Acutihumerus patagoniensis (Sieg, 1986)

Giachetti, Clara Belen & Roccatagliata, Daniel, 2014, Acutihumerus patagoniensis (Sieg, 1986) (Tanaidacea: Kalliapseudidae): supplementary description and remarks on its taxonomic status, Zootaxa 3861 (4), pp. 345-354 : 347-350

Acutihumerus patagoniensis (Sieg, 1986)

Figs. 3–5

Bacescapseudes patagoniensis: Sieg (1986): 22 , 25–30, figs. 11–14 (description of male); Guţu (1998): 180; Guţu (2006): 171,

179; Araújo-Silva & Larsen (2010): 30, 32, 35, 45; Drumm & Heard (2011): 10, 24 (junior synonymy of A. cavooreni ). Acutihumerus patagoniensis: Araújo-Silva & Larsen (2010): 47 , 48; Drumm & Heard (2011): 24; Guţu (2011): 346, 347. Acutihumerus patagonensis : lapsus calami, Araújo-Silva & Larsen (2010): 41, 42.

Description of Acutihumerus patagoniensis from Playa Colombo, Golfo Nuevo.

Material examined. Off Puerto Madryn, Golfo Nuevo, Brenda Doti, Ignacio Chiesa, Romina Centurión and Daniel Roccatagliata colls.: Sta. 3, 42º46.324'S, 65º01.361'W, 10 m, 3 Feb 2006, one ♂ and four ♀ (MACN-In. 39637). Sta. 8, 42º46.999'S, 64º59.256'W, 9 m, 3 Feb 2006, eleven ♂ and 55 ♀ (MACN-In. 39638). Sta. 9, 42º46.991'S, 64º59.088'W, 12 m, 3 Feb 2006, three ♂ and six ♀ (MACN-In. 39639). Sta. 11, 42º47.019'S, 64º58.890'W, 11 m, 3 Feb 2006, three ♂ and 26 ♀ (MACN-In. 39640).

Playa Colombo, Golfo Nuevo, approximately 42º 37’30”S, 64º14'W: shallow waters, 22 Jan 1990, by scuba diving, Daniel Martínez coll., 1701 ♂ and 780 (67 ovigerous) ♀ (MACN-In. 39641). Same locality, 2 m, 3 Nov 1995, by scuba diving, Fernando Meijide and Pablo Ianovski colls., 399 ♂ and 158 (47 ovigerous) ♀ (MACN-In. 39642).

Playa Villarino, Golfo San José: 42°24'25”S, 64°17'38”W, 2–5 m, Mar 2006, by scuba diving, Juan Pablo Lívore coll.: 20 ♂ and 86 (39 ovigerous) ♀. (MACN-In. 39699). 42º24'34”S, 64º17'38”, 1–5 m, Mar 2006, by scuba diving, Juan Pablo Lívore coll.: five (two ovigerous) ♀ (MACN-In. 39643).

Puerto Lobos: 41°59.808'S; 65°03.539'W, approximately 10 m, 20 Jun 2011, by scuba diving, Marina Güller coll.: one ♂ and one ♀ (MACN-In. 39644).

Diagnostic characters. Rostrum broad and with a slight concave indentation. Eye lobes well developed. Cheliped segment with a mid-ventral crest (cephalothoracic hyposphenium). Sterna of pleonites 1–2 with a forwardly directed hook. Epimera of pleonites 1–5 with an acute postero-inferior projection. Pleotelson margins with distinct notch and a hook-like spine. Antenna article 1 with inner lobe. Antennal squama, mandible palp, maxilliped palp and cheliped with simple (not setulate) setae. Maxilliped propodus and dactylus with serrulate setae distally. Basis of pereopods 2 and 3, anterior margin with a proximal hook curving upwards. Basis of pereopod 6 with a row of setulate setae dorsally. Chela palm of large males with a broad and deep U-shaped notch.

Dimorphic chelipeds. Significant ontogenetic changes in the morphology of the male cheliped are shown here ( Figs. 3 and 4 ). The propodus becomes larger and varies between slightly and distinctively longer than wide, from the juvenile to adult stages. In the juvenile male ( Fig. 3 B) the apophysis on fixed finger is small and triangular, but as the male grows it develops into a large and robust projection. Also, as the male grows, the apophysis rotates, turning almost parallel to the ventral margin of the propodus in the largest male. The tooth on the ventrodistal angle of the propodus is here referred to as “robust tooth”. The area between the robust tooth and the apophysis decreases in size as the male grows, being reduced to a small unevenness on the ventral margin of the propodus in the largest males. In contrast, the U-shaped notch is poorly developed in the juvenile male, but became wider and deeper as the specimen become larger. A detailed description of this ontogenetic process of the male cheliped is reported below:

Juvenile male (MACN-In. 39641a, carapace length 0.49 mm, Fig. 3 B). Propodus 0.9 times as long as carpus. Fixed finger with a small tooth-like projection (from now on called apophysis) on dorsal margin. U-shaped notch small, approximately 0.3 times fixed finger width. Dactylus, cutting margin even and with a few small setae; distal end with a sharp claw.

Male I (MACN-In. 39641b, carapace length 0.69 mm, Fig. 3 C). As the previous form except for: propodus 1.5 times carpus length. Apophysis roughly slanted 34º–43º upwards about propodus ventral margin. Area between robust tooth and apophysis narrower. U-shaped notch narrower than or as broad as fixed finger (slightly wider than fixed finger in other specimens examined). Dactylus, cutting margin with a proximal rounded process.

Male II (MACN-In. 39641c, carapace length 0.82 mm, Fig. 3 D). As the previous form except for: propodus 1.9 times carpus length. Apophysis roughly slanted 24º–31º upwards about propodus ventral margin. Area between robust tooth and apophysis narrower. U-shaped notch 1.3 times broader that fixed finger. Dactylus, proximal rounded process larger.

Male III (MACN-In. 39641d, carapace length 0.95 mm, Fig. 3 E). As the previous form except for: propodus huge, 2.6 times carpus length. Fixed finger, robust tooth blunt; apophysis roughly slanted 10º–16º upwards about propodus ventral margin, i.e., it becomes almost parallel to propodus ventral margin. Area between robust tooth and apophysis vestigial. U-shaped notch much wider, approximately 2.9 (2.3–2.6) times broader than fixed finger. Dactylus claw blunt. Note: in other specimens examined, the robust tooth, the apophysis and the claw are sharper than in the specimen drawn.

Juvenile female (MACN-In. 39641e, carapace length 0.53 mm, Fig. 3 A). Propodus 0.43 times as long as carpus. Similar to juvenile male but lacking U-shaped notch and incipient apophysis.

Ovigerous female (MACN-In. 39641f, carapace length 0.88 mm). As juvenile female but propodus 0.63 times as long as carpus.

Addenda to Sieg (1986) description. The specimens from Playa Colombo fully agree with the description of A. patagoniensis presented by Sieg but supplementary information is reported below:

Eye lobes as shown in Fig. 5 A, not pigmented. Corneal lenses not detected, but visual elements distinguished at high magnification in soft (decalcified) specimen.

Cheliped segment of juveniles (both sexes), female (with rudimentary oostegites) and male I with an anvil-like hyposphenium, bearing several teeth on anterior projection and a tooth on posterior projection ( Fig. 5 D). Posterior projection vestigial in male II ( Fig. 5 E) and completely absent in male III ( Fig. 5 F). Ovigerous female lacking hyposphenium.

Pleonites 1 and 2 ( Fig. 5 B) with forwardly directed hook mid-ventrally. Pleonites 1–5 with an acute projection on postero-inferior angle. Margins usually even, rarely with teeth ( Fig. 5 C).

Maxilliped propodus and dactylus with serrulate setae. Note: these setae are depicted as simple in the original description of A. patagoniensis (see Sieg, 1986, fig. 12). Pereopods 2 and 3, basis with an upwardly directed tooth on the anterior margin (like that one shown for A. cavooreni by Băcescu & Absalao, 1985 in their fig. 2D). Pereopod 6 basis with a row of 7–10 setulate setae along dorsal margin. Note: Sieg (1986, fig. 13) showed four setulate setae (he called them “pinnate”) restricted to the proximal half of article, and Băcescu & Absalao (1985, fig. 2A) illustrated them as simple setae.

Figures

FIGURE 3. Acutihumerus patagoniensis. A, juvenile female cheliped (MACN-In. 39641 e); B, juvenile male cheliped (MACN-In. 39641 a); C, male I chela (MACN-In. 39641 b); D, male II chela (MACN-In. 39641 c); E, male III cheliped (MACN-In. 39641 d). In all figures the outer surface is shown. Scale bars: 0.2 mm.

FIGURE 4. Acutihumerus patagoniensis. Gradual changes of the fixed finger and apophysis over a growing series. The propodus distal outlines were transferred from the preceding figure, and all adjusted to the same scale. The vertical bars indicate the propodus-dactylus inner articulation. Scale bar: 0.2 mm.

FIGURE 5. Acutihumerus patagoniensis. A, male II carapace and first pereonite in dorsal view (MACN-In. 39641 c); B, male III pereonites 6 – 7 and pleonites 1 – 2 (MACN-In. 39641 g); C, male III pleonites 1 – 5 in lateral view (MACN-In. 39641 h); D – F, cephalothoracic hyposphenium of a female with rudimentary oostegites (MACN-In. 39641 i), a male II (MACN-In. 39641 j), and a male III (MACN-In. 39641 k), respectively. Abbreviations: acp, anterior crest projection; ap, acute projection; ph, pleonal hook-like teeth; pcp, posterior crest projection; P, pereonite; pe, penis; Pl, pleonite. Scale bars: A – C: 0.5 mm; D – F: 0.2 mm (D – F, share the same scale).