Palaemon intermedius (Stimpson)

Walker, T. M. & Poore, G. C. B., 2003, Rediagnosis of Palaemon and differentiation of southern Australian species (Crustacea: Decapoda: Palaemonidae), Memoirs of Museum Victoria 60 (2), pp. 243-256 : 247-251

Palaemon intermedius (Stimpson)

Figures 1d , 2a–e , 3a, 3b , 4 , 5

Leander intermedius Stimpson, 1860: 41 .— Haswell, 1882: 195.— Whitelegge, 1889: 224 (record in Port Jackson).— Thomson, 1893: 51 (record in Tas.).— Stead, 1898: 210.— Sayce, 1902: 155 (record in Port Phillip Bay).— McCulloch, 1909: 309, pl. 89 figs 13, 14.— Hale, 1927a: 58–59, fig. 53 (record in SA).— Hale, 1927b: 309.— Anderson, 1938: 351 (record in Spencer Gulf).— Mack, 1941: 108 (diet of cormorants, Gippsland Lakes).— Thomson, 1946: 59, 67 (record in WA).— Holthuis, 1950: 20.

Palaemon (Leander) intermedius . — Miers, 1884: 295.

Macrobrachium intermedium . — Holthuis, 1952: 207–209 (redescription).— Poore et al., 1975: 35, 71 (distribution in Port Phillip Bay).— Walker, 1979 (redescription and ecology in Tas.).— Boulton and Knott, 1984: 769–784 (ecology in WA).— Davie, 2002: 296.

Material examined for redescription. 15 males, 12.7–27.3 mm body length, 20 females including 7 ovigerous, 12.7–34.5 mm body length, Margate Beach, mouth of North West Bay River Estuary , Tasmania, T. Walker, 1975 . 4 adult females, D’Entrecasteaux Channel, Middleton , 14 m, Tasmania, T. Walker, Khin Khin U and T. Sward, 11 Apr 1975 . 4 ovigerous females, 2 mature males, Western Port , Victoria, Fisheries and Wildlife Department, Victoria, 29 Nov 1973 . 3 ovigerous females, 1 mature male, Spalding Cove , 4–12 m, South Australia, 5 Nov 1969 .

Additional material. Numerous sites in Tasmania, Victoria, South Australia, Western Australia, New South Wales, Queensland; including many lots registered in Museum Victoria.

Diagnosis. Carapace smooth; branchiostegal spine set back from anterior edge of carapace and open posteriorly; branchiostegal groove running from carapace edge upwards and posteriorly to dorsoposterior edge of the spine where it stops. Rostrum upper border with 7–10 teeth (usually 8 or fewer, commonly 9); 2–3 of these (usually 2) postorbital; dorsal teeth evenly spaced although proximal 3 or 4 often closer together than remainder and incompletely articulated; ventral rostral border with 4–6 teeth (usually 5) evenly spaced over distal two-thirds;

Description. (based on 15 males, 20 females from Margate Beach, Tasmania) Maximum body length (orbit to telson tip) c. 30 mm in males, c. 40 mm in females.

Carapace smooth; antennal spine strong and marginal; branchiostegal spine set back from anterior edge of carapace and open posteriorly; branchiostegal margin rounded, branchiostegal groove running from carapace edge upwards and posteriorly to dorsoposterior edge of the spine where it stops.

Eyes well developed, with ocellus; interocular tooth well developed.

Rostral tip level with or exceeding terminal setae of scaphocerite; length:depth ratio 6.9–10.0 in males, 6.2–8.8 in females; upper border straight to concave; body length:rostral length ratio 2.5–3.1 in males, 2.8 – 3.6 in females; lateral carina gently and concavely curved, degree of curvature variable; third to half rostrum above lateral carina; upper border with 7–10 teeth (usually 8 or less commonly 9); 2–3 of these (usually 2) postorbital; dorsal teeth evenly spaced although proximal 3 or 4 are often closer together than remainder and incompletely articulated; rostral tip usually bifid but may be trifid or a single point; single row of plumose setae along upper border between but not on teeth; ventral rostral border with 4–6 teeth (usually 5) evenly spaced over distal two-thirds; 2 rows of plumose setae on ventral border between but not on teeth.

Antennule well developed, article 1 of peduncle about 2.5 times length of articles 2 and 3; article 2 slightly longer than 3, bearing elongate, blunt projection on medial edge; basal article elongate and rectangular, about 2.3 times as long as wide, expanded and flattened on its inner edge, bearing several transverse and longitudinal rows of plumose setae, including subapical row extending across dorsal surface; setae longer over inner half of this row; basolateral spine slender, sharply pointed, reaching over half article 1; outer flagellum of antennular exopod much longer than inner flagellum; inner flagellum fused with outer usually over basal third of its length, about 13 articles in adult, fused up to half its length in juvenile; each free article of inner flagellum with medial and terminal transverse row of sensory setae, medial row bearing 3-4 setae and transverse row 4 setae in males, both rows bearing 3 setae in females.

Antenna with well developed peduncle with strong distolateral tooth, well developed flagellum and scaphocerite; proximal article of flagellum with blunt anteroventral projection; flagellum naked. Scaphocerite elongate, rectangular, extending well beyond peduncle, widest just anterior to its base, about one quarter of body length, 3.3–4.3 times as long as wide; distal and inner lateral edges bearing row of long plumose setae; outer edge naked, slightly concave, ending distally in well developed tooth that just fails to overlap anterior edge of lamella; inside edge straight or slightly concave.

Mandible- incisor of one side with 3 teeth (either side), incisor of the other usually with 4; palp with 3 articles; article 3 longest, with 3 terminal setae longer than article.

Maxillule endopod with bifid tip; distal lobe acute, naked; proximal lobe bearing 1 plumose seta; coxal endite with long setae and terminally 4–5 stout setae; basal endite with 3 rows of stout setae along terminal, inner edge extending down proximal margin as longer setae.

Maxilla basal endites elongate, nearly rectangular, both bearing long, stout setae terminally, distal endite with row of 5 setae along distal margin near its base; endopod with 3 short setae; scaphognathite proximal lobe wider and shorter than distal; coxa with small expansion near base (?epipod).

Maxilliped 1 with rectangular coxa with endite and bilobed epipod; basis with endite; endopod with 1 long, subterminal seta; well developed exopod with prominent lateral lobe; endites with stout setae along mesial edges, and distal on basal endite; both with single row of similar setae on posterior face.

Maxilliped 2 with well developed exopod; coxa with poorly developed endite (on its outer edge), epipod and podobranch; ischiobasis about twice as long as wide, with scattered setae; endopod merus half length of ischiobasis, carpus about half length of merus, propodus expanded, about as long as merus but twice as wide, dactylus short and wide; anterior and mesial margin of propodus bearing rows of setae, some on anterior margin strong.

Maxilliped 3 epipod, medial margin setose; exopod extending beyond article 1 of endopod. Endopod ischio-merus 1.4–2 times as long as propodo-dactylus; carpus 1.2–1.6 times as long as latter; ischio-merus with 2 rows of long setae, one on each of posterior and anteromesial margins; carpus with similar rows and additional row on lateral surface; propodo-dactylus with stout terminal seta and numerous plumose and serrate setae, parallel rows of shorter, serrate setae across anteromesial surface and longer plumose setae elsewhere. Two arthrobranchs, one rudimentary and obscured by the larger; maxilliped endopod relatively shorter in males than females. Body length: maxilliped 3 length ratio 3.7– 4.5 in males, 3.5–4.3 in females.

Pereopod 1 articles smooth; reaching approximately to level of scaphocerite spine; tufts of serrate setae on posteroproximal region of palm and distomesial surface of carpus; outer surface of propodal finger with tufts of serrate setae, simple setae on both fingers; posteromesial ridge of ischium and merus with single row of long setae; fingers with simple cutting edge, 0.8–1.2 times as long as palm; carpus 1.5–2.5 times as long as chela and 1.1–1.4 times as long as merus; merus 1.1–1.9 times as long as ischium. Body length:pereopod 1 ratio 2.5–3.1 in males, 2.0– 2.6 in females.

Pereopods 2 equal, similar in males and females, articles smooth, usually exceeding scaphocerite by all of palm; fingers slender, curved, with small tooth at base, cutting edges serrate, sometimes one or both smooth, particularly in smaller individuals; palm swollen, laterally flattened, 2.8–3.4 times as long as wide; palm 0.9–1.2 as long as fingers, usually longer; carpus long and slender, narrow proximally, 6.0–8.5 times as long as wide at that point, distally 1.7–2.4 times as wide as at base, length 6.0–8.5 times distal width; chela 0.9–1.4 times as long as carpus and 1.2–1.5 times merus; merus 1.0–1.3 times as long as ischium. Body length:pereopod 2 ratio 1.6–1.9 in males, 1.3–1.8 in females.

Pereopods 3–5 progressively longer, mainly owing to increase in lengths of propodi.

Pereopod 3 simple, slightly less than half body length; dactylus with small cutting edge on posterior border; propodus with 2 rows of long setae anteriorly, 2 variable rows of short plumose setae, outer row with 5–9 setae; propodus 2.0–2.5 times as long as dactylus and 1.5–1.9 times as long as carpus in males, 1.6–2.4 in females; merus 1.1–1.3 times as long as propodus and 1.1–1.5 times as wide; merus 1.9–2.4 times as long as ischium; 1.9–2.1 times as long as carpus in males, 1.9–2.4 in females.

Pereopod 4 similar to 3, but slightly longer; propodus length about 2.5 times as long as dactylus, about twice as long as carpus; merus about same length as propodus and twice as long as ischium.

Pereopod 5 similar to 3 and 4, slightly longer than 4; row of 5–7 short setae on lateral posterior margin of propodus with 5–7 parallel rows of serrate setae distally; mesial posterior edge with row of 7–10 short setae. Propodus 2.6–3.1 times as long as dactylus in male, 2.0– 2.8 in female.

Branchial formula (r = rudimentary).

Maxillipeds Pereopods Total gills

12 3 12345 Pleurobranchs – – – 1 1 1 1 1 5 Arthrobranchs – – 1+1r – – – – – 1 + 1r Podobranchs – 1 – – – – – – 1 Exopods 1 1 1 – – – – – 3 Epipods 1 1 1 – – – – – 3

Pleopod 1 with well developed exopod and smaller endopod; appendix interna absent. Endopod of male little more than half as long as exopod, with convex outer edge, concave inner edge, about 4 times as long as wide. Endopod of female smaller, about one third as long as exopod, about 3 times as long as wide.

Pleopods 2–5 with equally developed exopod and endopod; endopod with appendix interna. Endopod of male pleopod 2 with appendix masculina, longer than appendix interna, usually with 22 setae along its length, 6 of which are apical or subapical; each seta up to half as long as appendix masculina. Pleopods 1–2 and to a lesser extent 3–5 with keel-shaped, flattened extension on lateral edge, smaller in male than female.

First abdominal pleuron about 2–3 times as long as wide; second abdominal pleuron about 1.5 times as long as wide; apex of fifth pleuron acute, with short terminal spine; sixth abdominal article 1.4–1.8 times as long as fifth. Ventral edges of abdominal pleura with row of short, plumose setae.

Telson 2.0–2.5 times wider at base than apex, length 2.9–4.2 times basal width; 1.1–1.4 times as long as sixth abdominal somite; with 2 pairs of dorsal stout setae and larger inner and smaller outer terminal pair; apex produced into acute spine flanked by a 1 simple seta on each side and occasionally a shorter second pair; apical spine much shorter than the terminal setae; tuft of long plumose setae dorsomedially near base of telson.

Uropods endopod elongate, fringed with long plumose setae; exopod rectangular; transverse suture on exopod about two-thirds of distance from base; outer edge of exopod entire, ending at suture line in an immovable spine; second movable seta often present inside spine; remainder of margin fringed by row of long plumose setae; posterior to immovable spine, dorsally and ventrally, a row of about 12 long, non-plumose setae set back from margin, extending almost to apex of exopod; ventrally, outer margin from base of the exopod to the immovable spine with row of stout, simple setae just inside the margin.

Colour pattern. Carapace chromatophore lines usually red; abdominal markings generally olive green, black and red; accessory flagellum distinctly marked with alternate red and white bands.

Sexual dimorphism in adults. Males are smaller than females; with larger sternal process on the eighth thoracomere; smaller keel-like expansion on outer edge of peduncles of pleopods; appendix masculina on pleopod 2; significantly larger endopod on pleopod 1; 4 setae in distal sensory row on each article of antennular inner flagellum (3 in adult female); rostrum more slender and longer; longer carpus in pereopod 2; maxilliped 3, pereopods 1 and 3 shorter relative to body length; the ratio of length of propodus and dactylus of pereopod 5 significantly greater.

Females ovigerous from 19.5 mm body length; bearing approximately 100–700 ovoid eggs, larger females bearing more eggs; egg size 0.55–1.0 mm depending on developmental stage, 0.9–1.0 mm when ready to hatch.

Ontogenetic changes. Some characters alter as the size of males and females increases. In females, the scaphocerite becomes stouter and shorter relative to body length; the number of articles over which the antennular flagella are fused increases; the carpus and merus of pereopod 1 become longer relative to other articles; the number of parallel rows of setae on the propodus of pereopod 5 increases, and pereopod 2 becomes longer. In males, the number of articles over which the antennular flagella are fused increases; length ratios between articles of pereopods 1–5 differ; pereopod 1 becomes slightly shorter relative to body length.

In early post-larval stages, the mandibular palp and the branchiostegal groove are absent and a branchiostegal spine is present on the edge of the carapace. Over a series of moults, a palp of three articles and the branchiostegal groove form and the branchiostegal spine migrates posteriorly and upwards to its final position in adults.

Variation. The type or types of Leander intermedius Stimpson, 1860 are lost. They were collected from Port Jackson, NSW. Examples of the species from nearby Port Hacking most resemble the typical Tasmanian form from Margate Beach but examples from other locations including Tasmania differ .

Deep-water form (5 adult females, 29.3–36.6 mm, D’Entrecasteaux Channel). More slender and longer legged than shallow water form. Scaphocerite more slender, rostrum with 2–3 but usually 3 postorbital teeth rather than 2; Pereopods 1, 3, 5 longer, body length 2.2–2.3 times as long as pereopod 1, 1.7–1.9 times as long as pereopod 2, 1.5–1.6 times as long as pereopod 5; carpus of pereopod 2 longer, carpus length 2.0–2.3, 3.7–4.7, 1.2–1.4 and 1.9–2.1 times as long as chela, fingers, merus and ischium respectively; palm more swollen, length 2.6–2.8 times its maximum width; apex of carpus more expanded; pereopods 3 and 5 with longer propodus; telson stouter, at least at its base, 2.2–3.8 times as long as basal width.

Intermediate form (4 ovigerous females, 21.2–33.0 mm, 2 adult males 26.2 mm, Western Port, Vic.). More similar to the deep-water form particularly in number of postorbital rostral teeth, length of pereopods 2, 3, 5, and the degree the palm is swollen on pereopod 2.

South Australian form (3 females (2 ovigerous) 21.9–35.9 mm, 1 adult male 20.8 mm, Spalding Cove, Port Lincoln. SA). Resembles closely Tasmanian material except for 3 postorbital rostral teeth and a more swollen palm on pereopod 2 .

Remarks. Palaemon intermedius bears what appears to be an hepatic spine but it is set lower down and not as far back from the carapace edge as is usual in Macrobrachium , the genus to which it was assigned by Holthuis (1952). The branchiostegal groove appears to run back to the spine and over it, but ceasing at the back of the spine. The spine is open posteriorly, having no suture line between it and the carapace in that region. The migration of the branchiostegal spine from the carapace edge during ontogeny is arrested partly completed and the value of this character for generic assignment is therefore limited. Generic assignment is based principally on the other characters.

Figures

Figure 1. SEMs of carapace spines. a, Macrobrachium rosenbergii; b, Palaemon serenus; c, Palaemonetes australis; d, Palaemon intermedius; e, Palaemon dolospina.

Figure 2. Migration of the carapace spine during growth to final position. a–e, Palaemon intermedius; f–j, Palaemon dolospina. Body lengths of shrimps (mm): a, 6.0; b, 6.2; c, 6.5; d, 6.6; e, 6.6; f, 6.3; g, 6.2; h, 6.3; i, 6.8; j, 8.4.

Figure 3. Habitus with colour pattern. a, Palaemon dolospina; b, telson of P. dolospina; c, Palaemon intermedius.

Figure 4. Palaemon intermedius. a, rostrum (female, 33.2 mm); b, rostrum (male, 20.8 mm); c, carapace spine (female, 30.2 mm); d, e, antennule and scaphocerite (female, 30.2 mm); f, scaphocerite (male, 28.0 mm); g, mandible; h, maxillule; i, maxilla; j–l, maxillipeds 1–3; m, mandible of post-larva (all mouthparts, female, 30.2 mm).

Figure 5. Palaemon intermedius. a–f, pereopods 1–5; b details of chela of pereopod 1 (male, 28.0 mm). g, h, pleopods 1, 2 (male); i, j, pleopods 1, 2 (female). k, telson. l, appendix masculina.