Liropus minusculus, Guerra-García, José M. & Hendrycks, Ed A., 2013

Guerra-García, José M. & Hendrycks, Ed A., 2013, A new species of Liropus (Crustacea, Amphipoda, Caprellidae) from California, USA, with an illustrated key of the genus, Zootaxa 3718 (5), pp. 467-476 : 468-475

Liropus minusculus n. sp.

Diagnosis. Eyes present. Body dorsally smooth. Anterolateral projections on pereonites 2, 3 and 4 in males and absent in females. Flagellum of antenna 1 more than two-articulate. Basis of gnathopod 2 longer than pereonite 2. Pereopods 3 and 4 one-articulate. Pereopods 5 one-articulate (although with a second article incompletely tabicated). Abdomen with two pairs of one-articulate appendages in males, one of them rudimentary

Type material. Holotype: male, 3.3 mm (body and 2 slides) (CMNC 2013-0001) and paratype female, 2.1 mm (body) (CMNC 2010-6721), collected from a small cave at Isthmus Reef, 9,1 m depth, Santa Catalina Island, California, USA, approximately 33º26’50’’N, 118º29’25’’W.

Etymology. The specific name minusculus refers to the small size of the specimens, which is the smallest species of Liropus .

Distribution. Only known from the type locality.

Description. Holotype, male (3.3 mm).

Lateral view ( Fig. 1 ). Body dorsally smooth. Head rounded, lacking any projections, eyes present. Pereonite 1 fused with head, suture present. Pereonites 2, 3 and 4 provided with a pair of anterolateral projections. Pereonites 3 and 4 with a developed pleura laterally. Pereonite 5 the longest. Pereonite 7 the shortest. Pereonites 6 and 7 slightly tabicated.

Gills ( Fig. 1 ). Present on pereonites 3-4, oval, length about 1.5 times width. Gills on pereonite 3 larger than those on pereonite 4.

Mouthparts ( Fig. 2 ). Mandibles with trituritive molar and three-articulate palp; distal article of palp the longest, with one setae apically; left mandible with incisor and lacinia mobilis five-dentate, accessory spine row with two spines; incisor of right mandible five-dentate, lacinia mobilis looking like a spine, followed by two more spines; molar flake present in the right mandible as a broad blade. Lower lip without setae; inner lobes almost fused. Maxilla 1 outer lobe carrying seven spines, palp two-articulate, distal article with four apical spines and one medial setae. Maxilla 2 inner lobe trapezoidal, shorter than outer lobe, carrying five distal setae; outer lobe rectangular, with seven apical setae. Maxilliped inner plate rectangular carrying two setae and a two nodular setae; outer plate oval, with three setae; palp four-articulate, second article the longest, third article provided with a distal projection and dactylus with two setae and tiny setulae distally.

Antennae ( Figs. 1 and 3 ). Antenna 1 about one third of body length; peduncular articles 1-3 in ratio of 1: 1.5: 0.6, proximal article of peduncle without projection; flagellum 5-articulate. Antenna 2 about two-thirds of antenna 1; peduncular articles 3–4 in ratio of 1: 1.5, proximal peduncular article with a well developed acute gland cone distally; swimming setae absent; flagellum two-articulate.

Gnathopods ( Figs. 1 and 3 ). Gnathopod 1 basis longer than the combination of ischium, merus and carpus; margin of propodus relatively straight, palm finely serrated; proximal grasping spine present, dactylus bifid distally. Gnathopod 2 inserted on the anterior half of pereonite 2; basis twice as long as pereonite 2 in length; ischium rectangular; merus rounded; carpus short and triangular; propodus elongated, as long as basis, anterior margin strongly convex; palm long and concave, setose, with proximal projection provided with one grasping spine, followed by a strong toothlike projection; dactylus with setulae and narrowed medially, reaching grasping spine.

Pereopods ( Figs. 1 and 4 ). Pereopod 3 and 4 extremely reduced, one-articulate, with two and three setae distally. Pereopod 5 one-articulate (with a minute article distally, not totally tabicated), with 4 setae distally. Pereopod 6 six-articulate, attached to the posterior end of the pereonite, basis without carina, ischium short and rectangular, propodus and carpus palm carrying a row of spines, dactylus strongly curved. Pereopod 7 larger than pereopod 6, but similar in feature, carpus and propodus proportionately longer, dactylus longer and straighter.

Penes ( Fig. 4 ) situated medially, distinctive, oval, length ca 1.5 times width.

Abdomen ( Fig. 4 ) with two pairs of one-articulate appendages, one of them rudimentary, a pair of lobes, and a single dorsal lobe.

Paratype, female (2.1 mm). Similar to the male except for the following characteristics: head relatively shorter. Antenna 1 flagellum 4-articulate. Presence of oostegites on pereonites 3 and 4, oostegites setose on pereonite 3 ( Fig. 1 ). Pereonite 2, 3 and 4 lacking lateral projections. Gnathopod 2 ( Fig. 3 ) basis much shorter than in male, propodus much smaller and more oval in shape, palm slightly convex with only one weak proximal projection, dactylus straighter, not setose. Abdomen ( Fig 4 ) without any projections.

Remarks. The genus Liropus , established by Mayer (1890) now includes nine species: Liropus africanus Mayer, 1920 ; Liropus azorensis Guerra-García, 2004 ; Liropus cachuchoensis Guerra-García, Sorbe & Frutos., 2008 ; Liropus elongatus Mayer, 1890 (type species); Liropus gracilis Chevreux, 1927 ; Liropus japonicus Mori, 1995 ; Liropus minimus Mayer, 1890 ; Liropus minusculus n. sp. and Liropus nelsonae Guerra-García, 2003 . A morphological comparison among Liropus species is given in Table 1. The new species Liropus minusculus can be distinguished from all its congeners mainly by the following characteristics: presence of anterolateral projections on pereonites 2, 3 and 4 in males, pereopod 5 one-articulate and abdomen with two pairs of abdominal appendages in males. L. minusculus is the smallest Liropus species, although L. africanus , L. japonicus and L. minimus are also characterised by small body size.

Liropus minusculus represents the first record of the genus Liropus in the north-east Pacific ( Fig. 5 ). The only other species described from the Pacific Ocean is L. japonicus from the north-west Pacific. The remaining species have been collected from Atlantic or Mediterranean waters. The genus is mainly distributed in the border area between the tropical and temperate zones. Further studies are necessary to check if the genus Liropus is also distributed along the Indian Ocean and to elucidate the global distribution of Liropus species.

Illustrated key to the world species of Liropus Mayer, 1890

(Modified from Guerra-García, 2004 and Guerra-García et al., 2008)

See figure 6, which illustrates the morphological characters used in conjunction with the key

1a. Pereopods 3 and 4 two-articulate.............................................. .. L. azorensis Guerra-García, 2004 1b. Pereopods 3 and 4 one-articulate......................................................................... 2 2a. Pereopod 5 one-articulate................................................................ L. minusculus n.sp. 2b. Pereopod 5 two or three-articulate........................................................................ 3 3a. Pereopod 5 three-articulate..................................................... L. nelsonae Guerra-García, 2003 3b. Pereopod 5 two-articulate............................................................................... 4 4a. Flagellum of antenna 1 two-articulate................................................... L. japonicus Mori, 1995 4b. Flagellum of antenna 1 more than two-articulate............................................................. 5 5a. Head with one or two projections......................................................................... 6 5b. Head smooth.........................................................................................8 6a. Head with a single anterior projection (= rostrum)........................................ L. gracilis Chevreux, 1927 6b. Rostrum absent, but a pair of anterolateral projections present.................................................. 7 7a. Body smooth dorsally............................................................... L. africanus Mayer, 1920 7b. Dorsal projection on pereonites 3, 4 and 5 in males, and 3 and 5 in females.........................................

......................................................... L. cachuchoensis Guerra-García, Sorbe & Frutos, 2008 8a. Gnathopod 2 basis with a basal constriction.............................................. L. minimus Mayer, 1890 8b. Gnathopod 2 basis with parallel margins, lacking constriction............................... L. elongatus Mayer, 1890

Figures

FIGURE 1. Liropus minusculus n. sp. Lateral view, left side, holotype male and paratype female.

FIGURE 2. Liropus minusculus n. sp. Holotype male mouthparts.

FIGURE 3. Liropus minusculus n. sp. Holotype male antennae, gnathopod 1 and 2. Paratype female gnathopod 2.

FIGURE 4. Liropus minusculus n. sp. Holotype male pereopods 3 - 7 and abdomen. Paratype female abdomen.

FIGURE 5. Distribution map of Liropus species. Information has been obtained from Mayer (1890, 1903, 1920), Chevreux (1927), Krapp-Schickel (1993), Mori (1995), Guerra-García (2003, 2004) and Guerra-García et al. (2008).