Chroestia amoa, Lowry & Fanini, 2023

Lowry, James K. & Fanini, Lucia, 2023, The Coastal Talitroid Amphipods of New Caledonia (Amphipoda: Talitroidea), Records of the Australian Museum (Rec. Aust. Mus.) 75 (4), pp. 471-484 : 476

Chroestia amoa sp. nov.

urn:lsid:zoobank.org:act:D0A16782-C24F-453B-BC44-311A6875D5F0

Figs 2–4

Holotype: Male , 10.8 mm, AM P.100369 (SEM pin and 4 SEM stubs), Malabou, Grand Terre, New Caledonia, 20°17.530'S 164°6.426'E, bay, supralittoral, sandy beach covered in wrack, mainly Zostera , coll. J. K. Lowry & L. Fanini, 31 December 2014 . Paratypes: 1 female, AM P.100370 (SEM pin and 1 SEM stub) ; 19 males, 22 females (wet specimens), AM P.97473 ; 6 males, 3 females (wet specimens), AM P.97474, same data as holotype . 3 males, 24 females (wet specimens), AM P.97477, nearAmoa, Grand Terre , New Caledonia, 20°45.713'S 165°11.541'E, estuary supralittoral, sandy beach, coll. J. K. Lowry & L. Fanini, 2 January 2015 .

Type locality. Malabou , Grand Terre, New Caledonia (20°45.713'S 165°11.541'E), estuary supralittoral, sandy beach.

Ecological type. Beach-hopper.

Habitat. Estuary supralittoral, sandy beach.

Etymology. Named for the town of Amoa, Grande Terre, New Caledonia.

Description. Male (based on holotype, 10.8 mm, AM P.100369).

Head. Eye medium (⅕–⅓ head length). Antenna 1 short, not reaching midpoint of peduncular article 5 of antenna 2. Antenna 2 peduncular articles slender, with many small robust setae; article 1 enlarged, bulbous. Mandible left lacinia mobilis 4-cuspidate. Maxilla 1 inner plate with 2 apical plumose setae; palp vestigial, 2-articulate, without apical seta. Maxilla 2 inner plate with one large plumose seta along inner margin. Maxilliped palp broad, article 2 with distomedial lobe; article 4 reduced, button shaped.

Pereon. Gnathopod 1 sexually dimorphic; subchelate; coxa much smaller than coxa 2; posterior margin of carpus and propodus each with lobe covered in palmate setae; carpus longer than propodus, length more than 2 × width; propodus anterior margin with 3 groups of robust setae, “subtriangular” with well-developed posterodistal lobe, palm transverse; dactylus simplidactylate. Gnathopod 2 subchelate; with distally rounded anterodistal lobe on medial surface; posterior margin of merus, carpus, and propodus each without lobe covered in palmate setae; propodus palm acute, evenly rounded, without proximal sinus, without large distal sinus, without proximal spine or thumb defining palm, without large projection near dactylar hinge; dactylus attenuated distally, slightly curved, subequal or slightly longer than palm; posterior margin smooth; shorter than posterior margin of propodus. Pereopods 3–7 dactyli cuspidactylate (bicuspidactylate), with anterodistal denticulate patch. Pereopod 4 significantly shorter than pereopod 3; carpus significantly shorter than carpus of pereopod 3; dactylus amplidactylate, thickened proximally with notch midway along posterior margin. Pereopod 5 short, less than ⅔ length of pereopod 6; merus broad, longer than broad, expanded distally. Pereopod 6 shorter than pereopod 7; not sexually dimorphic; coxa posterior lobe with anteroventral corner rounded, not produced; basis expanded. Pereopod 7 not sexually dimorphic; posterior margin with broad, small serrations, each with a small seta, posterodistal lobe present, shallow, broadly rounded; merus expanded distally, subtriangular, anterior margin straight; carpus unexpanded; subrectangular; shorter than propodus; propodus broad; length 6.6 × width. Oostegites (female) present, setae with curled tips.

Pleon. Pleopods 1–3 all well-developed. Epimera 1–3 ventral margin without robust or slender setae. Uropod 1 peduncle distolateral robust seta present (large), large (¼ length of outer ramus), with simple tip; exopod without marginal robust setae; endopod with marginal robust setae in 1 row. Uropod 2 exopod with marginal robust setae in 1 row; endopod with marginal robust setae in 1 row. Uropod 3 ramus shorter than peduncle; peduncle with 1 or 2 very long robust setae dorsal margin, linear (narrowing). Telson as broad as long, tapering distally, completely cleft, with apical and marginal robust setae, with at least 10 robust setae per lobe.

Female (sexually dimorphic characters). Based on paratype female, AM P.100370. Gnathopod 1 posterior margin of merus, carpus, and propodus each without lobe covered in palmate setae. Propodus subrectangular, anterior margin with 2 groups of robust setae, palm acute; dactylus simple, longer than palm. Gnathopod 2 mitten-shaped; basis slightly expanded; ischium without lobe on anterior margin; posterior margin of merus, carpus, and propodus each with lobe covered in palmate setae. Carpus well developed (not enclosed by merus and propodus), posterior lobe present, projecting between merus and propodus. Palm obtuse, nearly straight. Dactylus curved, posterior margin smooth, shorter than palm. Oostegites long (length greater than 2 × width), longer than wide, setose, setae with curled tips.

Remarks. This is the first record of Chroestia outside Australia. Chroestia amoa is very similar to C. lota Marsden & Fenwick, 1985 from Moreton Bay, Queensland, Australia. The main morphological difference between these species is the shape of the palm of male gnathopod 2, which is evenly rounded in C. amoa , but has a distinctive proximal sinus in C. lota .

Distribution. New Caledonia: Malabou and Amoa, Grand Terre.

Figures

Figure 2. Chroestia amoa sp. nov., holotype, male, 10.8 mm,AM P.100369; paratype, female,AM P.100370, New Caledonia. Scale: MD 0.02 mm; H, LL, MP, UL, oost, T 0.2 mm; EP1–3, U1–2, UR 0.5 mm.

Figure 3. Chroestia amoa sp. nov., holotype, male, 10.8 mm, AM P.100369; paratype, female, AM P.100370, New Caledonia. Scale: male G2 0.2 mm; remainder 0.1 mm.

Figure 4. Chroestia amoa sp. nov., holotype, male, 10.8 mm, AM P.100369, New Caledonia. Scale: 0.5 mm.