Acutihumerus petronius Araújo-Silva & Larsen, 2010, n. sp.

Acutihumerus petronius n. sp.

(Figs. 2–4)

Material examined. Holotype. Ovigerous female (DOUFPE – 14.090), 4.48 mm, TRANSPETRO/ ANGRA # 29 C (23º01.329’ S 44º15.1295’ W). Allotype. Male (DOUFPE – 14.091), # 29 C (23º01.329’ S 44º15.1295’ W). Paratypes. 1 ovigerous female (DOUFPE – 14.092), # 31 B (dissected) 23º02.3974’ S 44º15.1182’ W). 2 males, 1 non-ovigerous female (DOUFPE – 14.093), # 17 C (23º03.3449’ S 44º14.1946’ W). 1 ovigerous female, 1 male (DOUFPE – 14.094), # 19 B (23º03.4005’ S 44º13.5657’ W). 1 male (DOUFPE – 14.095), # 9 C (23º03.909’ S 44º13.2941’ W). 1 non-ovigerous female (DOUFPE – 14.096), # 5 A (23º03.3238’ S 44º14.3975’ W).

Type locality. Baía de Jacuecanga, Angra dos Reis, Brazil. Depth 20 – 30 meters.

Etymology. Named in honor to Dr. Petrônio Alves Coelho, in recognition of his many contributions to crustacean research in Brazil.

Diagnosis (ovigerous female). Cephalothorax without hyposphenian. Pleonites with anterior directed ventral hyposphenians, with hook-shaped lateral epimera. Antenna article 1 with very small inner lobe. Right and left mandibular incisor with 1–5 denticles, respectively. Maxilliped basis setose. Epignath terminal setae setulose. Cheliped basis without spine, merus and carpus with multiple semi-plumose setae. Pereropod 1 basis long and thin. Pereopod 4 basis not bulging, propodus with 2 sensory aesthetascs. Pereopod 6 basis with with multiple semi-plumose, merus carpus dorsal margin uneven with multiple semi-plumose setae.

Male. Pereonites 2–5 of trapezoidal shape, all with clearly anterior and posterior lateral hook-shaped spines; Pereopods 2–3 with stout proximodorsal spine; cheliped strongly dimorphic, carpus short: propodus prominent, fixed finger short but with pronounced spiniform projection; dactylus marginally much longer than fixed finger, with four denticles and spiniform projection on inner margin.

Description of female. Length, 4.48 mm

Body (Fig. 2 A). slender (about 6 times longer than broad) dorsoventrally flattened.

Cephalotorax marginally longer than broad. Rostrum short and bilobate. Ocular lobes present, without visual elements.

Pereonites. All wider than long. Pereonite 1 without lateral hooks or spines. Pereonites 2–4 with anterior and posterios hook-shaped spines. Pereonites 5 and 6 with anterior hook-shaped spines and small posterior spines.

Pleonites (Fig. 2 E). All of similar proportions. Dorsally and laterally with several setae, with acute lateral spines. Pleonites 1 and 2 with large anterior directed ventral spines.

Pleotelson (Fig. 2 C). Shorter than two pleonites combined. With mediolateral depression and hookshaped spines, with two simple setae.

Antennule (Fig. 3 A) about 25% longer than cephalotorax. Article 1 marginally larger than rest of antennule, with eight proximal and three distal setulated setae on outer margin and multiple simple setae on both margins, concentrated in a medial and a distal cluster. Article 2 thinner and about one-third as long as article 1, with multiple long and short setulated scattered setae. Article 3 less than half as long as article 2, with three simple distal setae. Common article naked. Outer rami, with four articles, last article with five setulated terminal setae and one aesthestasc with multiple constrictions. Inner rami with two articles, distal article with three setulated distal setae and one aesthetasc.

Antenna (Fig. 3 B) Article 1 wider than other articles but with only small inner lobe, naked. Article 2 twice as long as article 3, with a small spiniform seta on distoinner margin; squama small and elongated, with six setulated setae spaced with regular intervals. Article 3 shorter than other articles, naked. Article 4 longer than other articles, with three short and four long setae scattered along the margins. Articles 5–8 subequal and all with simple setae.

Mouthparts. Labrum (Fig. 3 C) with flat or slightly concave and setulated apex. Clypeus with ventral groove anterior to the mouth-opening. Mandibles (Figs 3 G, 3H). Molar typical for Apseudomorpha, long broad and with heavily chitenous apex. Palp with three articles, article 1 with four long semi-plumose setae, article 2 very long and slender (twice as long as article 1) with nine distal setulated setae, article 3 shorter than other articles and with about eight simple setae. Right mandible (Fig. 3 G) incisor with one denticle only. Lacinia mobilis completely missing. Setal row with five, bi- or trifurcate setae originating from a common peduncle. Left mandible (Fig. 3 H) incisor with five denticles. Lacinia mobilis with four denticles. Setal row with six, bi- or trifurcate setae originating from a common peduncle. Labium (Fig. 3 D) palp with three short simple terminal setae and multiple setules. Lobes with medial setules only. Maxillule (Fig. 3 E) without palp. Outer endite with ten spiniform terminal setae of which one is serrated and four outer simple setae. Inner endite with three bi or trifurcate spiniform setae and two setulated setae with several simple setae on outer margin. Inner proximal margin with several simple setae and one spiniform projection. Maxilla (Fig. 3 I) Outer lobe of movable endite with three long pinnate setae. Border with inner lobe indistinct. Inner lobe with two pinnate setae. Fixed endite inner lobe with three spiniform serrated setae, two trifurcate spiniform setae and few pinnate setae. Outer lobe with multiple distally curved setae. Maxilliped (Fig. 3 J) with small naked coxa. Basis very large, with uneven outer margin and eight regularly spaced setulated setae. Endite with eight distal spiniform setae of which at least two are complex and four simple setae; inner margin with three coupling hooks; outer margin five circum-setulated setae. Palp article 1 with four inner semiplumose setae and seven small simple outer setae. Article 2 with two long semiplumose and several simple inner setae and one large outer seta. Article 3 with several long semiplumose setae. Article 4 very small with six long semiplumose and two simple inner setae. Epignath (Fig. 3 F) with medial depression, long setulose terminal spine and setulose inner apex.

Cheliped (Fig. 4 A), rather small, without exopod. Most- but not all setae of the ‘semiplumose’ type. Basis without spinifom apophysis, with two clusters of ventrodistal setae. Merus long (longer than half as long as carpus), with distoventral rounded expansion and multiple semiplumose setae. Carpus with four clusters of mostly semiplumose setae, one proximodorsal, one distodorsal, one distoventral and one medioventral. Propodus only marginally wider than carpus, shorter than merus, with several scattered setae, some semiplumose some simple. Fixed finger with seven to eight small denticles on inner margin, one semiplumose and one ventral simple setae. Dactylus marginally longer than fixed finger, with five denticles on inner margin and mediodorsal cluster of simple setae; unguis stronger than the same of fixed finger.

Pereopod 1 (Fig. 4 C) coxa with strong spine (not illustrated). Exopodite absent. Basis fairly short, less than twice as long as merus, but not broader, more than twice as long as broad, with one small proximodorsal setae and three ventrodistal setae. Ischium short and almost reduced at the dorsal margin. Merus longer than carpus and widening distally, with ventromedial and proximodorsal cluster of simple setae, with large ventrodistal and dorsodistal spiniform seta. Carpus about as long as propodus, with three spiniform and four simple ventral setae and one large spiniform seta and cluster of simple setae dorsodistally. Propodus with three ventral and two dorsal spiniform setae and simple setae along entire ventral margin and distal dorsal margin, one serrated seta and additional dorsomedial setulated seta. Dactylus as long as propodus, with one proximodorsal and six subterminal aesthetascs of with the terminal display at least three offshots. Unguis one/ fifth the length of dactylus.

Pereopod 2 (Fig. 4 D) much smaller than pereopod 1. Basis longer than combined length of three succeeding articles, with one spine, three plumose and two dorsoproximal setae, three ventrodistal simple setae. Ischium not reduced, with one ventrodistal seta. Merus, shorter than carpus, with five ventral setae. Carpus wider than merus, with three spiniform and six simple ventral setae, two simple dorsodistal setae and one spiniform dorsodistal seta. Propodus with ten evenly spaced setae along entire ventral margin and four dorsodistal, four subequal spines and two setae distoventral. Dactylus longer than propodus, without unguis but with sensory apparatus consisting of five aesthetascs.

Pereopod 3 (Fig. 4 E) of similar proportions as pereopod 2; carpus with ventral but lacking dorsal spiniform seta; propodus more elongated and with dorso and ventromedial setulated seta; apex of dactylus with ‘non-aestetascs ‘distal offshots.

Pereopod 4 (Fig. 4 F) similar to pereopod 3 except basis slightly wider and with ventroproximal process. Carpus without spiniform setae. Propodus with distal row of small spiniform setae and two dorsomedial setulated seta.

Pereopod 5 (Fig. 4 G) similar to pereopod 4 except coxa with simple dorsodistal seta, basis with three setulated proximal setae. Merus, carpus and propodus with long spiniform setae.

Pereopod 6 (Fig. 4 H) Basis with seven plumose and two simple dorsal setae. Ischium with two ventral setae. Merus, shorter than the carpus, with a small dorsal process, five simple ventral setae, two plumose and one simple dorsal setae. Carpus with seven simple ventral setae, dorsal margin uneven with six plumose setae and one distal spiniform seta. Propodus, shorter than carpus, with four long sparsely setulated dorsodistal- and one ventrodistal spiniform setae, ventral and distal margin covered with regularly spaced short serrated spiniform setae. Dactylus with very weak sensory apparatus. Unguis very small.

Pleopods (Figs. 2 D, 2E) well developed, five subequal pairs, biramous. Basal article

Rather long and elongated, with two plumose setae. Exopod shorter than endopod, with 16–17 plumose setae. Endopod with 18–20 plumose setae (not all setae illustrated).

Uropod (Figs. 2 A, 2C) Basal article not much longer than individual endopod articles, with one simple outer setae. Exopod with three articles, number 1 and 3 setulose, individually smaller than endopod articles. Endopod longer than pleon but shorter than pereon, with less than 20 articles, many of them with long setae.

Male (where different from female)

(Figs. 2 B, 4B)

Length, 3.96 mm

Body (Fig. 2 B). Pereonite 1 with posterior lateral hook-shaped spine, rectangular shape; pereonite 2–6 with anterior and posterior lateral hook-shaped spines more pronounced, in trapezoidal shape.

Pereopods. With proximodorsal spines on basis os pereopods 2–3

Cheliped (Fig. 4 B) Basis much wider than merus. Carpus 4–5 times shorter than propodus; fixed finger with several simple setae with a strong spiniform projection; dactylus with four serrated denticles and one spine on inner margin.

Manca I larvae (removed from the female marsupium).

(Fig. 5A)

Length, 0.28 mm

Body (Fig. 5A). Slender (about 6 times longer than broad) but cylindrical.

Cephalothorax almost completely round, much wider than somites, no trace of ocular lobes, rostrum indistinct.

Pereonites. All without lateral hooks, spines or lateral shield. Pereonite 1 wider than long. Pereonites 2–5 cylindrical. Pereonite 6 weekly developed and of the size of a pleonite.

Pleonites All of similar proportions. Without setae, spines, pleopods or lateral shield.

Pleotelson. Shorter than two pleonites combined. Without the mediolateral depression and hook-shaped spines.

Antennule (Fig. 5A). About as long as cephalotorax. Article 1–3 of the same proportions as the adult female but devoid of setae. Both rami, with 3 articles with only a few setae.

Antenna (Fig. 5A). Squama better developed (relative to rest of antenna) than in adult, with two simple distal setae. Flagellum not developed.

Mouthparts. Not dissected but visibly well developed.

Cheliped (Fig. 5A). No trace of exopod.

Pereopod 1 (Fig. 5A). Anlage for sensory apparatus visible. No trace of exopod.

Pereopod 4 and 5 (Fig. 5A). with large but apparently uniarticulated exopod with distal setose.

Pereopod 6 not developed in the manca I larval stage.

Pleopods not developed in the manca I larval stage.

Uropod (Fig. 5A). Basal article poorly developed. Exopod about half as long as endopod, with few pseudoarticulations without setae. Endopod as long as pleotelson and 2 pleonites combined, with few pseudoarticulations without setae.

Remarks. This species is closely related to Acutihumerus cavooreni, however the cheliped and dorsal margin of pereopod 6 display plumose or semi plumose setae. The new species differ from A. patagonensis by the absence of visual elements, the small antenna article 1 inner lobe and the second article without prolongations, the pereopod 4 basis not bulging and by the pereopod 6 merus and carpus dorsal margin being uneven. Furthermore, A. patagonensis appears not to have the sparsely-plumose setae on the first mandibular palp article and the maxilipod palp, the format of the second palp of maxilipod is more robust in A. petronius.

Guţu’s (2006) redescription of Acutihumerus cavooreni, differs substantially from that of Băcescu & Absalao (1985) in that it displays a rectangular carapace and a pleotelson devoid of lateral processes, while Băcescu & Absalao (1985) illustrate an almost square carapace and clear lateral processes on the pleotelson. This is to be expected as Băcescu & Absalao took this information from the female while Guţu’s redescription figures the male. The´missing´pleural processes could also be an artifact cause by the ventral flexing of the prosterior somites typically for this taxon.

Acutihumerus petronius has a rectangular carapace and a pleotelson with clear spiniform lateral processes. It also displays a ventral keel on pleonites 1–3 and lateral pleonal spines. The ventral keel is also indicated by Băcescu & Absalao (1985:52, fig. 2A) for A. cavooreni, but is not mentioned by Sieg (1986) for A. patagonensis.

The anterior pereopod basis seems equipped with a proximal hook in A. patagonensis and A. petronius but we have been unable to find any information about this character in A. cavooreni. If present in A. cavooreni also, this would be a good generic character.

Guţu (2006) state that the Hemikalliapseudinae lack plumose setae on the maxilliped palp and cheliped carpus but in the new species we did observe sparsely-plumose setae on the cheliped merus and carpus, the first mandibular palp article as well as on other appendages. These setae are plumose in the sense of having regularly spaced setules on both margins but they are clearly not as dense as the plumose setae in the Kalliapseudinae or those on the pleopods of most Apseudomorpha; they are also not present in great numbers as in Kalliapseudinae. Such setae are unlikely to sustain any filter-feeding strategy and are considered a rudiment that does, however, suggest affinities with the Kalliapseudinae.