Tanais adelaidensis, Tait & Conlan & Dittmann, 2021

Tait, Valerie K., Conlan, Kathleen E. & Dittmann, Sabine, 2021, Tanaididae (Crustacea, Tanaidacea, Tanaidomorpha, Tanaidoidea) on a Floating Dock, West Beach, Adelaide, South Australia: Introduced or Indigenous?, Zootaxa 4996 (1), pp. 83-125 : 87-105

Tanais adelaidensis n. sp.

( Figures 2–7 , Table 2)

Material examined. Holotype: Ovigerous female, from Gigartina macroalgae, collected by K. Conlan, from West Beach Boat Ramp , 34.958°S, 138.504°E, 18 February 2010, SAMA Catalogue (Cat.) Number (No.) C14331 . Allotype: Mature male, among Gigartina , collected by K. Conlan, from West Beach Boat Ramp, 34.958°S, 138.504°E, 18 February 2010, SAMA Cat. No. C14333 .

Dissected. Four females (three ovigerous, 4.5, 4.4, and 4.2 mm; one preparatory, 5.8 mm) dissected from February 2010 sampling of Gigartina . Two ovigerous females (3.6, 3.7 mm) dissected and additional two females (ovigerous, 3.7 mm; preparatory, 3.7 mm) sequenced for CO1 from January 2015 sampling. Three copulatory males (4.5, 4.7, 4.7 mm) and one preparatory male (4.3 mm) dissected from February 2010 sampling. Two copulatory males dissected (3.3, 3.4 mm) from January 2015 samples.

Additional material used for size measurements. Five samples from the February time-series sampling point, with a total of 35 ovigerous females, 30 post-ovisac females, 147 preparatory females, 25 copulatory males, 104 preparatory males, 40 juvenile females, 84 juvenile males, and 642 mancae.

Species diagnosis. FEMALE. Antennule five-articled (three main and two short distal) with three or four distal aesthetascs; antenna eight-articled (five main and three short distal). Left mandible lacinia mobilis well-developed, tooth-like, distal margin with four low peaks, with two pectinate accessory setae; right lacinia mobilis peg-like, widening distally with two pectinate accessory setae. Maxilliped palp article 1 with no distal setae. Pereopod 6 with seven to eleven leaf-like setae, four to six finely biserrate setae and one elongate bipectinate seta on mediodistal margin. Pleopod 3 slightly smaller than pleopods 1 and 2. Pleopods 1 and 2 basal articles with two or three short setae on the medial margin, pleopod 3 with one or two. Uropod three-segmented (two segments and the peduncle). Pleotelson with small anterolateral processes, suggestive of residual pleonite 5.

Specimen sizes. Based on counts and sizing of five samples from February 2010 assessed in more detail, mature ovigerous and post-ovigerous (with scars) females ranged in size from 3.4–6.0 mm. Preparatory females reached a length of 6.4 mm. Males had a transverse band of pigmentation on the ventral surface of pereonite 6 that encompassed the developing or developed gonadal pores. Males with more exaggerated chelipeds and clear penile cones and gonadal pores were 3.7–5.5 mm. Preparatory males with less developed chelipeds but with observable sexual differentiation (visible gonadal pores, cheliped fixed finger shape), to varying degrees, were 2.6–5.2 mm. The smallest specimens that had gross morphology complete with observable beginnings of sexual differentiation (tiny ovisac buds) were 1.9 mm. Juvenile males had a transverse band of light pigmentation ventral on pereonite 6.

Sex ratio. For the five February samples, considering only ovigerous and post-ovigerous females and males with well-developed chelipeds and clear penile cones and gonadal pores as adult, the mean adult female to male ratio was 3.3 (median 2.8; range 1.2–5.0). Including all sizes for which sexual differentiation was observable, the mean female to male ratio across the samples was 1.3 (median 1.1; range 1.1–1.9). No intersex specimens were observed in these five samples.

Description: FEMALE. Holotype full body, SAMA Cat. No. 14331; appendages from dissected paratype, SAMA Cat. No. 14332 ( Figures 2–5 & 7 , Table 2).

Body ( Figures 2A, 2B ). Body 4.9 mm long, 5.4x as long as maximum pereonal width. Cephalothorax 18% of total specimen length. Cephalothorax sub-triangular, with rounded posterolateral margins, length similar to width and 0.8x length of pereonites 1 to 3 combined. Small triangular eyes, dark-coloured with visual elements. Two or three setae behind each eye lobe. Cephalothorax also with two or three setae on each dorsolateral surface about onethird of the way from the anterior end. Pereonite 1 0.4x length of pereonite 4, length 0.3x width. Pereonite 2 wider anteriorly, 0.7x length of pereonite 4, length 0.5x width. Pereonite 3 also wider anteriorly, 0.8x length of pereonite 4, length 0.6x width. Pereonite 4 length 0.7x width. Pereonite 5 similar length to pereonite 4 with length 0.7x width. Pereonite 6 0.8x length of pereonite 4, with length 0.6x width. Pereonites 4 to 6 widen posteriorly. Pereonites 1 to 3 combined are 1.3x as long as their maximum width. Pereonal setation sparse. Pereonite 1 with sparse setae along the anterior margin—single short seta (in some cases two) at each dorsolateral corner, and, on each side of centre, two pairs of unequal setae. Pereonite 2 with unequal pair of setae in each anterolateral region, unequal pairs of anterodorsal setae (second seta of each pair very small, not seen in all specimens examined) each side of centre, and one or two short setae in each posterolateral corner. Pereonite 3 similar to pereonite 2. Pereonites 4 to 6 similar to pereonites 2 and 3, but with as many as three unequal setae in antero-dorsolateral and posterolateral regions.

Pleon 24% of total specimen length, consisting of four pleonites and pleotelson. Pleonite 1 length 0.4x width and 0.7x length of pereonite 6. Pleonite 2 0.7x length of pleonite 1 with length 0.3x width. Pleonite 3 0.65x length of pleonite 1 with length 0.3x width. Pleonite 4 0.3x length of pleonite 1 with length 0.2x width. Pleonite 4 0.7x width of pleonite 3. Pleonite 4 similar width to pleotelson. Pleotelson 0.9x length of pleonite 1, with length 0.5x width. Pleonite 1 with row of plumose setae extending onto posterior region of dorsal surface from each side, almost meeting in centre; also with sparse longitudinal row of three setae dorsolaterally each side anterior to transverse plumose row. Lateral ventral margins of pleonite 1 each with row of plumose setae. Pleonite 2 setation as for pleonite 1. Pleonite 3 with row of plumose setae along lateral ventral margin joining with short row of simple setae extending onto posterolateral surface, but not further onto dorsal surface; also with dorsolateral grouping of simple setae each side of two long and one shorter seta. Pleonite 4 with short, single lateral seta each side (possibly very small additional seta visible on one side) and three or four setae (one long plus two or three short) up onto each dorsolateral surface. Pleotelson ( Figure 2B ) with single anterolateral seta each side on small but clear bulge (possible residual pleonite 5), posterolateral corner with single short seta on one side (but cluster of two very short setae visible on other corner and on other specimens); each side of centre a row of three (sometimes four) setae, one long the others short, and single short PSS; posterior margin with small central process carrying two pairs of simple setae.

Variability in pereonite measurements. Some variability observed in ratios of body length to maximum width and length to width ratio of pereonites 1 to 3. Among 8 mature females with body lengths 4.0– 5.8mm, median (range) of body length to maximum pereonite width 5.5 (4.9–6.0); ratio of cephalothorax length to pereonites 1 to 3 combined length 0.75 (0.69–0.86); cephalothorax 17.3% (16.2–19.3%) of body length; ratio of pereonites 1 to 3 combined length to maximum width 1.27 (1.14–1.41); and pleon length 25.0% (23.9–25.9%) of body length. We did not find a relationship between this variability in extension of pereonites and other morphological characters.

Antennule ( Figures 2C, 2D ). Antennule with five articles, 0.8x length of cephalothorax. First article longer than second article (2.4x), length 2.1x width [some damage], with dorsolateral cluster of three PSS in proximal half of article (attachment sites visible, slight crush damage; confirmed on other antennule). Distally, first article with dorsolateral cluster of four simple setae and three shorter PSS, a dorsomedial pair of unequal setae, and ventromedial pair of short PSS (total distal: six simple and five PSS; range: 4–7 simple, 4 or 5 PSS). Second article 1.3x as long as wide, 0.4x length of first article. Distally, second article with dorsolateral cluster of four setae (two long, one medium, one short) and at least three PSS extending down to ventrolateral region (other antennule with clear view of five PSS in this location), with single simple seta and pair of unequal setae in the ventromedial region (total distal: seven simple setae, several PSS, range: 5–7 simple,>3–7 PSS). Third article slightly shorter than second article (0.9x), length 2.1x width. Distally, third article with single dorsal simple seta and, in the ventromedial region, two PSS and one simple seta (range: 2 or 3 simple setae, 1 or 2 PSS). Fourth and fifth articles very short ( Figure 2D ; with only aesthetascs and setae distal on third article shown). Fourth article with four simple setae attached in row dorsal to medial and two aesthetascs attached ventrally. Attachment site of third aesthetasc obscured by setae. Other antennule examined; clearly shows attachment of two aesthetascs to fourth article and one to fifth article. Fifth article with one short PSS, three long setae, one shorter seta, and two very short simple seta, in addition to single aesthetasc. Fourth and fifth articles together with, ten simple setae (two very short), one short PSS, and three aesthetascs (range: 3–4 aesthetascs, 8–10 simple setae, consistently 1 PSS).

Antenna ( Figures 2E, 2F ). Antenna same length as antennule, with eight articles, terminal three articles very short. First article without setae. Second article length 1.3x width, with two (only one visible on other antenna) ventromarginal setae. Distally, second article with one ventral seta, and two dorsal setae, one lateral and the other medial. Second article with extensive microtrichia on dorsal, ventral, and medial surfaces. Third article half length of second article, length 0.8x width, distally with single dorsal and single ventral setae (other specimens and other antenna of this specimen all with only the dorsodistal seta). Fourth article similar length to second article, length 1.9x width; distally with one long seta and one PSS in the ventral region, a single shorter dorsal seta, and two simple lateral setae of unequal lengths (total setae distally: 4 simple setae, 1 PSS; range: 3–5 simple, 1 or 2 PSS). Fifth article longer than wide (2.0x), 0.8x length of second article; distally with two medial PSS, two simple ventromedial setae, two short PSS and one simple seta in the ventrolateral region, and one short dorsolateral PSS. Overall, this gives three simple setae and five distal PSS (range: 2 or 3 simple, 2–5 PSS). Sixth, seventh, and eight articles very short ( Figure 2F ; only setae on fifth and seventh articles shown). Sixth article half as long as wide, only 0.1x length of second article, distally with two long lateral setae and one shorter medial seta. Seventh article 0.8x as long as wide, 0.1x length of second article with four setae. Eighth article minute, also carrying four setae. Seventh and eighth articles together carry eight distal setae, in total, two of the setae shorter [some damage to the longer setae in the illustrated specimen] (range: 8 or 9 simple, 0 or 1 PSS).

Cheliped ( Figure 2G ). Basis slightly shorter than carpus, length 1.2x width, with two unequal setae on outerfacing surface close to join with sclerite, and with two (sometimes three) unequal ventrodistal setae. Merus subtriangular, no ventrodistal indentation, with three unequal setae (two in one female) in dorsal corner, and ventrally with four setae (five in the largest specimen) about two-thirds of way along margin. Carpus length, C(L), slightly shorter than propodus length including fixed finger, P(L) (C(L):P(L)=0.9, range: 0.8–0.9), carpus length 1.6x width (range: 1.4–1.6). Carpus without any ventral process, dorsally with one short seta about a third of way along margin, dorsodistally with tuft of four setae (group of 3 + 1 in all female specimens), ventrally with three (rarely two) unequal setae about three-quarters of way along margin; also with row of five (sometimes four) unequal setae, shortest setae at either end of row, in ventral half of distal region of lateral surface. Propodus about twice as long as wide. Propodus medial surface with single seta close to dorsodistal junction with dactylus. Fixed finger cutting edge rounded distally, smooth with slight process midway along dorsal margin, with cluster of four setae at proximal end close to junction with dactylus. Fixed finger with five (or four) ventral setae, dorsally with seven setae (nine in largest female) in row on lateral surface attached below cutting edge, and two setae on medial surface close to terminal claw. Dactylus not arcuate, as long as fixed finger, with terminal claw; ventrally with row of small setules, a medial seta, and small, obtuse triangular ventral process about mid-margin.

Mouthparts ( Figures 3A–L ). Labrum ( Figure 3A ) rhomboidal with rounded corners, with distal covering of very fine setae and setules. Left mandible ( Figure 3B ) incisor smooth with acute, blunted tip and distal margin roughness. Left lacinia mobilis ( Figure 3C ) broad, well-developed with four small distal processes and two strong adjacent pectinate setae. Right mandible ( Figure 3D ) incisor smooth with acute tip. Right lacinia mobilis ( Figure 3E ) reduced, narrow, broadening distally with very fine denticulations along the distal margin and two adjacent pectinate setae. Mandibular molars strong, broad with corrugated striations on grinding surface. Labium ( Figure 3F ) inner lobes rounded, covered distally with fine setae and setules; anterior-facing surface also covered with sparser fine setae. Outer lobes distally setulose, each with a distally setulose, oval, articulated terminal process. Maxillule endite ( Figures 3G, 3H, 3I ) with eight terminal spiniform setae, three finely serrate and one more slender; attachment area surrounded by fine setae. Lateral margin of endite with sparse rows of short setae, stronger and denser in the middle half of the margin giving the appearance of fine serrations. Maxillule palp ( Figure 3G ) slender, uniarticulate, tapering distally; damaged, carrying only three terminal setae in the illustrated specimen. Based on four other more successful dissections of this appendage, five or six terminal setae are expected. Maxilla (also Figure 3G ) oval with a single long distal seta and very fine, minute setae on distal surface and distal third of medial surface. Maxilliped ( Figure 3J ) coxae each with single long seta. Maxilliped bases not joined medially, each with three or four setae on medial margin—consisting of single shorter seta more proximal and two (to four) longer setae in proximal half of margin. Maxilliped basis with four or five (range: 3–6) setae in the distal half of the lateral margin, distally with row of four (sometimes five) long setae (decreasing in length towards lateral margin); anterior-facing surfaces covered with arcs of microtrichia. Maxilliped endite ( Figures 3J, 3K ) finely setulose, with sparse setae on distal lateral margin and surface; distally with two simple setae and mediodistally with two short spiniform setae (coupling hooks). Maxilliped palp with four articles of similar length. Article 1 length 1.1x width, medial and lateral margins with microtrichia arcs, giving impression of small serrations. Article 2 length 1.3x width, lateral margin with single distal seta, medial margin with row of five simple setae in distal half, and two stronger finely setulate setae in distal third. Article 3 length 1.8x width, with no lateral setae; medial margin with two parallel rows of setae—a row of ten (sometimes nine) stronger setae, very finely setulate on their distal two-thirds, and row of seven simple, shorter more slender setae (sometimes six). Article 4 length about three times width, with a single lateral marginal seta and two simple lateral subdistal setae (other palp with three lateral subdistal setae, one of them short but with no marginal seta; all other specimens dissected consistent with two lateral subdistal setae and single marginal seta). Palp article 4 medial margin with two parallel rows of setae on the distal third, one containing seven (range: 5–7) finely serrate setae and the other seven (sometimes six) simple setae [five finely serrate and seven simple setae visible on the other palp of illustrated specimen]. Epignath ( Figure 3L ) an elongate kidney shape with terminal circumplumose process, surface with only very fine, sparse setae.

Pereopod 1 ( Figures 4A, 4B ). Coxa with two setae (one very small), without anterior apophysis. Ischio-basis 3.7x as long as wide, 1.7x length of propodus, with dorsoproximal cluster of three short setae (two simple setae and one PSS) and one ventrodistal seta. Merus length 1.5x width, 0.6x as long as propodus, ventrodistally with two short setae, one medial and one lateral; dorsodistally with a single short seta. Carpus length 1.7x width, 0.7x as long as propodus, dorsal margin with two setae in distal half, ventrodistally with row of three setae. Propodus 3.2x as long as wide, 0.7x length of merus and carpus combined, 1.4x length of carpus, dorsal margin with short PSS and seta about two-thirds of way and single subdistal seta. Ventrally, propodus with a cluster of three setae subdistal and two (or one) shorter setae spaced in the distal third of the margin. Distal half of the ventral surface with microtrichia arcs. Dactylus and unguis combined shorter than propodus (x0.8), dactylus 1.3x length of unguis, with short dorsomarginal seta.

Pereopod 2 ( Figures 4C, 4D, 4E ). Coxa (not shown) with two setae, one very short. Ischio-basis length 2.8x width, 3.0x length of propodus, dorsoproximally with cluster of three setae (two PSS and one simple) about one quarter of way along and ventrodistally with three setae (very short, medium, and longer). Merus length 1.9x width, 1.5x as long as propodus. Merus with short medial seta and short lateral seta dorsodistally, ventrally with one mid-marginal seta plus sparse microtrichia in proximal half, with one short simple, one long simple and two crotchets ventrodistally; microtrichia in the distal fifth. Carpus length 1.1x width, 0.8x length of propodus. Carpus with single seta dorsodistally reaching four-fifths the length of the propodus, mediodistal margin with row of four crotchets and laterodistal margin with row of six crotchets, microtrichia in arcs towards ventrodistal end of article. The largest carpal crotchet with midlevel spines ( Figure 4D ). Propodus length 3.0x width, 0.7x length of merus. Propodus dorsally with single PSS in distal third, dorsodistally with longer seta and sparse microtrichia, ventrally with two (one in smaller females, three in the largest female) marginal setae, also with single distal seta; microtrichia visible towards the distal end of ventral surface. Dactylus and unguis combined 0.45x length of propodus and dactylus 2.8x length of unguis.

Pereopod 3 ( Figure 4F ). Similar in structure and ornamentation to pereopod 2 but overall slightly shorter. For completeness, ischio-basis length 2.4x width and 2.4x length of propodus, with dorsoproximal cluster of three short setae (one simple and two PSS) about one quarter of way down margin and three setae (short, medium, and long) ventrodistally. In contrast to pereopod 2, pereopod 3 with a single short PSS about two-thirds of way down ventral margin. Merus 1.7x as long as wide, 1.4x length of propodus, dorsodistally with only single short seta, ventrodistally with two crotchets and pair of unequal setae, ventromarginally with single seta about mid-point and microtrichia visible on proximal half and distal quarter. Carpus 1.3x as long as wide, 0.9x length of propodus, dorsodistally with pair of unequal setae, one very short (not seen on pereopod 2), the mediodistal margin with row of five crotchets, laterodistal margin with row of six crotchets, and microtrichia ventrodistally; the largest carpal crotchet with midlevel spines. Propodus length 3.3x width, shorter than merus (0.7x), dorsally with single PSS in distal third (other specimens also with additional small dorsodistal seta), and with sparse microtrichia at the distal end. Propodal ventral margin with two marginal setae, single distal seta, and microtrichia. Dactylus and unguis combined shorter than propodus (x0.4). Dactylus without setae, 2.9x as long as unguis.

Pereopod 4 ( Figures 4G, 4H ). Ischio-basis length 2.1x width, twice length of propodus, slightly wider than ischio-basis on pereopods 2 and 3. Ischio-basis with dorsoproximal grouping of four setae (three in a cluster [one simple and two PSS] and an additional short PSS), a PSS about three-quarters of the way down the ventral margin, a subdistal shorter PSS, and pair of unequal ventrodistal setae. Merus length 2.1x width, 1.2x length of propodus. Merus with mid-margin ventral seta, microtrichia visible proximal to this, dorsodistally with single medial and lateral setae, ventrodistally with single lateral crotchet and pair of medial crotchets, single seta between them, and microtrichia in the distal region of the ventral margin (not shown). Carpus length 1.5x width, 0.9x length propodus. Carpus with row of six crotchets on mediodistal margin, row of six crotchets on laterodistal margin, dorsodistally with single medial and lateral setae, and microtrichia in attachment area of crotchets; largest crotchet with mid-level spines (not shown). Propodus length 2.6x width, slightly shorter than merus (0.8x), with strong microtrichia arcs, scale-like, on distal two-thirds of medial and lateral dorsal surfaces. Propodus with single dorsodistal PSS, medial and lateral dorsodistal corners each with single long distally pinnate seta (finely setulate on one side in its distal half), single setae in both medial and lateral ventrodistal regions and two (three in the largest dissected female) setae on ventral margin. Dactylus and unguis fused to claw, with five or six spinules in lateral comb rows on medial and lateral surfaces and microserrations along proximal half of ventral edge of claw.

Pereopod 5 ( Figures 4I, 4J ). Similar to pereopod 4. For completeness, ischio-basis length 2.0x width, 1.9x length of propodus, slightly wider than ischio-basis on pereopods 2 and 3. Ischio-basis with dorsoproximal grouping of four setae (three in a cluster [one simple and two PSS] and an additional short PSS), a PSS about three-quarters of the way down the ventral margin, a subdistal shorter PSS, and pair of unequal ventrodistal setae. Merus length 2.2x width, 1.1x length of propodus. Merus with mid-margin ventral seta, microtrichia visible proximal to this, dorsodistally with single medial and lateral setae, ventrodistally with single lateral crotchet and pair of medial crotchets, single seta between them, and microtrichia in the distal region of the ventral margin (not illustrated). Carpus length 1.5x width, 0.9x length propodus. Carpus with row of five crotchets on mediodistal margin, row of five crotchets on laterodistal margin, dorsodistally with single medial and lateral setae, and microtrichia in attachment area of crotchets; largest crotchet with mid-level spines ( Figure 4J ). Propodus length 2.7x width, slightly shorter than merus (0.9x), with strong microtrichia arcs, scale-like, on distal two-thirds of medial and lateral dorsal surfaces. Propodus with single dorsodistal PSS, medial and lateral dorsodistal corners each with single long distally pinnate seta (finely setulate on one side in its distal half), single setae in both medial and lateral ventrodistal regions and two (three in the largest dissected female) setae on ventral margin. Dactylus and unguis fused to claw, with five or six spinules in lateral comb rows on medial and lateral surfaces and microserrations along proximal half of ventral edge of claw.

Pereopod 6 ( Figures 4K, 4L ). Ischio-basis length 2.3x width, 2.4x as long as propodus. Ischio-basis with dorsoproximal grouping of setae (one simple, two PSS and possibly a fourth underneath), very short proximal seta towards ventral side, and sparse arcs of microtrichia plus pair of unequal setae ventrodistally. Merus length 2.3x width, 1.3x length of propodus. Merus with single medial and lateral dorsodistal setae, ventrally with sparse microtrichia and single marginal seta, ventrodistally with three crotchets, two medial and one lateral, single seta between them and microtrichia around their base. Carpus length 1.5x width, similar length to propodus. Carpus with single medial and lateral dorsodistal setae, microtrichia arcs on dorsal surface, row of six crotchets on mediodistal margin and five on the laterodistal margin, largest carpal crotchet with mid-level spines as in pereopods 4 and 5 (not shown). Propodus length 2.0x width, 0.8x length of merus, with extensive microtrichia arcs, two (sometimes three) ventromarginal setae and single short dorsodistal PSS. Propodus with single long strong pinnate seta in lateral dorsodistal region and smaller seta attached in lateral ventrodistal region. Medially, propodus with single long strong pinnate seta mediodistal, row of five shorter biserrate setae (range: 4–6, size effect), and row of nine flat, leaf-like setae (range: 7–11; size effect) extending down to ventrodistal corner. Dactylus and unguis fused to strongly curved claw, with lateral comb rows of eleven fine spinules on medial surface and lateral surfaces, and microserrations along proximal half of ventral edge.

Pereopods 2 and 3 have two ventrodistal meral crotchets and pereopods 4 to 6 three ventrodistal meral crotchets in all dissected females, despite a body length range of 3.6–5.8 mm. Total carpal crotchets on pereopod 2 varied little between female specimens (9 or 10; 4 medial and 5 or 6 lateral). On pereopod 3, total carpal crotchets showed a range of 9 to 13, 13 (7 medial and 6 lateral) occurring in the largest dissected female (5.8 mm). Pereopods 4 to 6 had 10–12 distal carpal crotchets in the six dissected females. The number of propodal ventromarginal setae showed some evidence of a size effect.

Pleopods ( Figures 5A, 5B ). Three pairs of similar pleopods; pleopod 3 of same form but slightly smaller than first two pleopods (by about 15% based on measurements of lengths and widths of articles) and with fewer plumose setae. Specimen size effect evident in numbers of plumose setae. Pleopod 1 basis with three short plumose setae on medial margin (range: 2–3) and 14 (range: 11–14) plumose setae on lateral margin. Exopods one-articled, medial margins with very fine sparse setae, lateral margins with about fifty plumose setae. Endopods one-articled, medial margins with 18 plumose setae (range: 15–21) and very fine, short setae on distal portion; lateral margin with 25 plumose setae in illustrated specimen plus a short, terminal seta consisting of three leaf-shaped structures ( Figure 5B ). Pleopod 2 as pleopod 1. Pleopod 3 basis with one (or two) medial plumose setae and ten (range: 7–10) lateral plumose setae, one of them very short. Endopod one-articled, medial margin with 12 plumose setae (range: 12–18) and very fine, short setae on distal portion; lateral margin with 21 plumose setae plus a short, terminal seta of same form as pleopods 1 and 2. Exopod one-articled with very fine sparse seta on medial margin and 45 plumose setae on lateral margin.

Uropods ( Figure 5C ). Uropod with three segments (including the basal segment or peduncle). Basal segment length 2.2x width, distally with three setae (small, medium, long) towards lateral side and pair of unequal setae towards medial side; sparse microtrichia visible distally. Second segment approaching 4.0x as long as wide, slightly longer than basal segment; with two short lateral marginal PSS, distally with two PSS, five simple setae of various lengths, and, towards medial side, three simple setae (short, medium, long). Third segment 0.4x basal segment length, about 2.5x as long as wide, with six simple setae and single short PSS terminally.

Description: MALE. Allotype full body, SAMA Cat. No. 14333; appendages from dissected paratype, SAMA Cat. No. 14334, partially dissected paratype, SAMA Cat. No. 14335 ( Figures 6–7 , Table 2.)

Male similar to female, but more compact, with weak sexual dimorphism in chelipeds, antennule and antennae.

Body ( Figure 6A ). Slightly stouter than female, 5.0x as long as maximum pereonal width. Cephalothorax a fifth of total specimen length, rounded anteriorly, length similar to width (1.1x) and 0.9x length of pereonites 1 to 3 combined. Setation as in female, with two or three setae in dorsolateral cluster about one-third of way from anterior end. Relative lengths of pereonites similar between male and female. Pereonite 1 0.5x length of pereonite 4, length 0.3x width. Pereonite 2 0.8x length of pereonite 4, length 0.4x width. Pereonite 3 0.9x length of pereonite 4, length 0.5x width. Pereonite 4 length 0.6x width. Pereonite 5 similar length to pereonite 4, with length 0.6x width. Pereonite 6 0.9x length of pereonite 4, with length 0.6x width. Pereonites 5 to 6 widen only slightly posteriorly. Pereonites 1 to 3 1.2x as long as maximum width. Pereonal setation and pleosome dimensions and setation similar to female. Males also showed variability in pereonite spread; younger males tending to be more extended and mature males more compact ( Figure 7 ). Among 6 mature males, body lengths 3.9–4.9 mm, median (range) of body length to maximum pereonite width was 5.0 (4.8–5.2); ratio of cephalothorax length to combined length of first three pereonites 0.85 (0.81–0.86); cephalothorax 19.9% (19.1–20.3%) of body length; ratio of combined length of pereonites 1 to 3 to maximum width 1.16 (1.15–1.23); and pleon 25.1% (24.4–26.4%) of body length.

Antennule ( Figures 6B, 6C ). Antennule with five articles, relatively longer than cephalothorax compared with female (1.1x cf. 0.8x). Relative lengths of articles similar between sexes, but male articles slightly more elongate. Setation and ornamentation similar, minor differences; tendency for an additional aesthetasc in males compared with females. For completeness, first article longer than second article (2.6x), more elongate than in female (2.9x as long as wide cf. 2.1x), with cluster of three short dorsolateral PSS in proximal half. Distally, first article with four dorsolateral setae (two of these subdistal), row of four short PSS in ventrolateral region, two PSS ventromedially, and pair of unequal simple setae dorsomedially (range: 6–7 subdistal/distal simple setae, 3–6 distal PSS). With reference to other antennule mounted for this specimen and other specimens, antennule first article also has two or three setae on medial margin. Second article 1.6x as long as wide, 0.4x as long as first article. Distally, second article with four unequal setae in row extending dorsolateral to lateral, row of four PSS in ventrolateral region, single ventral PSS, and pair of shorter simple setae ventromedial and dorsomedial. Second article with total of eight simple setae and five PSS (range: 6–8 simple, 4–5 PSS) distally. Third article only slightly shorter than second article (0.9x), 2.4x as long as wide, distally with simple medium length dorsolateral seta, single shorter ventromedial seta, and two short medial PSS ( Figure 6C ). Fourth and fifth articles very short ( Figure 6C ; only aesthetascs and setae distal on third article shown). Fourth article with four simple setae attached in dorsal region (range: 3–5) and three (range: 2–4) aesthetascs attached ventrally. Fifth article also short, with smaller diameter than fourth article, with short PSS, one (or two) aesthetasc(s), and five terminal setae (range: 4–6), one of these very short. Fourth and fifth articles together with seven longer simple setae plus three shorter, fine setae (range: 8–10, total simple setae), one short PSS, and four (range: 4–6) aesthetascs distally.

Antenna ( Figures 6D, 6E ). Antenna as long as antennule, with eight articles. Relative lengths of antennal articles similar between sexes, but articles more elongate in male, particularly articles 2, 4 and 5. First article length similar to width, without setae. Second article 2.5x as long as third article, length 1.7x width, with extensive microtrichia arcs. Second article with one short ventromarginal seta, distally with three setae (one ventral, one dorsomedial, and one dorsolateral). Third article 0.4x length of second article, 0.9x as long as wide; distally with single simple dorsal seta, also with microtrichia arcs on dorsal surface (not shown). Fourth article 1.2x length of second article, length 3.8x width; distally with one long ventral simple seta, one ventral PSS, pair of unequal simple dorsolateral setae, and single medium length dorsomedial seta (total setae distally: 4 simple, 1 PSS; range: 3–4 simple, 1PSS). Fifth article 3.3x as long as wide, 0.8x length of second article; distally with three simple setae attached ventrally and five short PSS, two attached ventromedially, two ventrolaterally, and one dorsolaterally ( Figure 6E ) (range: 3 simple (5 in one specimen of six), 2–5 PSS). Sixth, seventh, and eighth articles very short ( Figure 6E ; only setae on fifth and seventh articles shown). Sixth article very short, half as long as wide, only 0.1x length of second article, with four simple distal setae (range: 2–4), one pair attached dorsolaterally, the other shorter pair in the ventromedial region. Seventh article also very short, half as long as wide, with four long distal setae, three attached ventrally, the other dorsally, and single short PSS. Eighth article tiny, half as long as wide, with five longer terminal setae. Seventh and eighth articles with total of nine distal setae (range: 8–9) and single short PSS.

Mouthparts. As in female, with minor differences in setation as follows. Maxillule palp slender, tapering distally, with (at least) four terminal setae (five to seven setae were observed in other dissections, finely setulate in their distal halves). Maxilliped bases each with four (or three) setae on the medial margin, a shorter seta proximal and three (or two) longer setae regularly spaced along the proximal half of margin. Each maxilliped basis with distal row of five (or four) long setae, increasing in length lateral to medial, and six lateral setae (four long and two shorter; range: 4–6). The maxilliped palp article 3 medial margin with two rows of setae—a row of nine (range: 8–10) stronger setae along central bulge and parallel row of six (range: 5–7) simple slender setae. Article 4 length about three times width, similar length to article 2, with single lateral seta and two simple subdistal setae. Article 4 medial margin with two parallel rows of setae on distal third, one containing six or seven slender simple setae and other with six or seven finely serrate setae.

Cheliped ( Figure 6F ). Cheliped larger than in female with notably arcuate, slender dactylus and fixed finger with different form. Basis relative dimensions and setation as in female, except for three or four rather than two or three unequal ventrodistal setae. Merus shape, dimensions and setation as in female, with five (sometimes four) setae ventrally. Carpus length notably shorter than propodus length (C(L):P(L)=0.6; range: 0.6–0.75), carpus length

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1 Table abbreviations: f, female; m, male; is., island; PSS, plumose sensory seta(e); P1, Pereopod 1; pl, pleopod.

2 Neotype designated by Sieg 1980.

3 “Figure” indicates that the data was not in the text of the article but was extracted from the figure(s).

1.2x width (range: 1.2–1.4), otherwise of form similar to female. Setation similar to female with three ventral setae and four or five setae in row on distoventral region of lateral surface. Propodus of similar relative dimensions to female, about twice as long as wide (length including the fixed finger) with cluster of four or five setae at proximal end of fixed finger cutting edge close to junction with dactylus. Fixed finger form differs from female—narrow, with a smooth cutting edge and no mid-edge process, but with small triangular process close to articulation with dactylus; with six (range: 5–6) ventral setae, also with nine (range: 7–9) lateral dorsal setae in row attached just below cutting edge, and two medial setae close to terminal claw. Dactylus arcuate, smooth, similar length to fixed finger, with medial seta, a terminal claw, and ventrally with sparse row of small setules.

Cheliped (preparatory male, Figure 6G ). Cheliped with less arcuate dactylus, appendage more similar in form to female but larger. Basis and merus with relative dimensions and setation as in female. Carpus shorter than propodus (C(L):P(L)=0.75), length 1.3x width, setation as in female with three rather than two setae ventrally. Propodus about twice as long as wide (length including the fixed finger). Setation and fixed finger form similar to female. Fixed finger cutting edge rounded distally, smooth with blunt triangular process mid-way, with cluster of five (four or five) setae at proximal end close to junction with dactylus. Fixed finger with five (four or five) ventral setae, dorsally with nine (seven to nine) lateral setae in row attached just below cutting edge, and two medial setae close to terminal claw. Dactylus not arcuate, as long as fixed finger, with terminal claw, ventrally with row of small setules, single medial seta, and obtuse triangular process about mid-margin.

Pereopods. Pereopod 1 coxa and articles similar to those in female with the following differences. Pereopod 1 overall more slender but relative lengths of articles consistent between sexes. Pereopod 2 in male similar to female with the following minor differences in ornamentation: merus sometimes with three rather than two simple crotchets ventrodistally; carpus with pair rather than single seta dorsodistally; and propodus sometimes with three rather than two ventromarginal setae. Pereopod 3 similar to that in female. Merus more commonly with three short, simple crotchets ventrodistally compared with two in the females. Pereopods 4 and 5 similar to each other and similar in males and females with the following differences in setation between sexes: ischio-basis sometimes with three rath- er than two simple unequal ventrodistal setae; merus sometimes with four rather than three ventrodistal crotchets.

Pereopod 6 similar to female with small differences in setation as follows: ischio-basis with dorsoproximal grouping of as many as five rather than four setae; merus with single mid-margin seta ventrally and consistently with three crotchets ventrodistally, unlike pereopods 4 and 5, but as in female; propodus with as many as four, but usually three, ventromarginal setae. Distomedial setal row on propodus with eight or nine flattened setae (six on one specimen) and five or six serrate setae.

Pleopods. Pleopods similar to each other, but pleopod 3 with slightly reduced setation. Pleopod 1 basis with three short plumose setae on medial margin and 12 (range: 10–13) plumose setae on lateral margin. Exopods one-articled with very fine sparse setae on medial margin and approaching fifty plumose setae on lateral margin. Endopods one-articled, medial margin with 17 (range: 13–19) plumose setae, distally with very fine, short setae, and lateral margin with around twenty plumose setae plus one stout, leaf-like terminal seta, similar to female. In one specimen on one pleopod, two of these terminal setae were present; this is likely an aberration. Pleopod 2 basis with three medial and 10–12 lateral plumose setae; endopod with 12–18 medial plumose setae. Pleopod 3 basis with only one or two medial plumose setae and 7–9 lateral plumose setae; endopod with 9–14 plumose setae.

Uropods. Uropods with three segments including basal segment (peduncle), as in female with respect to setation and relative lengths.

Comparison between January 2015 specimens and February 2010 time-series specimens. The single sampling in January 2015 contained specimens towards the smaller end of the size range of mature specimens observed in 5 samples from February in the time-series. In the January 2015 sampling, mature females ranged from 3.6–3.8 mm and mature males from 3.0– 3.4 mm compared with 3.4–6.0 mm in females and 3.7–5.5 mm in males from the February 2010 time-series subset. We did not observe consistent morphological differences between dissected Tanais specimens collected in February 2010 and those from January 2015. Numbers of uropodal segments and antennal articles agreed as did the numbers of antennule aesthetascs and the presence of anterolateral processes on the pleotelson suggestive of a residual pleonite 5. Setation and form of mouthparts were consistent including laciniae mobiles and adjacent setae, distal ornamentation on the maxilliped endites, the absence of setae on the maxilliped palp first article and the single seta lateral on the second article. There was variability in the number of setae lateral (range: 3–6) and distal (range: 4–5) on the maxilliped basis and on the number of setae ventral on the propodi of pereopods 2 to 6 (range: 1–4) suggestive of an effect from specimen size.

Figures

FIGURE 2. Tanais adelaidensis n. sp. (West Beach, Adelaide, February 2010). Female, holotype (SAMA Cat. No. C14331): A Full body (please refer to text and drawings of appendages for complete details of setation, ornamentation and somite measurements). Female, ovigerous, paratype (SAMA Cat. No. C14332): B Pleotelson (dashed line where folding of tissue obscured margin); C Antennule (small circles on first article show setal attachment sites); D Antennule distal articles (aesthetascs and setae distal on third article illustrated only); E Antenna; F Antenna distal articles (setae on fifth and seventh articles illustrated only); G Cheliped. Scale bars: A 1.0 mm, B–G 0.1 mm.

FIGURE 3. Tanais adelaidensis n. sp. (West Beach, Adelaide, February 2010). Female, ovigerous, paratype (SAMA Cat. No. C14332):A Labrum; B, C Left mandible; D, E Right mandible; F Labium; G Maxillule (see *) & maxilla 2; H, I Maxillule endite tips; J Maxilliped with palp and endite; K Maxilliped endite detail; L Epignath. * Damage to terminal setae on the maxillule palp in this paratype during dissection. Based on four other more successful dissections of this appendage, five or six terminal setae are expected. Scale bars: 0.1 mm.

FIGURE 4. Tanais adelaidensis n. sp. (West Beach, Adelaide, February 2010). Female, ovigerous, paratype (SAMA Cat. No. C14332): A, B Pereopod 1; C, D, E Pereopod 2; F Pereopod 3; G, H Pereopod 4; I, J Pereopod 5; K, L Pereopod 6. Scale bars: 0.1 mm.

FIGURE 5. Tanais adelaidensis n. sp. (West Beach, Adelaide, February 2010). Female, ovigerous, paratype (SAMA Cat. No. C14332): A Pleopod 1; B Endopod distal end; C Uropod. Scale bars: 0.1 mm.

FIGURE 6. Tanais adelaidensis n. sp. (West Beach, Adelaide, February 2010). Male, allotype (SAMA Cat. No. C14333): A Full body (please refer to text and drawings of appendages for complete details of setation and ornamentation and somite measurements). Male, paratype (SAMA Cat. No. C14334): B Antennule; C Antennule distal articles (aesthetascs and setae distal on third article illustrated only); D Antenna; E Antenna distal articles (setae on fifth and seventh articles illustrated only); F Cheliped. Male, preparatory paratype (SAMA Cat. No. 14335): G Cheliped. Scale bars: A 1.0 mm, B–G 0.1 mm.

FIGURE 7. Tanais adelaidensis n. sp. (West Beach,Adelaide, February 2010). From left to right: preparatory female, ovigerous female, preparatory male, mature more dimorphic male.