Liocarcinus depurator (Linnaeus, 1758)

Guerao, Guillermo & Abelló, Pere, 2011, Early juvenile development of Mediterranean Liocarcinus depurator (Crustacea: Decapoda: Brachyura: Portunidae), Journal of Natural History 45 (35 - 36), pp. 2171-2189 : 2173-2183

Liocarcinus depurator (Linnaeus, 1758)

( Figures 1–7 )

First crab

Lebour, 1928: plate VI, figure 1; Ingle and Rice, 1984: figures 1d,e,3c,4c.

Carapace ( Figures 1A , 2A ). Slightly broader than long; frontal region less than half carapace width (see Table 1), medial and submedial lobes broad; orbital dorsal margin broad, forming a more or less even curve, not strongly angular; lower orbital margin slightly angular, without incision; the anterolateral margins are developed into five teeth: first broad and obtuse, second represented as a small obtuse lobe, third large, stout and acute, fourth small and acute, fifth large and acute.

Antennule ( Figure 2F ). Endopod two-segmented with three setae in basal segment and five subterminal and three terminal setae in distal segment; exopod seven-segmented, with 0, 10–12, 11, 8–10, 5, 0 and 0 aesthetascs, respectively, and 0, 0, 0, 2, 0, 4 and 2 setae.

Antenna ( Figure 2H ). Peduncle thee-segmented, with 13–16, 9, 3 setae; flagellum eight- or nine-segmented (segments 2 and 3 not completely differentiated), with 0, 3, 4, 0, 2, 5, 1, 4 and 4 setae.

Mandible ( Figure 3A ). Palp two-segmented, with about 25 plumose setae on distal segment.

Maxillule ( Figure 3B ). Coxal endite with more than 20 setae; basal endite more than 30 setae (25–26 setae plus 3–5 setae on its inner lateral margin); endopod unsegmented with 9–11 setae.

Maxilla ( Figure 3C ). Coxal endite bilobed, with 10+8 setae; basal endite bilobed, with 13+15–16 setae; endopod unsegmented, with two setae on its inner margin and six plumose setae on its outer lateral margin; exopod (scaphognathite) with about 100 marginal plumose setae and numerous minute lateral setae.

First maxilliped ( Figure 4A ). Epipod with more than 25 long setae; coxal endite with about 16–19 setae; basal endite with more than 35 setae; endopod unsegmented, without mesial lobe (“portunid lobe”) and with more than 10 setae; exopod twosegmented, proximal segment with about 20 setae (eight or nine distal plumose setae); distal segment incipiently flagellated, with six annulations, each annulation bearing a pair of plumose setae.

Notes: CL, carapace length; CW, carapace width; FL, frontal length; Gp, genital porus; L, length; P, pereiopod; s, number of segments; W, width.

Second maxilliped ( Figure 4E ). Epipod with 10 long setae (not figured); endopod foursegmented, with 30, 8, 19 and 16 setae; exopod two-segmented, proximal segment with about 35–40 setae, distal segment incipiently flagellated, with six annulations, each annulation bearing a pair of plumose setae.

Third maxilliped ( Figure 5A ). Epipod with 20 long setae (not figured); endopod fivesegmented, with about 43, 30, 15, 14 and 11 setae; ischium inner margin without teeth (crista dentata); exopod two-segmented, proximal segment with about 25 setae and a triangular structure in inner margin, distal segment incipiently flagellated, with six annulations, each annulation bearing a pair of plumose setae.

Pereiopods ( Figure 6 ). Chelipeds with no ornamentation in palm, similar to those of later juveniles and adults; with heterochely (right-handedness) in all first crabs examined (n = 15): mobile finger (dactylus) of right chela with basal molariform tooth; pereiopods 2–4 resembling the adult form, with dactylus stout, terminally curved and as long as merus; pereiopod 5 differ in shape from that of the adult, the L/W ratio of segments is greater in first crab, especially that of dactylus ( Table 1).

Pleon ( Figure 7A ). Six somites and telson present, broader than long; dorsoventrally flattened, flexed underneath the thorax, and covered with many setae; there is no apparent sex-related dimorphism in the relative dimensions of the crabs examined; pleopods reduced to minute buds, without setae.

Morphological changes during post-larval ontogeny (crab stages C2–C5)

Carapace ( Figure 1B–E ). Carapace measurements for each stage are given in Table 1. The ratio CL/CW (0.90–0.77) showed a slight decrease with increasing crab stage. The ratio FL/CW also showed a slight decrease, particularly evident from stage C4 ( Table 1, Figure 8 ). The definitive adult morphology of carapace antero-lateral teeth is not apparent until stage C4 ( Figure 1 ); the second tooth is more conspicuous in C2–C4, and in C5 it is already a well-developed acute tooth; the fourth tooth increases in size along the development from C1 to C5, in which this tooth has a similar size to the other antero-lateral teeth (more similar to the adult condition). The orbital dorsal margin of the carapace is more angular in C2 than in C1, and shows a notch from C3 ( Figure 1 ). The lower orbital ventral margin shows a shallow notch in C2 and develops to a deep incision from C3 to C5 ( Figure 2A–E ).

Antennule and antenna ( Figure 2G ). The number of segments of the antennule exopod and the antennal flagellum increases in successive stages ( Figure 2F–H , Table 1).

Maxillipeds ( Figures 4 B-D and 5B–D). The ovate mesial lobe (“portunid lobe”) was present on the first maxilliped endopod only from stage C3 and is already well developed in C5 ( Figure 4C,D ). The size of the outer part of the third maxilliped merus increases progressively with respect to the propodus from C2, and expands adopting in C5 a similar morphology to that of the adult crab ( Figure 5B–D ).

Pereiopods. The pereiopods increase in size from C2 to C5. The dactylus of pereiopod 5 changes in shape; the length/width ratios decrease gradually in successive stages ( Table 1).

Sexual dimorphism. Based on pleopod morphology, sexual differentiation becomes recognizable from stage C2. After moulting to C2, females retain the four pairs of appendages (located on pleonites 2–5), which become biramous, with exopod longer than the endopod and without setae ( Figure 7D–G ), whereas they are reduced to two pairs of uniramous buds in males, located on the first and second pleonites ( Figure 7H–L ). Pleopods of the males increase in length in the successive crab stages; in C4 and C5 the male pleopod 1 has apical spinule and six or seven basal setae ( Figures 7J–L ). Pleonites 3–5 are fused in males from C2 ( Figure 7B,C ).

Figures

Figure 1. Liocarcinus depurator (Linnaeus, 1758). Carapace, dorsal view: (A–E), first to fifth crabs (C1–C5), respectively. Scale bar 10 mm.

Figure 2. Liocarcinus depurator (Linnaeus, 1758). Carapace, ventral view of orbital ventral margin: (A–E), first to fifth crabs (C1–C5), respectively. Antennule: (F) first crab; (G) second crab. Antenna: (H) first crab. Scale bars: A–E = 10 mm; F,G = 0.3 mm; H = 0.2 mm.

Figure 3. Liocarcinus depurator (Linnaeus, 1758). First crab: (A) mandibular palp; (B) maxillule; (C) maxilla. Scale bars: A = 0.1 mm; B,C = 0.2 mm.

Figure 4. Liocarcinus depurator (Linnaeus, 1758). First maxilliped. (A) first crab; (B) second crab, endopod; (C) third crab, endopod; (D) fifth crab, endopod. Second maxilliped. (E) first crab. Scale bars: 0.3 mm.

Figure 5. Liocarcinus depurator (Linnaeus, 1758). Third maxilliped: (A) first crab; (B) second crab, merus and carpus; (C) third crab, merus and carpus; (D) fifth crab, merus and carpus. Scale bar: 0.3 mm.

Figure 6. Liocarcinus depurator (Linnaeus, 1758). First crab: (A) left cheliped; (B) right cheliped; (C) pereiopod 4; (D) pereiopod 5. Measures (length and weight) in Table 1 indicated in pereiopod 5. Scale bar: 0.3 mm.

Figure 7. Liocarcinus depurator (Linnaeus, 1758). Pleon: (A) first crab; (B) second crab, male; (C) second crab, female. Pleopods 1–4: (D–G) second crab, female. Pleopods 1 and 2: (H–K) second to fifth crab; (L) fifth crab, magnification of the tip of first pleopod. Scale bars 0.5 mm. Pl, pleopod.

Figure 8. Liocarcinus depurator (Linnaeus, 1758). (A) CL/CW ratio in juveniles 1–5 and adults (21–30 mm CL); (B) FL/CW ratio in juveniles 1–5 and adults (21–30 mm CL).