Eulimnadia centenaria , Brian V Timms, 2016

Brian V Timms, 2016, A partial revision of the Australian Eulimnadia Packard, 1874 (Branchiopoda: Spinicaudata: Limnadiidae), Zootaxa 4066 (4), pp. 351-389: 365-367

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Eulimnadia centenaria

sp. nov.

Eulimnadia centenaria  sp. nov.

( Figs. 3 View Figure H,I, 8)

Etymology. This species was collected in 1915 and lay unrecognised in the National Museum, Victoria for 100 years. This is the approximate time period of the near hiatus in research on Australian clam shrimps (from Sayce, 1903 to Timms and Richter, 2003 and Richter and Timms, 2005, except for Henry, 1924 and Webb and Bell, 1979). So its name reflects both phenomena, based on the Latin ‘centum’ meaning 100.

Type locality. Northern Territory, Katherine district, King River bluffs, ca. 14 o 42 ’S, 132 o 04’E, 21 November, 1915, W. McLannan.

Type material. Holotype. Male deposited in National Museum, Victoria, length 5.9 x 3.4 mm, registration number NVM J 67914.

Allotype. Female deposited in National Museum, Victoria, length 6.0 x 3.8 mm, registration number NVM J 67915

Paratypes. Two males, 6.0 x 3.7 mm and 5.4 x 3.1 mm and two females, 6.0 x 3.8 mm and 5.9 x 3.9 mm, NMVJ 67916; two males both 6.0 x 3.8 mm and two females 6.0 x 3.9 mm and 5.4 x 3.2 mm, AM P 87324.

Other material. 5 males and 21 females, from the type locality, same date and collector, NMVJ 54048.

Diagnosis. Egg astraform with a lacey surface. Eighteen trunk segments. Male with a triangular rostrum, a little larger than the ocular tubercle. Male with about 11–14 telsonic spines, irregular in spacing and size. Both sexes with about 10 long to medium length cercopod setae. Female with 11–14 telsonic spines irregular in spacing and size.

Description. Egg ( Fig 3 View Figure H,I) astraform with about extruded 18 points, each flatish or slightly concave in cross section and rounded apically at right angles to its protruded axis. The extrusions arise from a few grooves separated by rounded ridges. External layer with large pores and hence appears lacey. Diameter 246 µm, range 232–255 µm).

Male. Head ( Fig 8 View Figure C) with a prominent ocular tubercle with a round compound eye occupying most (ca 80 %) of it. Rostrum equilateral triangle a little larger than ocular tubercle on an extended base so that the base angle is ca 70 o to the frons, but the dorsal surface of the triangle is ca. 120 o angle. Ocellus ovate, about one quarter the size of the compound eye and located in the dorsal base. Dorsal organ posterior to the eye by about half its height, pedunculate and asymmetrical and slightly lower than the height of the ocular tubercle.

First antennae a little longer than peduncle of second antennae and with sensory about nine lobes each with numerous tiny sensory papillae.

Second antennae with spinose peduncle and each flagella with about 12 antennomeres dorsally with 1–3 spines and ventrally with 1–5 long setae. Spines more numerous in basal antennomeres and setae more numerous in distal antennomeres.

Carapace ( Fig 8 View Figure A) elongated oval, pellucid and with at least one growth line easily visible. Dorsal edge slightly convex. Adductor muscle scar lying at about 45 o to the horizontal body axis.

Thoracopods. Eighteen pair. The first two modified as claspers ( Fig 8 View Figure G). Both claspers with hand trapezoid but with a swelling mediodistally at the base of the thumb. Thumb spherical with apex with short blunt denticles mediodistally and spines laterodistally and a small palp laterally. Finger arcuate with a blunt rounded apex bearing a suctorial disc anterioventrally and many rounded pits dorsally. Long palp inserted on the apical edge of the hand, about 1.25 times as long as the hand in clasper I and 1.5 times as long a clasper II, two segmented and with 4–5 stout setae at the segmental junction and many small setae terminally.

Other thoracopods of typical structure for Eulimnadia  , decreasing in size and complexity posteriorly.

Trunk. Dorsal surface of with 1–3 spines posteriorly on at least each of the posterior 8 trunk segments.

Telson ( Fig 8 View Figure F) with about 14 pairs of dorsal spines, the first the largest, then four well spaced spines about half the size of the first, followed by about 9 spines of varying size with many smaller the anterior spines. Dorsal spines tend to be denticulate. Caudal filaments originating from a mound a little higher than the dorsal floor of the telson between spines 3 and 4. Dorsal floor posterior to the mound sloping away to the cercopod base. Cercopods subequal in length to the telson dorsum, the basal half bearing about 10 long setae, shortening distally, followed by a short spine and then slowly thinning to an acute apex. Basal setae about 3 x basal cercopod diameter while distal setae 1.5 x basal cercopod diameter. Setae two segmented and well feathered. Narrowing apical half of cercopod with many small denticles dorsally. Prominent blunt triangular projection beneath the cercopods at the ventroposterior corner of the telson.

Hermaphrodite. Head ( Fig 8 View Figure D) with ocular tubercle prominent, with compound eye occupying most (ca 80 %) of it. Rostrum prominent, about as much as the ocular tubercle, asymmetrical and with dorsal surface at angle of about 95 o with the frons. Ocellus and dorsal organ as in male.

First antennae a little shorter than the peduncle of the second antennae, with about 4 lobes each with many short sensory setae.

Second antennae as in male.

Carapace ( Fig 8 View Figure B) elongated oval, pellucid and with at least one obvious growth line. Dorsal edge distinctly convex. Adductor muscle lying at about 45 o to horizontal body axis.

Thoracopods. Eighteen of typical Eulimnadia  structure.

Trunk dorsum with 3–9 setae terminally, these setae few, short and stout on last few segments, numerous and longer on segments 8–15, and hardly any setae on anterior trunk segments 1–7.

Telson ( Fig 8 View Figure H) as in male, though perhaps one dorsal spine fewer.

Variability. Given specimens were available from only one site, it is not surprising little variability was observed. All specimens seen had 12 antennomeres in flagella, not 8 as in most species of Australian Eulimnadia  . Male and female telsonic spines varied between 11 and 14, and cercopod setae between 9 and 12 but always long basially varying to moderate length distally.

Comments. The most distinctive features of this species are: (a) the division in the cercopod between the seta l and denticle bearing regions (ca. 50 % each as compared to only 20–25 % apical cirrus region); (b) the numbers and nature of the telsonic spines and cercopod setae and (c) the presence of 12 antennomeres instead of 8 in undamaged second antennal flagella. The egg closely resembles that of Eulimnadia palustera Timms 2015  , but there are subtle differences in the cross sections of the extruded points (roundish in L. palustera  and flatish in E. centenaria  sp. nov.) and in the ridges between the grooves (sharp in L. palustera  , mainly rounded in E. centenaria  sp. nov.).

Putative hermaphrodites outnumber males in the collection, probably indicating androdioecious reproduction.

Distribution. Katherine area, Northern Territory.