Melita mirzajanii, Krapp-Schickel, Traudl & Sket, Boris, 2015

Krapp-Schickel, Traudl & Sket, Boris, 2015, Melita mirzajanii n. sp. (Crustacea: Amphipoda: Melitidae), a puzzling new member of the Caspian fauna, Zootaxa 3948 (2), pp. 248-262 : 249-251

Melita mirzajanii n. sp.

Type material. Holotype: male 8 mm, MVRCr in alcohol, in Amphibalanus cf. improvisus ( Darwin 1854) growth, Bandar-e-Anzali port, Gilan P., IRA, leg. A. Mirzajani & B. Sket, 29 Sept. 2009. Paratypes: 1 ovigerous female, 5 mm, dissected, slide MVRCr 7713; anterior part of a male, 8 mm, dissected, slide MVRCr 7712. Locality as above; male 6.5 mm, in alcohol; 6 males 5–8 mm, in alcohol.

Type locality. Bandar-e-Anzali port, Caspian Sea.

Etymology. Dedicated to Alireza Mirzajani, an Iranian marine biologist (see acknowledgement).

Diagnosis. Maxilla 2 lobes with marginal setae; mandible palp densely setose; lower lip with inner lobe. Gnathopod 1, 2 sexually weakly dimorphic. Gnathopod 2 male propodus with wide and scarcely pronounced palmar corner, hind margin regularly convex; dactylus partly hidden on inner face when folded. Coxa 6 female anterior lobe as long as width of coxa, posteriorly excavated. Pleon smooth, urosome segments smooth except of two spines posterolaterally on urosomite 2. Uropod 3 exopodite twice as long as peduncle, with one article. Telson entirely cleft, lobes distally acute, with 3 strong spines subdistally and one shorter on inner margin.

Description. Head: Eyes well developed, irregularly rounded. Head anteroventrally with small notch, lateral cephalic lobe broad, apically rounded. Antenna 1> Antenna 2, weakly setose; peduncular article 1 ≤ article 2, with several spines along hind margin; peduncle article 2 clearly longer than article 3; accessory flagellum 2+1 (female), 3+1 (male) articles, flagellum with 16–19 articles. Antenna 2 weakly setose, peduncle article 4> 5, flagellum with 7 or 8 articles. Mandibular molar weak (female) to strong (male), palp well developed, 3 articles, article 2 subequal with article 3, both beset with long setae laterally and terminally. Maxilla 1 long inner plate, subrectangular, with plumose setae mostly apically. Maxilla 2 setae only marginally, no oblique setal row on inner plate. Lower lip with inner lobes. Maxilliped palp with 3 articles, ratio article 1: article 2 = 2.

Pereon: Coxa 1 rectangular, much longer than wide, anterior margin straight; both gnathopods weakly sexually dimorphic. Gnathopod 1 merus without posterodistal tooth, densely beset with stiff spines; carpus about twice as long as wide, longer than propodus; gnathopod 1 propodus rectangular, anterodistally lobed, excavated at basal part of palm on inner surface; palmar margin short, transverse, with bifurcated thin terminal spines and minute subterminal setae; posterior margin with groups of simple setae; dactylus short, basally bulged, attached at 2/3 of anterodistal margin of propodus, with 1 seta on outer margin. Female gnathopod 1 propodus somewhat more slender and less spinose than in male, palm defined by posterodistal rectangular corner. Coxa 2 elongate, ratio l:w>2, with parallel margins, distally rounded. Gnathopod 2 subchelate, carpus only slightly shorter than propodus in female, much shorter in male, not lobate; merus distoventral corner acutely extended; propodus ovoid, hindmargin regularly rounded, palmar corner defined by strong spine in female which is lacking in male; dactylus closing with palm, tip visible from both sides in female, moved to inner side in male. Coxa 3 rectangular, coxa 4 posterior margin excavate, with posteroventral corner lobate. Pereopods 3–4 similar to each other, slender. Pereopods 5–7 bases tapering distally, posterior margin slightly serrate, straight in apical third, with no posterodistal lobe; anterior margin with short spines. Coxa 6 in female anterior margin strongly produced, (in male much less), distally rounded, on distal margin semicircularly excavated in female.

Pleon: Pleonites without dorsal teeth, spines or setae. Urosomites lacking teeth, but urosomite 2 on posterodorsal margin a pair of spines, situated a bit laterally. Epimeral plates 1–3 posterodistally rectangular with a small tooth on the corner.

Uropod 1 peduncle with one basofacial spine, another stronger one distally, and a row of lateral and marginal spines. Uropod 3 without second article on exopodite; peduncle about half length of exopodite; endopodite scalelike, short, exopodite about 5 × as long as wide, beset with many groups of strong spines.

Telson totally cleft, about as long as wide, lobes acutely ending, subdistally with 3 and laterally with 1 strong spine each.

Brood plates 2–5 long and narrow, with long marginal setae.

Remarks. The here described new species is morphologically similar to M. zeylanica Stebbing, 1904 ( Sri Lanka, 7.5 mm), M. kauerti J.L. Barnard 1972 (Western Australia, 8 mm), M. setiflagella Yamato, 1988 ( Japan, 7.8 mm) and M. corticis Appadoo & Myers, 2005 ( Mauritius, 6 mm). All these species lack strong spines on the outer margin of the telson, have one spine on the inner margin and three terminally. Antenna 2 is weakly setose in our material, matching M. zeylanica , M. kauerti and M. corticis but different in M. setiflagella (densely setose). Gnathopod 2 carpus in M. zeylanica and M. kauerti is compressed, in all other species it is longer than wide. Urosomite 2 has on each side three or four spines in M. kauerti , three spines in M. setiflagella , two or three spines in M. zeylanica and two spines in M. corticis and in the present animals. The similarity to M. corticis from Mauritius is especially striking, but the male antenna 1 flagellum is somewhat longer in M. mirzajanii , the mandibular palp is more densely setose, the gnathopod 2 propodus palm is different and coxa 6 in the female is posteriorly less excavated: these are very tiny morphological differences indeed!

It is evident that the new species shows no particular similarity to any of the five species known from the Mediterranean as presented by Karaman (1982). In none of them the distal article of the mandibular palp is (at least slightly) longer than article 2. Only in M. coroninii , the basis of pereopod 7 is similarly shaped, remarkably narrower in its distal part and with distal third of the hind border straight. Only in M. bulla , the dactyli of the hind pereopods are as long (longer than the propodus diameter) as in the Caspian species. Only in M. bulla and M. valesi , both slightly troglomorphic interstitial species, the urosomites are without dorsal teeth. Only in M. hergensis and M. palmata , the hind epimera are not remarkably produced posterodistally, as is also the case in the new M. mirzajanii .

Only the very different M. palmata is mentioned ( Mordukhai-Boltovskoi et al. 1969; Karaman 1982) from the Black Sea. Its main characteristic is the uniquely shaped male gnathopod 1, but it differs from M. mirzajanii also in the epimera shapes, in urosome armature, in the shape of posterior pereopod bases, and some other details.

Ecology, biogeography. Melita mirzajanii n. sp. was common in a dense growth of Amphibalanus cf. improvisus ( Darwin, 1854) on concrete piers of the port of Bandar-e Anzali, Gilan province, Iran, at the southwestern corner of the Caspian coast. Nearby was a similar colony of the clam Mytilaster cf. lineatus ( Gmelin, 1791) .

These sessile animals are very recent immigrants to the Caspian Sea. Mytilaster cf. lineatus has been known from the Caspian since the 1920s ( Zenkevich 1947) and Amphibalanus cf. improvisus since the 1950s (Mordukhai- Boltovskoi 1960), and they probably replaced earlier endemic Dreissena spp. growths as a habitat. Single specimens of the introduced crab Rhithropanopaeus harrisii (Gould) and of the endemic fish Proterorhinus sp. were found in our samples, but no other amphipod species.

The type locality is a port on the Caspian shore, exhibiting strong freshwater influence from the Anzali wetlands inland, which may be drenched by the Caspian water during storms. Therefore, the salinity may vary yearly between 0 and 12.7 PSU (= Practical Salinity Units; Mirzajani pers. com.; Mirzajani 2009).

Identification. The species actually classified in the genus Melita differ by very slight characters. The groups presented below are prepared for practical purposes only, facilitating comparison and not intending to indicate phylogenetic relations. Melita mirzajanii n. sp. belongs to the Group B1, for which an identification key is provided.

Group A1: Pleonites and urosomites with prominent dorsal teeth (21 spp.)

The presence of teeth on pleonite 1, 2, 3 = Pl 1,2,3 resp. urosomites 1, 2 = Us 1,2 is indicated in brackets. M. aculeata Chevreux, 1911 (Pl 1,2,3; Us 1); M. bousfieldi García-Madrigal, 2010 (Pl 1,2,3, Us 1); M. celericula Croker, 1971 (Pl 3, Us 1,2); M. dentata ( Krøyer, 1842) (Pl 1,2,3, Us 1,2); M. denticulata Nagata, 1965 (P. 1,2,3, Us 1,2);? M. excavata Ledoyer, 1979 (Pl 1,2, Us 1,2); M. formosa Murdoch, 1866 (Pl 2,3, Us 1,2); M. japonica Nagata, 1965 (Pl 2,3, Us 1,2); M. kodiakensis J.L. Barnard, 1964 (Pl 1,2,3, Us 1,2); M. lignophila J.L. Barnard, 1961 (Pl 1,2,3, Us 1,2); M. machaera K.H. Barnard, 1955 (Pl 3, Us 1,2); M. mucronata Griffiths, 1975 (Pl 1,2,3, Us 1,2); M. obtusata ( Montagu, 1813) (Pl 2,3, Us 2); M. pallida Sars, 1879 (Pl 1,2,3, Us 1,2); M. richardi Chevreux, 1900 (Pl. 1,2,3, Us 1,2); M. rylovae Bulycheva, 1955 (Pl 2,3, Us 2); M. sexstachya Gamo, 1977 (Pl 1,2,3, Us 1,2); M. subchelata Schellenberg, 1925 (Pl 1,2,3, Us 1,2); M. tuberculata Nagata, 1965 (Pl. 1,2,3, Us 2); M. unamoena Hirayama, 1987 (Pl 1,2, Us 1,2); M. virgula Krapp-Schickel, Ruffo & Schiecke, 1994 (Pl 1,2,3, Us 1,2).

Group A2: Only urosomites with dorsal teeth (29 spp.)

M. abyssorum Stephensen, 1944 ( Us 1,2); M. amoena Hansen, 1888 ( Us 1); M. cognata Stock & Vonk, 1992 ( Us 1); M. coroninii Heller, 1867 ( Us 2); M. desdichada J.L. Barnard, 1962 ( Us 1,2); M. dulcicola Stock & Vonk, 1990 ( Us 1);? M. festiva (Chilton, 1885) ( Us 1,2);? M. gayi ( Nicolet, 1849) ( Us?); M. hergensis Reid, 1951 ( Us 1,2); M. hoshinoi Yamato, 1990 ( Us 2); M. inaequistylis ( Dana, 1852) ( Us 2); M. ophiocola Lowry & Springthorpe, 2005 ( Us 1,2); M. oregonensis J.L. Barnard, 1954 ( Us 2); M. orgasmos K.H. Barnard, 1940 ( Us 1,2); M. palmata ( Montagu, 1804) ( Us 1,2); M. persona Karaman, 1987 ( Us 2); M. pilopropoda Hirayama, 1987 ( Us 2); M. planaterga Kunkel, 1910 ( Us 1,2); M. plumulosa Zeidler, 1989 ( Us 1,2); M. quadridentata Yamato, 1990 ( Us 2); M. quadrispinosa Vosseler, 1889 ( Us 1,2); M. reidi Hamond, 1965 ( Us 1,2); M. setimera Appadoo & Myers, 2005 ( Us 1); M. shiodamari Yamato, 1995 ( Us 1); M. simplex Myers, 1985 ( Us 1);? M. solada J.L. Barnard, 1961 ( Us 1,2); M. sulca ( Stout, 1913) ( Us 1,2); M. tristanensis K.H. Barnard, 1965 ( Us 1?, Us 2); M. valida Shoemaker, 1955 ( Us 1,2).