Parapseudes arenamans
Creators: name: Larsen, Kim
name: Shimomura, Michitaka
Publisher: name: Zenodo
Year: 2008
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Tanaidacea
Parapseudidae
Parapseudes
Parapseudes arenamans

description: Parapseudes arenamans n.sp
(Figs 1–4)
Material examined. Holotype ovigerous female, body length 4.7 mm (KMNH IvR 500,218), 6–6.5 meters depth, fine sand, by Majanohama reef, off Akajima (Aka Island), East China Sea, 2–7 June 2007. Paratypes 1 non ovigerous and 1 ovigerous females (dissected) (KMNH IvR 500,219), 3 non ovigerous females 1 male, (KMNH IvR 500,220), same locality.
Etymology. The species is named after the sandy habitat of the type locality (Latin: arena-amans = sandlover).
Diagnosis. Pereonites 4–6 lateral margins almost straight and gaps between pereonites small (<10% pereonite length). Pereonites 5–6 almost square. Pleotelson about 0.75 times the length of all pleonites combined. Maxilla inner lobe of fixed endite with row of short stout setae. Cheliped fixed finger apex blunt and dactylus bifurcate. Pereopod 1 basis without spines. Pereopod 4 dactylus less than one third as long as dactylus of pereopods 2, 3, and 5; unguis reduced. Pleopod basal articles as long as endites.
Description of female (body from holotype, appendages from dissected paratype).
Body (Fig. 1 A, B). Dorso-ventrally flattened (about 5.5 times longer than wide).
Cephalothorax. Longer than pereonites 1–2 combined (including rostrum). Ocular lobes well developed, with visual elements. Rostrum pointed and ventrally curved in lateral view but appears blunt in dorsal view due to the curvature.
Pereonites. Pereonites 1 and 2 naked. Pereonites 3–6 with lateral setae. Pereonites 1–5 wider than long. Pereonites 4–6 longer than other pereonites and almost square. Lateral shoulders barely visible in dorsal view as posterior lobes. Small ventral hyposphenia on pereonites 1–4 (obscured by oostegites) and pereonite 6.
Pleon. Tapering, about 0.2 times total body length. Pleonites all wider than long, with posteriorly directed pointed epimera. Pleonite 1 with weak band of dorsal and dorso-lateral setae, all other pleonites bearing individual dorsal and lateral setae. Pleonite 5 without pleopods. Pleotelson longer than last three pleonites combined.
Antennule (Fig. 1 C). 1.5 times longer than carapace. Peduncle article 1 twice as long as article 2, with eight simple setae. Article 2 almost twice as long and wide as than article 3, with six simple setae. Article 3 only marginally larger than flagellum articles, with cluster of five distal simple setae. Common article naked. Outer flagellum about as long as peduncle, consisting of 11 articles, with 0–3 simple setae, articles 6 and 8 each with one aesthetascs. Inner flagellum almost as long as outer flagellum, consisting of seven articles, with 0–4 simple setae but no aesthetascs.
Antenna (Fig. 1 C, c1). About half as long as antennule. Article 1 with sharply serrated, lobate ventral process and two ventral setae. Article 2 with three setae, carrying squama in a distal position. Squama well developed, twice as long as article 3, with 8–12 simple setae (individual variation). Articles 3–13 of diminishing width, with 0–4 simple setae but only article 10 with one aesthetascs.
Mouthparts (Fig. 2 A–E). Labrum (Fig. 2 A) distal margin finely setulose. Mandible molar with numerous distal spines. Palp with three articles; article 1 with three or four equally sized distal setae; article 2 with distomedial row of weakly bipinnate setae; article 3 with eight, weakly bipinnate, setae. Left mandible (Fig. 2 B) incisor trifurcate; lacinia mobilis as large and of the same shape as incisor; setal row consists of four multifurcate spiniform setae arising from common peduncle. Right mandible (Fig. 2 C) incisor in the shape of single spine with weak denticle: lacinia mobilis present but reduced and fused with setal row peduncle: setal row of four multifurcate setae arising from common peduncle. Labium (Fig. 2 D) palp with numerous setules and three stout terminal setae; basis with outer spines and distal setules. Maxillule (Fig. 2 E) palp with two articles, distal article tipped by four distally hooked setae. Outer endite tipped by ten spiniform distal setae and scattered setules on outer margin; inner endite with four setulated setae. Maxilla (Fig. 2 F) outer lobe of movable endite with two clusters of five and two- thick weakly serrated setae respectively. Inner lobe of movable endite with five weakly serrated setae. Outer lobe of fixed endite with two simple, five bipinnate and four complex setae. Inner lobe of fixed endite with one row of stout bipinnate setae and numerous weakly bipinnate setae originated from a wider peduncle. Maxilliped (Fig. 2 G,H) basis with denticulate process at distal outer corner, inner corner with one seta. Endite (Fig. 2 G) with four complex setae and row of simple setae and setules on distal margin: inner side with four coupling hooks and seven setulose setae. Palp (Fig. 2 H) article 1 outer margin with one short seta, inner margin with one long seta; article 2 inner margin with row of simple setae, outer margin with row of long setae distally; articles 3 and 4 lost during dissection. Epignath lost during dissection.
Cheliped (Figs. 3 A, B, b1). Basis shorter than carpus, with strong ventral spiniform seta and single ventrodistal seta. Merus half the length of carpus, with six simple ventrodistal setae and scattered setules. Carpus with individual seta medial and three on ventrodistal margin. Propodus with long setae at dactylus insertion. Fixed finger with at least eight simple setae on ventral margin and seven on inner margin. Inner margin also with at least five short rigid setae, apex blunt. Dactylus bifurcate and as long as fixed finger. Exopod consisting of three articles, distal article with four plumose setae.
Pereopod 1 (Fig. 3 C). More robust but of similar length as other pereopods. Coxa without apophysis. Basis stout, about 1.5 times longer than wide and shorter than merus and carpus combined, without proximal spines (see remarks), dorsal margin with relatively long setae, ventral margin with short setae, one ventrodistal spiniform seta. Ischium with three ventral setae. Merus longer than carpus with one dorsal and two ventral spiniform setae and scattered simple ventral setae. Carpus wider than propodus, with one distodorsal and four ventral spiniform setae and scattered simple setae on both margins, with ventrodistal scale cluster. Propodus longer than dactylus/unguis, with two dorsal and five ventral spiniform setae and scattered simple setae on both margins, with ventro scale cluster. Dactylus 0.75 times as long as propodus, with two dorsal setae and two ventral spines. Unguis one third as long as dactylus. Exopod (not illustrated) consists of three articles, distal article with five plumose setae.
Pereopod 2 (Fig. 3 D). Coxa with one seta. Basis longer than ischium, merus and carpus combined, with 1–3 short simple setae and cluster of long simple ventrodistal setae. Ischium with five simple ventral setae. Merus shorter than carpus, with two ventral and one dorsal spiniform setae and few simple ventral setae. Carpus as long as propodus, with several simple and four ventral and four dorsal spiniform setae, one additional outer proximal spiniform seta. Propodus with three dorsal, five ventral spiniform setae, several simple setae on ventral margin and outer surface, one setulated seta on dorsal margin. Dactylus with one medial simple ventral seta; dactylus and unguis shorter than propodus.
Pereopod 3 (Fig. 3 E). As pereopod 2 except: ischium with two setae. Merus with three ventral- but without dorsal spiniform setae. Carpus with two outer spiniform setae. Propodus with one additional dorsal spiniform setae as long as dactylus; dactylus naked.
Pereopod 4 (Fig. 3 F). Basis much wider than pereopod 2 and 3, with few setules and long ventrodistal setae. Ischium with both ventral and dorsal setae. Merus shorter than carpus, with three rather slender ventral spiniform and several simple setae. Carpus longer and wider than propodus, with three dorsal spiniform, six spiniform ventral and several simple ventral setae. Propodus with one proximal plumose dorsal seta, seven spiniform setae of varying length and few simple setae. Dactylus (Fig. 3 G) reduced and unguis reduced to a setae.
Pereopod 5 (Fig. 3 H). As pereopod 4 except: merus with only two spiniform setae. Carpus with one dorsal and eight ventral spiniform setae. Dactylus and unguis not reduced.
Pereopod 6 (Fig. 3 I). As pereopod 5 except: basis densely covered with plumose setae on dorsal margin. Merus with one and carpus with three plumose setae on dorsal margin. Propodus with four ventral, two dorsal and three smaller spiniform setae on outer margin, with few small simple setae. Dactylus naked.
Pleopods (Fig. 1 D). Basal articles as long as endites, with eight plumose setae. Exopod with one article, with 13 plumose setae. Endopod longer than exopod, with 14 plumose setae (not drawn for clarity).
Uropod (Figs 1 E). Long (longer than combined length of pleon and last two pereonites). Basal article three times as long as wide. Endopod with more than 30 articles. Exopod of seven articles. Many articles naked, others with one–three simple setae.
Juvenile male (where differing from female)
Antennule (Fig. 4). Both flagella with numerous large aesthetascs.
Pereopod 4 dactylus more reduced than female. Unguis completely reduced.
Remarks. All members of this genus are superficially similar and difficult to separate. Previous studies have mainly focused on the variations in the male cheliped and the number of articles in the antennae and uropods as means to separate these species. As all of these characters are also known to be ontogenetic (Menzies 1953, Larsen 2005 and references therein) this situation is unfortunate and the identification of species of Parapseudes is consequently very difficult. Lang (1966) and Sieg (1983) listed all described species of Parapseudes as synonymous with the type species P. latifrons. It is our view that such cosmopolitan distribution is unlikely for a single species and closer examination of the literature also suggests that differences are present between several of the species, notably characters such as the shape of the pereonites, and shape of the first antenna article.
The situation is complicated by the fact that the type specimen of the type species is considered lost (Sieg 1983:104) and the description made by Grube (1864) is insufficient for modern taxonomy. The redescription by Lang (1966) is made of a specimen from Japan, while the type locality is ‘Yugoslavia’, and thus probably deals with a different species than Grube’s original P. latifrons. On the other hand Lang (1966) did document (by description and/or illustration) an unsettling amount of intra-specific variation, making species identification even more uncertain. Such high intra-specific variation combined with low inter-specific variation is known from other tanaids as well (Larsen 2001). For these reasons a key is not constructed to the Parapseudes.
The new species is obviously not Parapseudes latifrons sensu Lang, 1966 and can be separated by the almost parallel margins and short space between pereonites 4–6. The same character separates the new species from and P. neglectus Miller, 1940, P. latifrons sensu G.O. Sars, 1886, P. g r u b e i Băcescu, 1977, P. pedispines Boone, 1923, and P. spongicola Brown, 1958. The new species can also be separated from the above species and from P. algicola Shiino, 1952, and P. goodie Richardson, 1905, by the blunt cheliped fixed finger and the bifurcate dactylus.
Another character that seems to have been ignored within the Parapseudes is the reduced dactylus of pereopod 4. The new species have a decidedly reduced pereopod 4 dactylus/unguis. Only Lang (1966) vaguely illustrates this character for P. latifrons, but does not mention it in his description. Shiino (1952) illustrated a fully developed pereopod 4 dactylus but this may well be a mistake as the propodus is heavily armed with thick spiniform setae. All other descriptions of Parapseudes neglect this character completely. It is thus not known if the character is generic or specific but it is assumed that it is specific but not uniquely so, as the same character is seen to be in Leviapseudes (Lang 1968).
The proximal spines on the basis of pereopod 1, illustrated by Lang (1966:561fig.7a) are in our view an artifact. We observed spine-like structures around that and other locations on some specimens, but these were shown by closer examination to be setae covered with mucus giving a spine-like appearance (Fig. 3 c1).
Although we are certain that Parapseudes arenamans is a new species, we abstain from making conclusions about the validity of the species synonymized by Lang (1966) as this would require a major revision and is outside the scope of this paper. Suffice to mention that when “wide-spread” and “similar looking” tanaids, like Paratanais (Larsen 2001), several genera of Typhlotanaidae (Blażewicz-Paszkowycz 2007), or Leptochelia (Bamber in press) are submitted to detailed studies, they have all revealed the presence of a species complex’. The situation regarding Parapseudes may be yet another such an example of conservative inter-specific morphology combined with significant intra-specific variation.
description: Published as part of Larsen, Kim & Shimomura, Michitaka, 2008, Tanaidacea (Crustacea: Peracarida) from Japan. IV. Shallow-water species from Akajima with notes on the recolonization potential of tanaids, pp. 1-24 in Zootaxa 1678 on pages 3-9, DOI: 10.5281/zenodo.274064