Akanthoparapseudes, Heard, Richard W. & Morales-Núñez, Andrés G., 2011

Heard, Richard W. & Morales-Núñez, Andrés G., 2011, Akanthoparapseudes alfaroae, a new genus and species of apseudomorphan tanaidacean (Crustacea: Malacostraca: Peracarida) from Puerto Rican coastal waters, Zootaxa 3111, pp. 49-63 : 51-52

Akanthoparapseudes , new genus

Diagnosis (Subadult). Apseudomorpha, Parapseudidae , Parapseudini . Carapace without spinous processes. Triangular, apically-subacute rostrum. Epistomal spine present. Pereonites 2–6 with posterolateral margins armed with small, but distinct spiniform seta. Left mandible with tridentate lacinia mobilis, palp with article 1 having cluster of 10 or more simple distally-attenuated setae. Eye lobe distinct; eyes appearing poorly developed, lacking distinct pigment (in preserved specimens), ommatidia (about 8) small, poorly-formed. Maxilliped having distolateral margin of article 2 with strongly-developed spiniform seta. Pereopod 1 with strongly-developed spiniform setae on anterior margin of basis, coxa with reduced process present, not visible in dorsal view. Pereopod 2 with spine on anterior margin of basis; pereopods 2–6 with ischium bearing one, occasionally two narrow, acute spines on the anterior margin. Crenulate, rod-like, spiniform setae present on the merus, carpus and/or propodus of pereopods 2– 6. Pereopod 4 with dactylus, not greatly reduced, but with some adjacent setae about equal or greater in length. Uropodal peduncle with subdistal and distal setae only. Pereopod 6 having long simple setae along anterior margin. First pleonite lacking distinct transverse row of small setulate setae.

Type-species. Akanthoparapseudes alfaroae , n. sp.

Etymology. Akantho, from the Greek = spiny, plus the generic name Parapseudes , from the Greek; gender feminine.

Remarks. Although Akanthoparapseudes , n. gen., also appears to share several characters with the Apseudidae , with reservations we refer it to the Parapseudidae . Previously 22 genera have been referred to this family (see Anderson 2011). Of these genera, Akanthoparapseudes appears, at least superficially, to have affinities with Brachylicoa Guţu, 2006 , Longipedis Larsen and Shimomura, 2006 , and Podictenius Guţu, 2006 , all of which lack a distinct dorsal row of setae on the first pleonite. The new genus can be distinguished from these and from the other members of the family by a combination of characters, including having (1) pereopod 1 with a strongly developed spiniform seta on the anterior margin of the basis, (2) long, distally blunt, rod-like setae on the pereopods, and (3) pereopods 2–6 with the anterior margin of the ischium armed with one, occasionally two, spiniform setae. The following key may be used to distinguish Akanthoparapseudes further from Brachylicoa , Podictenius , and Longipedis .

Key to parapseudid genera within the Tribe Parapseudini sensu Gu ţ u lacking a distinct, dense transverse row of setae dorsally on the first pleonite

1. Pereopod 4 with dactylus greatly reduced, shorter than adjacent setae. Often with diffuse transverse row of setae on the first pleonite. Usually only four pairs of pleopods present....................................... Parapseudes Sars, 1882

- Pereopod 4 with dactylus not greatly reduced, not distinctly shorter than adjacent setae. Five pairs of pleopods present. No obvious dorsal transverse row of setae on first pleonite........................................................ 2

2. Mandibular palp with article 1 bearing single long seta........................ Longipedis Larsen and Shimomura, 2000

- Mandibular palp with article 1 having 5–15 simple setae....................................................... 3

3. Palp of maxilliped with tip of outer margin of article 1 armed with well-developed spiniform seta. Pereopod 2 with anterior margin of basis armed with distinct spine........................................... Akanthoparapseudes , n. gen.

- Palp of maxilliped with article 1 having distal corner of outer margin armed with minute spiniform seta. Pereopod 2 with anterior margin of basis lacking distinct spine................................................................. 4

4. Pereopod 1 with anterior margin of basis armed with row of 5–12 spiniform setae often increasing in length distally. Mandibular palp with first article bearing five or six simple setae..................................... Podictenius Guţu, 2006

- Pereopod 1 with anterior margin of basis lacking spiniform setae. Mandibular palp with first article bearing cluster (about 15) of simple setae..................................................................... Brachylicoa Guţu, 2006

Though the presence on the pereopods of spines on the anterior margin of the ischium is quite pronounced in the new genus; it is not unique and occurs in other apseudomorphans genera, including the apseudid genus, Bunakenia (see Guţu 1995, 1996; Bamber 2005) and the parapseudid genera, Brachylicoa (see Guţu 2006); Saltipedis Guţu, 1995 (see Guţu 1998; Morales-Nuñez et al. 2010); Gutuapseudes Edgar, 1997 (see Guţu and Angsupanich 2004b); and Swireapseudes (see Guţu and Iliffe 2008). It should be noted that within the genus Parapseudes , the anterior margin of the ischium on some pereopods bears a long simple seta; in some species this seta can extend well-past the merus (see Lang 1966, Shiino 1952); these long setae may be unique to Parapseudes , and possibly homologous with the ischial spines discussed above. Also, in at least in one apseudid species, Androgynella fecunda Guţu, 2006 , a plumose seta is present on the anterior face of the ischium of pereopod 6 (see Guţu 2006); this may be an independently-derived character.

Akanthoparapseudes also appears to have some affinities with the family Apseudidae ; however, pending further study we tentatively refer it to the family Parapseudidae , within the Tribe Parapseudini Guţu, 2008 . This Tribe was characterized by Guţu (2008) as having the pereonites distinctly broader and longer than those of the pleon, which is compressed (i.e. usually less than half the length of thorax) with the pleonites being distinctly wider than long). The Parapseudini also contains tube- or burrow-dwelling genera such as Halmyrapseudes Bačescu and Guţu, 1974 and Discapseudes Bačescu and Guţu, 1975 that have a distinct transverse row of tightly spaced, short setulate setae present on the dorsoproximal surface of at least the first pleonite. Akanthoparapseudes , along with three other genera, Brachylicoa Guţu, 2006 ; Podictenius Guţu, 2006 ; and Longipedis are characterized by lacking a distinct dense row of setulate setae. Within the genus Parapseudes Sars, 1882 some species appear to have a weak transverse row of setae (e.g., P. latifrons sensu Lang 1966 ), but they are simple and not setulose as in the known tubedwelling genera and others only have a few diffuse setae (e. g. P. neglectus Miller, 1940 , R. Heard, per. obser.).

As exemplified by Parapseudes , the overall presence or absence of the transverse row of setae on the first pleonite may not be as an important phylogenetic character as previously thought. Whether the other genera assigned to the Parapseudini (e. g., Ctenapseudes Bamber et al., 1996 ; Pseudohalmyrapseudes Larsen & Hansknecht, 2004 ; Saltipedis Guţu, 1995 ) having a dense transverse row of finely setulate setae on the first pleonite are tube, burrow, or" “nest” builders remains to be discovered. Notwithstanding this, for the species attributed to the Parapseudini , this condition appears to be an important and distinctive character, which may be associated with a tube, burrow, or “nest” dwelling as exemplified by the genera Halmyrapseudes , Discapseudes , and Pseudoapseudes ( Bačescu and Guţu 1974, 1975; R. Heard, per. obser.). Based on observations of living specimens of Halmyrapseudes bahamensis Bačescu and Guţu 1974 from southern Florida, the transverse dorsal rows of setulate setae on the pleon appear to filter out silt and other fine particles. This might be a mechanism to prevent fouling of the pleopods and, possibly, to retain potential food particles (R. Heard, per. obser.).

Such setae appear to be absent in members of the Tribe Pakistanapseudini , which, beside the distinctive sexual dimorphism of the male antenna and body form mentioned previously, appear to have no tube- or burrow-dwelling representatives. In our opinion the Pakistanapseudini appear to form a more natural group than the more heterogeneous genera currently placed within the Parapseudini .

A small, reduced coxal process or lobe is present on the first pereopod of Akanthoparapseudes , but it is not visible from the dorsal aspect ( Fig. 2 H). A similar more reduced coxal process has been reported for a few other parapseudids (e.g., Longipedis fragilis Larsen and Shimomura, 2006 ; Saltipedis puertoricensis Morales-Núñez , Heard, and Alfaro, 2010). It is possible, however, that this structure may have been overlooked in other parapseudid taxa.

Akanthoparapseudes appears to be related to “Parapseudid? species A” sensu Heard et al. (2004) from the eastern Gulf of Mexico. Except for the lack of a strongly developed and dorsally visible, coxal spine or process, Akanthoparapseudes and “Parapseudid? sp. A” appear to share several characters with some members of the apseudid genus Bunakenia Guţu, 1995 , especially those species attributed to the subgenus Extensibasella Guţu, 1998 . The possible affinity of Bunakenia with the family Parapseudidae also has been broached previously by Guţu (2006). These morphological similarities are most event in the mouth parts (e.g., tridentate or bidentate lacinia mobilis), setation and shape of the maxilliped, and the setation of the pereopods (e.g., presence of spiniform setae on the anterior margin of the ischium for pereopods 2–6,), and propodal setae on pereopod 4 extending to or beyond the dactylus. Since members of the genus Bunakenia appear to share some distinctive homologous characters with them, Akanthoparapseudes and “Parapseudid? species A” may represent transitional links between the families Apseudidae and Parapseudidae

Some of the systematic problems exhibited by several apseudomorphan families are exemplified by overlapping characters within the Parapseudidae and Apseudidae . As indicated by Guţu (2007), the designation of a variety of apseudomophan genera during the past 20 years, has eroded and diluted some of the basic differences between these two families. This is especially true for some of the genera discussed in this paper. M. Guţu (per. comm., 2011) considers the most consistent family character for the Parapseudidae to be the extension of the propodal setae on pereopod 4 to or beyond the tip of the dactylus. Except for the small deep-water family Gigantapseudidae and the apseudid genus Bunakenia , this character appears to hold for all of the presently known parapseudid species (see Guţu and Heard 2002; Guţu 1998, 2006; Guţu and Angsupanich 2004 a, b). The occurrence of a reduced coxal process of the first pereopod on some parapseudids (e.g., Longipedis , Akanthoparapseudes ), weakens this once definitive morphological maker for the separation of the two families making it difficult to identify unique delineating characters to distinguish them. As mentioned by Bamber (1998) and Guţu and Heard (2002), another factor complicating apseudomorphan systematics, is the presence of a distinctive leaf-shaped spine on the inner distal margin of the maxillipedal endite in some parapseudid genera (e.g., Pakistanapseudes , Saltipedis ). This “leaf-shaped spine appears to be similar to those found in the same location on members of the apseudid subfamily Leviapseudinae Sieg, 1983 and family Whiteleggiidae Guţu, 1972 ; whether this condition is due to homoplasy or has systematic significance remains to be seen. Based our present limited knowledge, an adequate understanding of the present systematic status of the family Parapseudidae is beyond the scope of this study. Its resolution will require detailed morphological studies with robust systematic analyses (e.g., cladistics), coupled with new information derived from comparative molecular genetic studies.

Figures

FIGURE 2. Akanthoparapseudes alfaroae n. gen., n. sp., subadult female holotype. A, body, dorsal view; B, enlargement of posterolateral margin of pereonite 2; C, enlargement of posterolateral margin of pereonite 3: D, E. enlargement of lateral margins of first and fifth pleonites, repectively, 1; F, enlargement of pleotelson; G, enlargement of uropod; H, lateral view of cephalothorax and pereonite 1. Scale line: A = 1.0 mm; H = 0.2 mm.