Actenos, Bamber, Roger N., 2013

Bamber, Roger N., 2013, Tanaidaceans from Brunei, IV. The Families Kalliapseudidae, Pagurapseudopsidae, Parapseudidae and Apseudidae (Crustacea: Peracarida: Tanaidacea: Apseudomorpha), with descriptions of a new genus and six new species, Zootaxa 3734 (4), pp. 401-441 : 407-408

Genus Actenos gen. nov.

Diagnosis: Pakistanapseudin without ventral-distal row of fine or lanceolate spines on propodus of pereopod 6; dactylus of pereopods 1 to 3 distally bifurcate, without distinct unguis; carpus of pereopod 1 dorsal margin with conspicuous array of long setae. Mandibular molar with or without rugose or denticulate distal flange. Eyes present, pigmented, rostrum centrally extended to a point; pereonite 4 (and either 3 or 5) as long as or longer than wide; all pleonites together nearly twice as long as carapace; epistome with up-curved spine-like apophysis; maxillule inner endite with proximal inner apophysis. Pereonites mostly wider at attachment of pereopod coxae. Pereopod 1 with spine(s) on coxal apophysis, without spines on dorsal margin of propodus. Pleonites expanded posterolaterally to accommodate ventrolateral attachment of pleopods; pleopod bases with both inner and outer setae. Peduncle articles 2 and 3 of mature male antenna fused.

Etymology: From the Greek— A (not) and ktenos (a comb), referring to the lack of a row of spines/spinules along the ventral to distal margin of the propodus of pereopod 6. Masculine.

Type species: Actenos marshalli sp. nov. by original designation.

Other species: Actenos kalimantus sp. nov., A. tenuicorporeus (Shiino, 1963) comb. nov.

Remarks: With the relatively elongate pereonites and pleonites, a labial palp with an inner apophysis and two distal spines, and the secondary segmentation of the antennal and antennular flagella, the two new species described below are clearly members of the Pakistanapseudinae , and constitute the new genus established here.

However, only one other species of the subfamily, Biropalostoma tenuicorporeus (Shiino, 1963) , lacks the ventral-distal row of fine spines on the propodus of pereopod 6, where that pereopod is known; it is unknown in Pakistanapseudes brasiliensis Guţu, 1996 (a), Leptolicoa thokozele (Bamber & Sheader, 2003) and B. goofi (Bamber & Sheader, 2003) , but those species have other clear distinctions from Actenos gen. nov.. B. tenuicorporeus also has a pereopod 1 carpal setal array, no dorsal marginal spines on the carpus or propodus of pereopod 1, has very similar claw morphology on pereopods 2 to 6 to the species of Actenos , and apparently does not have a distinct unguis on the bifurcate pereopod1 dactylus.

Having been moved originally from Apseudes to Pakistanapseudes Băcescu, 1978 by Băcescu (1978), B. tenuicorporeus was placed in the genus Swireapseudes Bamber, 1997 by Bamber (1997), returned to Pakistanapseudes by Bamber & Sheader (2003), and moved to Biropalostoma by Guţu & Angsupanich (2004) on the basis of having some outer ornamentation on the mandibular body, a feature not present in Actenos . The type-species of Biropalostoma , B. spiniferum Guţu & Angsupanich, 2004 , has a distinct unguis on pereopod 1, a row of spines on the propodus of pereopod 6, and dorsal marginal spines on propodus and carpus of pereopod 1 (as well as a large tubercle on the outer margin of the mandible, a diagnostic character of that genus). Features such as the spination of the pereopod 6 propodus and carpus and the propodus of pereopod 1, as well as the presence of an unguis on the anterior pereopods, together with the ventrolateral placement of the pleopods, are considered here to be of greater phylogenetic significance than the presence or absence of some cuticular ornamentation on the mandible body, and so Shiino’s species is transferred to Actenos .

Further, within the Pakistanapseudinae , the lack of a distinct unguis on pereopod 1 is only found in the generotype of Pakistanapseudes , P. leptochelatus Băcescu, 1978 , based on the figure of Băcescu (1978), and no mention of this was made in his description. Unlike the two species described below, P. leptochelatus lacks the bifurcate claw on pereopods 2 and 3 and the large array of setae on the dorsal margin of the pereopod 1 carpus, as well as having far more spines on the carpus and propodus of pereopod 1, but no setae on the outer margin of the basis of the pleopods; there are other distinctions of the mouthpart proportions and setation. Băcescu (1978) makes no mention of a comb of fine spines around the ventrodistal margin of the propodus of pereopod 6, although he does describe and illustrate it for P. shiinoi Băcescu, 1978 in the same paper. If P. leptochelatus lacks the spine-row on pereopod 6, then a complete revision of the Pakistanapseudinae may be necessary.

The dorsal setal array on the carpus of pereopod 1 invites speculation as to its function. It may act as an aid in locomotion (swimming), although where such a functional modification is known within the Parapseudidae—in Remexudes toompani BłaŻewicz-Paszkowycz & Bamber, 2007 —it has been achieved by an adaptation of the distal articles of pereopod 2. An alternative hypothesis is as some filter-feeding function: the gut contents of the species described below were found to be organic detritus rather than the sedimentary particles commonly found in guts of other parapseudids. The elaborate distal flange on the mandibular molar in both new species described below also suggests some atypical feeding strategy. Elaboration of dorsal setae on the distal articles of pereopod 1 are present in some other parapseudid genera, such as Platylicoa Guţu, 2006 and Ctenapseudes Bamber, Ariyananda & Silva, 1997 , although not in a similar conformation, but again their function is unknown.