Caromiobenella jeoni, Suárez-Morales & P.M.B, 2025

Caromiobenella jeoni sp. nov.

urn:lsid:zoobank.org:act:C2ADE33E-2974-4CB7-81F9-5FA95E5D34F5

( Figs 4–6 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Material examined. Adult male holotype partly dissected, mounted on slide in glycerine, (ECO-CHZ-12530).

Type locality. Port Phillip Bay , Victoria, Australia (37°57.085’ S, 144°47.128’ E) coll. on 21 May 1985 GoogleMaps .

Diagnosis (based on male holotype). Cephalothorax relatively short, about half of total body length; anterior margin widely rounded, smooth. Cephalothorax and succeeding pedigerous somites 2–4 with crater-like integumental processes. Antennules 5-segmented, with setal elements on segments 2–3 unusually short, spiniform, with 4–5 rows of subdistal spinules on fifth segment. Urosome relatively short, about 1/3 or less of total body length. Genital somite carrying compact genital complex with robust, short shaft and pair of compact, short genital lappets with medial pair of pear-shaped opercular flaps, and distally furnished with rows of papilla-like integumental elements. Anal somite with small posterolateral projections. Caudal rami with 5 setae; seta IV reduced.

Description of male holotype. Body short, robust; total body length 1.47 mm in dorsal view. Cephalothorax almost 50% of total body length, ventral margin straight, dorsal surface with two pairs of integumental crater-like depressions on anterior half with adjacent field of integumental wrinkles ( Fig. 4A View FIGURE 4 ), with posterolateral expansions of incorporated first pediger reaching almost midlength of succeeding second pedigerous somite ( Fig. 4A View FIGURE 4 ); anteriorly rounded, with moderately protuberant forehead ( Fig. 4A, B View FIGURE 4 ), the latter with medial cluster of integumental pores (mpc in Fig. 4B View FIGURE 4 ); preoral anterior surface with field of integumental wrinkles and three pairs of nipple-like processes on ventral surface ( Fig. 4B View FIGURE 4 ). First to fourth pedigerous somites each with crater-like processes sensu Jeon et al. (2018) (clp in Fig. 4A, C View FIGURE 4 ). Oral cone at about halfway along ventral surface of cephalothorax; cone low, with adjacent pores. Eyes represented by two lateral cups and medial cup at anterior ¼ of cephalothorax, moderately developed, weakly pigmented; medial eye cup positioned slightly anterior to lateral eye cups; lateral cups rounded, slightly larger than medial cup in dorsal view (mec, lec in Fig. 4A View FIGURE 4 ).

Urosome 25% of total body length; urosome comprising fifth pedigerous somite, genital somite, one free somite, preanal and anal somite, latter holding pair of caudal rami; relative length of urosomites, from proximal to distal as: 21.8: 20.6: 21.3: 22.7: 13.6 = 100 ( Fig. 5E View FIGURE 5 ). Fifth pedigerous somite with weakly expanded proximal half, ventral surface smooth. Genital double-somite with compact genital complex on ventral surface. Preanal somite almost twice as long as anal somite ( Fig. 5E View FIGURE 5 ), latter with short, rounded projections (arrowheads in Fig. 5E View FIGURE 5 ). Genital complex ( Fig. 5E View FIGURE 5 ), with short proximal shaft and corrugate lateral margins: genital lappets short, separated by medial distal invagination, distal margin ornamented with rows of integumental papillae ( Fig. 5F View FIGURE 5 ); pair of opercular flaps (of in Fig. 5F View FIGURE 5 ) present on ventral surface of complex covering paired genital openings; flaps thick, pear-shaped. Anal somite carrying pair of caudal rami armed with 5 caudal setae (setae I–V); setae I–III, and V subequal in length and width; seta IV lightly setulated, shorter and slenderer than others, slightly longer than caudal ramus ( Figs 4D View FIGURE 4 , 5E View FIGURE 5 ).

Antennules ( Figs 5A–C View FIGURE 5 , 6A, C View FIGURE 6 ) 0.46 mm long, almost 45% of total body length; 5-segmented; segments 1–3 clearly divided, segments 4–5 partially fused ( Fig. 5A View FIGURE 5 ). Following antennule armature nomenclature by Grygier & Ohtsuka (1995), first segment with short, spiniform element 1; second segment carrying short, spiniform proximal elements 2d 1,2 and 2v 1,2, dorsal seta IId absent; third segment with short, pinnate elements 3 and IIIv; element IIId setiform, slender; fourth segment with reduced armature including proximal spiniform element 4d 1, flexible setae IVd, IVv, and slender ventral aesthetasc 4aes. Following Huys et al.’s (2007) nomenclature for male antennulary setation, short, slender setae 1–4 on outer margin, setae unbranched ( Fig. 5B View FIGURE 5 ); apical elements 6 1 and 6aes present ( Fig. 5A, B View FIGURE 5 ); distal margin with 4–5 transverse rows of spinules arranged in tight pattern; all rows incomplete, with a looser pattern at their ends.

Swimming legs 1–4 biramous, with three-segmented rami; endopods slightly smaller than exopods. Outer basipodal seta present in all legs, subequally long. Inner distal corner bulging (arrowhead in Fig. 5D View FIGURE 5 ). Outer spines on first and third exopodal segments short, about half as long as bearing segment. Armature of swimming legs:

Leg Basis Endopod Exopod

1 1-0 0-1; 0-1;1-2-2 I-1; 0-1; I-2-2

2–4 1-0 0-1; 0-1;1-2-2 I-1; 0-1; I-2-3

Leg 5 absent.

Etymology. The species name is a masculine genitive eponym honouring our colleague Dr. Donggu Jeon (Hanyang University, Korea), who described the genus Caromiobenella in 2018.

Remarks. The male holotype from Australia shows the main generic characters of Caromiobenella described by Jeon et al. (2018), including: (1) short cephalothorax nearly 50% of the body length, (2) inconspicuous ventral oral cone, (3) urosome relatively short, about 1/3 or less of total body length, (4) cephalothorax dorsal surface with at least 2 pairs of crater-like integumental processes, (5) antennules with 4–5 rows of spinules partially circling the distal end of the antennulary fifth segment, (6) inner margin of basipodal segment of swimming legs 1–4 with bulging process, (7) genital complex with medially invaginated shaft and pair of genital lappets, (8) anal somite with small posterolateral projections, 9) caudal rami with 5 setae, seta IV reduced.

Currently, there are 10 nominal species of the genus ( Walter & Boxshall 2024) most only known by the males. The female of C. brasiliensis was recognized recently by both molecular and morphological evidence (Cruz Rosa et al. 2021) and C. hamatapex is known only from the female ( Grygier & Ohtsuka 1995).

One of the most striking characters of the new species, C. jeoni sp. nov. is the number and position of the crater-like integumental processes. It has two pairs in the usual dorsal position as described by Jeon et al. (2018) for both C. castorea Jeon, Lee & Soh, 2018 and C. polluxea Jeon, Lee & Soh, 2018 . Contrastingly, C. jeoni sp. nov. has additional ones on the posterolateral expansion of the incorporated first pedigerous somite and on the pedigerous somites 2–4 ( Fig. 4A View FIGURE 4 ). These crater-like processes were not reported in the descriptions of other species of Caromiobenella , i.e. C. serricornis ( Sars, 1921) , C. pygmaea (Suárez-Morales, 2000) or C. brasiliensis . In the latter, the anterior dorsal surface of the cephalothorax has a field of wrinkles probably related to the position of the crater-like processes (Cruz Rosa et al. 2021, fig. 2A). The new species, C. jeoni sp. nov., also differs from these congeneric species in its size (1.47 mm). It is smaller than C. serricornis (1.75 mm) and larger than C. pygmaea (0.43 mm) and C. brasiliensis (0.98 mm).

Overall, the most distinctive character to distinguish the new species, C. jeoni sp. nov., from its known congeners is the peculiar structure and size of the genital complex. In the other species, C. polluxea , C. castorea , C. pygmaea , M. serricornis , and C. brasiliensis , the genital complex has a longer shaft and clearly defined, divergent genital lappets. The genital complex of the new species is noticeably compact, with a very short, thick shaft and with short thick, symmetrical lappets furnished with two distal rows of papilliform elements. Caromiobenella brasiliensis bears a set of short, parallel, ornamented genital lappets with rows of spinules on the lappets distal surface (Cruz Rosa et al. 2021, fig. 5D, E), which is most similar to the genital complex of C. jeoni sp. nov. According to Jeon et al. (2019) males of Caromiobenella , form two distinct groups based on their type of genital complex, one with a deep medial notch on the posterodistal position (type I) e.g. C. castorea and the other with a homologous medial distal protrusion (type II) e.g. C. polluxea . The genital complex of C. jeoni sp. nov. could be classified as type I, with a distinctive deep medial notch, thus joining C. castorea , C. helgolandica , C. pygmaea and C. patagonica in this group. Thus, the new species can be distinguished from its known congeneric species by the structure and ornamentation of its genital complex as well as the number and position of crater-like elements. These differences appear to be sufficient for the proposal of the new Australian species, C. jeoni sp. nov. Our finding of C. jeoni sp. nov. in Australian waters represents the first species of the genus described from outside Korea.