Aegophila cappa Williams & Boyko 2021, n. sp.

Aegophila cappa n. sp.

(Figs 1; 2)

urn:lsid:zoobank.org:act: 4FF870BA-A6D1-4A86-87AE-84160A0EA65F

“parasite” – Richardson 1909: 125, figs 49, 50.

“eine Form ohne Namen auf dem Isopode Aega symmetrica vom Behring-Meer” – Nierstrasz & Brender à Brandis 1931: 220.

“ Aegophila socialis sp. nov.?” – Bresciani 1966: 108-109, fig. 6 (after Richardson 1909) (not A. socialis Bresciani, 1966).

TYPE MATERIAL. — Holotype. Bering Sea • USNM 39524; ovigerous female (3.4 mm W, 2.4 mm L); attached to pereopod of Aegiochus symmetricus (Richardson, 1905) (USNM 39293); Sta. 4772; 54°30’30”N, 179°14’E; “Bowers Bank”; 344-372 fathoms (= 629- 680 m); coll. United States Bureau of Fisheries steamer Albatross, taken by 12-foot Tanner beam trawl (Anonymous 1907); 4.VI.1906.

Allotype. Bering Sea • USNM 1616634; mature male (920 µm L); same data as for holotype.

TYPE LOCALITY. — 54°30’30”N, 179°14’E, “Bowers Bank”, Bering Sea, 629- 680 m.

TYPE HOST. — Aegiochus symmetrica (Richardson, 1905) [Crustacea: Isopoda: Aegidae] (originally as Aega symmetrica in Richardson, 1909; see WoRMS 2008b onwards).

ETYMOLOGY. — The species name is derived from the Latin for cloak or cape (cappa), in reference to the fused oostegite 5 and lateral body wall of the female’s resemblance to a cloak drawn around the body. The gender is feminine.

DISTRIBUTION. — Known only from the type locality and type host.

DESCRIPTION

Female

Body (Fig. 1A, B) semicircular, approximately 1.25 times as wide as maximum length, dorsoventrally flattened, with pair of broad lateral lamellae filled with numerous embryos; lateral lamellae not reaching beyond frontal margin of cephalon. Cephalon (Fig. 1 A-C) indistinctly dorsally separated from pleon, without eyes. Antennules and antennae apparently absent. Oral cone (Fig. 1B, D) with flaring rounded mandibles, extended, distal surface covered with scale-like structures; posterior margin of oral cone with two finger-like projections. Maxillipeds subquadrate (Fig. 1E). Pereon with few faint transverse and longitudinal folds in cuticle (Fig. 1A). Pereopods 1-5 subequal in size and shape, without setae (Fig. 2 F-I, K); dactylus short but highly recurved, propodus and carpus fused, carpus expanded into cup receiving tip of dactylus, basis elongate. Oostegite 1 ovate, expanded, few small setae on posterior margin (Fig. 1H); oostegite 2 slender, rounded at narrowed distal tip, fringe of setae on proximoventral margin (Fig. 1I); oostegite 3 broader than 2, fringe of thick setae on proximoventral margin (Fig. 1J); oostegite 4 subquadrate, fringe of thick setae on proximoventral margin (Fig. 1K); oostegite 5 fused with lateral pleon, medioventral area with region of setae and small, rounded lobe (Fig. 1B, L). Pleon segments fused, minute, vermiform, without lateral plates or pleopods (Fig. 1B).

Male

Body not recurved ventrally (Fig. 2A). Cephalon wider than long (Fig. 2A, B), fused with pereomere 1, anterior margin rounded, posterolateral margins (pereomere 1) as small, rounded lobes; lacking eyes, cephalic slits present. Antennules each as single flattened lobe with five or six long setae on medial and distal margins (Fig. 2B, C). Antennae of three segments each with single distal thin flagellum (Fig. 2B, C). Oral cone triangular (Fig. 2B, C). Pereomeres 2-7 distinct, 4-6 subequal in width, others narrower (Fig. 3B); lateral margins of pereomeres 2-7 extended ventrally, with multiple thin setae on margins (Fig. 2B, E). Pereopods with all segments distinct; 1, 2 each with recurved dactylus approximately as long as rounded propodus (Fig. 2 B-D), 3-7 with recurved dactylus approximately 25% as long as slender elongate propodus (Fig. 2E); all ischia and bases elongate. Pleon elongate, subtriangular, segments fused but faint indication of pleomere 1 by rounded lobes and presence of lateral setae similar to those on pereomeres 2-7 (Fig. 2A, B); pleon tapering posteriorly with small distal rounded protrusion bearing terminal setae surrounding anal slit (Fig. 2A, B); pleopods lacking.

REMARKS

The new species is clearly conspecific with Aegophila socialis; females of both species show dorsoventral compression of the body, lack of antennules and antennae, expanded, clublike mandibles, the same arrangement of oostegites 1-4, the presence of a rounded knob and fringe of thin papillae on the mediovental margin of oostegite 5, as well as fusion of the fifth oostegites with the ventral body wall, and the pleon being a small, unsegmented protuberance. Males of the two species are similar in having fusion of the cephalon with the first pereomere and presence of rounded posterolateral lobes corresponding to the side of pereomere 1, the antennules as unsegmented flaps fringed by setae, and the pleon with all segments fused and lacking pleopods.

Diagnostic differences between females of the two species include: oostegite 1 large, ovate in A. cappa n. sp. (small, “spoon-like” in A. socialis), oostegite 2 narrow in A. cappa n. sp. (broad in A. socialis), and oostegite 4 subquadrate in A. cappa n. sp. (ovate in A. socialis). Bresciani (1966) described A. socialis as lacking maxillipeds, but they are clearly present in A. cappa n. sp. and it is unclear if he overlooked them or if they are truly lacking in A. socialis; the latter appears unlikely since maxillipeds are required for oxygenation of the brood (Gilson 1909; Cericola & Williams 2015). Bresciani (1966) described the pereopods of A. socialis as “small and badly segmented, and do not show any special characters” but did not illustrate them well. In A. cappa n. sp., the pereopods have highly recurved dactyli and show fusion only of the propodus and carpus, with the carpus inner margin being expanded as a cup for insertion of the dactylus.

The males of the two species differ in the form of the antennae (multisegmented with a single flagellum in A. cappa n. sp. vs a single segment with a single flagellum in A. socialis) and the shape of the pleon (much longer than wide in A. cappa n. sp. vs length and width subequal in A. socialis). Bresciani (1966) did not describe the pereopods in detail but did illustrate them. His illustrations appear to show a difference in pereopods 1 and 2 (rounded propodus with typically recurved dactylus) vs 3-7 (elongate propodus and highly recurved dactylus) that is also seen in A. cappa n. sp. However, he drew pereopod 1 as having the propodus and carpus fused whereas in A. cappa n. sp., they are distinct.

It is not clear which specimen of Aegiochus symmetrica was the host of A. cappa n. sp. as all the of the potential host aegids collected at the parasite’s type locality (Sta. 4772, USNM 39293) have their legs intact and no evidence of damage is visible; however, a label reading “1 sent to W. W. Alpator / Jan 1923 ” is present in the jar and it is possible that this gifted specimen was the (now lost) host specimen of the holotype of A. cappa n. sp.