Archaeoscina Stebbing 1904

Genus Archaeoscina Stebbing, 1904

Archaeoscina Stebbing, 1904: 19. Stephensen & Pirlot 1931: 534. Vinogradov 1956: 199. Bowman & Gruner 1973: 10. Vinogradov et al. 1982: 44. Vinogradov 1999: 1169. Micromimonectes Woltereck, 1906: 189 –190.

Type species

Archaeoscina bonnieri Stebbing, 1904, by monotypy. The unique type is in the BMNH (1905.3.8.21) on one microscope slide.

Type species of synonyms

The type species of Micromimonectes is M. irene Woltereck, 1906. Type material could not be found in any European or North American museum and is considered lost. However, the description and figures of an ovigerous female, are consistent with females of Archaeoscina.

Diagnosis

Cuticle of males with hexagonal markings (not seen in females). Head of mature females immersed in first pereonite; with lateral shield, curved ventrally, adjacent to A1, shielding most of peduncle of A1. Head of males rectangular, length about half depth, as long as first pereonite. Eyes very small or absent (not seen in specimens examined). Antennae 1; peduncle 3­articulate in females, 2­articulate in males; flagellum with elongate callynophore, 1.0–2.0x length of peduncle in females, 2.0–4.0x length of peduncle in males, and three small terminal articles, the terminal one slightly longer than the preceding one. Antennae 2; length 0.5–0.7x A1, rarely males with long, whip­like flagellum, much longer than A1; the two terminal articles much shorter than preceding one; terminal article with long apical seta. Mandibular palp; length third article 1.7–2.0x length of first two combined; article 3 with robust seta one­third from base, distal twothirds covered with series of denticles ventrally. Maxillae 1; palp with two terminal spines; outer lobe with four robust setae; inner lobe apically rounded, barely reaching to base of palp. Maxillae 2; inner lobe broader and shorter than outer, with three robust setae; outer lobe with two robust setae. Maxilliped; outer lobes with outer margin undulated for distal half, inner margin with fine setae and few longer setae distally; inner lobes fused for proximal one­third, length about 0.8x outer lobes but barely reaching middle of outer lobes. Gnathopod 2; dactylus inserted terminally. Pereopods 5–7 with normal dactyls, inserted terminally to propodus, not retractile or hooded. Uropod 3; peduncle width 0.3–0.5x length. Telson length 0.3–0.4x peduncle of U3.

Three species.

Sexual dimorphism

Archaeoscina is characterized by the extreme sexual dimorphism of the body as detailed in the family diagnosis. Immature females (2.0–3.0 mm) resemble males but are readily distinguished by oostegite buds on pereonites 2–5 in addition to gills on pereonites 3–6, and the pereon is often slightly more inflated than in males of similar size. It seems that as females mature, the pereon inflates to help accommodate eggs and developing young but the pereopods and urosome retain their relative dimensions.

The structure of the antennae also differs markedly between the sexes. In females the first antennae are 7­articulate, consisting of a 3­articulate peduncle and a 4­articulate flagellum composed of an elongate callynophore and three, much smaller, terminal articles; the second antennae are 6­articulate with the two terminal articles being much smaller than the preceding one. In males the first antennae are 6­articulate, consisting of a 2­articulate peduncle followed by a relatively larger and more rounded callynophore than in females and three smaller terminal articles as in females; the second antennae are 7­ articulate.

In addition to the above, the telson of males is relatively longer, about 0.4x length of the peduncle of uropod 3 (0.3x in females).

Remarks

Archaeoscina is uncommon but widely distributed in all oceans, including sub­Arctic and sub­Antarctic waters. Very little is known about the biology of species except that they seem to inhabit meso­ and bathypelagic layers having been found in catches from depths of 200–500 m, 300–500 m and also in catches from depths of 700 m, 1000 m and more to the surface (Vinogradov 1956, Vinogradov et al. 1982).

Male specimens appear to be very rare and, apart from the type of A. bonnieri Stebbing, 1904, I have seen only six male specimens that could be assigned to Archaeoscina. Only one exceeds 3.0 mm in length (4.2 mm), two are 2–3 mm long and three are less than 2.0 mm in length. All have well­developed aesthetascs on the callynophore of the first antennae. The only other record of males is by Woltereck (1909), who illustrated and described A. stebbingi from the eastern tropical Pacific, and Vinogradov (1956) who recorded specimens of A. steenstrupi (Bovallius, 1885) from the west Bering Sea; all 2–3 mm in length.

The unique type of A. stebbingi, a mature or almost mature male, about 3.0 mm long, appears to be lost. Wolterecks (1909) description is brief, and his figure schematic, so it is difficult to compare characters with other specimens. Woltereck distinguishes his species from A. bonnieri (considered a synonym of A. steenstrupi) by the broader carpus of the gnathopods, minor differences in the articles of the antennae and that the third article of the mandibular palp is at least three times longer than the first two combined. The differences in the articles of the gnathopods and antennae can be attributed to the fact that Stebbing (1904) had a juvenile specimen and, in part, to Wolterecks schematic drawing. Also, his drawing of the mandibular palp indicates that the third article is only about 1.5x longer than the first two combined. Thus, in the absence of the type, it is difficult to determine the specific status of A. stebbingi. Judging by Wolterecks figure, it closely resembles A. steenstrupi in the mandibular palp, dactyls and ratio of pleon to pereon. However, pereopod 5 is illustrated as relatively long so that pereopods 3, 6 & 7 are much shorter, with pereopod 7 only about half as long as pereopod 5. This contrasts with A. steenstrupi in which pereopods 3–7 are of similar length or pereopod 5 is only slightly longer than the other pereopods. It is this difference, which prevents me from considering the two species synonymous.

One additional species, represented by six females and two males, is here described as new to science. It resembles A. steenstrupi but, apart from several distinctive characters, is readily recognized by the relatively larger pereopods and urosome when comparing specimens of similar size. Thus, Archaeoscina is currently represented by three species.