Palinustus mossambicus Barnard, 1926

Palero, Ferran, Guerao, Guillermo & Clark, Paul F., 2008, Palinustus mossambicus Barnard, 1926 (Crustacea: Decapoda: Achelata: Palinuridae); morphology of the puerulus stage, Zootaxa 1857, pp. 44-54 : 46-52

Palinustus mossambicus Barnard, 1926

Figs 1–4

Puerulus stage

The morphological description is based on the puerulus from Zanzibar.

Carapace ( Fig. 1 A, B, C). Rostrum absent; anterior margin of carapace with a pair of spines plus a minute solitary spine, without medium spine; supraorbital horns widely separate and truncate, with a strong spine on the outer margin, anterior margin smooth and unarmed; inner margin of supraorbital horns without spines; anterior margin of epistome with a small spine on anterolateral corners, anterior margin without spines or tubercles; postorbital, antennal and branchiostegal spines present, postorbital more short than antennal and branchiostegal; cervical groove well defined; well-developed stridulating organs present; post-cervical spines as showed.

Sternum ( Fig. 2 B). Sternites 1 and 2 completely fused; lateral margins of sternites 4–5 and sternites 6–8 with one and two processes respectively; with nine minute medial tubercles arranged 2,2,2,2,1. Antennule ( Fig. 1 A). Well developed; proximal segment of peduncle shorter than antennal peduncle; outer flagellum 25-segmented, more robust than the inner (missing distal part). AP1 = 7.0 mm, AP2 = 2.0 mm, AP3 = 4.3 mm.

Antenna ( Fig. 1 A, 2A). Peduncular spines as illustrated; plectrum present on basal segment of the peduncle; flagellum very spinose.

Mandible. Incisor and molar processes undifferentiated, uncalcified and without teeth; palp unsegmented and without setae.

Maxillule ( Fig. 3 A). Poorly developed and sparsely setosed; coxal endite with seven terminal minute spines; basial endite with about 8 terminal minute spines and two minute setae; endopod unsegmented, with three terminal simple setae.

Maxilla ( Fig. 3 B). Three endites present, the distal endite elongated, with four spines and eleven setae, longer than the others, proximal endite with six setae and medial with four setae; endopod unsegmented with two apical simple setae and nine plumose setae on outer margin; scaphognathite (exopod) large and well developed, with about 150 plumose marginal setae.

First maxilliped ( Fig. 3 C). Endites absent, the unsegmented endopod rudimentary and sparsely setosed; exopod large and flagellated, with 22 proximal plumose setae on outer margin, flagellum with about 20 segments, more differentiated distally, each segment with 2 setae (minute proximally; long and plumose distally).

Second maxilliped ( Fig. 3 D). Gill present and well developed; endopod 4-segmented, with 5,0,6,6 setae; exopod long and flagellated, approximately twice the endopod length; flagellum with about 23 segments more differentiated distally; each segment with two setae (minute proximally; long and plumose distally).

Third maxilliped ( Fig. 4 A). Endopod 5-segmented; ischium sparsely setosed with 6 acute spines on inner margin (crista dentata); merus with a few small setae, and an acute distal outer spine; carpus, propodus and dactylus densely setose; exopod large with a flagellum reaching beyond base of carpus; flagellum with about 23 annulations more differentiated distally, each annulation with two setae (minute proximally; long and plumose distally).

Pereiopods ( Fig. 1 A). 1–5 with segmented and well developed endopod; heavily spinulose; merus and carpus of pereiopods 1–5 with a two acute distal marginal spine; pereiopods 1 and 5 are the shortest (16.7 and 16.0 mm, respectively) and pereiopods 2 and 3 are the longest (about 18 mm); pereiopod 5 is thinner and not as spinulate or setosed as the other pereiopods.

Abdomen ( Fig. 1 A, 2A). Transverse groove present in somites 1–4, and slightly marked in somites 5 and 6; tergite of somite 6 with three pairs of spines, posterior margin with two pairs of spines ( Fig. 1 D); pleural plates of the somites 2–6 terminating in two strong spines directed ventrally.

Pleopods ( Fig. 4 ). Somites 2–5 each with one pair of well developed biramous pleopods; protopod with about 13 plumose setae and a few spines on inner margin; endopod unsegmented with about 58 long marginal plumose natatory setae and appendix interna with 7 distal setae on outer margin and about 12 terminal coupling hooks on inner margin; exopod unsegmented with about 60 long marginal plumose natatory setae.

Uropods ( Fig. 1 A). Biramous; with 3–4 spines on inner margin of the calcified part; the posterior margin of the uncalcified part setose.

Telson ( Fig. 1 A). With two pairs of dorsal spines; the lateral margin of the calcified part with two pairs of spines (one medial and one distal) and the inner margin bears three pairs of spines; the posterior margin of the uncalcified part setose.

Table 1. Comparative morphology of the second and third maxillipeds of several palinurid species

Adult Adult Puerulus Puerulus Puerulus Puerulus Source

exopod exopod CL (mm) exopod exopod 3rdmxpd

2nd mxpd 3rd mxpd 2nd mxpd 3rd mxpd crista

flagellated flagellated flagellated flagellated dentata

Panulirus argus + + 6 - - - Wolfe and Felgenhauer, 1991 Panulirus gracilis + - 7.0-8.9 - - - Bÿez, 1983 Panulirus guttatus + - 9.0 - - - Lyons and Hunt, 1997 Panulirus homarus - - 7.9-8.3 - - - Michel, 1971 Three species of Palinustus have been reported from the eastern coast of Africa, namely P. mossambicus Barnard, 1926 , P. w a g u e n s i s Kubo, 1963 and P. unicornutus Berry, 1979 . The morphology of the puerulus specimen described above is different from that of P. unicornutus described by Chan and Yu (1995), since the anterior margin of the carapace between the supraorbital horns bears a pair of sub-median spines, while a single median spine is always present in P. unicornutus ( Holthuis, 1991) . Moreover, the two distal segments of the antennal peduncle are much more spinose than those of P. unicornutus . The comparison with P. waguensis is not so straightforward, given that two specimens of P. waguensis have also been described with the anterior margin of the carapace between the supraorbital horns bearing only a pair of sub-median spines, like in P. mossambicus . Nevertheless, P. mossambicus is still unique in having all comparatively long postorbital, antennal, and branchiostegal spines ( Chan and Yu, 1995), a characteristic observed in the present larval specimen. Moreover, P. mossambicus and the puerulus specimen described in this study further differ from P. waguensis by their epistome being more tuberculate and the lateral margins of the thoracic sternum less serrated. Furthermore, the spines on the abdominal sternites are also in agreement with those found in P. m o s s a - mbicus. All these morphological observations of the puerulus specimen described above suggest that this larval stage can be confidently identifed as Palinustus mossambicus .

Externally the puerulus resembles an adult Palinustus mossambicus in form, though it is somewhat dorsoventrally flattened, and has proportionally large natatory pleopods. These two features are found in all the palinurid pueruli known to date, and are indicative that the puerulus is specialized for swimming pelagic existence ( Phillips and Olsen, 1975). Another important feature of the P. mossambicus puerulus is the presence of the long flagellated exopod in maxillipeds 2 and 3 and the crista dentata (a row of teeth on the ischium of the third maxilliped), which are also present in the puerulus stage of the ancient genera Projasus and Palinurus ( Webber and Booth, 1988; Báez and Ruiz, 2000; Guerao et al., 2006), but not in Jasus or Panulirus (Table 1).

Within Palinurus , the reduction of the second and third maxilliped exopods is considered a derived character ( McWilliam, 1995; Patek and Oakley, 2003). The key characteristics, useful for diagnosis, of the P. m o s s a m - bicus puerulus are the absence of a rostrum, with the presence of two sub-median spines on the anterior margin of carapace, the proximal segment of antennular peduncle being much longer than the other segments and the supraorbital horns being widely separated and truncate.

The fact that most specimens of Palinurus puerulus have been collected from fish stomach contents of species such as Centrolophus niger Gmelin, 1789 and Thunnus alalunga Bonnaterre, 1788 ) (see Fage, 1927) is of interest. Aggregations of skipjack tuna, K. pelamis tend to be associated with convergences, boundaries between cold and warm water masses, upwelling and other hydrographical discontinuities, which are the typical environments were the phyllosoma larvae are found ( Booth and Phillips, 1994). In fact the larval specimen off Somalia was captured in a small pelagic trawl in mid-water at 100 m. Moreover, skipjack tuna exhibit a strong tendency to school in surface waters and its depth distribution ranges from the surface to about 260 m during the day ( Collette and Nauen, 1983). This would indicate that it is not by chance that the stomach contents of skipjack tuna are a source of deep water Palinustus puerulus and therefore are a starting point for collecting such rare deep water larval stages.

Figures

FIGURE 1. Palinustus mossambicus Barnard, 1926. Puerulus. A, dorsal view; B, dorsal view of the rostral region; C, anterior margin of the epistome; D, posterior margin of somite 6. Scale bars A = 5 mm and B – D = 2.5 mm.

FIGURE 2. Palinustus mossambicus Barnard, 1926. Puerulus. A, latteral view; B, sternum. Scale bar = 5 mm.

FIGURE 3. Palinustus mossambicus Barnard, 1926. Puerulus. A, maxillule; B, maxilla; C, first maxilliped; D, second maxilliped. Scale bar = 1 mm.

FIGURE 4. Palinustus mossambicus Barnard, 1926. Puerulus. A, third maxilliped; B, pleopod 4. Scale bar = 1 mm.