Pseudopenilia bathyalis Sergeeva, 2004

Korovchinsky, Nikolai M. & Sergeeva, Nelli G., 2008, A new family of the order Ctenopoda (Crustacea: Cladocera) from the depths of the Black Sea, Zootaxa 1795, pp. 57-66 : 59-64

Pseudopenilia bathyalis Sergeeva, 2004

Sergeeva, 2004a: 41–42, Fig. 1–4 .

Female. Head large, high, and more or less clearly separated from trunk (structure of its ventral part remains unknown) ( Fig. 1 A). Eye small (its diameter is about 3% of body length), with 14 ommatidia, ocellus comparatively large ( Fig. 1 A, B). Antennules long, with large basal part somewhat dilated distally, and bearing long terminal sensory seta (about two times as long as basal part) and five aesthetascs ( Fig. 1 A, C).

Second antennae large, with long and massive basipodite dilated distally and bearing six transverse rows of denticles ( Fig. 1 A, F, H) which may indicate a strong sclerotization of antennal integument. Distal end of basipodite bears one large spine and three pointed outgrowths. Two-segmented antennal branches are of almost equal length (about 22% of body length). Exopodite with long proximal segment, bearing one apical seta and one lateral seta situated close one to another and one large apical spine dorsally, and short distal segment, bearing five seta on its apical and lateral sides and one large apical spine ( Fig. 1 G, I) (in the original description of Pseudopenilia ( Sergeeva, 2004a) one additional large ventral spine was depicted erroneously on distal segment of the branch (see Fig. 1 F));. Lower branch also possesses long proximal segment with four proximal pairs of small denticles ( Fig. 1 F), bearing apically one seta and one large spine, and short distal segment, bearing four apical setae and one spine ( Fig. 1 G). Formula of antennal setae 2–5 / 1–4. All setae are not segmented, stout, needle-shaped and lack setules (length of terminal setae of both branches are about 25–33% of body length).

Mouth parts consist of a pair of mandibles and a pair of maxillulae (mx I), both of which are strongly asymmetric. Right mandible is larger, its molar surface is covered with numerous spines and prominences, while left one is less armed ( Fig. 1 D). Maxillulae are plate-like and lack long terminal setae, being supplied instead by small setae and denticles ( Fig. 1 E). Maxillae (mx II) are absent.

Shell elongated, transparent, with weak mesh-like reticulation, postero-dorsal side prominent ( Fig. 1 A). Dorsal side of shell and posterior and postero-ventral valve margins with rows of small denticles ( Fig. 1 A, 3E). Brood pouch seems to be closed ( Fig. 3 G).

Six pairs of similar thoracic limbs ( Fig. 2 ). Each limb consists of a long, distally strongly dilated leaf-like exopodite and a shorter endopodite separated in two to three lateral lobes (endites). Gnathobases are absent, small epipodites present only in tl I. Exopodite of tl I possesses five terminal (about 9% of body length) and five lateral setae ( Fig. 2 A, I), endopodite with one large thorn-shaped terminal seta ( Fig. 2 A, G). Exopodites of tl II - tl V possess six terminal setae each (about 6% of body length) and endopodite with one terminal thorn-shaped seta and two to five thin setae ( Fig. 2 B–E, J). A more detailed analysis revealed one additional lateral spine-shaped seta in tl IV ( Fig. 2 H) overlooked by Sergeeva (2004a). Exopodite of tl VI possesses five terminal setae, endopodite with one terminal seta, which is longer and thinner than those in previous limbs, and four thin setae ( Fig. 2 F). All exopodal setae lack setules.

Postabdomen wide and massive, narrowed distally. Setae natatoriae sit on very small prominences; they are stout, not segmented, needle-like and lack setules ( Fig. 3 G). There are two parallel rows of small prominences with 2–4 small denticles each along the dorsal side of postabdomen ( Fig. 3 G). Postabdominal claws large (about 7% of body length) and stout, having one small basal denticle and some smaller denticles situated along their dorsal side; some larger denticles sit along ventral side of claws ( Fig. 3 G), the latter were not indicated on Sergeeva’s original figures.

Resting eggs oval ( Fig. 4 A), their sizes are 0.23 x 0.28 and 0.22 x 0.30 mm. All surface of their thin hard shell (~ 3 µm), densely covered with small prominences possessed widened and marginally indented tops ( Fig. 4 B–D). Thin inner membrane lies under the outer egg shell ( Fig. 4 C). At hatching, the outer egg shell cracks transversally and casts ( Fig. 4 F). Embryo proves to be enclosed in the inner membrane ( Fig. 4 E).

Gut is straight, without appendages. Ovaries lie along the gut, opening dorsally with short oviducts in the brood pouch.

Female body length: 0.56 mm,

Male Unknown.

Juvenile specimens. Body structures of larger juveniles remind those of the adult. However, head and postabdomen, especially in smaller individuals, are comparatively larger. In just hatched juvenile specimen with body length 0.31mm, postabdomen occupies about 32–36% and setae natatoriae about 48% of body length ( Fig. 3 A, B, D). In larger individuals these structures seem to become relatively shorter. Postabdomen lacks small lateral prominences with small denticles and postabdominal claws are comparatively shorter and lack denticles. The latter appear only in larger juveniles ( Fig. 3 C, F). Juvenile body length: 0.30–0.41 mm.

Type material. Holotype: adult female mounted on a slide with body length of 0.56 mm is deposited in the collection of the Institute of Biology of Southern Seas (No AC-1), Sevastopol’ City, Ukraine. Two total mounts with paratypes (2 juvenile females) as well as mounts with other specimens (8 juvenile females) are deposited in the same collection.

Figures

FIGURE 1. Pseudopenilia bathyalis Sergeeva, 2004. Adult female (holotype), Black Sea. A, general lateral view. B, eye and ocellus; C. antennule, distal part. D, mandibles of holotype (above) and paratype (juvenile female) (below). E, maxillulae. F, G, second antennae. H, basipodite of second antenna, lateral view. I, distal segment of upper antennal branch. A – F, after original drawings by Sergeeva; G – I, new drawings.

FIGURE 2. Pseudopenilia bathyalis Sergeeva, 2004. Adult female (holotype), Black Sea. A – F, thoracic limbs of firstsixth pairs. G, endopodite of thoracic limb of first pair. H, thoracic limb of fourth pair. I, J, distal ends of exopodites of first and fourth limbs, respectively. A – F, after original drawings by Sergeeva; G – J, new drawings. All limbs are drawn from inner side; epipodite of tl I is indicated by arrow.

FIGURE 3. Pseudopenilia bathyalis Sergeeva, 2004. Adult female (holotype) (E, right, G), juvenile females (paratypes) (A – D, E, left, F). A, early juvenile specimen, general lateral view. B, postabdomen of the same specimen. C, postabdomen of large juvenile specimen. D, postabdomen, lateral view. E, dorso-posterior shell margin. F, postabdominal claw. G, posterior body part. G, after original drawings by Sergeeva; all others are new drawings. In the adult specimen (Fig. E, right) not all marginal denticles were visible during the reinvestigation.

FIGURE 4. Pseudopenilia bathyalis, 2004. Resting eggs. A, general view. B, surface of outer shell. C, egg shell in the region of its crash (arrows indicate outer shell and inner membrane). D, surface prominences of outer shell. E, embryo enclosing in the inner egg membrane. F, hatching of embryo. Scale bars: 100 µm (A, E, F), 10 µm (B, C), 5 µm (D).