Palaemon dolospina, Walker & Poore, 2003

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 : 251-255

Palaemon dolospina sp. nov.

Figures 1e , 2f–j , 3c , 6 , 7

Palaemon sp. — Walker, 1979.

Material examined. Holotype. Margate Beach, North West Bay, Tas. (lat long) in Zostera muelleri and Heterozostera tasmanica on sand, 0.2–1 m, T. Walker, 12 Dec 1973, NMV J52659 (male, 6.5 mm postorbital carapace length, 42 mm total length).

Allotype. Collected with holotype, NMV J52660 (ovigerous female, 8.9 mm postorbital carapace length, 45 mm total length)

Paratypes. Collected with holotype, NMV J52661 (92 specimens, 4.7–9.0 mm postorbital carapace length)

Material described. 26 males, 12–35 mm body length, 28 females, including 6 ovigerous, 12.6–40 mm body length, Margate Beach and in brackish water from North West Bay River Estuary, Margate , Tasmania, in seagrasses Zostera muelleri and Heterozostera tasmanica, T. M. Walker, 1975 . 1 ovigerous female, 32.1 mm body length, Western Port , Victoria, intertidally on mud, Fisheries and Wildlife Department , Victoria, 8 Jan 1974 . 8 females, 2 ovigerous 13.9–34.6 mm, 6 males, 15.3–23.8 mm, ICI Saltfields, Port Gawler , South Australia, ICI staff, 13 Jan 1973 . 6 ovigerous females, 37.7–50.7 mm, Newport Power Station , Victoria. H.A. Morrison, 21 July 1949 .

Additional material from 50 sites in Tasmania (including Flinders and King Islands ), 2 in Victoria, 3 in South Australia .

Diagnosis. Carapace smooth; branchiostegal spine set back from and its tip barely reaching anterior carapace edge, set high up on brachiostegite; branchiostegal groove runs up to, loops over the spine and sweeps down again posteriorly. Rostrum upper border with 6–9 teeth; 1–2 of these (usually 2) postorbital; dorsal teeth unevenly spaced, first set back from rest on carapace, next 3 or 4 evenly spaced, incompletely articulated, increasingly longer gap between next 3 until penultimate tooth close to distal tooth; ventral rostral border with 3–6 teeth (usually 4), evenly spaced over distal two-thirds.

Description. (based on 26 males, 28 females from Margate Beach, Tasmania. Characters resembling P. intermedius not described) Maximum body length (orbit to telson tip) c. 42 mm in males, c. 51 mm in females.

Carapace smooth; antennal spine strong and marginal; branchiostegal spine set back from and its tip barely reaching anterior carapace edge, set high up on brachiostegite; branchiostegal groove runs up to, loops over the spine and sweeps down again posteriorly.

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

Rostral tip exceeding lamella of scaphocerite; length:depth ratio 6.5–9.3 in males, 5.3–7.6 in females; upper border straight to concave; body length:rostral length ratio 2.4–3.6 in males, 2.5–3.5 in females; lateral carina gently concave and directed upwards at tip; third to half rostrum above lateral carina; upper border with 6–9 teeth; 1–2 of these (usually 2) postorbital; dorsal teeth unevenly spaced, first set back from rest on carapace, next 3 or 4 evenly spaced, incompletely articulated, increasingly longer gap between next 3 until penultimate tooth close to distal tooth; rostral tip appears bifid; single row of plumose setae along upper border between but not on teeth; ventral rostral border with 3–6 teeth (usually 4), evenly spaced over distal two-thirds; 2 rows of plumose setae on ventral border between but not on teeth.

Antennule well developed; basal article bearing subapical transverse row of 10 plumose setae, not extending onto stylocerite; basilateral spine moderately slender, sharply pointed, reaching over half basal article of peduncle; inner flagellum fused with outer usually over basal third of its length, about 11–12 articles in male and 14–15 in female, fused up to half its length in juveniles; each free article of inner flagellum with mesial and terminal transverse row of sensory setae, mesial row of 3–4 and distal of 4 setae in female, mesial row of 4 and distal of 5 (occasionally 4) setae in male; sensory setae noticeably shorter than those in P. intermedius .

Antennal scaphocerite elongate, rectangular, widest near base, 3.2–4.1 times as long as wide; outer edge slightly convex to slightly concave, with terminal spine that just fails reach anterior edge of lamella; inside edge straight or concave over distal two thirds, convex proximally.

Mandible incisor of one side with 3 teeth (either side), incisor of the other usually with 4; palp with 3 articles; article 2 with 10 or more setae; article 3 slightly swollen, setose including 3 terminal and 2 subterminal setae; article 3 length about twice article 2, article 1 about 1.5 times article 2. Maxillule endopod with bifid tip, naked, distal lobe acute. Maxilla endopod with 2 short setae on inner edge and about 10 on proximal half of outer edge. Maxilliped 1 endopod without seta.

Maxilliped 3 epipod, mesial margin setose; exopod extending to end of article 1 of endopod. Endopod ischio-merus 1.3–2 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; propodo-dactylus with stout terminal seta Body length:maxilliped 3 length ratio 3.8–4.5 in both sexes.

Pereopod 1 articles smooth; reaching approximately to tip of scaphocerite lamella; 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, 0.8–1.4 times as long as palm; carpus 1.3–2.2 times as long as chela and 1.0–1.4 times as long as merus; merus 1.3–1.8 times as long as ischium. Body length:pereopod 1 ratio 2.4–2.9 in both sexes.

Pereopods 2 equal, similar in males and females, articles smooth, usually exceeding scaphocerite by at least fingers; fingers slender, curved, with small tooth at base, cutting edges serrate, sometimes one or both smooth, particularly in smaller animals; palm slightly swollen, laterally flattened, 2.6–4.0 times as long as wide; palm 1.0–1.4 as long as fingers; carpus long and slender, narrow proximally, thickens distally to be 1.5–2.5 times wider than at base, length:apical width ratio 6.4–8.8 in males, 5.2–7.7 in females; chela 0.8–1.2 times as long as carpus and 1.0–1.4 times merus; merus 1.0–1.5 times as long as ischium. Body length:pereopod 2 ratio 1.6–2.2 in both sexes.

Pereopods 3–5 progressively longer, mainly due to increase in lengths of propodi. Pereopod 3 reaching about end of scaphocerite; dactylus with small cutting edge on posterior bor- der; propodus with 2 rows of long setae anteriorly, 2 variable rows of short flagellate setae, outer row usually with 4–5 setae in male, 5–6 in female, inner row usually with 3–5 in male, 5 in female; propodus 1.5–2.1 times as long as dactylus and 1.4–1.8 times as long as carpus in males, 1.6–2.0 in females; merus 1.0–1.4 times as long as propodus and 0.9–1.5 times as wide; merus 1.8–2.4 times as long as ischium; 1.6–2.2 times as long as carpus in male, 1.8–2.4 in female.

Pereopod 4 similar to 3, but slightly longer. Pereopod 5 similar to 3 and 4, slightly longer than 4.

Branchial formula as for P. intermedius .

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 24 setae along its length, 6 of which are apical or subapical; each seta less than third 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 1.3–1.9 times as long as fifth. Ventral edges of abdominal pleura with row of short, plumose setae.

Telson 2.0–2.8 times wider at base than apex, length 3.0–4.3 times basal width; 1.0–1.3 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 1 simple seta on each side and occasionally a shorter second pair; apical spine much shorter than 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 incomplete laterally, 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 9 long, non-plumose setae set back from margin, extending almost to apex of exopod; ventrally, outer margin from base of the exopod three quarters of the way to the immovable spine with row of stout, simple setae just inside the margin.

Colour pattern. Carapace chromatophore lines red; distinct transverse abdominal bars generally red but may be olive green; abdominal bars present on first post-larva as single lines of orange or yellow chromatophores; lateral carina of rostrum often with row of large, white chromatophores; hexagonal matrix of abdominal segments most distinct in large females, made up of small, olive green and some scattered white chromatophores; viewed dorsally, tail fan with white, transverse bands or patches.

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

Females ovigerous from 25 mm body length; bearing approximately 140-840 ovoid eggs, larger females bearing more eggs; egg size 0.65-1.15 mm depending on developmental stage, 0.9–1.15 mm when ready to hatch.

Ontogenetic changes. Some characters alter as the size of recognisably male and female animals increases. In females, the rostrum and scaphocerite becomes stouter and shorter relative to body length; the number of articles over which the antennular flagella are fused increases; pereopods 2, 3, 5 become longer relative to the body; the fingers of pereopod 1 become shorter relative to other articles; the palm of pereopod 2 becomes less swollen, the carpus more expanded and fingers shorter; the number of parallel rows of setae on the propodus of pereopod 5 increases; and the telson becomes stouter. In males, the number of articles over which the antennular flagella are fused increases; length ratios between articles of pereopods 1–5 differ; carpus of pereopod 1 becomes relatively longer; pereopod 2 palm becomes less swollen and fingers shorter.

In early post-larval stages, the mandibular palp and branchiostegal groove are absent and a branchiostegal spine is present on the edge of the carapace. Over a series of moults, a palp of 3 articles and branchiostegal groove form and the branchiostegal spine migrates posteriorly and upwards to its final position in adults.

Etymology. From Latin, dolus meaning deceit and spina, a spine, alluding to the deceptive position of the branchiostegal spine.

Remarks. Palaemon dolospina bears a branchiostegal groove looping over a spine set back from the carapace edge albeit displaced dorsally somewhat. Consequently, although the spine is situated unusually high on the carapace between the usual branchiostegal and hepatic position, it can be defined as branchiostegal. Females are larger than males and the second pereopods of males are not spinulose or markedly sexually dimorphic. The mandibular palp is of three articles. In spite its unusual branchiostegal spine/groove arrangement, this species clearly belongs to Palaemon .

Keys to species of Palaemon and Palaemonetes from southern Australia

The shallow marine and estuarine Australian palaemonid fauna includes eight, possibly nine, species distributed as follows:

Palaemon debilis Dana, 1852 – Widespread in Indo-West Pacific, Qld, redescribed by Holthuis (1950) and Chace (1972).

Palaemon cf. debilis Dana, 1852 – NSW, eastern Vic., also similar to Palaemonetes atrinubes but its status remains unresolved.

Palaemon dolospina sp. nov. – Vic., Tas., SA.

Palaemon intermedius ( Stimpson, 1860) – Qld (N to Moreton Bay), NSW, Vic., Tas., SA, WA.

Palaemon litoreus ( McCulloch, 1909) – NSW, Vic., SA, WA. Palaemon serenus and P. litoreus have in the past, been separated on the basis of the carpus exceeding the palm of pereopod 2 in P. serenus but being shorter in P. litoreus ( McCulloch, 1909; Hale, 1927b; Bray, 1976). Examination of material of both species from Western Australia has shown that, the carpus exceeds the palm in both species.

Palaemon macrodactylus Rathbun, 1902 – NSW, SA [native to Japan, Korea, northern China, introduced to San Francisco Bay and two Australian localities ( Buckworth, 1979; Walker, 1979). Identifications of Australian material confirmed by TW and L. Holthuis, 1976].

Palaemon serenus (Heller, 1862) – southern Qld, NSW, Vic., Tas., SA WA.

Palaemonetes australis Dakin, 1915 – WA.

Palaemonetes atrinubes Bray, 1976 – NT, Qld, Vic, WA

1. Carapace spine set back from carapace edge by less than its length and situated between branchiostegite and ridge of antennal spine; open posteriorly; branchiostegal groove runs up to dorsoposterior edge of spine but not past it ( Figs 1d , 4c ); pereopod 2 smooth and equal; rostrum with 7–10 dorsal teeth, usually 8, 2–3 postorbital, proximal 4 incompletely articulated; 4–6, usually 5, ventral teeth................................... Palaemon intermedius

— Carapace spine set below branchiostegal groove which may deviate up and over the spine; spine may be on or set back from edge of carapace; pereopod 2 and rostrum not as above...................................... 2

2. Branchiostegal spine set back from the carapace edge, overlapping it at most only with tip............... 3

— Branchiostegal spine at or very near carapace edge just under start of branchiostegal groove; groove running back from carapace edge in a shallow arc, not upwards sharply and down again.............................. 4

3. Branchiostegal spine almost or just reaching carapace edge with tip only; set above level of starting point of branchiostegal groove which runs upwards to front of spine, loops sharply over it and sweeps down again posteriorly ( Figs 1e , 6c ); pereopod 2 carpus 1–1.5 times as long as merus; mandibular palp with 3 articles........................................... Palaemon dolospina

— Branchiostegal spine set well back from the carapace edge which it never overlaps; branchiostegal groove deviating only slightly as it passes over spine ( Fig 1c ); pereopod 2 carpus 1.3–1.5 times as long as merus; mandibular palp absent..................... Palaemonetes australis

4. Antennule inner flagellum fused for greater than half of its length, usually over about two thirds, 16–20 articles fused in adults; mandibular palp absent........................................ Palaemonetes atrinubes

— Antennule inner flagellum fused for half or usually less of its length, less than 15 articles fused in adults....... 5

5. Pereopods slender (carpus of pereopod 2 1.5–2.0 times as long as chela, 1.4–1.7 times as long as merus)....... 6

— Pereopods not unusually slender (carpus of pereopod 2 shorter than chela, 0.9–1.1 times as long as merus.... 7

6. Rostrum exceeding scaphocerite by at least quarter of its length; proximal 2 dorsal teeth fully articulated; 5–7 ventral teeth.................... Palaemon debilis

— Rostrum exceeding scaphocerite by less than quarter of its length; no fully articulated dorsal teeth; 3–4 ventral teeth............................ Palaemon cf. debilis

7. Pereopod 2 stout but short, 0.4–0.5 times body length.............................. Palaemon litoreus

— Pereopod 2 stout but long, 0.7–0.9 times body length..8

8. Rostrum with 9–15 dorsal teeth (usually 10–12), all incompletely articulated; teeth directed upwards; only one sixth of the antennule inner flagellum fused (4–6 articles)........................ Palaemon macrodactlyus

— Rostrum with 6–9 dorsal teeth, proximal 3 incompletely articulated; about one third of antennule inner flagellum fused (about 12 articles in adults).... Palaemon serenus

In fresh material, pigmentation pattern can help separate species in this alternative key. The colour description for Palaemon litoreus was taken from a description by McNeill in Holthuis (1952) and those for Palaemonetes australis and P. atrinubes from Bray (1976).

1. Without dorsal hump on abdominal somite 3........ 2

— Distinct dorsal hump on abdominal somite 3........ 4

2. Long, slender rostrum, substantially exceeding scaphocerite.......................... Palaemon debilis

— Rostrum at most just exceeding scaphocerite........ 3

3. Distinct black spot at posterolateral end of sixth abdominal somite; 3 distinct red and blue lines on carapace; 1 transverse line across posterior edge of third abdominal somite.......................... Palaemonetes atrinubes

— Without black spot at base of sixth abdominal somite............................... Palaemon cf. debilis

4. Broad, red band across most of palm of pereopod 2; fingers white; abdomen with longitudinal rows of few large spots of red, blue and black chromatophores; distinct longitudinal stripes on carapace............ Palaemon serenus

— Without wide red band or only a narrow one across palm of pereopod 2; if narrow red band present, abdomen with saddle stripes of red on dorsal and lateral surfaces.................................... 5

5. Grey or olive-green; distinct wide, grey band across palm of pereopod 2; diffuse longitudinal and oblique rows on carapace; diffuse transverse lines on posterior edges of abdominal articles.......... Palaemon macrodactylus

— Without wide grey or olive-green band on palm of pereopod 2.................................. 6

6. Saddle stripes of red across back and sides of whole body; less distinct on carapace; palm of pereopod 2 with narrow red band; fingers with similar band half way along................................... Palaemon litoreus

— Without longitudinal stripes on abdomen........... 7

7. Distinct red lines either obliquely on carapace or transversely on abdomen........................... 8

— Overall olive-green or brown due to red, white, yellow and blue chromatophores; carapace with diffuse dorsal and anterior bands and indistinct mottling posteriorly; antennule inner flagellum pale red............................................ Palaemonetes australis

8. Distinct transverse red and/or occasionally olive stripes across all abdominal somites; less distinct longitudinal and oblique red stripes on carapace ( Fig. 2a, b ); antennule inner flagellum pink with few white flecks; often row of white chromatophores along lateral carina of the rostrum...................... Palaemon dolospina

— Distinct oblique and transverse red lines on carapace; few scattered red, olive and black chromatophores forming indistinct transverse lines on abdominal segments ( Fig. 2c ); antennule inner flagellum with definite red and white bars, persisting as purple bars in ethanol-preserved specimens.................. Palaemon intermedius

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 6. Palaemon dolospina. a, rostrum (female, 31.8 mm); b, rostrum (male, 32.8 mm); c, carapace spine (female, 31.8 mm); d, e, antennule and scaphocerite (female, 31.8 mm); f, scaphocerite (male, 31.8 mm); g, mandible; h, maxillule; i, maxilla; j–l, maxillipeds 1–3 (all mouthparts, female, 31.8 mm).

Figure 7. Palaemon dolospina. a–f, pereopods 1–5; b details of chela of pereopod 1 (male, 32.8 mm). g, h, pleopods 1, 2 (male); i, j, pleopods 1, 2 (female). k, telson. l, appendix masculina.