Mexctenapseudes, Drumm & Heard, 2022

Drumm, David T. & Heard, Richard W., 2022, Mexctenapseudes boeschi, a new tanaidacean genus and species (Crustacea: Peracarida: Apseudomorpha: Parapseudidae) from the Mexican coast of Campeche with the designation of a new related Australian genus to receive Longiflagrum caeruleus (Boesch, 1973), Zootaxa 5116 (2), pp. 200-222 : 205

Mexctenapseudes n. gen.

Diagnosis. Carapace with smooth lateral margins; rostrum subtriangular. Pereon, except on pereonite-1, in both sexes with hyposphenia weakly-developed or appearing absent. Pleon having first pleonite with complete, anterodorsal, transverse row of short setulate setae; pleonites 2–5 lacking such transverse rows. Pleonal hyposphenia well-developed, decreasing in size posteriorly. Pleotelson elongate, lateral margins straight and sparsely setose. Antenna peduncle article-1 with antero-medial tooth-like projection with plumose setae; peduncle article-5 shorter than combined length of articles 2 and 3 and lacking long plumose setae on inner margin. Mandibular palp articles bearing long simple setae, lacking plumose setae; last two articles each with row of short pectinate setae; article-3 shorter than article-2. Labial palp with three distal spiniform setae. Maxilliped basis with outer distal margin forming small subacute process. Chelipeds strongly sexually dimorphic, basis in both sexes lacking spiniform setae on mid-ventral margin; exopodite with terminal article of male and female bearing four plumose setae; exopodal article-2 having two minute setae on ventral margin. Pereopod-1 having carpus with moderate distal expansion, with dorsodistal spiniform seta and two ventral spiniform setae; propodus having dorsodistal margin with two spiniform setae near or adjacent to insertion of dactylus; ventral margin with four or five strongly developed spiniform setae; dactylus length subequal to that of propodus length. Pereopod-4 dactylus distinct, not greatly reduced. Five pairs of pleopods, basal article and rami with numerous plumose setae, rami moderately foliaceous.

Type-species. Mexctenapseudes boeschi n. sp.

Etymology. Mex - referring to Mexico + generic name Ctenapseudes.

Remarks. Mexctenapseudes n. gen. appears to have its closest taxonomic and systematic affinities with Indian and western Pacific Ocean genera Ctenapseudes, Longiflagrum, and Pseudolongiflagrum . Mexctenapseudes is superficially similar to Pseudolongiflagrum by both having (1) a labium with three terminal spiniform setae, (2) the propodus of pereopod-1 having the dorsodistal and ventral margins bearing two and four or five, well-developed spiniform setae, respectively, and (3) both genera having a strongly developed dactylus on pereopod 1, a combination of nonexclusive characters that distinguishes them from both Ctenapseudes and Longiflagrum.

The new Mexican genus is distinguished from Pseudolongiflagrum by (1) the antennal flagellum having only simple setae, (2) the mandibular palp article-3 shorter than article-2; (3) the basis of the cheliped lacking a stout spiniform seta on mid-ventral margin, and (4) lacking strongly developed hyposphenia on the pereonites. Specifically, Mexctenapseudes can be separated from Ctenapseudes by having a labium with three terminal spiniform setae (two in Ctenapseudes), the first peduncle article of the antenna with setae near the medial margin (lacking such setae in Ctenapseudes), and as previously mentioned the pereopod-1 dactylus subequal in length to propodus (much shorter than propodus in Ctenapseudes). Mexctenapseudes is distinguished from Longiflagrum (except L. estuarius), by having antennal article-2 lacking long setae on the inner margin. It, however, exhibits affinities with both Ctenapseudes and Longiflagrum by having: 1) the first article of antenna peduncle with tooth-like medial projection, 2) the last two articles of mandibular palp with numerous long and short setae, 3) pereopod-1 with carpus having a broadly lobate, anterodistal expansion, and 4) pleopods with fully foliaceous rami.

Zoogeographically, members of Ctenapseudes are distributed in coastal regions of the Indian Ocean (off India, Sri Lanka, and Thailand), whereas those of Longiflagrum are distributed along the coasts of the Indian and western Pacific Oceans (off Australia, Thailand, and Japan).

The morphologically distinct genus Discapseudes Băcescu & Guţu, 1975, which is represented by five extant and one fossil species in tropical American waters (SE Mexico, Central America, northern South America) and a single SW Asian species (see Heard et al. 2018), is distinguished from both Mexctenapseudes and Pseudolongiflagrum by (1) the pleotelson having a row of short setae on the lateral margins; (2) the antenna having a long peduncle article-5 with numerous long, plumose setae on the inner margin, and lacking a tooth-like expansion on the first peduncle article; (3) the mandibular palp with numerous plumose setae on each article; (4) the labial palp having two terminal spiniform setae; and (5) the dactylus of pereopods 1 and 4 being reduced and shorter than adjacent spiniform setae.

Mexctenapseudes can be readily separated from the widely distributed genus Halmyrapseudes Băcescu & Guţu, 1974 by (1) having a well-developed, multiarticulate, inner antennular flagellum, while that of the latter is reduced having just two or three articles; (2) the dactylus of pereopods 1 and 4 subequal in length to propodus (reduced and much shorter than propodus in the latter); and (3) only the first pleonite with a transverse anterodorsal row of short setulate setae, while the latter has transverse rows on all five pleonites.