Haploniscus cassilatus, Brökeland & Raupach, 2008

Brökeland, Wiebke & Raupach, Michael J., 2008, A species complex within the isopod genus Haploniscus (Crustacea: Malacostraca: Peracarida) from the Southern Ocean deep sea: a morphological and molecular approach, Zoological Journal of the Linnean Society 152 (4), pp. 655-706 : 658-659

HAPLONISCUS CUCULLUS COMPLEX

Composition: Haploniscus cassilatus sp. nov., H. cucullus sp. nov., H. weddellensis sp. nov., H. procerus sp. nov., H. kyrbasia sp. nov., H. nudifrons sp. nov., H. microkorys sp. nov.

Diagnosis: Body oval, length about 3¥ width. Head more than twice as long as wide, frontal margin concave. Anterior margin of pereonite 5 strongly serrated in intersegmental gap. Posterolateral processes of pleotelson short. Dorsal surface of pleotelson with two sharp longitudinal keels, ventral surface with cuticular bulge surrounding the branchial chamber and tapering towards anus. Antenna 1 with four flagellar articles. Peduncular articles of antenna 2 covered by cuticular scales. Mandibular palp article 3 with more than seven serrated spine-like setae. Carpus with ventral flagellate setae, apical and ventral combs of carpus spinose, pereopod 6 with dorsal flagellate seta subapically on carpus. Pleopod 1 without distal extensions or extensive sculpturing of apical part in adult males. Pleopod 2 endopod short, extending slightly beyond terminal margin of basipod.

Remarks: Five of the seven species described below, H. cucullus , H. cassilatus , H. weddellensis , H. procerus and H. kyrbasia , possess a rostrum that has a characteristic and complex basic shape, although its proportions vary between species. In dorsal view the rostrum has almost parallel lateral margins and tapers anteriorly into an acute spine. The dorsal surface of the rostrum has a shallow depression that is flanked by the sharp lateral margins and resembles a shovel. The anterior spine is curved dorsally in lateral view, and the lateral surfaces of the rostrum each have a shallow longitudinal depression. Across the ventral surface runs a shallow groove that is visible as a notch in lateral view. Posteriorly of the groove the rostrum is separated from the head by a sharp ventral notch. SEM pictures revealed that the rostrum is covered with small tubercles, each bearing several tiny sensory setae with the exception of the anterior spine and the small ventral part posteriorly of the shallow groove ( Fig. 41 ). The rostrum is subject to interspecific variation. It differs in size and proportions. Besides, intraspecific variation of this structure can be observed. In relation to body size ovigerous females possess a smaller rostrum than other specimens belonging to the same species. Due to this conspicuous morphological similarity of the five species a close relationship between them may be assumed.

Apart from the rostrum H. nudifrons and H. microkorys share a number of characters with the other five species. All species are characterized by a relatively broad body shape, the concave frontal margin of the head, the short posterolateral processes of the pleotelson and the characteristic setation of the pereopods with flagellate setae on merus, carpus and propodus.

Pleopod 1 of adult males is similar to that of subadult males, the endopod of the male pleopod 2 is short, and sexual dimorphism is restricted to the pleopods. Scales on the peduncular articles of antenna 2 seem to be a common character as well. Although they were not visible under the compound microscope in some species, e.g. H. cucullus , these scales were found in a specimen of H. cucullus that was prepared for SEM studies. The size and number of scales is subject to interspecific variation, and perhaps also of intraspecific variation. The proportions of the peduncular articles of antenna 2 are variable as well; antenna 2 of H. cassilatus is relatively stout, whereas antenna 2 of H. microkorys is more slender. While the setation of the flagellar articles of antenna 2 is usually more strongly developed in males, such dimorphism could not be found in the two species where adult males and females were present: H. cassilatus and H. weddellensis . This corresponds to the generally weakly expressed sexual dimorphism of the group.

The size range of the species is large; the smallest adult specimens belonged to H. weddellensis and the biggest specimen was the H. nudifrons female (11.3 mm in length). However, it is difficult to determine the size range of most species due to lack of material. The size ranges of H. cassilatus , H. cucullus and H. weddellensis broadly overlap. Ovigerous females seem to be among the largest specimens of each species.

The setation of the pereopods includes flagellate spine-like setae ventrally on merus, carpus and propodus of all species, but their number varies within and between species. By far the most setae can be found in H. microkorys , while specimens of H. cassilatus possess only 1–3 flagellate setae on the ventral carpus. Because of the intraspecific variation, the number of setae is problematic as a diagnostic character; to define discrete character states a statistical analysis would be necessary. This is not possible at the moment, because not enough specimens were found of most species.

Where adult males were found, pleopods 1 and 2 looked more or less alike between species. In contrast to most species of the Haploniscidae , pleopod 1 of subadult and adult specimens does not differ greatly; it has to be dissected to identify the ontogenetic stage. In adult males the dorsal surface of pleopod 1 has two transversal grooves, which are only weakly indicated in the subadult stage V males (stages after Wolff, 1962).

The complex is named after the new species Haploniscus cucullus , whose holotype male (ZMH K40758 ) was the first specimen of the complex found in the samples and also the specimen in which the rostrum was most striking when first observed. Despite this, the species described in full detail below is H. cassilatus because the material of this species contained adult males, which is not the case for H. cucullus . For all other species only the characters that differ from those of H. cassilatus are described. Because only a single specimen of H. nudifrons and H. microkorys was found, the mouthparts of these species were not dissected to avoid damaging of the important diagnostic features of the head in the holotypes. The mouthparts themselves were found to hold no important diagnostic characters in the remaining species, except for the mandibular palp, which was dissected carefully in H. microkorys , but was lost in H. nudifrons .

Figures

Figure 41. Haploniscus cucullus sp. nov., SEM: A, rostrum and antennae, lateral view; B, rostrum and antennae, dorsal view; C, detail of dorsal rostrum structure; D, detail of B, showing antennal scales. Scale bars = 100 Mm (A, B, D), 1 Mm (C).