Coulmannia rossensis sp. n. (Isopoda, Asellota, Paramunnidae) from the Ross Sea, Southern Ocean

Abstract A new species of Coulmannia, Coulmannia rossensis, is described from the Ross Sea, Antarctica. It is most similar to Coulmannia ramosae Castelló, 2004, but can easily be distinguished from this species bythe males yielding a pair of granulate humps on the dorsum of the pereonites 1–6 and a single granulate hump on the pereonite 7 and the free pleonite. Coulmannia rossensis sp. n. is sexually dimorphic. The dorsal sculpture of the female bodies yield a single granulate hump on all the pereonites and free pleonite. The species of the genus Coulmannia are restricted to the Southern Ocean, and Coulmannia rossensis sp. n. is the fourth species included in it.


Introduction
Paramunnidae Vanhöff en, 1914 is a large family of asellote isopods; at present it includes 42 genera, many of them recently erected (see Just and Wilson 2004, 2006Doti et al. 2009;Just 2009a, b;Shimomura 2009). Th is family has a worldwide distribution, but with an overwhelming preponderance of species in temperate to cold water of the Southern Hemisphere (Wilson 1980;Just and Wilson 2004). In agreement with this observation, Choudhury and Brandt (2007) found Paramunnidae to be one of the most abundant and frequent families among the Isopoda collected in the Ross Sea with RV Italica in 2004. A preliminary study of this collection showed that many of the species found in this survey were new to science ). Based on this material, a new paramunnid of the genus Coulmannia is described.
To date species in the genus Coulmannia have been exclusively reported from the Southern Ocean. Hodgson (1910) erected the genus Coulmannia to include two new species from the Ross Sea, viz.: C. australis Hodgson, 1910 from Coulman Island and C. frigida Hodgson, 1910 from McMurdo Sound. More recently, Castelló (2004a) described the third species of the genus, C. ramosae Castelló, 2004 from the South Shetland Islands. In the present paper Coulmannia rossensis sp. n. is described from the Ross Sea. Th e morphological diff erences of the four species belonging to this genus are discussed and presented in a table, an identifi cation key is off ered.

Material and methods
Specimens of Coulmannia rossensis sp. n. were collected during the 19 th Antarctic expedition to the Ross Sea on board the RV Italica, in February 2004. Samples were taken along a latitudinal transect between Cape Adare and Terra Nova Bay with a modifi ed Rauschert dredge (Lörz et al. 1999). Th e material was sieved using a 500 μm mesh and fi xed in pre-cooled 96% ethanol for later DNA analysis.
For the taxonomic description some specimens were stained with Chlorazole Black E ® , and their appendages were dissected and temporarily mounted in glycerine. Pencil drawings of the whole animal and dissected appendages were prepared using a Carl Zeiss (Axioskop 2) compound microscope equipped with a camera lucida. Digital illustrations were made with a Wacom tablet and the Adobe Illustrator program following Coleman (2003).
Th e length of the head, pereonites, free pleonite, and pleotelson were all estimated along the mid-dorsal line. Th e width of the head was measured between the tips of the eyestalks. Body length as well as lengths of the articles of the appendages were measured according to Hessler (1970).
Th e material examined of Coulmannia rossensis sp. n. is lodged at the Zoological Museum of Hamburg (ZMH). For comparison purposes, the type material of C. ramosae Castelló, 2004(holotype male MZB 2003-1229A and paratype male MZB 2003 deposited in the Museum of Z oology, Barcelona (MZB) was also examined.
Pleopod I (Fig. 4b, c), lateral lobes at level of 2/3 of its length, each lobe with 8 simple setae; ventral surface with 8 simple setae; distal margin with 8 simple setae.
Description of adult female (Figs 1d, e; 4i). As male in body shape, except for: dorsal sculpture with a single granulate hump on all pereonites and free pleonite; hump on pereonite 1 widest and shallowest, following humps gradually becoming narrower and higher towards distal end. Operculum width 0.74 length, margins fi nely setose, ventral surface with 6 simple setae. Remaining appendages as those of the male.
Etymology. Th e species name refers to the type locality, the Ross Sea. Remarks. Because of the dorsal ornamentation and the lateral margins of the pereonites Coulmannia rossensis sp. n. is most similar to C. ramosae Castelló, 2004. Th e main diff erences between these two species are (characters found in C. ramosae in parentheses): two granulate humps on pereonites 1-6, single granulate hump on pereonite 7 and free pleonite (two granulate humps on pereonites 1 and 2, single granulate humps on remaining segments); pleotelson width 0.76 length (width 0.51 length, apex of pleotelson more produced); basis of pereopods with simple setae only (with simple and robust setae); propodi of pereopods II-IV with 3 robust setae (with 4 robust setae).

Discussion
At present, the genus Coulmannia Hodgson, 1910 contains four species, each one with a particular arrangement in the dorsal sculpture of the body and in the lateral margins of the pereonites (see Table 1). It is worth noticing that other genera of Paramunnidae, such as Heterosignum Gamô, 1976;Meridiosignum Just and Wilson, 2007;Holodentata Doti, Choudhury and Brandt, 2009;and Pentaceration Just, 2009 also include species with diff erent dorsal sculptures and/or lateral margins arrays. Th e pereonites of Coulmannia rossensis sp. n. and C. ramosae Castelló, 2004 show lateral margins similar to those present in the species of the genus Heterosignum. Th is genus, however, diff ers from Coulmannia in having long and slender eyestalks, antenna with an elongate third article, and pleotelson with denticulate margins, anteriorly narrow and cylindrical.  Castelló, 2004 (triangle); C. australis Hodgson, 1910 (square); C. frigida Hodgson, 1910 (circle). Full square and full circle stand for the type locality of the latter two species.
Coulmannia rossensis sp. n. has a remarkable sexual dimorphism in the arrangement of the dorsal sculpture. Contrary, no sexual dimorphism was found in C. australis Hodgson, 1910 (José Castelló, pers. comm.). Regarding C. frigida Hodgson, 1910, both the original description andthat presented by Vanhöff en (1914) were based on a single specimen, and none of these authors mentioned the sex of the specimens examined. Th us, sexual dimorphism in C. frigida remains unknown. Similarly, Castelló (2004a) had only two males when he described C. ramose; therefore, the sexual dimorphism in this species is also unknown.
Th e four species belonging to Coulmannia were found exclusively in the Southern Ocean, Coulmannia australis being the most widely distributed (Fig. 5). Th is species was originally described by Hodgson (1910) from a single specimen collected on Coulman Island, Ross Sea at 183-400 m depth. Afterward, Nordenstam (1933) reported C. australis from the Antarctic Peninsula at 360-400 m depth, and the South Georgia Island at 252-310 m depth, and more recently Castelló (2004b) recorded it from the South Shetland Islands at 89-220 m depth. Limited distributions have been reported for many asellote species (see Hessler 1970;Just and Wilson 2004). Besides lacking free-living larvae, paramunnid species display a reduced mobility; hence, Table 1. Character comparison of the species included in Coulmannia Hodgson, 1910. Abbreviations: Prns. = pereonites; PI= fi rst pereopod; RS = robust setae. * Th is range includes the data from the specimens described by Hodgson (1910) and Nordenstam (1933). limited distributions are expected. Coulmannia australis, however, seems to have a circumpolar distribution. Th ere are some minor diff erences between the specimens of Coulmannia australis described by Hodgson (1910) and Nordenstam (1933), mainly in the body length and in the number of robust setae on the ventral margin of carpus of fi rst pereopod. Th e variation in the number of setae most probably is related to the body length: the specimen described by Hodgson (1910) is 5 mm long and has 2 or 3 robust setae on the carpus of pereopod I, whereas the specimen described by Nordenstam (1933) is 9 mm long and has 5 robust setae. A carefully examination of the type specimen of C. australis and those reported from other areas is required to corroborate this wide distribution.

Lateral margins of pereonites
Records from the remaining three species of Coulmannia are scarce: C. frigida was described by Hodgson (1910) from McMurdo Sound at 229 m depth, and later on reported from the Gauss Station, Wilkes Land at 385 m depth by Vanhöff en (1914); C. ramosae was found only in the South Shetland Island at 89-220 m depth by Castelló (2004a); and C. rossensis is herein reported from the Ross Sea at 196-474 m depth (Fig. 5).