Austinograea rodriguezensis Tschuchida & Hashimoto, 2002

Demidow, Olga, Kihara, Terue C., Arbizu, Pedro Martínez & Clark, Paul F., 2021, The megalopal stage of the hydrothermal vent crab Austinograea rodriguezensis Tsuchida & Hashimoto, 2002 (Decapoda: Bythograeidae): a morphological description based on CLSM images, Zootaxa 5040 (3), pp. 365-387 : 370-383

Austinograea rodriguezensis Tschuchida & Hashimoto, 2002

( Figs. 4–15 )

Megalopa

Size: SMF 57020 CW 2.8 mm, CL 3.4 mm; SMF 57021 CW 2.8 mm, CL 3.6 mm.

Carapace ( Fig. 4A–E ): longitudinally rectangular; setation as figured; ventrally directed small, bilobed rostral protrusion; central protrusion between eyes approximately 1/5 to 1/3 distance from frontal margin; anterolateral margin slightly concave with 3 anterolateral teeth, last tooth approximately 2/5 to 1/2 length of carapace from frontal margin; intestinal region slightly depressed.

Antennule ( Figs. 5A ; 7A, B ): peduncle comprising 3 articles with 11,4,4 setae respectively; primary flagellum comprising 4 articles, 1 st unarmed, 2 nd with 6 aesthetascs, 3 rd with 2 simple setae and 7 aesthetascs, 4th with 5 subterminal aesthetascs and 2 (1 subterminal + 1 terminal) long simple setae; accessory flagellum comprising 1 article with 2 subterminal + 3 terminal setae.

Antenna ( Figs. 4A, B ; 6A–C ; 7C ): uniramous; coxa with 2–6 pappose setae; basis with 1–3 pappose setae; endopod with 9 divisions, ischium comprising 1 article with 2–3 pappose setae distally; merus comprising 3 annulations with distal most possessing 4 distal pappose setae; carpus with 2 annulations with distal most possessing 4–5 distal pappose setae (1 long + 1 small simple seta, fused basally); propodus with 2 annulations with distal most possessing 4 distal simple setae; dactylus with 1 article possessing 2–5 terminal simple setae; exopod absent. (SMF

57021, SMF 57022, SMF 57025, SMF 57023, SMF 57024).

lateral view. Scale bars = 0.5 mm.

Mandible ( Figs. 5B ; 8D, E ): uniramous; comprising coxa and basis without setae; endopod with two articles, proximal article with 2 basial pappose setae, distal article with 18 marginal (14 pappose + 4 plumoserrate) setae; exopod absent.

Maxillule ( Figs. 5C, D ; 8A–C ): biramous; 3 simple epipod setae present; coxal endite with ca. 38 (2 serrate + 36 pappose) setae; basial endite with ca. 42 (12 cuspidate + 30 pappose) setae; endopod with 2 articles, proximal article with 2 (1 medial + 1 terminal) plumose setae, distal article with 3 (2 basal plumose + 1 terminal serrate) setae; exopod represented by 1 plumose seta.

Maxilla ( Figs. 5E, F ; 9A–C ): biramous; coxal endite bilobed with ca. 28 (21 plumose + 7 serrate) + 14 plumose setae; basial endite bilobed with 10 + 24 pappose setae; endopod simple, with 8 marginal + 1 subterminal + 1 terminal plumose setae; exopod (scaphognathite), with ca. 103 marginal plumose setae (setae on distal margin ca. 4 times longer than on medial margin) and 7 lateral simple setae.

First maxilliped ( Figs. 10B–E ; 12B ): biramous; epipod with 24 long + 3 short simple setae; coxal endite with ca. 28 (3 serrate + 25 pappose) setae; basial endite with 28 simple/plumose + 22 serrate setae; endopod not articulated, with 5 basal + 10 distal marginal setae; exopod with 2 articles, proximal article with 4 distal plumose setae, distal article with 5 terminal plumose setae.

Second maxilliped ( Figs. 10A ; 12A ): biramous; epipod with 18 simple setae plus small podobranch gill bud; larger arthrobranch gill present, coxa and basis fused; endopod with 5 articles with 7,18,2,10,15 (6 plumose + 9 serrate) setae respectively; exopod with 2 articles, proximal article with 8 short simple setae; second article damaged.

Third maxilliped ( Figs. 11A–F ; 12C ): biramous; epipod with 41 simple setae plus podobranch gill; larger arthrobranch gill present; coxa and basis with some delimitation; coxa with ca. 30 simple/serrate setae; basis with ca. 6 distal papposerrate setae; endopod with 5 articles with 39,21,14,21,11 simple setae respectively, merus, carpus, propodus, dactylus with 1,1,2,6 serrate setae respectively; exopod with 2 articles, proximal article with 6 simple setae, distal article with 5 (1 subterminal + 4 terminal) pappose setae.

Pereiopods ( Fig. 13A–K ): uniramous, setation as figured; chela with podobranch and arthrobranch gill; pereiopods 2 and 3 each with podobranch gill, exopod absent.

Sternal plates ( Fig. 4D ): sternites 1 & 2 fused with demarcation between sternites 2 & 3, slight demarcation between sternites 3 & 4.

Pleon ( Fig. 14A; B ): 6 pleomeres present; pleomere 1 with 11 pairs of setae; pleomere 2 with ca. 15 pairs of dorsal and 13 pairs of dorsal marginal setae; pleomere 3 with ca. 13 pairs of dorsal, ca. 11 pairs of dorsal marginal and 4 dorsal medial setae; pleomere 4 (damaged) with ca. 22 pairs of dorsal setae and ca. 1 dorsal medial seta; pleomere 5 with ca. 14 pairs of dorsal, 6 pairs of dorsal marginal and ca. 4 dorsal medial setae; pleomere 6 with ca. 10 dorsal and 4 dorsal marginal setae; pleomeres 1–6 as figured.

Pleopods ( Figs. 14B–F ; 15A–D ): biramous; pleomere 1 without pleopods; pleomeres 2–5 with 1 pair of pleopods each; coxa and basis fused (=protopod?); endopod not articulated, with 4,6,4,5 cincinulli respectively; exopod not articulated, but distally annulated with 22, 23 (22 distal + 1 proximal), 22, 22 long marginal plumose natatory setae on pleopods 1–4 respectively.

Uropods ( Figs. 14G ; 15F ): uniramous; present on pleomere 6, coxa and basis fused (=protopod?) and with seta on external margin; endopod absent; exopod without articulation comprising 16 long marginal plumose natatory setae. (SMF 57021).

Telson ( Figs. 14G ; 15E, F ): trapezoidal shaped; telson forks absent; 7 pairs of dorsal setae, 2 pairs of ventral setae, 1 dorsal marginal and 1 ventral medial seta. (SMF 57021).

Figures

FIGURE 4. CLSM images of Austinograea rodriguezensis, megalopa. A. habitus dorsal (SMF 57021); B. habitus ventral (SMF 57021); C–E, cephalothorax without left eye, pleon and pereiopods (SMF 57020); C. dorsal view; D. ventral view; E.

FIGURE 5. CLSM images of Austinograea rodriguezensis, megalopa (SMF 57020). A. antennule; B. mandible; C. maxillule without coxal endite; D. maxillule; E. maxilla: coxal and basial endites and endopod; F. maxilla, scaphognathite. Scale bars = 0.1 mm. CLSM images of Austinograea rodriguezensis, megalopa A. antenna (SMF 57021); B. fluorescence-labelled phalloidin antennal musculature (SMF 57022); C. detail of annulation on carpus with phalloidin stained musculature (SMF 57022). Scale bars = 100 µm.

FIGURE 6. CLSM images of Austinograea rodriguezensis, megalopa A. antenna (SMF 57021); B. fluorescence-labelled phalloidin antennal musculature (SMF 57022); C. detail of annulation on carpus with phalloidin stained musculature (SMF 57022). Scale bars = 100 µm.

FIGURE 7. Austinograea rodriguezensis, megalopa. A. antennule with primary and accessory flagellum (SMF 57020); B. antennule, first article of the peduncle (SMF 57020); C. antenna (SMF 570219. Scale bars = 0.1 mm.

FIGURE 8. Austinograea rodriguezensis, megalopa (SMF 57020). A. maxillule, missing coxal endite; B. coxal endite of maxillule; C. same appendage as A, basial endite; D. incisive/molar terminal part of the mandible; E. mandibular palp, composed by 3 articles comprising a proximal basis and a 2-articulated endopod. Scale bars = 0.1 mm.

FIGURE 9. Austinograea rodriguezensis, megalopa (SMF 57020). A. maxilla, scaphognathite; B. same appendage as A, magnification of plumose setae; C. maxilla, coxal endites, basial endites and endopod. Scale bars = 0.1 mm.

FIGURE 10. Austinograea rodriguezensis, megalopa (SMF 57020). A. second maxilliped; B. coxal endite of first maxilliped, same appendage as D; C. basial endite of first maxilliped, same appendage as D; D. first maxilliped; E. same appendage as D, detail of terminal setae on distal article of exopod. Scale bars = 0.1 mm.

FIGURE 11. Austinograea rodriguezensis, megalopa (SMF 57020). A. third maxilliped, exopod; B. third maxilliped, missing epipod and exopod; C. third maxilliped, epipod; D. same appendage as A, detailed dactylus; E. Same appendage as C, enlargement of terminal setae of epipod; F. same appendage as A, detail of terminal setae on distal article of exopod. Scale bars = 0.1 mm.

FIGURE 12. CLSM images of Austinograea rodriguezensis, megalopa (SMF 57020). A. second maxilliped; B. first maxilliped; C. third maxilliped, arthrobranch gill detached. Scale bars = 0.2 mm.

FIGURE 13. CLSM images of Austinograea rodriguezensis, megalopa (SMF 57020). A. left chela, anterior view; B. right chela, posterior view; C. coxa of P1; D. second pereiopod; E. coxa of P2; F. third pereiopod; G. coxa of P3; H. fourth pereiopod; I. coxa of P4; J. fifth pereiopod; K. coxa of P5. Scale bars = 0.5 mm.

FIGURE 14. CLSM images of Austinograea rodriguezensis, megalopa. A. pleon, dorsal view (SMF 57020); B. pleon, lateral view (SMF 57020); C. second pleopod (SMF 57021); D. third pleopod (SMF 57021); E. fourth pleopod (SMF 57021); F. fifth pleopod (SMF 57021); G. sixth pleopods (uropods) and telson, ventral view (SMF 57021). Scale bars = 0.1 mm.

FIGURE 15. Austinograea rodriguezensis, megalopa (SMF 57021). A. first pleopod, cincinulli; B. second pleopod, cincinulli; C. third pleopod, cincinulli; D. fourth pleopod, cincinulli; E. telson, dorsal view; F. uropods and telson, ventral view. Scale bars = 0.1 mm.