (fig. 3B) flagellum of nine articles. Maxilliped inner plate apical margin with three spine-like setae. Gnathopod 1 (fig. 3C) coxa longer than broad, distal margin with 12 short simple setae. Gnathopod 2 (fig. 3C) coxa distinctly longer than broad, with seven short setae along margin. Pereopods 3 and 4 (fig. 3C) lacking setae along coxal margin and the dorsal margin of the propodus. Pereopods 5-7 (fig. 3C) with fewer coxal setae, with fewer numbers of setal clusters along articles.

Pleopod 1 (fig. 3G) rami with fewer articles than in large male.

Uropod 1 (fig. 3E) peduncle slightly longer than rami, dorsal margin with up to nine robust setae along the length of the outer margin and up to three along the inner margin; rami straight (not curved as in large male); outer ramous with distal cluster of four robust setae and two rows of robust setae along length, outer margin with four robust setae, inner margin with one robust seta; inner ramous with distal cluster of five or six robust setae and two rows of robust setae along length, outer margin with two robust setae, inner margin with three robust setae. Uropod 2 (fig. 3D) peduncle similar length to rami, dorsal margin with four to five long robust setae; outer ramous slightly smaller than inner ramous, with distal cluster of four robust setae, with one row of three robust setae along length; inner ramous with distal cluster of five robust setae, with two rows of robust setae along length, outer margin with two robust setae, inner margin with three to four robust setae. Uropod 3 (fig. 3F) second article distal margin with one short robust seta, and one to two long robust seta apically.

Female (based on female NMV J46780). Length: 8.2mm. Similar morphology to (large) male except for the following: Antenna 1 (fig. 4A) flagellum of 11 articles, with ventral aesthetascs on the proximal margins of the six distal articles. Antenna 2 (fig. 4B) flagellum of ten articles. Maxilliped inner plate apical margin (fig. 4C) with three spine-like setae. Gnathopod 1 (fig. 4D) coxa longer than broad, distal margin with 12 short simple setae; propodus rectangular in shape, around 2.5 times as long as broad, inner face with 10 robust setae. Gnathopod 2 (fig. 4E) similar to gnathopod 1 except propodus over 3 times as long as broad, coxa with eight short setae along margin. Pereopod 4 (fig. 4H) coxa ventral margin not as broadly rounded as in large male.

Uropod 1 (fig. 4J) peduncle similar length to or slightly longer than rami, dorsal margin with up to 10 robust setae along the length of the outer margin and up to five robust setae along the inner margin; outer ramous with distal cluster of five robust setae and one row of six robust setae along length; inner ramous with distal cluster of four robust setae and two rows of robust setae along length, outer margin with three robust setae, inner margin with three robust setae. Uropod 2 (fig. 4I) peduncle dorsal margin with up to four long robust setae; outer ramous slightly smaller than inner ramous, with distal cluster of three robust setae, with one row of four robust setae along length; inner ramous with distal cluster of four robust setae, with two rows of robust setae along length, outer margin with up to five robust setae, inner margin with up to five robust setae. Uropod 3 (fig. 4F) second article with one short robust seta, and one to two long robust seta apically.

Telson (fig. 4G) longer than broad, apically blunt with pairs long setae apically and laterally.

Oostegites present on coxae 2 to 5 (figs. 4K-N) to form the marsupium, margins with scattered curved hooks.

Variation. Antenna 1: the number of flagellum articles varied from nine to 14 with no clear correlation between sex or body size. Antenna 2: the number of flagellum articles varied from seven to nine with no clear correlation between sex or body size. Despite the differing number of flagellar articles in both antennae, the standard lengths of the two were consistent between sexes and sizes, with antenna 1 1.4-1.6 times as long as antenna 2. It should be noted that Williams (1962) recorded antennal length ratios from 1.4 to 2.0 for A. australis . This could reflect sample size differences between this study and Williams’ but there may be reason to suspect that cryptic species may have been inadvertently included in his study (see discussion).

Mouthparts are generally well conserved throughout the Chiltoniidae however two of the large male morphotypes, exhibited a reduction in setation on the maxilliped inner plate (from 3 to 2 spine-like setae) (fig. 1E). Both males showing the reduction in setae were at the smaller end of the “large male” morphotype (7.3mm, 7.7mm). Other large males had three setae, along with all the small males and the females (fig. 4C), which is the consistent state across the family. When Williams (1962) described A. australis and A. subtenuis , he illustrated A. subtenuis with two setae on the maxillipedal inner plate but did not further mention it compared to A. australis (which he illustrated and described with three setae). This character may be variable within both species.

Remarks. Lowry and Stoddart (2003) accepted Williams’ interpretation of Austrochiltonia australis and relabelled his invalid type names (“lectoholotype” became the lectotype NMV J11247 and “lectoallotypes” became paralectotype NMV J11248). However, they indicated that NMV J11247 was a male and NMV J11248 was a female, which is incorrect. They also did not refer to the additional paralectotypes identified by Williams.

Both the lectotype male ( NMV J11248 View Materials ) and the paralectotype female ( NMV J11247 View Materials ) designated by Williams have been damaged over time.Examination of the paralectoypes ( NMV J11249 View Materials ) showed better preserved specimens and so the descriptions here have been based on two males ( NMV J46778 View Materials , NMV J46779 View Materials ) and a female ( NMV J46780 View Materials ) taken from NMV J11249 View Materials and then compared with all existing types to note any variability .