Oncopagurus africanus ( de Saint Laurent, 1972 )

Lemaitre, Rafael, 2014, A worldwide taxonomic and distributional synthesis of the genus Oncopagurus Lemaitre, 1996 (Crustacea: Decapoda: Anomura: Parapaguridae), with descriptions of nine new species, Raffles Bulletin of Zoology 62, pp. 210-301 : 214-217

Oncopagurus africanus ( de Saint Laurent, 1972)

Figs. 1A–I , 51

Parapagurus bicristatus – Forest, 1961: 231.

Parapagurus africanus de Saint Laurent, 1972: 109 , figs 3, 15 (type locality: Angola, western Africa).

Sympagurus africanus – Lemaitre, 1989: 37; 1990: 229, figs 6, 7.

Oncopagurus africanus – Lemaitre, 1996: 194; McLaughlin et al., 2010: 39; Zhadan, 1997: 63 (table).

Type material. Holotype, Angola, western Africa , 1968, coll. A. Crosnier: M 6.0 mm ( MNHN – IU –2008–15097, ex MNHN Pg. 2689).

Presumed paratypes (see Remarks ), West Africa: Congo, off Pointe-Noire, radiale 21, 05°04'S, 11°20'E, 500 m, 12 January 1964: 6 M 3.0– 3.5 mm, 2 F 2.9, 3.4 mm ( MNHN – IU –2009–3499, ex MNHN Pg. 2690); [ Congo], 05°30'S, 11°32'E, 500–505 m, 5 July 1967: 1 M 3.6 mm ( MNHN – IU –2009–3500, ex MNHN Pg. 2691); Atlantide Expedition, sta 135, 07°55'S, 12°38'E, 440– 360 m, 17 March 1946: 1 M 4.5 mm ( MNHN – IU –2009–3501, ex MNHN Pg. 2692); Angola, 09°27'S, 12°38'E, 545–555 m, 18 April 1968, coll. A. Crosnier (2 lots): 1 M 5.2 mm, 1 F 4.4 mm ( MNHN – IU –2009–3497, MNHN–IU–2009–3498, both ex MNHN Pg. 2689) .

Additional material. Eastern Africa : southwestern Indian Ocean , SE of Durban Bluff, Division of Sea Fisheries, sta K 220, 29°56'S, 31°12.5'E, 366 m, 30 June 1964: 1 M 4.7 mm ( SAM A12715 ) .

Diagnosis. Shield ( Fig. 1A ) about as broad as long, rostrum broadly rounded, with short mid–dorsal ridge; lateral projections subtriangular, usually terminating in small spine. Ocular peduncles about half length of shield, interocular plate rarely with pair of distinct, forwardly directed spines; corneas weakly dilated. Ocular acicles terminating in strong spine (rarely bifid). Antennular peduncle exceeding distal margin of cornea by about 0.2 length of penultimate segment. Antennal peduncle reaching to about same level as distal margin of cornea; fourth segment with dorsolateral distal spine; acicle nearly straight (in dorsal view) at most slightly exceeding distal margin of cornea, mesial margin armed with 8–14 spines; flagellum exceeding extended right cheliped, with few short setae <1 article in length (placed usually every 2 or 3 articles). Third maxilliped with crista dentata armed with about 15 unequal corneous teeth (4–6 teeth distinctly larger, interspersed with smaller teeth). Right cheliped ( Fig. 1B–D ) moderately setose, chela operculate; dactyl set at strongly oblique angle to longitudinal axis of palm; palm with dorsolateral and dorsomesial margins well delimited by row of small spines, ventromesial face rounded, ventral face with scattered or numerous small tubercles; carpus with numerous small tubercles or small spines on dorsal surface, lateral margin often well defined by row of strong spines. Left cheliped usually well calcified; palm with dorsomesial row of small spines. Ambulatory legs with ventromesial margins of dactyls ( Fig. 1E ) lacking corneous spines or at most each with row of 3–5 minute spinules; carpus with small dorsodistal spine. Anterior lobe of sternite XII (between second ambulatory legs) rounded, setose, with 1 or 2 terminal spines. Fourth pereopod propodal rasp ( Fig. 1F ) with 1 row of rounded scales at least distally. Fifth pereopod propodal rasp extending to midlength of segment. Uropods and telson markedly asymmetrical. Telson ( Fig. 1G ) lacking or with obsolete, transverse suture; posterior lobes separated by shallow cleft, terminal margin of lobes armed with long, often strongly curved corneous spines. Male with paired first and second gonopods ( Fig. 1H, I ); first gonopod distal lobe with weakly concave mesial face; second gonopod with distal segment flat and with setae on distal margins. Female with vestigial second right pleopod or occasionally with normal, biramous right second pleopod.

Variations. A marked sexual dimorphism in the right cheliped of this species was observed in the available material. The palm and carpus of the right cheliped in females is typically much shorter than in males of comparable sizes. The length/ width ratio of the right palm and carpus in females is at most about 0.7 and 1.2, respectively, whereas in males these ratios can be as high as 1.2 and 2.0 respectively.

Two unusual variations were observed. One female (sl 4.4 mm, MNHN Pg. 2689) has an interocular lobe with two distinct, forwardly directed spines. Another female (shield length 3.0 mm, MNHN–IU–2009–3499, ex MNHN Pg. 2690) has a normal right second pleopod, instead of the typical short bud seen in females of most species of parapagurids.

Colouration. Unknown.

Habitat. Gastropod shells often with anthozoan polyp.

Distribution. Southeastern Atlantic, from Congo to Angola; and southwestern Indian Ocean, from off SE of Durban. Depth: 235– 555 m.

Remarks. In the original description of this species, de Saint Laurent (1972) listed only the holotype from Angola, although she cited a distribution from Angola to Congo, and evidently examined specimens other than the holotype. Indeed a number of specimens used by de Saint Laurent are deposited in the MNHN as “ paratypes ”, and because these were not included in the original description are listed herein as “presumed paratypes ”.

Oncopagurus africanus is morphologically closest to O. gracilis . The two species exhibit similar morphologies and sex-related variations on the right cheliped, with females having a broader carpus and palm than males. The two species differ most distinctly in that O. africanus , has ocular peduncles about half the length of the shield, and the antennal acicles exceed the distal margins of the corneas, whereas the ocular peduncles are more than half the length of the shield, and the antennal acicles do not exceed the distal margins of the corneas in O. gracilis .

Based on limited materials, de Saint Laurent (1972) considered Oncopagurus africanus (as Parapagurus africanus ) to be related to the western Atlantic Parapagurus bicristatus bicristatus . The latter taxon was elevated to species level by Lemaitre (1989), and subsequently Lemaitre (1996) placed it in Oncopagurus . Although O. africanus and O. bicristatus share the basic overall similarities of Oncopagurus species , several important morphological details clearly set them apart. In O. africanus , the ocular peduncles are about half the length of the shield, whereas they are more than half the length of the shield in O. bicristatus ; the palm of the right chela has a rounded mesial face and rounded ventromesial margin, whereas in O. bicristatus the mesial face is concave, expanded distomesially (often strongly so in large males sl> 4.0 mm) and with a ventromesial margin well delimited by a row of spines. Additionally, in males of O. africanus , the first and second gonopods are more developed than in O. bicristatus . In O. africanus the first gonopods have a weak but distinct distal lobe, and the second gonopods are 2-segmented and symmetrical; whereas in O. bicristatus the first gonopods are represented by short buds, and the second gonopods can be either symmetrical and 2-segmented on both sides, or asymmetrical and 2-segmented in one side, and short, 1-segmented on the other side.

Of the three Atlantic species of Oncopagurus , O. africanus is the only one to range exclusively on one side of the Atlantic (eastern margin), whereas O. bicristatus and O. gracilis are amphi-Atlantic in distribution.

Figures

Fig. 1. A–I, Oncopagurus africanus (de Saint Laurent, 1972), paratype, male 5.2 mm, Angola (MNHN Pg 2689): A, shield and cephalic appendages, dorsal; B, carpus and chela of right cheliped, mesial; C, D, chela of same, dorsal (C) and lateral (D); E, dactyl of first left ambulatory leg, mesial; F, propodus and dactyl of right fourth pereopod, lateral; G, telson, dorsal; H, male sternite XIV, coxae of fifth pereopods, and first gonopods, ventral; I, male left second pleopod, posteromesial. J–T, Oncopagurus bicristatus (A. Milne-Edwards, 1880), J, L, M, P, male 3.1 mm, Straits of Florida (USNM 1100616); K, female 1.9 mm, Straits of Florida (USNM 1100616); N, O, R, S, male 3.0 mm, Caribbean Sea (UMML 32:4607); Q, male 4.4 mm Straits of Florida (UMML 32:4610); T, male 2.6 mm, Straits of Florida (USNM 1100615): J, shield and cephalic appendages, dorsal; K, carpus and chela of right cheliped of female, dorsal; L, carpus and chela of right cheliped of male, dorsal; M, right chela of same, lateral; N, dactyl of first left ambulatory leg, mesial; O, propodus and dactyl of left fourth pereopod, lateral; P, telson, dorsal; Q, male sternite XIV, coxae of fifth pereopods, and anterior portion of pleon with first and second gonopods, ventral. Scale bars = 2 mm (A, E); 3 mm (B–D); 1 mm (F, G, I); 2 mm (H); 1 mm (J, O, P); 2 mm (K–N); 2 mm (Q); 0.5 mm (R–T). [Adapted from Lemaitre (1989, 1990)].

Fig. 51. Bathymetric distribution of Oncopagurus species from the world, with maximum and minimum depths (meters) indicated for each.