Tytthocope Wilson & Hessler, 1981

Malyutina, Marina V. & Brandt, Angelika, 2014, New species of the deep-sea munnopsid genus Tytthocope (Crustacea, Isopoda, Asellota) from the South Atlantic and the Southern Ocean, Zootaxa 3786 (1), pp. 1-43 : 3-4

Tytthocope Wilson & Hessler, 1981

Tytthocope Wilson & Hessler, 1981: 410 –412 (diagnosis), Kussakin, 2003: 125.

Diagnosis (Revised after Wilson & Hessler 1981). Cephalic rostrum broader and longer than antennula article 1, antennula article 1 without distomedial lobe. Natasomal pereonites free, pereonite 6 longest medially, pereonite 7 shortest, subequal to ambulosomal pereonites in length. Posterior of pereonite 5 tergum with pair of rounded elevations with angular keel. Venter of natasomal pereonites protruded medially, ventral protrusion of pereonite 6 largest. Pleotelson inflated, anus separated from pleopodal cavity by weak preanal ridge. Opercular pleopods in both sexes inflated, covering anus. Mandibular palp slender, shorter than mandibular body (about 0.8–0.9 length). Maxilliped palp article 2 with long acute distolateral projection; article 3 distomedial margin rectangular projected distally; article 4 distomedial lobe well produced; epipod elongate, distal margin narrow, acute. Male pleopod 1 gradually tapering distally, distal lobes not well separated from each other. Male pleopod 2 stylet length about half protopod length. Pleopods 3–5 volumetric, pleopod 5 largest, encapsulating pleopod 4. Uropod tiny, near 0.1 pleotelson length, endopod about twice as long as protopod, exopod subequal to protopod in length.

Description. Cephalothorax with broad rostrum tapering slightly distally into sloping broad frons, rostrum broader and longer than antennula article 1, labrum about twice as long and much narrower than clypeus. Antennula of male visibly more stout than of female. Antennula article 1 tapering distally, without distomedial lobe. Pereonite 1 subequal to cephalothorax in length behind antennula insertion, pereonites 2–4 slightly broader than pereonite 1, laterally almost twice as long as pereonite 1. Pereonite 5 tergum has broadly rounded elevations with an angular keel in middle of each diametric half of the segment anterior to pereonite 6; pereonites 5 and 6 lateral length subequal, pereonite 6 longest medially, pereonite 7 shortest, subequal to anterior pereonites. Venter of natasomal pereonites protruded medially, pereonite 6 with largest ventral protrusion. Pleotelson about one third of body length, inflated, posterolateral margin slightly curved ventrally with flexion for uropod insertion, anus separated from pleopodal cavity by weakly pronounced preanal ridge. Opercular pleopods in both sexes covering anus, almost as long as pleotelson, ventrally inflated to same degree as pleotelson dorsally. Mandibular palp slender, length 0.8 mandibular body length, distal article elongate, reduced; molar tapering to distal spinose margin, condyle shorter than molar. Maxilliped palp article 1 with small acute distolateral projection, article 2 with long acute distolateral projection; article 3 distomedial margin projected distally, rectangular; article 4 distomedial lobe well produced; epipod elongate, subequal to basis in length, of roughly rhomboid shape, distal margin narrowly peaked. Pereopod 1 smallest, less than body length (0.55–0.8), slender, with scattered small simple setae, carpus broadest proximally, subequal in length to propodus and dactylus together. Pereopods 2–4 increase in elongation from pereopod 2 to 4, pereopod 2 subequal to body length; pereopod 4 about twice as long as body. Bases of pereopods 1–4 of similar length, basis 1 narrowest, with sparse simple setae; bases 2–4 with a few dorsal broom setae. Ischii with several simple setae; meri with 1 distodorsal UB seta and 1 distoventral UB seta; carpi with distodorsal set of 1 broom and a few long whip setae; propodus of pereopod 2 broadest, with long UB distoventral seta and dorsal broom seta subdistally; dactylus slender, tapering to slim acute claws. Pereopods 5–7 similar in shape, pereopod 6 slightly longer than pereopod 5, pereopod 7 length about 0.6 pereopod 6 length, all articles proportionally decreasing in size. Carpi almost semicircular: dorsal margin rounded, expanded and ventral margin nearly straight, slightly expanded, distodorsal margin with 1 broom seta. Propodi with more expanded ventral margin, but less expended dorsal margin, distodorsal margin with 1 long stout UB seta and 1 broom seta, distoventral margin with 1 short UB seta. Dactyli lanceolate, dorsal and distoventral margins with fringe of setulae, 2 small distal setae inbetween. Male pleopod 1 gradually tapering distally, distal lobes not well separated from each other. Male pleopod 2 protopod semicircular, stylet length about half of protopod length; exopod small, inserting close to endopod insertion. Female pleopod 2 ovoid in ventral view and conical in lateral view, reaching apex of pleotelson. Pleopods 3–5 volumetric, pleopod 5 largest, embracing pleopod 4. Pleopod 3 endopod with three distal plumose setae located on protruded medial half of distal margin, setae length about half of endopod length; exopod subequal in length and 0.25–0.3 width of endopod, distal article separated, length about half of proximal article length, with 1 or 2 distal plumose setae, subequal to endopod setae in length. Pleopod 4 exopod slightly shorter than endopod, width 0.5 endopod width, with one distal plumose seta subequal in length to pleopod 3 setae. Uropod near 0.1 pleotelson length. Protopod slightly broader than long, broadened distally; endopod about twice as long as protopod; exopod subequal to protopod in length, width about one third of endopod width.

Remarks. With regard to the small size, the general habitus, the large (broad and long) rostrum and the antennula article 1 without a distomedial lobe Tytthocope resembles Baeonectes , Belonectes and some species of Disconectes . However, it differs from these similarly small eurycopines by the separated natasomal pereonites, the short pereonite 7 and the inflated pleotelson. Species of the three genera mentioned have fused pereonites 5 and 6, a pereonite 7 which is comparable to pereonites 5 and 6 in length and a somewhat flattened pleotelsoon. Tytthocope is the only genus of the subfamily with a greatly reduced pereonite 7. This character of Tytthocope resembles that of the genus Coperonus , a member of the subfamily Lipomerinae Tattersall, 1905 which is characterized by a reduced or absent pereonite 7. The pereopod 7 of Tytthocope is reduced only in size like in Disconectes , Baeonectes and Belonectes (to a larger degree), but not in swimming morphology as in Coperonus . Tytthocope also shares with Coperonus and some species of Lionectes and Mimocopelates (Lipomerinae) a special structure of the natasome tergum, the dorsal surface of pereonite 5 in front of the suture with pereonite 6 has a pair of the broadly rounded elevations with an angular keel, therefore the suture between pereonites 5 and 6 looks compressed. Wilson & Hessler (1981: 411) already noted in their generic remarks that “highly convoluted branchial pleopods of Tytthocope megalura , are unusual among the genera of the Eurycopinae . This pleopod form may be characteristic of the genus. However, pleopods III–V are known in too few species.” Our study of the four other species of Tytthocope revealed the same structure of the pleopods that confirmed this assumption. We suggest that together with the size ratios of rostrum to antennula article 1 and pereonites 5–7 to pleotelson lengths, the ventral protrusion of pereonite 6 and the special characters of the pleopods, as well as those of the maxilliped may be distinguishing for the genus. Though all eurycopines have a somewhat expanded lateral margin of maxilliped palp article 2, only Tytthocope species have a projected acute distolateral margin on it. All studied species of Tytthocope possess a laterally expanded article 2 with the projected acute distolateral margin, an article 3 which is noticeably narrower than article 2, with produced rectangular distomedial margin, a relatively narrow distomedial lobe of article 4 (comparing with broad lobe in Belonectes ) and an elongate epipod. These characters (Fig. 31) are useful interspecific diagnostic characters. The five known species of Tytthocope have been collected from depths of less than 1461 m, therefore the records for the new species are the deepest ( Table 1 ), though Wilson and Hessler (1981) mentioned three undescribed species from the Atlantic deep sea.