Description. Based on holotype, male, 9.5 mm, AM P. 98282. Head. Eye large (greater than 1 / 3 head length). Antenna 1 short, not longer than peduncular article 4 of antenna 2. Antenna 2 shorter than head and first 3 pereonites; peduncular articles slender, peduncular articles with many small robust setae; article 5 longer than article 4; flagellar articles final article large, cone-shaped forming a virgula divina, flagellar articles with apical cluster of ' imbricated' setae. Labrum upper lip with apical setal patch; with many pores. Labium distolateral setal tuft present; with vestigial inner plates. Maxilla 1 with small palp, 1 - articulate. Pereon. Gnathopod 1 sexually dimorphic; parachelate; coxa smaller than coxa 2; posterior margin of carpus and propodus each with lobe covered in palmate setae (carpus lobe vestigial), palmate lobes in male only; carpus longer than propodus, 1.5 × as long as propodus, 2.9 × as long as broad; propodus subrectangular, anterior margin with 5 groups of robust setae, lateral surface with 4 large robust setae, palm transverse, with 3 serrate setae; dactylus longer than palm, simplidactylate, without anterodistal denticular patch. Gnathopod 2 sexually dimorphic; subchelate; posterior margin without palmate lobes; basis slender; ischium with slightly rounded lobe on midanterior margin, with distally rounded anterodistal lobe on medial surface; merus without distally rounded posterodistal lobe on medial surface; carpus triangular, reduced (enclosed by merus and propodus), posterior lobe absent, not projecting between merus and propodus; propodus subtriangular, twice as long as wide, palm extremely acute, reaching between 72 % along posterior margin, with small sinus midway (bimodal), without protuberance or shelf near dactylar hinge, lined with robust setae, without mid-palmar protuberences, posteroproximal corner without spine, posteromedial surface of propodus with short groove, with cuticular patch at corner of palm; dactylus subequal in length to palm, pick-like, posterior margin smooth, dactylus not modified distally, blunt. Pereopods 2 – 4 coxae as wide as deep. Pereopods 3 – 7 strongly bi-cuspidactylate, dactyli without anterodistal patch of many rows of tiny setae. Pereopod 4 significantly shorter than pereopod 3; carpus significantly shorter than carpus of pereopod 3; dactylus thickened proximally with a notch midway along posterior margin. Pereopod 5 propodus distinctly longer than carpus. Pereopods 6 – 7 longer than pereopods 3 – 5; with row of short setae along the posterior margin of the dactyli. Pereopod 6 not sexually dimorphic; longer than pereopod 7; coxa posterior lobe inner view posteroventral corner rounded, posterior margin oblique to ventral margin, posterior lobe without ridge, posterior lobe with about 11 marginal setae; basis broadly expanded. Pereopod 7 not sexually dimorphic; basis lateral sulcus absent, posterior margin with distinct minute serrations, each with a small seta, posterodistal lobe absent; distal articles (merus and carpus) slender; merus posterior margin straight. Pleon. Pleonite 1 with a pair of well developed dorsodistal spines. Pleonite 2 with 1 pair of well developed dorsoproximal spines and 1 pair of small dorsodistal spines. Pleonite 3 with 1 pair of well developed middorsal spines. Pleopod 1 – 3 biramous. Epimeron 2 subequal in length to epimeron 3. Epimeron 3 posterior margin smooth, without setae, posteroventral corner subquadrate. Uropod 1 peduncle with about 18 robust setae, distolateral robust seta present, small (less than 1 / 4 length of outer ramus) with a simple tip; rami without apical robust setae; inner ramus slightly shorter than outer ramus, with 5 lateral and 4 medial robust setae in 2 rows; outer ramus with 5 marginal robust setae in one row. Uropod 2 peduncle with about 11 robust setae; rami without apical robust setae; inner ramus subequal in length to outer ramus, with marginal robust setae in 3 lateral and 4 medial robust setae 2 rows; outer ramus with 4 marginal robust setae in 1 row. Uropod 3 peduncle with 4 robust setae; ramus longer than peduncle, ramus 3.1 × as long as broad, linear (narrowing), with 3 marginal robust setae, with about 7 apical robust setae. Telson broader than long, tapering distally, apically incised, dorsal midline entire, with marginal and apical robust setae, with 7 robust setae per lobe. Female (sexually dimorphic characters). Based on paratype, female. Gnathopod 1 simple; posterior margin of merus, carpus and propodus each without lobe covered in palmate setae; carpus 1.6 × as long as propodus; propodus tapering distally, anterior margin with 3 groups of robust setae, propodus 2.6 × as long as broad. Gnathopod 2 chelate; posterior margin of merus, carpus and propodus each with lobe covered in palmate setae; basis expanded anteroproximally, anteromedially; ischium without lobe on anterior margin, distal triangular anterodistal lobe on medial surface; carpus well developed (not enclosed by merus and propodus), posterior lobe present, projecting between merus and propodus; propodus 2.5 × as long as wide, palm obtuse, smooth, evenly rounded, not lined with robust setae, posteromedial surface without groove, without cuticular patch at corner of palm; dactylus shorter than palm, straight.
Types. Holotype, male, 10.4 mm, AM P. 98282, Mossel Bay, South Africa (~ 34 ° 10.6 ’ S 22 ° 8.2 ’ E), coll. Simone Baldanzi, 2010. Paratypes: female, AM P. 97673; 4 females, 5 males, AM P. 98283, same station data as holotype.
Remarks. Gnathopod 1 carpus lobe vestigial (small in A. spinifera). Gnathopod 2 similar to gnathopod 2 of A. spinifera, but A. meridionalis has fewer setae on the uropods and the telson has about seven setae (about 14 in A. spinifera). Immature males may not have dorsal spines on pleonites. Geographically they are widely separated. Africorchestia spinifera occurs in Morocco and A. meridionalis is found on the south coast of South Africa.
Distribution. South Africa. Cape Agulhas (Western Cape Province) to Kidd’s Beach (Eastern Cape Province) (current study).
Etymology. Named for its horizontal distribution along the south coast of South Africa.
Additional material examined. 10 males, AM P. 88479, 4 females, 2 juveniles, AM P. 88480 Kidds Beach, Eastern Cape, South Africa (~ 33 ° 8 ’ 39 ” S 27 ° 42 ’ 6 ” E), S. Baldanzi, February, 2011. Type locality. Mossel Bay, South Africa (~ 34 ° 10.6 ’ S 22 ° 8.2 ’ E).
Based on the collection survey in 2010, the spatial distribution of A. meridionalis seems to be restricted to the South Coast of South Africa (Fig 13), ranging from Cape Agulhas (Western Cape) to Kidd’s Beach (Eastern Cape). The pattern of abundance appears to be driven mainly by the temperature of the sand and water, measured at the time of collection (winter 2010, Baldanzi unpublished data). No differences in size have been found between males and females, furthermore no ovigerous females have ever been collected. This species seems to prefer macroalgae and debris of riverine origin, as it has mainly been found underneath such type of wrack and on the proximities of estuaries (Baldanzi, pers. obs). This observation could be interpreted both in terms of habitat exclusion due to interspecific competition with A. capensis (both can be found at the same location) or differences on feeding choice. We suggest that A. meridionalis falls under the category of beach-hopper (sensu Bousfield, 1992) as it does not modify the substrate, but rather lives underneath the macroalgae without burrowing deep in the sand (SB, pers. obs.).