Fredius reflexifrons Present
Creators: name: Vieira, Rony R. R.
name: Santos, Cleverson R. M.
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Pseudothelphusidae
Fredius
Fredius reflexifrons

description: Fredius reflexifrons (Ortmann, 1897)
(Figs. 1–3)
Description of the pre-juvenile stage. Pre-juveniles exhibit yellowish hue, attributable to residual yolk present. Carapace oval in shape. Appendages appear fully contracted, as if still within egg.
Carapace without calcification, strongly convex, with slightly cervical groove, tubercles non-visible (Fig. 1A).
Pleon strongly curved under carapace, with six pleonites wider than long; limits among pleonites not clear; telson with median distal notch and appendages non-calcified (Fig. 1B).
Antennule with basal segment well-developed; segments slightly marked; peduncle two-segmented; endopod (ventral flagellum) small and unsegmented; exopod (dorsal flagellum) two-segmented (Fig. 1C).
Antenna with peduncle two-segmented, first article with slight elevation in lateral margin and second segment slender; antennal flagellum with four segments, with no clear separation (Fig. 1D).
Mandible with rounded cutting blade; palp tip with rounded end (Fig. 1E).
Maxillule, maxilla and maxillipeds with rudimentary setae, no clear limits among segments; maxillule endites (coxal and basal) and endopod with segments limit not distinct (Fig. 1F); maxilla and maxillipeds with endites, endopod and exopod clearly formed including basal endite bilobed (Figs. 1G–J).
Pereopods with marked limits among segments, without functional locomotion (Fig. 1K–O); dactyl of chela with distal more calcified spot (Fig. 1K *).
Description of first juvenile stage. Carapace widest at mesobranchial region; dorsal surface smooth, convex, cervical groove straight and well defined, almost reaches anterolateral margins; post-frontal lobes low and small; carapace surface between post frontal lobes slightly inclined anteriorly; frontal orbital region slightly convex, with faint notch medially, marked with row of very small tubercles visible in dorsal view; lower front margin sinuous; anterolateral margins of carapace with small granules (Fig. 3A).
Pleon attached to sternum, with six pleonites wider than long; third pleonite widest and sixth pleonite longest, dorsal and lateral regions of all pleonites with simple and plumose setae (Fig. 3B); telson distally rounded, with slight narrowing in anterolateral region (Fig. 3B); ventral margin of pleon with 4 pairs of rudimentary pleopods from second to fifth pleonites (Fig. 3C).
Antennule with basal segment well-developed with 7–12 plumose setae; peduncle two-segmented, with 2 simple setae on each segment; endopod (ventral flagellum) small and unsegmented with 0-1 simple seta; exopod (dorsal flagellum) two-segmented, first segment with 1 simple seta and 2 small aesthetascs with dilated ends and second segment with 1 simple seta and 5 small aesthetascs with dilated ends (Fig. 3D).
Antenna with peduncle two-segmented, first segment without seta but with one spine in lateral margin, second segment with 4–6 plumose setae; antennal flagellum with four segments, first segment with 8–10 plumose setae, second segment without setae, third segment with 2–4 simple setae and 1 plumose seta, fourth segment with 6–8 simple setae (Fig. 3E).
Mandible with small depression on left mandible cutting margin, right mandible cutting edge with mesial extension which fits into the depression of left mandible; both palps three-segmented, first segment without setae, second segment with 2 pappose setae, third segment with distal region wider than proximal, forming two lobes: internal lobe with 10–16 pappose setae, external lobe with 6–10 pappose setae (Fig. 3F).
Maxillule with coxal endite with 22–28 setae:17–23 pappose, 4–6 plumose; basal endite with 48–54 setae: 1–3 simple setae, 10–12 denticulate, 10–13 cuspidate, 11–13 plumoserrulate, 11–14 plumodenticulate, 2–4 pappose; endopod two-segmented, first segment with 7–10 pappose setae, second segment with 8–10 pappose setae; protopod with 5–6 long plumose setae (Fig. 3G).
Maxilla with coxal endite with 12–16 pappose setae; basal endite bilobed with 11–14 setae on proximal lobe: 2 simple, 4–6 pappose, 5–8 papposerrate setae, and distal lobe with 14–17 setae: 3–4 simple, 6–8 pappose, 2–4 plumose setae; endopod with 8–10 plumose setae; exopod (scaphognathite) with 105–110 marginal pappose setae and 3–5 pappose setae on dorsal surface (Fig. 3H).
First maxilliped with coxal edite with 22–26 pappose setae; basal endite with 28–36 pappose setae; protopod with 4-6 pappose setae; epipod with 18–26 pappose setae, no gills present (Fig. 3I); endopod with distal region wider than proximal, forming two lobes: internal lobe with 13–16 pappose and 4–6 plumose setae, and external lobe with 10–15 pappose and 4-5 plumose setae (Fig. 3J); exopod two-segmented with 8–11 plumose and 4-5 pappose setae on proximal segment, and 4 plumose setae on distal segment (Fig. 3I).
Second maxilliped with protopod without setae; epipod with 36–40 pappose setae and presence of a rudimentary podobranchia; endopod five-segmented, ischium with 5–7 setae: 3–5 pappose and 2–3 plumose setae, merus with 6–8 pappose setae, carpus with 3–4 pappose setae, propodus with 4–7 pappose and 3–5 plumose setae, dactylus with 20–24 pappose setae. Exopod two-segmented with 16–20 setae: 11–16 pappose and 5–6 papposerrate on proximal segment, and 4 plumose setae on distal segment; (Fig. 3K).
Third maxilliped with protopod with 46–54 setae: 2–5 simple, 27–33 pappose and 11–16 plumose setae. Epipod with 40–46 pappose setae and presence of a rudimentary arthrobranchia. Endopod five-segmented, ischium with 25–30 setae: 5–8 simple and 15–22 pappose setae, merus with 12–16 setae: 4–6 simple and 8–12 pappose setae, carpus with 1–2 simple setae; propodus with 2–6 simple and pappose setae, dactylus with 8–10 pappose setae; exopod unsegmented, very small not reaching half of ischium of endopod (Fig. 3L).
description: Published as part of Vieira, Rony R. R. & Santos, Cleverson R. M., 2025, Pre-juvenile and first juvenile stages of the freshwater crab Fredius reflexifrons (Ortmann, 1897) (Crustacea: Decapoda: Pseudothelphusidae), pp. 367-378 in Zootaxa 5620 (2) on pages 371-373, DOI: 10.11646/zootaxa.5620.2.9, http://zenodo.org/record/15219692