Aegla paulensis, Schmitt, 1942

Moraes, Juliana Cristina Bertacini De & Bueno, Sérgio Luiz De Siqueira, 2013, Description of the newly-hatched juvenile of Aegla paulensis (Decapoda, Anomura, Aeglidae), Zootaxa 3635 (5), pp. 501-519 : 502-511

Post-embryonic development in Aegla paulensis is epimorphic.

Hatching is asynchronous taking approximately 3–5 days for all juveniles from a single brood to hatch. Newly-hatched juveniles initially remain under protection in the brood chamber formed by the flexed pleon of the female. Duration of maternal care has not been determined. Upon hatching juveniles are able to move with the 2 nd, 3 rd and 4 th pairs of functional pereopods and typically exhibit escaping reaction behaviour by flapping the pleon while keeping the tail fan spread when disturbed.

Carapace ( Figs 1 , 2 , 3 , 12d ): subcylindrical, slightly longer (mean: 1.47 mm; range: 1.39–1.56 mm) than wide (mean: 1.30 mm; range: 1.20–1.39 mm) ( Tab. 1 ). Surface of the branchial areas (anterior, interior and posterior) distinctly rougher than the surface of the anterior region of carapace and of the cardiac area. Rostrum triangular with carina along its length, except on distal third ( Fig. 3b ). Anterolateral spines acute and almost reaching base of cornea. Orbital spines rudimentary coalesced with anterolateral spines and defining a minute extraorbital sinus on each side ( Fig. 3a ). Orbital sinus well-developed, wide, U-shaped. Epigastric prominences distinct. Protogastric lobes conspicuous and granulate. Hepatic lobes and epibranchial tooth rudimentary. Cervical groove distinct, defining large elevated gastric area. Areola large and trapezoidal. Posterior margin of the cervical groove and the anterior margin of cardiac area merged to form a deep transverse groove. The following dorsal grooves are discernible: linea aeglica dorsalis (lad), linea aeglica lateralis (lal), branchial linea (brl) and dorsal longitudinal linea (dll); the latter visible as a subtle line running obliquely and parallel to each side of the areola. Transverse dorsal linea (tdl) not discernible. Laterally, the following grooves are recognized: linea aeglica (la), l inea aeglica ventralis (lav) and linea aeglica posterioris (lap). Pores scattered over general surface, mainly in the rostral area ( Fig. 12d ).

Sternum ( Fig. 9a ): Third through eighth sternites visible only. Coxo-sternal depression distinct. Articulation between posterolateral borders of sternites and concave pit in coxa of corresponding pereopod well-developed.

Pleon ( Figs 7a , 9b–c ): 6-segmented, second segment largest. Width of third to sixth somites decreasing progressively towards posterior end. Simple setae distributed dorsally on all somites.

Telson ( Figs 7b , 9d ): laminar, subtriangular, with longitudinal groove rudimentary (not visible under light microscopy), with 15–21 simple setae and 0 or 2 pappose seta distributed on dorsal surface, 8 or 9 long plumose setae along distal border.

Eye ( Figs 3a , 4a ): well-developed with 6–9 simple setae dorsally on the peduncle.

Antennule ( Fig. 4b ): Uniramous. Basal segment globose, with 2–4 simple setae, group of 14–18 pappose (12 of them forming a fringe) and 0–3 papposerrate setae. Peduncle: proximal segment with 3 simple setae; distal segment with 1–3 simple setae mesially and 3 pappose (distal half) setae near dorsal and ventral flagella, respectively. Dorsal flagellum three-articulated: proximal article bare; mesial article with 3 simple setae and 1 aesthetasc distally; and distal article with 2–4 simple setae and 2 aesthetascs distally. Ventral flagellum with 1 or 2 mesial, 2 or 3 subapical and 1 or 2 apical simple setae. One pore sensillum with crescent-shaped opening (type 1) subdistally on the ventral flagellum and another one near the distal border of the mesial article of the dorsal flagellum ( Fig. 8a–b ).

Antenna ( Fig. 4c ): Uniramous. Peduncle 5-segmented. First segment with 1 simple seta; second and third segments with 4 or 5 simple setae; fourth segment with 2 or 3 simple setae and fifth segment with 5 or 6 simple setae. Flagellum long, multi-articulated, with 16 or 17 articles; proximal article shortest and devoid of setae; remaining articles with variable number of simple setae (maximum of 6) on distal margin except for apical article with up to 9 simple setae on distal third. Three distinct types of pore sensilla observed in several articles of flagellum: type 1, larger, with crescent-shaped opening and resembling pore sensillum observed in the antennula; type 2, smaller than type 1, with free opening; and type 3, smaller than type 1, with opening ornamented with a tubule-shaped structure ( Fig. 12 ). When present, number of type 1 pore sensillum limited to 1 per article and always located on distal third and near a simple seta; few type 2 and 3 pore sensilla (average number not determined) may be found scattered on general surface of articles. Pore of type 2 and 3 may or may not occur together in single flagellar article.

Mandible ( Figs 4d , 8c , 11f ): Uniramous. Molar process rudimentary. Incisor process well-developed, bearing sclerotized teeth along free margin (asymmetrically arranged between left and right side), with mesial tooth as most strongly produced. Mandibular palp (endopod) 2-segmented: proximal segment with 2 serrate setae near proximal margin and 1 or 2 serrate setae subdistally; distal segment with 12–15 serrulate setae ( Fig. 11f ).

Maxillule ( Fig. 4e ): Uniramous. Protopod with 2–4 pappose setae near articulation with endopod. Coxal endite with 4 or 5 pappose setae, 2 papposerrate setae and 10–12 serrate setae. Basal endite with 5 papposerrate setae, 7 or 8 serrate setae and 10 cuspidate setae. Endopod 1-segmented, with 1 or 2 serrate setae subdistally; mesial and proximal third portions may each exhibit 1 serrate seta.

Maxilla ( Fig. 4f ): Biramous. Coxal endite of protopod bilobed; proximal lobe with 8–10 pappose setae, 7–9 serrate setae and 1 simple seta (bearing terminal pore and small scaly outgrowths subdistally); distal lobe with 2 or 3 pappose setae, 1 or 2 short serrate setae, 2 long serrate setae and 1 or 2 simple setae (bearing terminal pore and small scaly outgrowths subdistally). Basal endite of protopod bilobed: proximal lobe with 0–2 short serrate setae, 0 or 1 papposerrate setae, 2 long serrate setae and 9 or 10 simple setae (bearing terminal pore and small scaly outgrowths subdistally); distal lobe with 1 short serrate setae, 10 long serrate setae and 9 or 10 simple setae (bearing terminal pore and small scaly outgrowths subdistally). Endopod 1-segmented with 1–3 papposerrate setae and 0–2 serrate setae. Exopod (scaphognathite) with 4–6 simple setae on the surface and a fringe of 60–65 plumose setae marginally.

First Maxilliped ( Figs 5a , 8d ): Biramous. Coxal endite with 5 or 6 pappose, 0–3 papposerrate and 4–7 serrate setae. Base with incipient epipod; basal endite with 1–3 pappose, 5–8 papposerrate and 27–29 serrate setae. Endopod 1-segmented with 0–2 papposerrate and 0–2 plumose setae mesially, and 1 plumose setae subdistally. Exopod 1-segmented with 6–8 plumose setae ( Fig. 8d ).

Second Maxilliped ( Figs 5b , 10b ): Biramous. Protopod with 6 or 7 pappose setae. Endopod 5-segmented: basischium with 4–8 pappose setae; merus with 2 serrate setae; carpus with 1 serrate seta and 4 minute simple setae ( Fig. 10b ); propodus with 7–9 serrate setae; dactylus with 2 or 3 simple and 9–11 serrate setae. Exopod 2- segmented: proximal segment with 2 or 3 pappose, 0–2 papposerrate and 1–3 serrate setae; distal segment (“flagellum”) with 1 or 2 short simple setae subapically and 4 long plumose setae apically.

Third Maxilliped ( Figs 5c , 8e ): Biramous. Protopod with 0 or 4 pappose, 0 or 1 papposerrate and 6–11 serrate setae. Endopod 5-segmented: basischium with 24 or 25 serrate setae, crista dentata ( Fig. 8e ) with 7–9 corneous tubercles along the inner margin; 1 corneous tooth subdistally and near outer margin; merus with 8–11 serrate setae; carpus with 17–20 serrate and 5 or 6 minute simple setae; propodus with 25–28 serrate setae and 4–6 minute simple setae; and dactylus with 18–21 serrate setae. Exopod 2-segmented: proximal segment with 3 or 4 simple and 0 or 1 pappose setae; and distal segment (“flagellum”) with 1 or 2 short simple setae subapically and 4 long plumose setae apically.

Cheliped ( Figs 6a , 8f ): Uniramous, 6-segmented, with several simple setae distributed in all segments. Coxa bicondyle. Basischium and merus subrectangular, carpus trapezoidal, propodus subrectangular with projection and dactylus subtriangular. Cutting edge of both fixed (propodus) and movable (dactylus) fingers with row of short robust denticles obliquely and serially arranged. Propodus with corneous tooth on outer distal angle and minute simple setae on basal region. Carpus with 4 corneous teeth on dorsal margin and minute simple setae on basal region.

Second, third and fourth pereopods ( Fig. 6b ): Uniramous, 6-segmented. Coxa bicondyle with several simple setae sparsely distributed and 4 pappose setae. Basischium, merus, carpus and propodus subrectangular with several simple setae sparsely distributed. Dactylus subtriangular, with several simple setae sparsely distributed.

Fifth pereopod ( Figs 6c–d , 8g , 10f ): Uniramous. Reduced in size compared to other pairs of pereopods. Dactylus and fixed finger of propodus forming minute chela ( Fig. 8g ). Protopod with 0–3 simple setae. Ischium with 1 or 2 simple setae; merus with 2 simple setae; carpus with 4 simple setae and 2 minute simple setae; propodus with 20–24 serrate, 3 stout serrate setae and 2 minute simple setae; dactylus with 2 simple setae, 3 or 4 serrate and 3 stout serrate setae ( Fig. 10f ).

Pleopods ( Fig. 9b ): Uniramous and rudimentary; 1-segmented and digitiform. Present on pleonal somites 2 through 5; 1 pair per segment.

Uropods ( Fig. 7b ): Biramous. Protopod with 1 or 2 simple and 2 or 3 plumose setae. Endopod with 4–6 simple setae submarginally and 12–19 plumose setae along free margin. Exopod with 2 or 3 simple setae submarginally and 19–23 plumose setae along free margin. Distalmost group of plumose setae on both endopod and exopod longest.

Figures

FIGURE 1. Newly-hatched juvenile of Aegla paulensis showing measurements taken from the carapace: Carapace Width (CW) and Carapace Length (CL).

FIGURE 2. Dorsal view. Aegla paulensis newly-hatched juvenile. brl = branchial linea; cg = cervical groove; dll = dorsal longitudinal linea; ep = epigastric prominence; lad = linea aeglica dorsalis; lal = linea aeglica lateralis; pl = protogastric lobe; tdl = transverse dorsal linea. (Bar = 200 µm).

FIGURE 3. a) Eye with simple setae. b) Rostrum with carina. c) Carapace antero-lateral view. d) Carapace postero-lateral view. Aegla paulensis newly-hatched juvenile. als = antero-lateral spine; ca = carina; la = linea aeglica; lad = linea aeglica dorsalis; lap = linea aeglica posterioris; lav = linea aeglica ventralis; os = orbital spine. (Bars: a = 50 µm; b, c, d = 100 µm).

FIGURE 4. a) Compound eye. b) Antennule. c) Antenna. d) Mandible. e) Maxillule. f) Maxilla. Aegla paulensis newlyhatched juvenile. (Bars: a, c, f = 0.2 mm; b, d, e = 0.1 mm).

FIGURE 5. a) First maxilliped. b) Second maxilliped. c) Third maxilliped. Aegla paulensis newly-hatched juvenile. (Bars: a = 0.1 mm; b, c = 0.2 mm).

FIGURE 6. a) Cheliped. b) Second pereopod. c) Fifth pereopod. d) Propodus and dactylus of the fifth pereopod. Aegla paulensis newly-hatched juvenile. (Bars: a, b = 0.3 mm; c, d = 0.1 mm).

FIGURE 7. a) Pleon with telson and uropods (bar = 0.3 mm). b) Telson and Uropods (bar = 0.2 mm). Aegla paulensis newlyhatched juvenile.

FIGURE 8. a) Antennule: aesthetascs and pore type 1 (thin arrow) of dorsal flagellum (bar = 20 µm). b) Antennule: simple setae and pore type 1 (thin arrow) of ventral flagellum (bar = 10 µm). c) Mandible (bar = 50 µm). d) First maxilliped with rudimentary incipient epipod (thick arrow) (bar = 50 µm). e) Third maxilliped: basischium with crista dentata and corneous tooth (bar = 20 µm). f) Cheliped distal region (bar = 100 µm). g) Fifth pereopod distal region (bar = 20 µm). Aegla paulensis newly-hatched juvenile.

FIGURE 9. a) Sternum. b) Pleon with rudimentary pleopods (pl). c) Pleon dorsal view. d) Telson with rudimentary longitudinal groove (arrow). Aegla paulensis newly-hatched juvenile. (Bars: a = 200 µm; b, c, d = 100 µm).

FIGURE 10. a) Simple setae of antenna (bar = 5 µm). b) Minute simple setae of third maxilliped endopod propodus (bar = 5 µm). c) Simple seta with terminal pore and scale of maxilla endites (bar = 2 µm). d) Cuspidate setae of maxillule basal endite (bar = 10 µm). e) Plumose setae of uropods (bar = 20 µm). f) Stout serrate setae of fifth pereopod propodus and dactylus (bar = 5 µm). Aegla paulensis newly-hatched juvenile.

FIGURE 11. a) Pappose setae of first maxilliped coxal endite (bar = 20 µm). b) Pappose setae (distal half) of antennule (bar = 10 µm). c) Papposerrate seta of maxillule basal endite (bar = 10 µm). d) Serrate seta of third maxilliped endopod (bar = 10 µm). e) Serrate setae of third maxilliped endopod (bar = 10 µm). f) Serrulate seta of mandible palp (bar = 5 µm). Aegla paulensis newly-hatched juvenile.

FIGURE 12. a) Pore type 1 of antenna. b) Pore type 1 of antenna (lateral view). c) Pore type 2 of antenna. d) Pore type 3 of antenna. Aegla paulensis newly-hatched juvenile. (Bars = 2 µm).