Lycaea Dana, 1852

Zeidler, Wolfgang, 2021, Review of the hyperiidean amphipod family Lycaeidae Claus, 1879 (Crustacea: Amphipoda: Hyperiidea), Zootaxa 5081 (1), pp. 1-59 : 5-8

Genus Lycaea Dana, 1852

Lycaea Dana, 1852: 316 .— Dana 1853: 1009, 1017.— Spence Bate 1862: 338.— Claus 1873: 468.— Claus 1876: 519.— Claus 1879: 178 (32) (key), 183–185 (37–39).— Carus 1885: 426.— Gerstaecker 1886: 485–486.— Claus 1887: 55 (key), 61– 62.— Stebbing 1888: 1563.—Chevreux & Fage 1925: 427 (key), 429.— Pirlot 1929: 136.— Hurley 1955: 180 (incl. key).— Bowman & Gruner 1973: 46 (incl. key).— Zeidler 1978: 26 (incl. key).— Vinogradov et al. 1982 /1996: 381/471 (key), 381–382/471.— Shih & Chen 1995: 170 (key), 170–171.— Vinogradov 1999: 1194 (incl. key).— Zeidler 2016: 48–49 (incl. key), 53.

Pseudolycaea Claus, 1879: 178 (32) (key), 187 (41).— Carus 1885: 426.— Gerstaecker 1886: 486.— Claus 1887: 56 (key), 64.—Chevreux & Fage 1925: 427 (key), 430.— Pirlot 1929: 138.— Bowman & Gruner 1973: 46 (key), 47.— Shih & Chen 1995: 170 (key), 183.

Metalycaea Stephensen, 1925: 183 .— Nair 1993: 1172.— Nair 1995: 6 (key), 7.

Type species. Lycaea ochracea Dana, 1853 by subsequent designation. Type material could not be found in any major North American museum and is considered lost (see Evans 1967). The type locality is the S.W. Pacific, north of New Zealand, near Sunday Island, April 1840. Although the description and figures of Dana (1853) readily characterise this genus they have been considered insufficient to determine the status of his species. Dana (1853) illustrated a male, probably immature, judging by his figure of A2. His figures characterise a species where the peduncle of U1 is relatively long and the callynophore of A2 of males has a postero-distal bulge. These two characters, combined with the morphology of G2, exclude it from all its congeners except L. vincentii and L. bovallii . Dana’s small illustrations, however, make it difficult to determine the length of the dactyls and the exact position of the bulge on A2. If anything, the dactyls seem short and the antennal bulge is near the distal margin. Thus, it is more like L. vincentii than L. bovallii . However, nomenclatural stability would not be served by re-introducing Dana’s name because his species has not been recorded since first described and the true identity of his species cannot be confirmed.

Type species of synonyms. The type species of Pseudolycaea is P. pachypoda Claus, 1879 by monotypy. Type material could not be found in any major European institution and is considered lost. However, the description and figures of Claus (1879, 1887) readily characterise this species, which is considered to be insufficiently different from other species of Lycaea to warrant generic recognition (see Remarks).

The type species of Metalycaea is M. globosa Stephensen, 1925 by monotypy. Three female syntypes are in the NHMD (84411, 86799, 86800). This species is considered to be a synonym of Lycaea serrata Claus, 1879 (see Remarks).

Diagnosis. Body robust or globular. Head round, often enlarged in females. Eyes occupying most of head surface; grouped in one field on each side of head. A1 of males with 2-articulate peduncle; flagellum with large, crescent-shaped callynophore, with aesthetascs arranged in two-field brush medially, with or without antero-distal corner and small, rounded postero-distal lobe; with three smaller articles inserted on antero-dorsal corner. A1 of females with 2-articulate peduncle; callynophore narrowly rectangular, with two smaller articles inserted terminally. A2 absent in females. A2 of males 5-articulate, strongly zig-zagged, with most articles folded back on each other, extending anteriorly under head and posteriorly between the gnathopods and pereopods to pereonite 7; basal article distinctly inflated, about one-third the length of following article; following three articles of similar length; terminal article very short, not folded, pointing posteriorly. Mandibular incisor relatively broad, with several teeth, with small distal lobe medially; in males orientated more or less parallel to palp. Maxillae 1 consisting of tiny, rounded, plate-like lobes. Maxillae 2 absent. Maxilliped with inner lobes completely fused; medial margin of outer lobes with membranous fringe. G1 and G2 varying from almost simple to sub-chelate. P3 and P4 shorter than P5 and P6. P5 basis usually enlarged, length about 1.5–2.0 x maximum width, or relatively narrow and about 3.0 x as long as wide ( L. serrata ); articles 3–7 inserted terminally on basis. P6 basis also usually enlarged, length about 1.5–2.0 x maximum width; articles 3–7 inserted terminally on basis; dactylus retractile in some species. P7 reduced in size with large basis; all articles present; dactylus prehensile, rarely absent or vestigial. U1 endopod rarely fused with peduncle, sub-equal in length to exopod. U2 endopod sometimes fused with peduncle, exopod always shorter and more slender than endopod. U3 endopod fused with peduncle, exopod always shorter and more slender than endopod. Rami of U1–3 lanceolate, usually with serrated margins.

Species. Lycaea pulex Marion, 1874 ; L. nasuta Claus, 1879 ; L. serrata Claus, 1879 ; L. pachypoda ( Claus, 1879) ; L. vincentii Stebbing, 1888 ; L. bovallii Chevreux, 1900 ; L. lilia Volkov, 1982 ; L. intermedia sp. nov.; L. osbornae sp. nov. and L. proserrata sp. nov.

Sexual dimorphism. Apart from the morphology of the mandibles and the antennae, females are more robust than males, especially in the pereon. Males are generally more elongate and have a relatively smaller head, and in males of L. nasuta the head is more bulbous and produced into a small anterior knob; a character that also occurs in mature males of L. lilia , L. osbornae sp. nov. and L. proserrata sp. nov. But see diagnosis of L. serrata for exceptional sexual dimorphism.

Remarks. In the past the genus Pseudolycaea has been considered monotypic amongst the family Lycaeidae , because of the almost simple G1 and G2. In all other respects it resembles Lycaea . As the morphology of G1 and G2 of Lycaea can vary from strongly to weakly sub-chelate, as in L. serrata , the validity of Pseudolycaea seems unjustified, and, like Vinogradov et al. (1982, 1996), it is here regarded a synonym of Lycaea . Similarly, Metalycaea , which Nair (1993) resurrected as a valid genus of Oxycephalidae , is considered to be a synonym of Lycaea , because the type species, M. globosa , originally described only from female specimens, is indistinguishable from mature female specimens of L. serrata . Like Simorhynchotus , its inclusion in the Oxycephalidae on the presumed absence of the maxillae has been demonstrated to be invalid ( Zeidler 2016). An examination of the type material of M. globosa has confirmed the synonymy, although it was not possible to examine the mouthparts for the presence or absence of maxillae. The specimens referred to by Nair (1993) have not been examined.

Species of Lycaea have always been difficult to determine and a thorough revision of the genus is long overdue. Harbison & Madin (1976) provide a useful key to eight species, that they tentatively consider valid. Of these eight species, Vinogradov et al. (1982, 1996) recognise only three, but they regard L. pauli considered synonymous with L. pulex by Harbison & Madin (1976) as valid, and include L. pachypoda and L. lilia . Clearly the genus still presents many taxonomic difficulties that require resolution. In order to clarify the systematics of the group, it is necessary to review some of the morphological characters that have been used to distinguish species in the past.

Uropod 1. The peduncle length can vary considerably but most species can be placed into two groups based on the ratio of the length of the peduncle to the length of the exopod. The first group, with a relatively short peduncle and relatively long rami, where this ratio is about 2 x, consists of L. pulex , L. pauli , L. serrata , L. pachypoda and L. osbornae sp. nov. In addition, the peduncle is widest distally. The latter three species are readily distinguished by additional distinctive characters but this character, together with possessing short dactyls, also distinguishes Lycaea pulex from its other congeners. Lycaea pauli is considered a synonym of L. pulex . The second group, with a relatively long peduncle and relatively short rami, where this ratio is about 3 x or more, consists of the remaining species, except for L. lilia , which seems to be intermediate. In addition, the peduncle usually has evenly convex margins and is widest medially. Amongst this group this character is not sufficiently variable to be useful to distinguish species.

Uropod 2. Two species, L. nasuta and L. bovallii , have been recorded as having the endopod fused with the peduncle. This character has been used to distinguish these two species from all other congeners (e.g., Harbison & Madin 1976). While L. nasuta is also readily distinguished by a number of other characters (see remarks for L. nasuta ), L. bovallii is identical to L. bovallioides except for the urosome ( Stephensen 1925, Harbison & Madin 1976) and the same seems applicable for L. bajensis . An examination of more than 80 specimens with medium length dactyls, referable to L. bajensis , and more than 40 specimens with longer dactyls, referable to L. bovallii or L. bovallioides , revealed that in only a few specimens is the endopod of U2 clearly fused with the peduncle. In many specimens there seems to be a faint, or incomplete, suture between the endopod and the peduncle, depending on the angle of illumination under the microscope. Sometimes a faint suture is more evident on one side than the other in the same specimen. In all of the type material of L. bajensis available in the USNM, this suture is also faint. Thus, this character is unreliable and, in the absence of other distinguishing characters, L. bovallioides Stephensen, 1925 and L. bajensis Shoemaker, 1925 should be considered junior synonyms of L. bovallii Chevreux, 1900 . Lycaea intermedia sp. nov. also has the endopod of U2 fused with the peduncle and is morphologically very similar to L. bovallii but is readily distinguished by the shorter dactyls and other minor characters, as defined in the key and diagnosis of species provided further in this contribution.

Gnathopods. The morphology of G1 and G2 varies from almost simple to strongly sub-chelate. In most species the carpus is expanded distally, ending in a sharp, tooth-like postero-distal corner, often protruding just beyond the distal margin of the propodus. In L. pachypoda G1 and G2 are almost simple with the postero-distal corner of the carpus reduced and rounded, barely extending posteriorly ( Fig. 12 ). In L. lilia the postero-distal corner of the carpus is rounded and in L. nasuta and L. osbornae sp. nov. the corner is less sharp than in other species. In L. serrata the distal margin of the carpus is obliquely excavate, forming an imperfect sub-chela with the propodus but the postero-distal corner usually ends in a sharp, tooth-like point. Regarding the postero-distal corner of the propodus, the species can be divided into three groups; those without, where the margins of the propodus taper gradually to the base of the dactylus ( L. serrata and L. proserrata sp. nov.); those with a small rounded corner ( L. lilia , L. nasuta and L. osbornae sp. nov.), and the remaining species in which the postero-distal corner of the propodus is prominent, often serrated and ending in a rounded or sharp point. These characters, in combination with others as detailed in the key, are most useful to distinguish species.

Pereopod 5. Some species, such as L. vincentii and L. bajensis , have been recorded with minor serrations on the anterior margin of the propodus of P5. Harbison (1976) and Harbison & Madin (1976) use this character, amongst others, to distinguish some species. However, apart from L. vincentii , L. serrata and L. proserrata sp. nov. I have been unable to determine, with certainty, the presence or absence of such serrations in any other species, including the types of L. bajensis in the USNM. Mostly P5 appears smooth under high magnification using a dissecting microscope and, even with a compound microscope, only very minor serrations can be observed/determined, especially for some specimens of L. vincentii . This character is used by Harbison & Madin (1976) to distinguish L. bajensis from L. bovallii and L. bovallioides , adding that L. bovallioides “differs from L. bajensis only in the absence of serrations on the inner margin of the propodus of P3, 4 and 5”. However, they did not have any specimens that they could identify with L. bajensis or L. bovallioides and relied on the descriptions of Shoemaker (1925) and Stephensen (1925) to make their determinations. So, like the above, this character seems to be unreliable providing further support for the synonymy of L. bajensis and L. bovallioides with L. bovallii .

Male first antennae. There are three variations of the occurrence of a bulge on the anterior margin of the callynophore. In those without a bulge, the anterior margin tapers gradually to the insertion of the distal flagellar articles, without forming a prominent antero-distal corner ( Fig. 5 ). Most species of Lycaea , except L. bovallii (and junior synonyms) and L. vincentii , belong to this group. All of these species are distinguished by several additional characters as detailed under those species and in the key. There are two variations of a bulge that occurs on the anterior margin. In only one species, L. vincentii , the bulge occurs medially, and the anterior margin slopes distally to the insertion of the remaining flagellar articles without forming a prominent antero-distal corner ( Fig. 21 ). This character alone distinguishes L. vincentii from its congeners but it is only useful for males. In the remaining nominal species, a bulge occurs on the antero-distal corner forming a right angle with the distal margin ( Fig. 3 ). The anterodistal corner can be raised in some specimens, forming a slight “horn”. This group consists of the nominal species L. bovallii , L. bovallioides , L. gracilis and L. bajensis , tentatively accepted by Harbison & Madin (1976). But slight variations of this character alone are not useful to distinguish these species and, in the absence of other distinguishing characters, the latter three species should be considered synonyms of L. bovallii .

Pereopod dactylus length. Harbison & Madin (1976) consider the length of the dactylus of P3–6 a good diagnostic character, especially of P3 and P4, and define three main types based on the length of the dactylus of P4 relative to the propodus. Those with a short dactylus are about 0.2 x; those with a moderate dactylus 0.2–0.4 x; and those with a long dactylus are greater than 0.4 x, the length of the propodus. Using this system, the nominal species of Lycaea , accepted by Harbison & Madin (1976) fall into three groups: Lycaea nasuta , L. pulex , L. pachypoda and L. serrata with a short, almost stubby dactylus ( L. lilia and L. pachypoda are also in this group); Lycaea vincentii with a moderate length dactylus; and L. bovallii (and its synonyms, L. bovallioides , L. bajensis and L. gracilis ) with a long dactylus. The first group consists of species that are readily distinguished from each other by a number of other characters as defined in the following key and diagnosis of species. Amongst the latter group, L. gracilis Spandl, 1924 is considered a synonym of L. bovallii . It has not been recorded since its original description and Spandl’s (1924) illustrations of this and other species of hyperiideans (1924, 1927) are not always very accurate. The only character distinguishing L. gracilis from L. bovallii is the, apparently, rounded postero-distal corner of the propodus of G2. For the remaining three species with “a long dactylus”, the dactylus length seems to vary slightly from about 0.5 x to almost 0.7 x the length of the propodus. Those with a very long dactylus are otherwise indistinguishable from those with a slightly shorter dactylus, and often the tip of the dactylus seems very slender and fragile and may be prone to breaking off. Thus, the remaining three species of the “long dactylus” group cannot be distinguished on the basis of the dactylus length alone and, in the absence of other defining characters, should be considered synonymous. The last remaining species, L. vincentii , with a moderate length dactylus, is also distinguished from the long dactylus group by the structure of the callynophore of the first antennae of males and by the minor serrations on the anterior margin of the propodus of P5, as detailed above. Apart from these three characters, and that the endopod of U2 is always articulated with the peduncle, it is like L. bovallii . The three species described as new here all have P4 with a relatively short dactylus.

In consideration of the above we are left with ten species of Lycaea considered valid in this review, including three described as new.

Lycaea is a well-known associate of salps ( Dana 1853, Marion 1874, Chevreux 1900, Harbison 1976, Harbison & Madin 1976, Madin & Harbison 1977). Harbison (1976) records the distribution of males, females and juveniles of L. pulex and L. vincentii on salp chains, and Madin & Harbison (1977) provide more information on the parasitic behaviour of Lycaea on salp hosts and the distribution of species. From the available evidence, it seems that females may remain on the host, once settled, while males are more pelagic in habit, seeking out the settled females. The greater development of the pleon and urosome of the male supports this hypothesis.Also, the few light-trap samples that are available in museum collections consist almost exclusively of males, or usually in greater numbers than found in general plankton samples, suggesting that they are active swimmers attracted to the light.

Lycaea appears to be wide-spread in tropical and temperate regions of the world’s oceans. Because of the confused taxonomy of species, it is difficult to determine specific depth ranges, and these are often not recorded, but most seem to be epipelagic in habit.

Key to the species of the genus Lycaea Dana, 1852

1. Gnathopods 1 and 2 more or less simple.............................................. L. pachypoda ( Claus, 1879)

- Gnathopods 1 and 2 strongly sub-chelate, or carpus obliquely excavate but ending in sharp, or slightly rounded, postero-distal corner.............................................................................................. 2

2. Gnathopods 1 and 2; propodus without postero-distal corner, with margins tapering gradually to base of dactylus; dactylus length almost equal to propodus.......................................................................... 3

- Gnathopds 1 and 2; propodus with distinct postero-distal corner, often serrated, or small and rounded; dactylus length 0.3–0.7 x (usually less than 0.6 x) propodus....................................................................... 4

3. Gnathopods 1 and 2; carpus with oblique distal margin (especially G1), forming imperfect sub-chela with propodus; distal margin of merus obliquely V-shaped with anterior margin extending much further over carpus than its posterior margin. Pleonites with dorsal denticles. Uropod 1 peduncle length about 2 x exopod. Pereopod 5 of mature males (also very large females) with exceptionally broad merus and carpus......................................... L. serrata Claus, 1879

- Gnathopods 1 and 2; distal margin of carpus relatively straight or only slightly oblique, forming sub-chela with propodus; distal margin of merus straight, not V-shaped. Pleonites without dorsal denticles. Uropod 1 peduncle length about 3 x exopod. Pereopod 5 of males with normal merus and carpus......................................... L. proserrata sp. nov.

4. Gnathopods 1 and 2; propodus with small, rounded postero-distal corner. Gnathopod 2; propodus extends distally, well beyond postero-distal corner of carpus........................................................................... 5

- Gnathopods 1 and 2; propodus with prominent, often serrated, postero-distal corner, extending posteriorly to dactylus. Gnathopod 2; propodus not reaching beyond postero-distal corner of carpus....................................... 7

5. Gnathopods 1 and 2 similar, with propodus extending well beyond postero-distal corner of carpus..... L. osbornae sp. nov.

- Gnathopod 1; propodus almost reaching postero-distal corner of carpus.......................................... 6

6. Gnathopods 1 and 2; postero-distal corner of carpus ends in sharp tooth. Uropod 2 endopod fused with peduncle.............................................................................................. L. nasuta Claus, 1879

- Gnathopods 1 and 2; postero-distal corner of carpus rounded, not produced into sharp point. Uropod 2 endopod articulated with peduncle............................................................................. L. lilia Volkov, 1982

7. Uropod 2 endopod usually fused with peduncle............................................................. 8

- Uropod 2 endopod articulated with peduncle................................................................ 9

8. Gnathopods 1 and 2; postero-distal corner of carpus and propodus serrated. Pereopod 4 dactylus length about 0.5 x propodus, or longer. Pereonite 2 of females without dorsal hump. Antennae 1 of males; callynophore with anterior bulge on antero-distal corner, forming right angle with distal margin........................................... L. bovallii Chevreux, 1900

- Gnathopods 1 and 2; postero-distal corner of carpus and propodus without serrations. Pereopod 4 dactylus length about 0.2 x propodus. Pereonite 2 of female with slight dorsal hump. Antennae 1 of males; callynophore without anterior bulge.......................................................................................... L. intermedia sp. nov.

9. Uropod 1 peduncle length about 2 x exopod. Pereopods 3–6; dactylus stubby, very short, length about 0.2 x propodus or slightly less. Gnathopod 1; posterior margin of carpus slightly serrated. Antennae 1 of males; callynophore without anterior bulge..................................................................................... L. pulex Marion, 1874

- Uropod 1 peduncle length 3 x exopod. Pereopods 3–6; dactylus slender, length about 0.4 x propodus, or slightly less. Gnathopod 1; posterior margin of carpus distinctly scalloped, especially towards postero-distal corner. Antennae 1 of males; callynophore with anterior bulge set back slightly from distal margin.................................. L. vincentii Stebbing, 1888

Figures

FIGURE 3. Lycaea bovallii Chevreux, 1900. Male, 6.4 mm, USNM 1171017. Scale bars = 0.5 mm (habitus, G1–P7); 0.2 mm (remainder).

FIGURE 5. Lycaea intermedia sp. nov. Allotype male, 6.3 mm, NHMD-228225. P6′ from female 5.3 mm, collected with holotype. P6″ from female 6.1 mm (ovig.), NHMD-228185. Scale bars = 0.5 mm (habitus, A2, G1–P7); 0.2 mm (A1, Us).

FIGURE 12. Lycaea pachypoda (Claus, 1879). Female, 5.5 mm, SAMA C5268. Scale bars = 0.5 mm (habitus); 0.2 mm (G1–P7, Us); 0.1 mm (A1).

FIGURE 21. Lycaea vincentii Stebbing, 1888. Male, 5.3 mm, SAMA C12639. Scale bars = 0.5 mm (A2, habitus, G1–P7); 0.2 mm (A1, Us).