Vibilia Milne-Edwards 1830

Genus Vibilia Milne­Edwards, 1830

Vibilia Milne­Edwards, 1830: 386. — Milne­Edwards 1838: 308. Milne­Edwards 1840: 72–73. Lucas 1840: 233. Dana 1852: 315. Dana 1853: 980. Bate 1862: 299­300. Bate & Westwood 1868: 524. Carus 1885: 421. Gerstaecker 1886: 492. Bovallius 1887b: 554. Bovallius 1887c: 43. Stebbing 1888: 1278–1279. Vosseler 1901: 118–119. Behning 1913b: 212. Stephensen 1918: 33­34. Behning 1925: 379. Chevreux & Fage 1925: 382. Schellenberg 1927: 615. Pirlot 1929: 91. Hurley 1955: 124–125. Bowman & Gruner 1973: 24. Zeidler 1978: 5. Vinogradov et al. 1982: 199. Shih & Chen 1995: 37. Vinogradov 1999: 1178.

Thaumalea Templeton, 1836: 186.

Orattrina Natale, 1850: 11.

Elasmocerus Costa in Hope, 1851.

Type species

Vibilia peronii Milne­Edwards, 1830, by monotypy. Type material could not be found at the MNHN, BMNH or ANSP and is considered lost. This is not an ideal situation since the true identity of V. peronii is uncertain. However, although Milne­Edwards (1830) provided only a brief description of this species, his figures of V. peronii, published a decade later (Milne­Edwards 1840) are clearly of a species of Vibilia.

Type species of synonyms

The type species of Thaumalea is T. depilis Templeton, 1836. Type material could not be found at the BMNH and is considered lost. The figures and description of Templeton (1836) are insufficient to determine this species. However, the illustration is clearly of a species of Vibilia, possibly of a juvenile specimen. Thaumalea Templeton, 1836 is a primary homonym of the dipteran genus Thaumalea Ruthe, 1831.

The type species of Orattrina is O. pulchella Natale, 1850. Type material could not be found in any major Italian museum (see acknowledgments) and is considered lost. The figures and description of Natale (1850) are insufficient to determine this species. However, the figures represent a rather bizarre­looking Vibilia.

The type species of Elasmocerus is E. speciosus Costa, 1851. Type material could not be found in any major Italian museum (see acknowledgments) and is considered lost. This species is merely listed without description or figures, and is a nomen nudum. Previous authors have regarded it a species of Vibilia, probably because it may have been an earlier name for V. speciosa Costa, 1853.

Diagnosis

Body shape robust or globular. Head quadrate. Eyes occupying part of lateral head surface; grouped in one field on each side of head (absent in V. caeca). Antenna 1 inserted on anterior surface of head, but lacking groove. Antenna 1 with 3­articulate peduncle; flagellum with spatulate callynophore and 1–2 tiny articles, with aesthetascs arranged in twofield brush medially. Antenna 2 present in both sexes; inserted near anterior surface of head in small lateral pocket; consisting of 5–9 articles (only 2–4 in V. australis and four in V. caeca), together slightly longer than A 1 in males and slightly shorter than A 1 in females (except V. australis and V. caeca). Mandibular palp present in both sexes; 3­articulate. Mandibular molar well­developed. Mandibular incisor relatively broad, straight with several teeth, without medial lobe; in male orientated more or less parallel to palp. Maxilla 1 well­developed; bilobed; palp present. Maxilla 2 well­developed; bilobed, with numerous strong setae. Maxilliped with inner and outer lobes separate; inner lobes completely fused; outer lobes well­developed; medial margin of outer lobes without fringe of setae or membranous fringe. Pereonites all separate. Coxae all separate from pereonites. Gnathopod 1 simple. Gnathopod 2 chelate; carpal process knife­shaped, or spoon­shaped; carpal process armed with microscopic teeth or setae. Pereopods 3 & 4 simple; distinctly shorter than pereopods 5 & 6. Pereopod 5 simple; basis as wide or less than 5x as wide as following articles; articles 3–7 inserted terminally to basis. Pereopod 6 simple; basis as wide or less than 5x as wide as following articles; articles 3–7 inserted terminally to basis. Pereopod 7 reduced in size with large basis; all articles present; dactylus modified, rounded with microscopic scale­like structures. Uropods normal, with peduncle and articulated exopods and endopods. Telson articulated with double urosomite. Oostegites on pereonites 2–5. Gills on pereonites 2–6; all without folds.

Seventeen species.

Sexual dimorphism

The sexes are very similar morphologically and very difficult to distinguish (Stephensen 1918, Brusca 1973). The oostegites of females are more difficult to discern than in other hyperiideans, being small and without setae, and ovigerous females are rarely captured, probably because the young are transferred to the salp host at a very early stage (Laval 1963).

Some sexual differences have been observed, but they are not always consistent. Generally the head of males is slightly larger and more quadrate anteriorly, and the eyes are also larger. In some species the endopod of uropod 3 is broadened and longer than the exopod in males, but in females they are similar in size and shape. Sometimes the ornamentation of the rami of the uropods is also coarser in males. The most reliable character to differentiate the sexes seems to be the relative length of the second antennae. Generally, in males, antenna 2 is longer than antenna 1, consisting of 7–9 articles, while in females antenna 2 is shorter than antenna 1, consisting of 5–7 articles. Exceptions are V. australis, which has antenna 2 much shorter than antenna 1, consisting of 2–4 articles and V. caeca, in which antenna 2 extends only to the middle of antenna 1 and consists of four articles.

As females use the modified seventh pereopods to transfer young to the salp host (Laval 1963) it seemed reasonable that there might be some sexual dimorphism of that appendage, particularly in the ultra­structure of the dactylus. This possibility was investigated but no distinct sexual differences could be determined, even when ovigerous females were available for examination.

Remarks

Vibilia is a very distinctive genus and, apart from Vibilioides, does not resemble any other hyperiidean. Species are very similar in gross morphology and, apart from a few distinctive species, most require expert knowledge for a correct identification. In addition, researchers should be aware of ontogenetic changes, such as documented for V. robusta (Zeidler 1998) and V. armata (Laval 1963, 1965). These are most likely paralleled in other species and add to the difficulty of determining juvenile specimens. A thorough taxonomic revision of the genus is long overdue.

There are forty nominal species referable to Vibilia. However, the types of many are lost, and original descriptions are so poor, that it is impossible to determine their status with certainty. At least ten of these are considered nomen dubia and are discussed at the end of this section. The genus has been reviewed by Bovallius (1887c) who recognised 15 species, and by Behning (1913b), who recognised 24 species. Since then, more information has been provided by Behning (1925, 1927), but only two new species have been described, one by Behning (1939) and another by Bulycheva (1955). More recently, Vinogradov et al. (1982) reviewed the genus and reduced the number of recognisable species to seventeen. The current review, based on an examination of most of the world’s collections, is in general agreement with Vinogradov et al. (1982), except for V. affinis and V. bovallii, which are regarded indeterminable species (see notes on species of indeterminable status) and the addition of two species, described here, as new to science. However, it is limited by the loss of the types of many nominal species.

Species of Vibilia live in surface waters, usually in association with salps, which they use for shelter and as a source of food (Madin & Harbison 1977, Laval 1980). Developing larvae also reside on salps, and Laval (1963) describes the larval development of V. armata and its association with salps. The genus is relatively common in the tropical and subtropical regions of the world’s oceans, but some species venture beyond the Subtropical Convergence.

Morphologically, Vibilia is readily divided into two species groups, one in which the posterior lateral corners of the last urosomite project slightly next to the peduncle of uropod 3, and the other in which there is no such projection. This appears to be a good character, which is readily discernible in all species of Vibilia except perhaps for V. chuni. In this species the lateral projection can sometimes be minor and it is thus included in both parts of the following key. Fortunately V. chuni is one of the more easily recognisable species of Vibilia. Similarly, V. viatrix is included twice in the key because it can sometimes be difficult to determine if the distal margin of antennae 1 is rounded or pointed.