Akrophryxus milvus Williams & Boyko 2021, n. sp.

Akrophryxus milvus n. sp.

(Figs 3-5, 11Q, R)

urn:lsid:zoobank.org:act: AC0E5AFB-69BB-434D-86A6-A679F9EACDBC

“sacculinid (? parasite attached to antennular fossa)” – Castro 2013: 443.

TYPE MATERIAL. — Holotype. Madagascar • MNHN-IU-2014-20314; ovigerous female (3.1 mm diameter), attached to left antennule of male Ethusa machaera Castro, 2005 (9.2 mm CL, 9.0 mm CW; MNHN-IU-2010-1997); Sta. CP 3595; 25°35’28.2012’’S, 44°15’25.2’’E; south of Pointe Barrow; 821-910 m; coll. Bouchet et al. on the shrimper Nosy Be 11; ATIMO VATAE expedition, collected by trawling; 12.V.2010.

Allotype. Madagascar • MNHN-IU-2014-20315; mature male (740 µm L); same data as for holotype.

TYPE LOCALITY. — 25°35’28.2012”S, 44°15’25.2”E, Madagascar, south of Pointe Barrow, 821- 910 m.

TYPE HOST. — Ethusa machaera Castro, 2005 [Crustacea: Brachyura: Ethusidae].

ETYMOLOGY. — The species name is derived from the Latin for “kite” in reference to the plate partially surrounding the host antennule that is reminiscent of the shape of a kite shield, defensive armor used primarily in Western Europe in the 10th-13th centuries. The gender is masculine.

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

DESCRIPTION

Female

Body spheroid, length and width nearly equal, filled with numerous eggs (Figs 3A, B; 4A, C-G). Cephalon externally indistinguishable from pereon, without eyes. Antennules absent, antennae each as oblong flat plate lateral to oral cone, covered with minute scales (not shown) (Figs 4G; 5G). Oral cone rounded (Fig. 4G); mouthparts indistinct. Maxillipeds ovate with recurved digitiform extension (Fig. 5H). Pereopods 1-5 subequal in size and shape, without setae (Figs 4G; 5E, F); dactylus short, recurved, propodus carpus and merus fused, ischia and bases stout. Oostegite 1 largest (Figs 4G; 5J), broadly ovate with small posterior accessory lobe, broad lobe medially divided in lateral view (Fig. 5K); oostegites 2/3, 4, 5 progressively larger; oostegite 2 present, thin and closely applied to oostegite 3, lobes subequal in size and shape (Fig. 5L); oostegite 3 subtriangular (Fig. 5L), expanded posteriorly, medial and anterior finger-like extensions present with small setae distally, oostegites 4 and 5 subquadrate, small setae on medial and posterior margins (Fig. 5M). Pleon presumably modified (see Discussion) as oblong, narrow, thickened plate (Fig. 4 A-G) partially surrounding host antennule with three circular medial holes: largest surrounding antennule of host and closest to mouthparts of parasite, smallest hole at midpoint of plate, intermediate sized hole farthest from mouthparts of parasite.

Male

Body not recurved ventrally (Fig. 5A, B). Cephalon fused with pereomere 1 (Fig. 5A, B), anterior margin rounded, posterolateral margins evenly rounded; lacking eyes, cephalic slits present. Antennules reduced, each apparently composed of three flattened disc-shaped segments (Fig. 5C); antennae each as single broad elongate lobes lateral to oral cone, flagella absent (Fig. 5C). Oral cone triangular (Fig. 5B, C). Pereomeres 2-6 distinct, 4-6 subequal in width, others slightly narrower (Fig. 5A, B); pereomere 7 fused with pleon, lateral margins recurved ventrally. Pereopods 1-6 subequal in size and shape, all segments distinct, carpi rounded, ischia short, bases elongate; dactylus, propodus and carpus with isolated marginal setae (Fig. 5 B-D); pereopod 7 lacking. Pleon compact, rounded, all segments fused and fused with pereomere 7, rounded posteriorly; anal slit and pleopods lacking (Fig. 5A, B).

REMARKS

The female of Akrophryxus milvus n. gen., n. sp. is very different from those in all other dajids, excepting Telephryxus clypeus n. gen., n. sp. (Table 1). The spheroid shape of the body and possession of a plate partially surrounding the host antennule are shared only by these two genera. The male of A. milvus n. gen., n. sp. is likewise very different from those in all other dajid genera (Table 2), including T. clypeus n. gen., n. sp. in having only six pairs of pereopods with no trace of the seventh pair (pereopod 7 of two elongate segments in the sole species of Oculophryxus and of one or two stub-like segments in T. clypeus n. gen., n. sp.). The male of A. milvus n. gen., n. sp. also differs from those in most genera in having the pleon fused with pereomere 7 (distinct from pereomere 7 in males in all other genera except Holophryxus Richardson, 1905 and Oculophryxus), and from all other genera in having a reduced antennule and an antenna with a single large segment (males of other genera with antennules of at least one well-developed segment and all with antennae segmented and with distal flagella).

The female of A. milvus n. gen., n. sp. can be distinguished from that of T. clypeus n. gen., n. sp. in lacking antennules and in having three medial holes on the narrow, triangular attachment plate partially surrounding the host antennule with no additional lateral holes (T. clypeus n. gen., n. sp. has flattened antennules and a broad, subquadrate attachment plate partially surrounding the host antennule and having two large medial holes, the largest with two additional small lateral holes). The male of A. milvus n. gen., n. sp. can be distinguished from that of T. clypeus n. gen., n. sp. in having only six pairs of pereopods (six fully-developed pairs plus a rudimentary seventh pair of one or two small segments in T. clypeus n. gen., n. sp.), a reduced antennule and a single segmented antenna (large ovate single segmented antennule and two segmented short antennae in T. clypeus n. gen., n. sp.), and the short and rounded pleon fused to pereomere 7 (pleon distinct from pereomere 7, elongate and tapered pleon in T. clypeus n. gen., n. sp.).