Alpheopsis aristoteles sp. nov.

(Figs. 16–18)

Type material. Holotype: male (cl 3.9 mm), MZUSP 34508, São Tomé & Príncipe, São Tomé Island, Praia das Conchas, intertidal and shallow subtidal rocky-sand bottom, under rocks covered with mud, depth: 0–1 m at low tide, coll. A. Anker, 15 February 2006 [fcn 06-229] . Paratype: male (cl 2.8 mm), OUMNH.ZC. 2016-02-029, São Tomé & Príncipe, São Tomé Island, Ilha das Cabras, off beach near light house, depth: about 2 m, coarse sand and rubble, under rocks, coll. A. Anker, 8 February 2006 [fcn 06-177].

Description. Small-sized species of Alpheopsis (present material: maximum cl 3.9 mm). Carapace with moderately developed MDC running from rostral tip to about level of eyes, gradually flattening posterior to eyes, without additional carinae; dorsal and dorsolateral surface covered with stiff erect setae (Fig. 16 a).

Rostrum relatively short, about as long as wide at base, subtriangular in dorsal view, tip subacute falling short of distal margin of first article of antennular peduncle, with distinct rounded carina (Fig. 16 a, b, d). Orbital hoods with small, anteriorly projecting, distally acute orbital teeth; tips of orbital teeth not reaching rostral mid-length (Fig. 16 b, d). Pterygostomial area broadly rounded, angle with minute tooth (Fig. 16 b, c).

Pleomeres without mid-dorsal crests; all pleura rounded ventrally; fifth pleuron with posteroventral angle rounded; sixth somite with subacutely projecting posterior lobe and well-delimited, triangular, articulated plate (Fig. 16 e). Telson moderately broad, tapering distally, about 2.5 as long as anterior width; dorsal surface without median depression, with two pairs of stout spiniform setae situated at some distance from lateral margin, at about 0.5 and 0.75 telson length, respectively; posterior margin slightly less than half as long as anterior margin, broadly rounded; each posterolateral angle with one pair of stout spiniform setae, mesial much longer than lateral (Fig. 16 f).

Eyes completely concealed by orbital hoods, not visible in dorsal and lateral views; eyestalk with wellpigmented cornea (Fig. 16 b, d). Each epistomial sclerite with short process.

Antennular peduncles stout; stylocerite strong, with sharp tip, latter overreaching distal margin of second article; ventromesial carina with strong, anteriorly directed, acute tooth; second article slightly shorter than wide; lateral flagellum biramous; fused portion short, with two joints; accessory ramus long, with several groups of long aesthetascs (Fig. 16 b, d, g). Antenna with basicerite ending in sharp tooth distoventrally; scaphocerite ovate, with anteriorly rounded blade and stout sharp distolateral tooth, latter exceeding anterior margin of blade; anterior margin of scaphocerite almost reaching distal margin of antennular peduncles; carpocerite slightly overreaching end of scaphocerite (Fig.16 b, d).

Mouthparts typical for genus in external view. Third maxilliped slender, pediform; coxa with produced, distally acute lateral plate above mastigobranch; penultimate article stout, about 2.2 times as long as wide proximally; ultimate article tapering to slender corneous tip, with two subdistal spiniform setae; arthrobranch well developed (Fig. 16 h–j).

Chelipeds slightly unequal in size, asymmetrical in shape and armature on finger cutting edges, carried extended when not in use (Figs. 17; 18). Ischium stout, short, without or with two stout spiniform setae on distodorsal margin (Fig. 17 a, e). Merus stout, slightly (major cheliped) or noticeably (minor cheliped) longer than wide, broadening distally, subtriangular in cross-section, dorsal margin ending in blunt tooth, proximodorsal margin with stout spiniform seta (Fig. 17 a, e). Carpus very stout, short, cup-shaped, widening distally, with strong dorsomesial constriction, ventral margin with one stiff seta (Fig. 17 a–c, e). Major chela robust, with mesially flattened palm and fingers about 0.7 length of palm; dorsomesial surface of palm unarmed; fingers somewhat gaping, strongly crossing distally; cutting edges of fingers armed with stout subtriangular teeth, three on dactylus and three on pollex, proximal teeth very broad and low, distal-most teeth strongest, especially on pollex; adhesive disks not distinct (Fig. 17 e). Minor chela with mesially flattened palm and fingers about 0.9 length of palm; dorsomesial surface of palm unarmed; fingers not gaping, slightly crossing distally; cutting edges of fingers armed with few low irregular teeth, distal half of pollex mostly unarmed; row of setae present along cutting edges (Fig. 17 a–d).

Second pereiopod slender; ischium subequal to merus in length; carpus with five joints; ratio of carpal joints (from proximal to distal) approximately equal to: 2.3: 1: 1: 1: 1.7; chela longer than distal carpal article, with fingers equal to palm in length, simple (Fig. 16 k). Third pereiopod moderately slender; ischium with one spiniform setae on ventrolateral surface; merus about 4.7 times as long as wide, unarmed; carpus about half-length of merus, much slenderer, with slender spiniform seta on distoventral margin; propodus with three spiniform setae along ventral margin and pair of distal spiniform setae adjacent to dactylus; dactylus almost half-length of propodus, slender, simple, conical, gradually curving distally (Fig. 16 l). Fourth pereiopod similar to third pereiopod. Fifth pereiopod more slender than third and fourth pereiopods; ischium unarmed on ventrolateral surface; merus about 4.3 times as long as wide, unarmed; carpus about 0.75 length of merus; propodus long, slender, with at least four spiniform setae along ventral margin, one long distal spiniform setae adjacent to dactylus, and four or so rows of serrulate setae on distolateral surface; dactylus about 0.45 length of propodus, similar to that of third pereiopod (Fig. 16 m).

Male second pleopod with appendix interna subequal to appendix masculina, latter with several long stiff setae on apex and subapical margin (Fig. 16 n). Uropod with lateral lobe of protopod ending in stout sharp tooth; endopod and exopod broadly ovate; exopod with distolateral tooth moderately developed, adjacent spiniform seta stout; diaeresis with blunt tooth adjacent to spiniform seta and almost straight mesial portion (Fig. 16 o).

Gill-exopod formula as in A. trigona .

Colour pattern. Semitransparent whitish, with pale reddish transverse bands, two on carapace and six on pleon; antennular and antennal peduncles with scattered reddish chromatophores, flagella pale yellowish; chelipeds, walking legs and tail fan whitish (Fig. 15); red bands possibly brighter in shrimps not exposed to stress.

Type locality. São Tomé Island, São Tomé & Príncipe.

Etymology. The new species is named after the great Greek philosopher and scientist, Aristoteles (384–322 BCE), and also the first naturalist who attempted a classification of animals based on morphology, anatomy and reproductive systems, in his famous “History of Animals” ( Aristoteles 350 BCE).

Distribution. Tropical eastern Atlantic: presently known only from São Tomé Island.

Ecology. Shallow sand flats with mud-covered rocks and rubble; under rocks and rubble on fine sand; in depths less than 2 m.

Remarks. Alpheopsis aristoteles sp. nov. lacks a complete MDC and all lateral carinae characteristic of the three species of the A. trigona complex (see above) and appears to be only distantly related to them. In the African species, the MDC is well developed only on the rostrum and adjacent post-rostral area, flattening behind the level of the eyes (Fig. 16 d). This feature, in combination with hirsute carapace and sharp orbital teeth (Fig. 16 a, d), immediately separates A. aristoteles sp. nov. from all other species of Alpheopsis .

The general morphology of A. aristoteles sp. nov. invokes that this species may be in an intermediate position between the A. trigona complex and some other members of the A. aequalis Coutière, 1897 group (Coutière 1899; Anker 2001, 2015). Within this group, only three species have well-developed orbital teeth, viz. A. chalciope De Man, 1910, A. vietnamensis Tiwari, 1964 and A. undicola Banner & Banner, 1973; however, none of them has a rostral carina and they differ in several other aspects from A. aristoteles sp. nov., for instance, A. chalciope and A. vietnamensis by the much shorter stylocerite, and A. undicola by the much longer orbital teeth and rostrum, and the third to fifth pereiopods with biunguiculate dactyli (de Man 1910; Tiwari 1964; Banner & Banner 1973).

The only other species of Alpheopsis reported from the eastern Atlantic are A. africana Holthuis, 1952 and A. azorica Anker, d’Udekem d’Acoz & Poddoubtchenko, 2005, both members of the A. trispinosa Stimpson, 1860 group, which is morphologically very different from A. aristoteles sp. nov. (cf. Holthuis 1952; Anker et al. 2005).