Arenopontiidae Martínez Arbizu & Moura, 1994

Sak, Serdar, Karaytuğ, Süphan & Huys, Rony, 2024, Review of Neoleptastacus Nicholls, 1945 (Harpacticoida, Arenopontiidae), including an updated key to species and proposal of Phreatipontia gen. nov., Zootaxa 5525 (1), pp. 1-66 : 6-11

Family Arenopontiidae Martínez Arbizu & Moura, 1994

Genus Neoleptastacus Nicholls, 1945

Pararenopontia Bodiou & Colomines, 1986 (type species by original designation: Arenopontia breviarticulata Mielke, 1975 )

Diagnosis (adapted from Sak et al. 2008). Arenopontiidae . Urosomites occasionally with conspicuous surface ornamentation ( N. clasingi , ornamentus , reductaspina ). Anal somite with ( acanthus -group) or without (all other species groups) paired dorsolateral spinous processes. Anal operculum sometimes with median extension. Hyaline frills of abdominal somites with rectangular digitate or non-digitate lappets. Caudal ramus usually with dorsolateral spur near medial margin. P1 exopod 2- or 3-segmented; exp-1 with/without outer spine; exp-3 (or exp-2 when exopod 2-segmented) with one–two spine(s) and two geniculate setae. P1 endopod not prehensile, at least as long as exopod; enp-2 with outer spine and inner geniculate seta at distal margin. P2–P3 endopods 1- or 2-segmented. P3 endopod with outer distal element (when present) usually fused at base. P4 enp-2 with well developed outer distal element (except in trisetosus -group). Armature formula as follows:

Exopod Endopod

P1 0.0.02(1–2) or 0.021 1.011

P2 0.0.021 0.(0–1)(1–2)0 or 110

P3 0.0.021 0.0(1–2)0 or 010

P4 0.0.(0–1)21 0.020

P3 endopod ♂ not sexually dimorphic. P5 with outer basal seta and one–four discrete elements; innermost element fused to segment forming spinous process (weakly delimited in N. trisetosus and N. panamensis sp. nov.); length of process sometimes sexually dimorphic. P 6 ♂ with one–two elements.

Type species. Neoleptastacus spinicaudatus Nicholls, 1945 [by monotypy].

Other species. Twenty-three. See Table 1.

Species inquirenda. Neoleptastacus secundus Krishnaswamy, 1957 ; N. accraensis ( Lang, 1965) .

Taxa of doubtful identity. Arenopontia acantha Chappuis, 1954 sensu Božić (1967) ; Arenopontia? gussoae Cottarelli, 1973a sensu Mielke (1982b) [partim]; Arenopontia? gussoae Cottarelli, 1973a sensu Mielke (1987) [2nd form].

Gender. Masculine.

The genus shows considerable variation in swimming leg armature and segmentation, P5 morphology, abdominal ornamentation and caudal ramus structure. However, all species display a spinous apical process on the P5 which is derived from the fused innermost element (weakly delimited in N. trisetosus and N. panamensis sp. nov.). This apomorphic character state is unique in the Arenopontiidae and potentially serves as evidence in support of the monophyly of the genus. For practical reasons we have recognized several species groups within Neoleptastacus , some of which are monophyletic and may eventually be attributed separate generic status ( Table 2). The majority of these groups are characterized by one or several autapomorphic character states with the notable exception of the spinicaudatus -group which contains the type species. For this reason, we have refrained from proposing new genera (except for the speluncae -group) as this would render Neoleptastacus a paraphyletic taxon.

(1) acanthus -group

Diagnosis. Anal somite with paired dorsolateral processes. Anal operculum weakly developed, without medial extension. P1 exp-1 with outer spine; exp-3 with four setae/spines (except N. huysi ). P1 enp-2 with outer spine and inner geniculate seta distally. P2 exp-2 with outer spine of normal length (not extending far beyond distal margin of exp-3). Endopod P2–P3 2-segmented. P2 enp-2 with or without inner seta; with two distal spines. P3 enp-2 with 1–2 distal spines. P4 enp-2 with well developed outer seta.

Current name Original name and combination

Neoleptastacus Nicholls, 1945

Neoleptastacus spinicaudatus Nicholls, 1945

Neoleptastacus australis ( Chappuis, 1953) Arenopontia australis Chappuis, 1953

Neoleptastacus acanthus ( Chappuis, 1954) Arenopontia acantha Chappuis, 1954

Neoleptastacus longiremis ( Chappuis, 1955) Arenopontia longiremis Chappuis, 1955

Neoleptastacus secundus Krishnaswamy, 1957 *

Neoleptastacus africanus ( Chappuis & Rouch, 1961) Arenopontia africana Chappuis & Rouch, 1961

Neoleptastacus accraensis ( Lang, 1965) * Arenopontia accraensis Lang, 1965

Neoleptastacus indicus ( Rao, 1967) Arenopontia indica Rao, 1967

Neoleptastacus ishikarianus ( Itô, 1968) Arenopontia ishikariana Itô, 1968

Neoleptastacus gussoae ( Cottarelli, 1973a) Arenopontia gussoae Cottarelli, 1973a

Neoleptastacus trisetosus ( Mielke, 1982a) Arenopontia trisetosa Mielke, 1982a

Neoleptastacus clasingi ( Mielke, 1985) Arenopontia clasingi Mielke, 1985

Neoleptastacus pacificus ( Mielke, 1985) Arenopontia pacifica Mielke, 1985

Neoleptastacus spicatus ( Mielke, 1985) Arenopontia spicata Mielke, 1985

Neoleptastacus angolensis ( Bodiou & Colomines, 1986) comb. nov. Arenopontia (Neoleptastacus) africana f. angolensis Kunz, 1971 Neoleptastacus chaufriassei ( Bodiou & Colomines, 1986) Arenopontia (Neoleptastacus) chaufriassei Bodiou & Colomines, 1986 Neoleptastacus ornamentus ( Mielke, 1987) Arenopontia ornamenta Mielke, 1987

Neoleptastacus reductaspina ( Mielke, 1987) Arenopontia reductaspina Mielke, 1987

Neoleptastacus huysi ( Karanovic, 2000) Arenopontia (Neoleptastacus) huysi Karanovic, 2000

Neoleptastacus abbreviatus sp. nov. Arenopontia? gussoae Cottarelli, 1973a sensu Mielke (1982b) [partim] Neoleptastacus chilensis sp. nov. Arenopontia? gussoae Cottarelli, 1973a sensu Mielke (1987) [partim] Neoleptastacus emendatus sp. nov. Arenopontia (Neoleptastacus) acantha accraensis Lang, 1965 sensu Kunz (1971) Neoleptastacus panamensis sp. nov. Arenopontia trisetosa Mielke, 1982a sensu Mielke (1982b) Neoleptastacus pseudishikarianus sp. nov. Arenopontia? ishikariana Itô, 1968 sensu Mielke (1987) Neoleptastacus rectus sp. nov. Arenopontia? gussoae Cottarelli, 1973a sensu Mielke (1982b) [partim] Neoleptastacus supersetosus sp. nov.

Phreatipontia gen. nov.

Phreatipontia phreatica (Cottarelli, Bruno & Venanzetti, Arenopontia (Neoleptastacus) phreatica Cottarelli, Bruno & Venanzetti, 1994 1994) comb. nov.

Phreatipontia speluncae (Cottarelli, Bruno & Arenopontia (Neoleptastacus) speluncae Cottarelli, Bruno &

Venanzetti, 1994) comb. nov. Venanzetti, 1994

Subgroups included. acanthus -subgroup, gussoae -subgroup, ornamentus -subgroup.

Remarks. Members of this group can readily be identified by the presence of paired dorsolateral spinous processes on the anal somite. The presence of these backwardly directed extensions, not found in any other species of the Arenopontiidae , is an apomorphic character state supporting the monophyletic status of this lineage.

Various authors ( Itô 1978; Mielke 1982 b, 1987; Wells & Rao 1987) have recognized a gussoae -subgroup of morphologically extremely similar species characterized by the presence of only one spine on P3 enp-2: N. longiremis ( Chappuis, 1955) , N. indicus ( Rao, 1967) , N. gussoae ( Cottarelli, 1973a) and N. sakagamii ( Itô, 1978) . Neoleptastacus accraensis ( Lang, 1965) , which is generally believed to display this character (see below for a reinterpretation), has occasionally been cited as part of this species complex ( Mielke 1982 b, 1987). However, the absence of paired anal processes excludes this species from the acanthus -group. The 1-spine condition on the distal endopodal segment of P3 evolved convergently in the common ancestor of the trisetosus -group as well as in N. australis ( Chappuis, 1953) and N. reductaspina ( Mielke, 1987) ( Table 2). Wells & Rao (1987), inspired by the extensive variability observed in their material of N. indicus , proposed to sink N. sakagamii as a junior subjective synonym of the latter, but argued that that the caudal ramus and possibly P5 are sufficiently different to maintain A. gussoae as a distinct species. Neoleptastacus secundus should also be considered a member of the acanthus - group since Krishnaswamy (1957: 97) clearly stated that “...the anal segment bears two spines posteriorly” (hinted at in his illustration of the male habitus). Unfortunately, the P3 endopod was not figured and his statement that it resembles that of P2 (except for the absence of the inner seta on enp-1) has made most authors assume that P3 enp-2 bears two distal elements ( Lang 1965; Bodiou & Colomines 1986; Karanovic 2000). Given its close similarity to N. longiremis (see below), which bears one element on this segment, this character must await confirmation. The species is here treated as a species inquirenda in the gussoae -subgroup. Reassessment of Mielke’s (1982 b, 1987) descriptions of “ Arenopontia? gussoae ” resulted in the recognition of three additional members: N. abbreviatus sp. nov., N. chilensis sp. nov. and N. rectus sp. nov. Finally, Neoleptastacus emendatus sp. nov., proposed here (see below) for Arenopontia (Neoleptastacus) acantha accraensis Lang, 1965 sensu Kunz (1971) , also belongs to this subgroup which contains species from the northern Atlantic, Indian Ocean, Japan and the Pacific seaboard of South America.

The ornamentus -subgroup currently includes two closely related Chilean species, N. ornamentus ( Mielke, 1987) and N. reductaspina ( Mielke, 1987) , that display conspicuous surface ornamentation on the abdominal somites in the form of rectangular plates (areas of integumental reinforcement). Similar surface ornamentation has been reported for N. clasingi ( Mielke, 1985) in the spinicaudatus -group. Both N. ornamentus and N. reductaspina share the unique absence of the inner seta on P2 enp-2 ( Table 2), giving further credence to the monophyly of this subgroup.

Neoleptastacus acanthus ( Chappuis, 1954) , N. chaufriassei ( Bodiou & Colomines, 1986) and N. huysi ( Karanovic, 2000) exhibit the plesiomorphic 2-spine condition on P3 enp-2 and are united in the acanthus -subgroup. No synapomorphy has as yet been identified for this subgroup which includes species from the Mediterranean and the sub-antarctic Crozet Islands in the southern Indian Ocean.

(2) spinicaudatus -group

Diagnosis. Anal somite without paired dorsolateral processes. Anal operculum weakly developed, without rounded medial extension (except for A. pseudishikarianus sp. nov.). P1 exp-1 with outer spine; exp-3 with four setae/ spines. P1 enp-2 with outer spine and inner geniculate seta distally. P2 exp-2 with outer spine of normal length (not extending far beyond distal margin of exp-3). Endopod P2–P3 2-segmented; P2 enp-2 with inner seta and two distal spines; P3 enp-2 with two distal spines (outer one fused to segment). P4 enp-2 with normally developed outer seta.

Species included. N. spinicaudatus Nicholls, 1945 , N. ishikarianus ( Itô, 1968) , N. clasingi ( Mielke, 1985) , N. pacificus ( Mielke, 1985) , N. spicatus ( Mielke, 1985) and N. pseudishikarianus sp. nov.

The spinicaudatus -group accommodates six morphologically very similar species, all of which are currently restricted to the Pacific Ocean. All species display the plesiomorphic armature on P1–P4, except for N. pacificus which lacks the inner seta on P4 exp-3 ( Table 2). In the absence of any morphology-based apomorphies that could support the common origin of these species, assessment of the potential monophyly of this species group will have to await the arrival of molecular sequence data. Sak et al. (2008) provided a key to the members of the spinicaudatus - group (except N. pseudishikarianus sp. nov.).

Chappuis & Rouch’s (1961) description of Neoleptastacus accraensis ( Lang, 1965) is inadequate and incomplete. Based on a reinterpretation of the armature pattern of the P3 endopod (see below) the species is treated here as a species inquirenda in the spinicaudatus -group.

(3) australis -group

Diagnosis. Anal somite without paired dorsolateral processes. Anal operculum weakly developed, without rounded medial extension. P1 exp-1 with outer spine; exp-3 with four setae/spines. P1 enp-2 with outer spine and inner geniculate seta distally. P2 exp-2 with outer spine of normal length (not extending far beyond distal margin of exp- 3). P2 endopod 2-segmented; enp-2 with inner seta and two distal spines. P3 endopod 1-segmented; with one distal spine. P4 enp-2 with normally developed outer seta.

Species included. N. australis ( Chappuis, 1953) .

This species group includes one incompletely described African species which does not fit comfortably in either the spinicaudatus - or trisetosus -groups defined herein. The reduced armature on the P3 endopod (one apical element on the distal segment) is not exclusive to N. australis ( Table 2). More information is required before any statement can be made about its relationships, particularly whether it may be nested as an advanced member in the spinicaudatus -group.

(4) trisetosus -group

Diagnosis. Anal somite without paired dorsolateral processes. Anal operculum well developed, often produced into a rounded medial extension (not illustrated for N. trisetosa ). P1 exp-1 without outer spine (exopod sometimes 2-segmented); exp-3 with three setae/spines. P1 enp-2 with outer spine and inner geniculate seta distally. P2 exp-2 with very long outer setiform element (extending far beyond distal margin of exp-3). Endopod P2–P3 1-segmented. P2 endopod with inner seta and one distal spine. P3 endopod with one distal spine. P4 enp-2 outer seta reduced.

Species included. N. africanus ( Chappuis & Rouch, 1961) , N. trisetosus ( Mielke, 1982a) , N. angolensis ( Bodiou & Colomines, 1986) comb. nov., N. panamensis sp. nov., N. supersetosus sp. nov.

The common origin of the species included in this group is strongly supported by five apomorphic character states: (1) absence of outer spine on P1 exp-1, (2) presence of only three elements on the distal segment of P1 exopod, (3) 1-segmented P2–P3 endopods with reduced armature (110 and 010, respectively), (4) P2 exp-2 with very long outer setiform element, extending far beyond distal margin of exp-3, and (5) anal operculum well developed, often produced into a rounded median extension (unconfirmed for N. trisetosus and N. panamensis sp. nov.). Neoleptastacus africanus and N. angolensis comb. nov. share the plesiomorphic 3-segmented P1 exopod, a distinctly elongate P4 exopod and possibly reduced armature on the P5. Neoleptastacus trisetosus , N. panamensis sp. nov. and N. supersetosus sp. nov. exhibit the apomorphic 2-segmented condition of the P1 exopod. The group has a wide distribution with records from the Galápagos archipelago ( Ecuador), Panama, Kuwait and the Atlantic seaboard of Africa.

(5) speluncae -group

Diagnosis. Anal somite without paired dorsolateral processes. Anal operculum weakly developed, without rounded medial extension. P1 exp-1 with outer spine; exp-3 with 4 setae/spines. P1 enp-2 with two geniculate setae distally. P2 exp-2 with outer spine of normal length (not extending far beyond distal margin of exp-3). Endopod P2–P3 2- segmented; P2 enp-2 with inner seta but only one distal spine. P3 enp-2 with one distal spine. P4 enp-2 outer seta relatively short.

Species included. N. phreaticus ( Cottarelli, Bruno & Venanzetti, 1994) , N. speluncae ( Cottarelli, Bruno & Venanzetti, 1994) .

Members of this group are restricted to the Mediterranean and the Black Sea where they typically inhabit reduced salinity environments that are exposed to freshwater inflow. They also diverge morphologically from all species currently included in Neoleptastacus by the armature of the P1 endopod, displaying two geniculate setae on the distal segment instead of an outer spine and an inner geniculate seta. Another shared character is the reduced armature on P2–P3 enp-2, showing only one apical element (0.110 and 0.010, respectively). The speluncae -group cannot be accommodated in Neoleptastacus and is here attributed generic rank (see below— Phreatipontia gen. nov.).

a Krishna swamy (1957) states that P3 resembles P2 but does not figure it.

b Chappuis (1953) states that exopodal setal formula is as in A. subterranea Kunz, 1937 but does not illustrate the P4 exopod.

c Based on reinterpretation presented herein. Previous authorities ( Lang 1965; Bodiou & Colomines 1986; Karanovic 2000; Wells 2007) cited/interpreted the armature formula as 0.010.

d Chappuis & Rouch (1961) do not provide information about P3 exopod or P4 but Lang (1965), Bodiou & Colomines (1986) and Wells (2007) considered their armature patterns to be identical with those of N. longiremis without giving evidence underpinning their assumption.

e replaced by 2–3 spinules.

f The small outer element figured by Chappuis & Rouch (1961) on P1 exp-1 is here interpreted as a spinule.

g The fourth (innermost) marginal element is delimited at the base, representing the homologue of the spinous process in other members of Neoleptastacus .

h Four articulating elements in addition to the inner spinous process.

i Cottarelli et al. (1994) erroneously show the inner seta originating from enp-1.

j According to Cottarelli et al. (1994) the outer distal element of enp-2 is absent but this is contradicted by our re-examination ( Fig. 14D ).

Nomenclature and (re)descriptions

Figures

FIGURE 14. Phreatipontia phreatica (Cottarelli, Bruno & Venanzetti, 1994) comb. nov. (♀): (A) P1, anterior; (B) P2, anterior; (C) P3, anterior; (D) P4, anterior.