Palaemon maculatus ( Thallwitz 1892 )

Ashelby, Christopher W. & Grave, Sammy De, 2009, A new species of Palaemon (Crustacea, Decapoda, Palaemonidae) from West Africa, with a re-description of Palaemon maculatus (Thallwitz, 1892), Zootaxa 2085, pp. 27-44 : 28-33

Palaemon maculatus ( Thallwitz 1892)

Figures 1–2

Leander maculatus— Thallwitz 1892: 19 –20, 49, Fig. 4 .— Rankin 1898: 246.— De Man 1923: 3.— Kemp 1925: 290.— De Man 1925: 36 –38, Figs. 8 a–d.— Barnard 1950: 782 –783.— Dartevelle 1950: 33.

Palaemon edwardsii (nec Palaemon Edwardsii Heller 1863 ).— Rathbun 1900: 314.

Leander edwardsii (nec Palaemon Edwardsii Heller 1863 ).— Johnston 1906: 862.— Balss 1916: 26 –27.

Palaemon (Leander) Edwardsii (nec Palaemon Edwardsii Heller 1863 ).— Lenz 1910: 126

Palaemon maculatus .— Rathbun 1900: 314 –315.— Schmitt 1926: 25 –27, Fig. 65.— Holthuis 1951: 140 –142.— Holthuis 1952: 56 –57.— Dartevelle 1951: 1021.— Ribeiro 1970: 9, 12, 59.— Powell 1983: 274, fig. 16. – Powell 1985: 235.— Jayachandran 2001: 213.

Palaemon (Palaeander) maculatus .— Holthuis 1950: 8, 55.—Monod 1954: 111, 114, 127–128, 136.— Kensley 1972: 44, Fig. 19o.— Lefevere 1970: 2.

? Leander adspersus .— Sharp 1893: 119.

Material examined. 2 ɗɗ, pocl. 4.8, 5.0 mm; 10 ovigerous ΨΨ, pocl. 5.0 – 6.8 mm; 4 ΨΨ, pocl. 5.5 – 7.0 mm; Nigeria, Bonny River, Hughes Channel, right bank; 04º37’00’’N 07º07’25’’E; 31.05.1980; leg. C.B. Powell; USNM 181904.

Description. A small sized Palaemon species.

Carapace glabrous. Rostrum ( Figure 1 A) slender, straight or nearly so, without strong posterior ventral curve; approximately 1.2 times pocl., overreaching scaphocerite by at least 0.2 (occasionally up to 0.33) times length; armed with 7–8 dorsal teeth and 3–4 ventral teeth; proximal four dorsal teeth with weakly constricted bases, posterior most tooth situated behind orbit, about 1.5 times more distant than gaps between the other teeth, second tooth situated above or slightly behind margin of orbit; distal portion (approximately one third) unarmed but with bifid tip; double row of setae present in ventral unarmed portion, single row of setae present between the teeth. Antennal and branchiostegal teeth present, marginal. Branchiostegal groove originating dorsal to branchiostegal tooth, trending downwards and finishing just in front of half carapace length, slightly lower than at its origin. Sub-orbital lobe ( Figure 1 B) subquadrate to rounded, pterygostomial angle rounded. Bec ocellaire ( Figure 1 B) with strongly convex anterior margin, pronounced beak, almost pointing directly upwards, dorsal surface with strong concavity.

Eye ( Figure 1 A) well developed, with pigmented cornea; cornea slightly wider and longer than stalk; ocellus present on dorsomesial side.

Antennular peduncle ( Figure 1 F) extending to level of base of tooth of scaphocerite; basal segment 2.25 times as long as wide, slightly convex outer margin, stylocerite acute; antero-distal tooth falling short of laminar portion; inner ventro-mesial tooth present; statocyst with statolith; ultimate segment 2 times as long as penultimate, their combined length being slightly less than 0.75 times that of basal segment.

Dorsal flagellum of antennula fused for just under half its length (approximately 11–13 segments fused, 13–23 free); free portion with two aesthetascs on each segment.

Scaphocerite slender, laminar, 3.5 times as long as broad; outer margin straight terminating in tooth, falling short of distal margin of lamina; basal segment of antenna with large mesial tooth; antenna articulated to lateral margin of this segment. Flagellum of antenna about twice length of body.

Abdominal pleurae furnished with plumose setae on ventral margin ( Figure 1 C); fifth pleuron posterodistal angle with distoventral tooth; sixth segment approximately 1.8 times length of fifth; lateral margin ( Figure 1 D) with small tooth and notch disto-ventrally; median lobe acute, with ventral submedian process.

Thoracic sternal armature sexually dimorphic. Fourth thoracic sternite in females armed with sharp tooth and incomplete posterior ridge, remainder with low transverse ridge; in ovigerous and post-ovigerous females eighth sternite with flattened setose plate. Fourth thoracic sternite in males with two lateral bosses.

Abdominal sternal armature sexually dimorphic. Females with blunt process on fourth abdominal sternite and acute longitudinal ridge on fifth; in males first abdominal sternite with small conical tooth, low transverse ridges present on second to fourth abdominal sternites; longitudinal ridge on fifth. Pre-anal carina unarmed in both sexes.

Mandible ( Figure 1 G) with three segmented palp in current material (but see remarks); terminal segment about 1.5 times as long as penultimate segment; penultimate and proximal segment approximately equal in length; terminal segment with 3 apical, simple setae and 4 lateral setae; penultimate segment bearing three distolateral setae. Incisor process of mandible with 3 teeth on right mandible, the middle of which is the smallest, and 4 teeth on left mandible, the middle 2 being smaller than the outer ones; molar process with 6 teeth of varying sizes. Paragnaths covering about half the mandibles; alae formed by broad, transverse more or less oval, distal lobes, ventromesial lobes triangular. Corpus short, narrowly separated; base with two posteriorly diverging carinae. Epistome triangular with rounded anterior angle and strong anteromedial carina. Labrum broadly rectangular, flanked by triangular lobes on each side. Maxillula with lower lacinia near oval, smaller and narrower than upper lacinia; upper lacinia provided with several distal cuspidate and stout setae; bearing a number of plumose setae on its upper margin; palp with bifid tip; upper process naked, lower process broad with two median setiform processes and small unfurnished ventral tubercle. Maxilla with upper lacinia deeply cleft, ending in a number of stout setae, a number of simple setae on its upper margin; palp well developed, broad and naked, except for a few plumose setae proximally on its outer margin; scaphognathite large, fringed with plumose setae; the lower lobe is broader than the upper. First maxilliped with endites separated by distinct notch; palp slender and slightly twisted; exopod well developed, slender and furnished with plumose setae distally; caridean lobe well developed and broad; epipod large and bilobed. Second maxilliped with slender rectangular ultimate segment; penultimate segment broadly triangular, with convex, semicircular upper margin; exopod well developed; well developed podobranch present. Third maxilliped pediform; ultimate segment 0.7 times length of penultimate; antepenultimate and preceding segment fused, with strongly curved dorsal margin; single, subdistal spine; exopod reaching to about 0.75 of length of antepenultimate segment; epipodal plate cupped, slightly prolonged anteriorly into a weak point; well developed arthrobranch and reduced pleurobranch present.

Well developed pleurobranchiae present on all thoracic legs. First pereiopod ( Figure 2 A) overreaching scaphocerite by length of fingers; basis approximately 0.5 length of ischium; merus 1.5 length of ischium; carpus 1.3 times longer than merus; chela slightly less than 0.5 length of carpus, fingers slightly longer than palm, with tufts of setae; carpal-propodal brush well developed. Second pereiopod ( Figure 2 B) extending beyond scaphocerite by full length of chela and just over 0.5 length of carpus; ischium 4.5 times length of basis; merus equal in length to ischium; carpus elongate, 1.5 length of merus; chela ( Figure 2 C) about 0.7 times length of carpus, approximately equal in length to the merus, fingers approximately 0.3 length of palm and covered in stout setae, poorly developed dentition proximally between fingers. Ambulatory pereiopods increase in length, pereiopod 3 being shortest. Third pereiopod ( Figure 2 D) overreaching scaphocerite by 0.5 length of dactylus; ischium twice length of basis; merus 2.8 times length of ischium; carpus 0.5 length of merus; propodus 1.7 times length of carpus, slightly shorter than merus, ventral margin armed with 4–5 pairs of cuspidate setae; dactylus ( Figure 2 E) simple, about one third length of the propodus. Fourth pereiopod ( Figure 2 F) overreaching scaphocerite by 0.2 of propodus; ischium slightly more than 2.5 times length of basis; merus 2.4 times length of ischium; carpus 0.5 length of merus; propodus 2 times length of carpus and approximately equal to merus, ventral margin provided with 5 pairs of cuspidate setae; dactylus 0.25–0.2 length of propodus. Fifth pereiopod ( Figure 2 G) extending beyond distal margin of scaphocerite by 0.4 of propodus; ischium 2 times length of basis; merus 2.7 times length of ischium; carpus approximately 0.5 length of merus; propodus 2 times length of carpus and slightly longer than merus, ventral margin armed with 5 pairs of unevenly spaced cuspidate setae, grooming brush comprises 11 rows of serrulate setae and extends for about 0.3 length of propodus; dactylus 0.2–0.25 length of propodus.

First pleopod sexually dimorphic in proportions, lacking appendix interna in both sexes; in males ( Figure 1 H) endopod is 0.5 length of exopod, both exo- and endopods fringed with plumose setae but mesial portion of the inner margin of endopod devoid of plumose setae, with 6 spiniform setae; in females, endopod approximately 0.2 length of the exopod. Second to fifth pleopods broadly similar with the endopod being slightly shorter than the exopod, bearing an appendix interna. Second pleopod of males with appendix masculina; about 1.5 times length of appendix interna ( Figure 1 I and J), furnished with 7 lateral and 2 apical setae; lateral setae with minute setules, apical setae smooth.

Telson subequal in length to sixth pleonite; length:width ratio 4:1 proximally narrowing to 12.5:1 distally; dorsal surface with two pairs of cuspidate setae and 1 pair of simple setae subdistally on median process; proximal dorsal tuft of setae absent; proximal pair of cuspidate setae situated at about 0.4–0.5 of telson length, distal pair at about 0.7 length; marginal setae present along the full length; posterior margin ( Figure 1 E) prolonged into acute process, with 1 pair of plumose setae and 2 pairs of stout setae, inner pair about 4 times longer than outer pair; median process exceeding outer pair of stout setae.

Uropods broadly ovate, overreaching telson by 0.2 times length of endopod; exopod slightly longer than endopod, weak diaresis present; mobile lateral spine of exopod overreaching fixed tooth by length of tip.

Eggs numerous; 0.5x 0.4 mm.

Colour Pattern. “Transparent shrimp lacking conspicuous pigment lines on carapace or abdomen (very faint lies may be present). Small but conspicuous black-and-white pigment body in end of last abdominal segment. Eggs dull green. Pleura of ovigerous female with thin white ventral border” ( Powell 1983).

Distribution and habitat. Known from Senegal ( Holthuis 1980), Liberia ( Rathbun 1900; Johnston 1906; Holthuis 1952), Nigeria ( Balss 1916), Gabon ( Thallwitz 1892), Kabinda ( Lenz 1910), Congo ( De Man 1923, 1925; Schmitt 1926) and Southern Angola ( Balss 1916). In fully marine and brackish water above about 10ppt, especially along quiet muddy shores ( Powell 1983).

Remarks. Palaemon maculatus is a highly distinctive species and not easily confused with any other of the genus found in the eastern Atlantic. The combination of the elongate carpus and palm of the chela of the second pereiopod, the shape of the rostrum and the extent along the propodus and number of rows of setae of the grooming brush of the fifth pereiopod allow for easy separation from other species found in the eastern Atlantic. Previous authors ( De Man 1925; Schmitt 1926) have suggested that P. maculatus may be close to P. longirostris H. Milne-Edwards 1837 and Rankin (1898) suggested a possible affinity with the western Atlantic P. northropi ( Rankin 1898) . Palaemon longirostris differs in the shape of its rostrum and the number of rows of setae in the grooming brush of pereiopod 5 (4 rows versus 11 in P. maculatus ). Palaemon northropi has a strong pre-anal spine but also differs in the form of the rostrum. Palaemon maculatus may co-occur with P. powelli sp. nov.; differences between these two species are dealt with below (see remarks under P. powelli sp. nov.). Palaemon elegans has also been reported from the same geographic range as P. maculatus but may be distinguished by possessing a quadrate posterodistal angle of the fifth pleuron (versus small acute tooth in P. maculatus ) and by having fewer rows of setae in its grooming brush on the propodus of pereiopod 5 (4 rows in P. elegans ).

This species was included in the subgenus Palaeander by Holthuis (1950). The subgenus is defined solely by the number of segments of the mandible palp (2 in Palaeander , 3 in Palaemon s.s) and is usually disregarded in taxonomic literature, following a number of studies that demonstrate infra-specific variability in this character in some species ( Fujino and Miyake 1968; Chace 1972; Tirmizi and Kazmi 1984). On the basis of the current material it appears that the mandible palp is usually three segmented concurring with the report of Schmitt (1926; also cited by Barnard 1950). However, it is worthy of note that, one ovigerous female (pocl. 6.4 mm) examined here entirely lacks a mandible palp on the left hand side; on the right hand side a palp is present and three segmented. There is no evidence to suggest loss through damage so it is assumed that its absence is genuine. Based on Holthuis’s (1950) observations, it would appear that the number of segments on the mandible palp may be variable in P. m a c u l a t u s and cannot therefore reliably be used for species separation; however, a greater amount of material would need to be examined before the full extent of variability of this feature in P. maculatus can be described.

Schmitt (1926) comments on some variation between his material and that of other authors and some discrepancy is noted between his statements and the material examined here, notably in the proportions of the segments of the second pereiopod and the range of rostral tooth counts. Schmitt states that ‘the fingers of the second pair of legs are about two thirds the length of the palm’ whereas in the present material the fingers are one third, occasionally slightly longer but never more than half, the length of the palm. De Man (1925) also figures a specimen in which the fingers are one third the length of the palm. Curiously, in the figure provided by Schmitt, which is based on that of Balss (1916), the fingers are clearly about one-third the length of the palm, contradicting his description. In the present material the dactyli of the fourth and fifth pereiopods are 0.2–0.25 the length of the propodus, whereas Schmitt (1926) states they are one third and Thallwitz (1892) stated one half. The range of rostral teeth in the present specimens is 7–8(+1)/3–4. In material from the Congo, Schmitt (1926) reports that the range was 7–10/2–5, further stating that the extremes of these ranges are exceptional; it is assumed that Schmitt’s counts included the subapical tooth but this cannot be said with certainty. Barnard’s (1950) statement that the shorter ramus of the antennular flagellum is much shorter than the free part is based on Balss (1916, Fig. 8 ). This is in agreement with Kemp (1925) but contradictory to De Man (1925) and Holthuis (1951), who found the fused and free parts to be equal, the original description of Thallwitz (1892) where the fused portion was described as longer than the free, and the present study, where it is fused for slightly less than half. The number of cuspidate setae on the ventral margin of the propodus of the ambulatory pereiopods has not been mentioned by previous authors, except for Holthuis (1951) who simply stated ‘a few spinules’. The number appears to be slightly variable in this species in contrast to other members of the genus where the number seems to be fixed (pers. obs.). Occasionally these cuspidate setae were found to be lacking entirely.

Holthuis (1951) mentioned that a specimen reported as “ Leander adspersus ” from Liberia reported by Sharp (1893) may have been P. maculatus but as no description is given this cannot be stated with certainty. To our knowledge Palaemon adspersus has not been recorded as far south as Liberia.

The publication date of the original description of P. maculatus has variously been given as 1891 and 1892. On enquiry, the current editors of Arthropod Systematics and Phylogeny (previously Abhandlungen und Berichte des Königlichen Zoologischen und Anthropologisch-Ethnographischen Museums zu Dresden) confirmed that the actual date of publication was 1892.

Figures

FIGURE 1. Palaemon maculatus (Thallwitz). Bonny River, Nigeria. USNM 181904. A. Frontal region, lateral. B. Same, eye removed. C. Abdomen, lateral view. D. Sixth pleonite, lateral view. E. Telson, distal part. F. Antennule. G. mandible. H. First pleopod, male. I. Second pleopod, male. J. Appendices masculina and interna. A – G ovigerous female, pocl 6.8; H – J male, pocl 4.8. Scale bars indicate 2 mm (A, C), 1 mm (B, D, F, H, I), 0.5 mm (J), 0.35 mm (E) or 0.25 mm (G).

FIGURE 2. Palaemon maculatus (Thallwitz). Bonny River, Nigeria, ov. female (pocl 6.8). USNM 181904. A. First pereiopod. B. Second pereiopod. C. Same, chela. D. Third pereiopod. E. Same, dactylus. F. Fourth pereiopod. G. Fifth pereiopod. Scale bars indicate 1 mm (B, D, F – G), 0.7 mm (A), 0.5 mm (C) or 0.35 mm (E).

FIGURE 4. Palaemon powelli sp. nov., paratype NHM 1980.325 c. A. Mandible. B. Third maxilliped. C. Antennular peduncle, mesial view. D. Antennular flagella, proximal part. E. Telson. F. Same, distal part. Scale bar indicates 1 mm (B-E), 0.8 mm (A) or 0.5 mm (F).

FIGURE 8. Palaemon powelli sp. nov., rostral variation NHM 1980.325 d. A. Ov. female, pocl 4.6. B. Ov. female, pocl 5.0. C. Ov. female, pocl 4.6. D. Female, pocl 3.0. E. Female, pocl 3.4. F. Female (pocl 3.5). Scale bar indicates 1 mm.