Leptochelia ignota Chilton 1885
Creators: name: Edgar, Graham J.
Publisher: name: Zenodo
Year: 2012
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Tanaidacea
Leptocheliidae
Leptochelia
Leptochelia ignota

description: Leptochelia ignota (Chilton, 1885)
(Figs 1–5)
Paratanais ignotus Chilton (1885): 1042, plates XLVI and XLVII. Leptochelia ignota Lang (1973): 199.
Material examined. Neotype of Paratanais ignota Chilton, 1885, herein designated. Female (AM P85770), 3.8 mm, algal washings, Quarantine Bay, Sydney Harbour, NSW (33°48.9’S 115° 17.0’E), 1 m depth, 25 March 1994. Other material. Two males, 49 females (AM P85771), neotype location, 25 March 1994.
Description. FEMALE. Body (Fig. 1). Observed length 1.7–4.1 mm; body about seven times longer than broad; cephalothorax subrectangular, laterally slightly convex, approximately one-fifth body length; eyes relatively small, pear-shaped, about one-sixth length of cephalothorax.
Pereon about three-fifths of total length; pereonite-1 length about one-quarter width; pereonites 2 and 3 similar, about 1.5 times length of pereonite-1, length about two-thirds width; pereonites 4–6 similar, about 1.3 times length of pereonite-1, length about 1.2 times width.
Pleonites 1–5 similar, together one-sixth of total length.
Pleotelson about 1.3 times length of pleonite 5; posterior margin with paired central setae (one minute and one long), simple seta and plumose seta dorso-distally, a simple seta on lateral margin, two dorsal setae near anterior margin.
Antennule (Fig. 1). One-sixth length of body, article-1 about three times longer than wide, longer than distal articles combined, with numerous setae as figured; article-2 about one-third length of article-1, with two distal setae; article-3 about four-fifths length of article-2, with about three distal setae; article-4 minute, with about four distal setae and aesthetasc.
Antenna (Fig. 1). Six articles, together about as long as antennule; article-1 wider than long, with single seta; article-2 as long as wide, with ventro-distal spine and dorso-distal spiniform seta; article-3 similar length to article- 2, as long as wide, with dorso-distal spine; article-4 twice length of article-3, 3.5 times as long as wide; article-5 half length of article-4; article-6 minute.
Mouthparts (Fig. 2). Labrum rounded, setulose.
Left mandible with large crenulated lacinia mobilis, pars incisiva smooth and acute, pars molaris broad and with corrugated grinding surface; right mandible with crenulated distal margin and bifid apex.
Labium with inner and outer lobes finely setulose.
Maxillule endite setulose distally and marginally, with eleven terminal spiniform setae, each with length about 8% of total endite length; palp with two long terminal simple setae.
Maxilliped palp article-1 lacking setae; article-2 with one outer seta, three inner setae and long distal seta reaching distal margin of palp article-3; article-3 with row of about twelve pinnate setae; article-4 with row of about ten pinnate setae and additional outer seta; basis with six or seven long setae extending to midway along palp article-3; endites distally with three flat setae, two spiniform setae as coupling hooks and long simple seta.
Cheliped (Fig. 1). About 30% length of body; coxal sclerite triangular, confluent with posterior margin of cephalothorax; basis as long as wide; merus triangular with three setae near ventral margin; carpus with similar length to basis, 1.5 times longer than wide, with three or four setae on ventral margin, about three dorsal setae; propodus with similar length and width to carpus, inner comb-like row of about six setae near articulation with dactylus, fixed finger about equal in length to palm and set along the same axis, with terminal spine, about four setae on ventral margin, three setae near inner margin of fixed finger; dactylus ventral margin smoothly-curved with row of about eight very short spiniform setae, unguis short and solid, extending about one-quarter of length of dactylus.
Pereopod-1 (Fig. 3). Basis width one-quarter length, length 1.2 times length of merus and carpus together, with single plumose and simple setae about one-fifth distance along dorsal margin; ischium with one ventral seta; merus two-fifths length of basis, with strongly oblique articulation with carpus, with one seta near ventral margin; carpus slightly shorter than merus with about five distal setae; propodus slightly less than length of merus and carpus together, with five or six distal setae; dactylus long and slender, dactylus and unguis together slightly longer than propodus, unguis about three-quarters length of dactylus.
Pereopods 2 and 3 (Fig. 3). Similar; basis width one-third length, length 1.6 times length of merus and carpus together, with two or three setae about one-quarter distance along dorsal margin; ischium with two ventral setae; merus one-quarter length of basis, with spiniform seta and simple seta distally; carpus with similar length to merus, three spiniform setae and three simple setae near distal margin; propodus 1.6 times length of carpus, with spiniform seta and three long simple setae near distal margin; dactylus and unguis together about one-third length of propodus, unguis about half length of dactylus.
Pereopods 4 and 5 (Fig. 3). Similar; basis width about half length, length 1.4 times length of merus and carpus together, with one to three plumose setae ventrally and group of one to three plumose setae about one-third distance along dorsal margin; ischium with two ventro-distal setae; merus two-fifths length of basis, with two spiniform setae distally; carpus slightly longer and about equal in width to merus, with three spiniform setae and one or two simple setae near distal margin; propodus 1.5 times length of carpus, with two spiniform seta ventro-distally, and four simple setae and spinous margin dorso-distally; dactylus and unguis fused into claw, together about half length of propodus.
Pereopod-6 (Fig. 3). Similar to pereopods 4 and 5, other than with about seven simple setae dorso-distally on propodus, including one long seta about twice length of others.
Pleopods 1–5 (Fig. 3). Similar; basal article with plumose seta, exopod with about 29 plumose setae on inner margin, distinct gap between proximal seta 1 and others in series; endopod with about 19 plumose setae on inner margin, plumose seta midway on outer margin.
Uropod (Fig. 3). Basal article length about 1.7 times width, lacking distal setae; exopod with one article, about equal in length to article-1 of endopod, with two long terminal setae that extend to article-4 of endopod; endopod with five articles.
MALE. Body (Fig. 4). Observed length 2.8–3.2 mm; robust body, about five times longer than broad; cephalothorax rounded and narrowing anteriorly in dorsal view, length similar to width, approximately one-fifth body length; eyes pear-shaped, about one-fifth length of cephalothorax.
Pereon about half total length; pereonite-1 length about one-quarter width; pereonites 2 and 3 similar, 1.2 times length of pereonite-1; pereonites 4 and 5 similar, 1.6 times length of pereonite-1; pereonite-6 length about 1.3 times length of pereonite-1 and about 2.5 times width.
Pleonites 1–5 similar other than declining in width posteriorly with pleonite 5 three-quarters width of pleonite- 1, together one-fifth as long as body.
Pleotelson about 1.2 times length of pleonite 5; posterior margin with two pairs of small central setae, two or three posterio-lateral simple setae, one simple seta anterio-laterally and another near anterio-dorsal margin.
Antennule (Fig. 4). Two-fifths length of body, article-1 about four times longer than wide, with three small plumose setae and two simple setae distally; article-2 about 43% of article-1, with two simple setae and three or four plumose setae distally; article-3 about 57% of article-2, with two simple setae distally; articles 4-10 comprising flagellum with length about 37% of total antennule length, article-4 with three proximal and two distal aesthetascs, articles 5–7 with two distal aesthetascs, article-8 with three aesthetascs, article 9 with four aesthetascs, article-10 minute.
FIGURE 2. Leptochelia ignota. Quarantine Bay, Sydney Harbour, NSW. Female. Labrum (L), left mandible (Md l), right mandible (Md r), labium (La), maxillule (Mx), maxilliped (Mxp). Scale units 0.1 mm for full mouthparts.
Antenna (Fig. 4). Six articles, together about two-fifths as long as antennule; article-1 as long as wide, lacking setae; article-2 about length of article-1, with three setae, one on small apophysis; article-3 with similar length to article-2 but two-thirds width, with one distal seta; article-4 about 2.5 length of article-3, with two setae midway and three long setae distally; article-5 about length of article-4 but half width, with two long setae distally; article-6 minute, with numerous long setae that extend about length of antennule articles.
Mouthparts reduced and fused.
Cheliped (Fig. 4). Length about three-fifths length of body; basis about 1.2 times longer than wide with small seta distally near dorsal margin; merus triangular with two setae near ventral margin; carpus nearly twice length of basis, 2.5 times longer than wide, with two setae on ventral margin, about three smaller dorsal setae; propodus with similar length and width to carpus, inner comb-like row of about 15 seta and separate longer seta near articulation with dactylus, fixed finger similar in length to palm, with terminal spine, about five setae near ventral margin, three long setae below outermost of two tooth-like apophyses on inner margin of fixed finger; dactylus ventral margin smoothly-curved with row of about ten very short setae, unguis short and solid, extending about 10% of length of dactylus.
Pereopod-1 (Fig. 5). Basis width one-fifth length, length 1.4 times length of merus and carpus together, with single plumose and simple setae about one-fifth distance along dorsal margin; ischium with one ventral seta; merus one-third length of basis with one dorso-distal and two ventro-distal setae; carpus slightly longer than merus with about six distal setae; propodus slightly less than length of merus and carpus together, with four distal setae; dactylus long and slender, dactylus and unguis together about 88% of length of propodus, unguis about three-quarters length of dactylus.
Pereopods 2 and 3 (Fig. 5). Similar; coxa with single seta, basis width one-fifth length, length 1.3 times length of merus and carpus together, with two or three setae about one-quarter distance along dorsal margin; ischium with two ventro-distal setae; merus one-third length of basis, with spiniform seta and simple seta distally; carpus slightly longer and narrower than merus, with two spiniform setae and three simple setae near distal margin; propodus 1.5 times length of carpus, with spiniform seta and two or three simple setae near distal margin; dactylus and unguis together about half length of propodus, unguis about one-half length of dactylus.
Pereopods 4 and 5 (Fig. 5). Similar; basis width about one-third length, length 1.2 times length of merus and carpus together, with ventral seta and one or two plumose setae about one-third distance along dorsal margin; ischium with 2 ventro-distal setae; merus two-fifths length of basis, with two spiniform setae distally; carpus slightly longer and about equal in width to merus, with four spiniform setae and two simple setae near distal margin; propodus 1.5 times length of carpus, with two spiniform seta ventro-distally and about four simple setae dorsodistally; dactylus and unguis partially fused into claw, together about three-fifths length of propodus.
Pereopod-6 (Fig. 5). Similar to pereopod-5, other than propodus possessing long additional simple seta dorsodistally.
Pleopods 1–5 (Fig. 5). Similar; basal article with plumose seta, exopod with about 22 plumose setae on inner margin, slight gap between proximal seta 1 and others in series; endopod with about 17 plumose setae on inner margin, plumose seta midway on outer margin.
Uropod (Fig. 5). Basal article length about 1.5 times width, with about six distal setae; exopod with one article, slightly longer than article-1 of endopod, with long terminal seta that extends almost to end of endopod; endopod with four or five articles.
Distribution. Sydney Harbour, NSW.
Remarks. As recognised previously by Lang (1973) and others, the brief original description of a female specimen of Paratanais ignotus Chilton, 1885 relates to a species of Leptochelia rather than to Paratanais, as indicated by a uropod endopod with 5–7 articles, and a pair of spiniform processes on antennule article-2. In an attempt to clarify affinities of this poorly-known species, collections of epifaunal invertebrates were made at the type location, Mrs Macquarie’s Chair in Sydney Harbour. No leptocheliids were obtained in these collections, the only tanaidacean recorded comprising Zeuxo normani (Richardson 1905), a species likely introduced at that site (Edgar 2008). Conditions at the type locality had, however, degraded badly over the past century, with little macrophyte cover, relatively high silt levels and high turbidity.
Accordingly, the search for Leptochelia ignota was expanded to Quarantine Bay on the sheltered inner side of North Head in Sydney Harbour, a site ca. 8 km seaward from the type locality but with dense macro-algal cover and better water quality. Numerous Leptochelia of the species illustrated were collected. With minor exceptions in characters as discussed below, collected specimens matched the morphological description of Leptochelia ignota by Chilton (1885), which included figures of antennules, antennae, pereopods 1, 2 and 5, and uropods. Consequently, the newly-collected individuals are attributed to L. ignota. A neotype has been assigned given that Chilton’s holotype of Paratanais ignotus was deposited in an unknown location and is assumed lost.
Labelling of the figures of pereopods 2 and 5 and uropods is inconsistent in Chilton’s original description. The figure caption to figs 2a–c in his plate XLVII describes these illustrations as belonging to “ Paratanais tenuicornis. Haswell. (? or P. i g n o t u s, sp. nov.)”, while the text description for Paratanais ignotus references these figures as pertaining to the type description of P. ignotus. Given that the illustrated appendages clearly belong to a leptocheliid species rather than Paratanais tenuicornis Haswell, 1882 —now Zeuxo tenuicornis (Haswell, 1882), following Sieg (1980) —we consider them to unambiguously relate to L. ignota, the caption label perhaps reflecting initial uncertainty in Chilton’s mind as to whether P. ignotus differed from P. tenuicornis. Chilton (1885) considered the two very similar, stating “(P. ignotus) is very closely related to P. tenuicornis, Haswell, but differs in the presence of spines on the undersurface of the peduncle of the lower antennae and other minor points”.
Although brief by today’s standards, sufficient information is provided in Chilton’s description for specimens collected from Quarantine Bay to be assigned to L. ignota with reasonable confidence. In common with our Quarantine Bay specimens, Chilton’s illustrations indicate that the mature female L. ignota possess a uropod endopod with five articles (although five to seven is mentioned in the P. ignota type description), a uropod exopod with a single article about equal in length to article-1 of the endopod, an antennule with three longer articles plus minute distal article, a pereopod-1 basis with length about four times width, a propodus slightly shorter than dactylus plus claw, and an antennule article-1 about three times longer than wide. The relative proportions of antennule, antennae and pereopod articles in Quarantine Bay specimens and L. ignota generally match well, other than that the propodus of pereopods 2 and 5 appears slightly more elongate in the L. ignota description, and the basis of pereopod-5 narrower. Chilton’s written description does, however, state that the basis of pereopod-5 is “very stout, greatest width half its length”, which agrees with our Quarantine Bay specimens and differs from the illustration provided for P. ignotus, where this ratio is about 2.3:1 rather than 2.0:1. Setation of appendages of the Quarantine Bay specimens matches well with illustrated setation for L. ignota, with the notable exception that our specimens possess a distal seta on the basal antenna article whereas this seta is lacking on the L. ignota figure.
The validity of L. ignota as a species name remains to be confirmed because of the possibility that the species described by Haswell as L. ignota is the same as another member of the Leptochelia dubia / savignyi complex described from an overseas location prior to 1885. Although it is now clear that the Leptochelia dubia / savignyi complex includes numerous sibling species, many localised in distribution (Larsen & Rayment 2002; Bamber 2008; Bamber 2010), it is also possible that one or more circumglobal Leptochelia species exist. Any species strongly associated with fouling organisms on ship’s hulls would have been readily transported across ocean basins in the nineteenth century, a period when Sydney Harbour was a major shipping port. Whereas the presence of six or seven long setae on the maxilliped basis unambiguously distinguishes the species diagnosed here from other welldescribed species of Leptochelia (see Table 1 in Bamber 2005), a comparative examination of type specimens in the Leptochelia dubia / savignyi complex that predate L. ignota (L. algicola Harger, 1878, L. dubia Kröyer, 1842, L. edwardsi Kröyer, 1842, L. kroyeri Kossmann, 1880, L. limicola Harger, 1878, L. neapolitana Sars, 1882, L. savignyi Kröyer, 1842) is needed to definitively resolve the status of L. ignota (see Lang 1973).
With respect to other Australian Leptochelia species, female specimens recognised here as L. ignota are very similar to L. opteros Bamber, 2008, keying as that species in Bamber (2008). These two taxa differ from each other primarily in minor details of setation and the proportions of pereopod articles. Female Quarantine Bay specimens possess three rather than a single spiniform setae on the carpus on pereopods 2 and 3, maxilliped basis with seven rather than four long setae extending to third palp article; and wider pereopod-1 basis, longer merus on pereopods 1, 4 and 5, and longer uropod exopod than L. opteros.
Male Quarantine Bay specimens differ in a number of characteristics from the L. opteros male figured by Bamber (2008), keying as L. daggi. Compared to L. opteros, Quarantine Bay specimens possess a more elongate carpus and propodus, greater separation between the two tooth-like apophyses on the cutting edge of the fixed finger, and propodus on pereopod-1 that is similar in length rather than shorter than the merus plus carpus together. Quarantine Bay males differ from L. daggi in possessing a uropod exopod that is longer than the proximal article of endopod, antennule second article less than half length of first article (c.f. 85% length in text description of L. daggi, but with figure showing about half length), and a cheliped dactylus that is smoothly curved without proximal setose crenulations along the cutting edge.
The possibility that the male specimens diagnosed and illustrated here belong to a species that differs from the figured females cannot be excluded, although all females collected in Sydney Harbour appeared to belong to a single species, as did the set of males.
description: Published as part of Edgar, Graham J., 2012, New Leptocheliidae (Crustacea: Tanaidacea: Tanaidomorpha) from Australian seagrass and macro-algal habitats, and a redescription of the poorly-known Leptochelia ignota from Sydney Harbour, pp. 1-37 in Zootaxa 3276 on pages 3-12, DOI: 10.5281/zenodo.212118