Revision of the genus Cryptolarella Stechow, 1913 (Lafoeidae, Leptothecata, Hydrozoa)

The bathyal genus Cryptolarella, comprising three known species, Cryptolarella abyssicola (Allman, 1888), Cryptolarella diffusa (Allman, 1888) and Cryptolarella humilis (Allman, 1888), is reviewed after the study of the holotypes of the species. A complete redescription and characterization of the species, including new data concerning morphometry and cnidome is presented, and its literature data reviewed. We conclude that all species are conspecific, resulting in a single valid species, C. abyssicola. The distinctive characters of the species are the growth habit, gonothecal arrangement and cnidome.


Introduction
The genus Cryptolarella is relatively common in deep waters, and has been generally dealt with in monographic reviews of abyssal and bathyal hydroids (e.g. Vervoort 1966Vervoort , 1985Ramil and Vervoort 1992;Calder and Vervoort 1998). Cryptolarella was established by Stechow (1913a: 138) to accommodate those species originally assigned to the genus Cryptolaria Busk, 1857 by Allman (1888) that do not have coppinia or scapus.
Gonothecae arising at irregular intervals along stem and primary branches, solitary, on short pedicel; tubular to flask-shaped, ventricose at base, curving at median and distal parts. Highly varied in dimensions and shape, 1.15-3.25 mm (2.40¡0.81, n510) long (from base to aperture through adcauline side), 0.30-0.85 mm (0.62¡0.15, n510) maximum width at median region. Adcauline wall more or less parallel to longitudinal axis of branch; abcauline wall concave basally, convex in the middle, and again concave distally. Aperture circular, large, oblique to longitudinal axis of gonotheca and pointing upwards, 0.23-0.55 mm (0.47¡0.09, n510) in diameter. Gonothecal perisarc with fine transverse striae (seen only at high magnification). Gonothecae rarely (three out of ca 20) upside-down in relation to growth of colony. Most gonothecae single, but two were seen arising together, with contiguous adcauline walls.

Remarks
The species may be characterized by its unique gonophores, cnidome and colony shape. The gonothecae of the subfamilies Lafoeinae and Zygophylacinae are always aggregated, forming a coppinia. Cryptolarella abyssicola is unique because it bears solitary (or maximally paired) flask-shaped gonothecae much larger than the hydrothecae, instead of coppiniae. The cnidome of C. abyssicola includes only small microbasic euryteles. This type of cnidome contrasts with that of most Lafoeinae and Zygophylacinae, generally comprised of at least large microbasic mastigophores (personal observation).
Several genera of Lafoeinae and Zygophylacinae (namely Abietinella Levinsen, 1913, Acryptolaria Norman, 1875, Cryptolaria Busk, 1857, Grammaria Stimpson, 1854, and Zygophylax Quelch, 1885 have erect colonies in which the hydrothecae are regularly distributed along the branches, organized in two, four or six longitudinal rows. Lafoea Lamouroux, 1821 and Cryptolarella show a different organization, with hydrothecae scattered on hydrocaulus or, at most, with a tendency towards biserial arrangement (see Vervoort 1972: 47 and discussion on this material, below). Therefore, Stechow's (1913a) assertion that the hydrothecae in Cryptolarella are disposed in two rows is misleading as already noted by Kramp (1951: 121), and different from the original description of C. abyssicola by Allman (1888: 40, ''hydrothecae disposed on all sides of stem''). Cryptolarella, however, shows some variation in the general appearance of the colony and the size of the hydrothecae, with colonies varying from ''flexible with distinct but weak stems and main branches, all in one plane, some of such colonies have a bushy structure, whilst others have fairly rigid and comparatively thick main stem and branches'' (Vervoort 1985: 286). Vervoort (1966: 119) described the ontogeny of the colony of C. abyssicola: ''the material from St. 574 includes a very youthful colony creeping on an Antipathariid. The (few) hydrothecae are tubular, slightly narrower than in the adult stage, the basal portion is slightly curved and inserts directly on the hydrorhiza. Each theca has 2 or 3 renovations (Figure 19 b)''. Therefore, the initial growth of the species coincides with that of the adult stage of some species of Filellum (Lafoeinae), and possibly with many other younger stages of other Lafoeinae (namely Lafoea, Acryptolaria, Grammaria) or Zygophylacinae (namely Zygophylax, Abietinella, Cryptolaria). This similarity of form during ontogeny makes the identification of many young colonies of those genera and, therefore, the distribution of the species uncertain.
Cryptolaria diffusa, from Sierra Leone, was considered distinctive in its original description (Allman 1888) due to the presence of paired, tubular gonothecae. It was the second species assigned to Cryptolarella by Stechow (1913a). Vervoort (1966: 119) studied the holotype of the species remarking on the absence of such paired gonothecae, but with bodies on the branches that ''could represent gonothecae though their apical parts have disappeared'' and that they would be ''almost certainly worm tubes''. He concluded that there was no significant difference between C. diffusa and C. abyssicola, considering both conspecific (Vervoort 1966(Vervoort , 1985. Vervoort (1966) was not sure that the structures described by Allman (1888) as ''gonothecae'' for both C. abyssicola and C. diffusa, and that he had also seen in the Galathea material (for C. abyssicola), differing from the coppinia of other Lafoeinae, were true gonothecae. Later he (Vervoort 1985: 286), however, reconsidered his previous position, stating, ''I am now convinced that they do represent the gonothecae, though the nature of the gonophore is still a mystery''.
We restudied the holotype of C. diffusa and found the paired gonothecae described by Allman (1888, Plate 21 Figure 1a). A full re-description of the species is given below.
Colony badly preserved, erect, shrubby, 19 mm in height (apical part broken), polysiphonic almost over its total length, 0.40 mm in diameter at base. No hydrorhiza present. Colony sparingly branched in several planes; up to third-order branches observed, arising from a unique germinative tube. Hydrothecae irregularly arising from stem and branches. Unique first-order branch perpendicular to stem, polysiphonic, 35 mm long and 0.43 mm in diameter at base, with few lower-order branches in several planes. Second-and third-order branches with no definite branching pattern. Stem (germinative and accessory tubes) and branches not divided into internodes, without apophyses; distal part of stem bearing only hydrothecae. Stem and branches without nematothecae. Hydrothecae badly preserved, sessile, tubular and curved outwards, not widening distally, with smooth walls and thin perisarc; rim even and smooth, with almost inconspicuously flaring border; aperture circular, 0.11-0.14 mm (0.13¡0.02, n53) in diameter, perpendicular to long axis of free part of hydrotheca. Distribution of hydrothecae from nearly verticillate to an indefinite pattern; distance amongst hydrothecae variable, though subsequent ones generally arising at axil of previous one. Hydrothecae of stem and polysiphonic branches surrounded by accessory tubes. Hydrothecae with almost their total adcauline length adnate to branches; free part emerging from branches at angles larger than 45u. Adnate portion of hydrothecae 0.59-0.92 mm (0.74¡0.17, n53) long; free part 0.12-0.25 mm (0.19¡0.07, n53) long; ratio adnate: free part 1.09-2.80:1 (1.77¡0.71, n53). Hydranths not preserved at all. Gonothecae irregularly arising along stem, primary and secondary branches; solitary, tubular and flask-shaped, with short pedicel, ventricose at base, curving at median and distal parts, highly variable in general dimensions and form, 1.05-2.05 mm (1.83¡0.26, n54) long (from base to aperture at adcauline side), 0.23-0.40 mm (0.34¡0.09, n53) maximum width at median region. Gonothecal adcauline wall more or less parallel to branch long axis, abcauline wall concave basally, convex in the middle, and concave again distally in relation to long axis of branch. Terminal aperture circular, large, oblique to long axis of gonotheca, 0.18-0.38 mm (n52) in diameter. Gonothecal perisarc with striae perpendicular to gonothecal long axis. There are two gonothecae arising together, with contiguous adcauline walls.
The ''bodies'' mentioned by Vervoort (1966) are difficult to characterize, though we believe they could represent abnormal or damaged gonothecae. Kramp (1951: 122) and Vervoort (1966: 119-120) considered the presence of paired gonothecae as incidental or an abnormality. However, we also found paired gonothecae in the holotype of C. abyssicola, proving the event not to be rare. We concur with Kramp (1951), Vervoort (1996), and Calder and Vervoort (1998: 26) in regarding both species as conspecific.
We have had the opportunity to re-study the holotype of Cryptolaria humilis Allman, 1888 and a complete re-description is given below.
Colony badly preserved, erect, shrubby, 24 mm in height, polysiphonic though branches arising from a unique germinative tube, accessory tubes surrounding branching tube almost up to its distal part. Hydrorhiza composed of many long rhizoidal tubes. Colony scarcely branched in several planes, branches up to second order, hydrothecae arising from both stem and branches. Unique first-order branch 10 mm long, polysiphonic, 0.35 mm in diameter, branching of lower-order branches in several planes. Lateral branches arising at angles of 45-90u in relation to main stem, sometimes with axilar hydrotheca at origin. Stem (germinative and accessory tubes) and branches not divided into internodes, deprived of apophyses, distal part of stem bearing only hydrothecae; stem and branches without nematothecae. Hydrothecae sessile, tubular and curved outwards, irregularly arranged in several planes, with variable distance from each other though subsequent hydrotheca generally arising at axil of previous one. Hydrothecae of stem and polysiphonic branches surrounded by accessory tubes. Hydrothecae with more than half of their total length adnate to branches, free part emerging from long axis of branches at angles greater than 45u, usually 90u. Adnate portion of hydrothecae tubular, 0.83-1.88 mm (n52) long, perisarc smooth; free part cylindrical, smooth, 0.20-0.28 mm (n52) long, ratio adnate: free part 3.14-4.15:1 (n52); perisarc thin; hydrothecae not widening distally, margin even and smooth, with up to five shallow-medium renovations, with almost inconspicuously flaring rim; hydrothecal aperture circular, 0.23-0.25 mm (n52) in diameter, perpendicular to long axis of free part of hydrotheca. Hydranths not preserved at all. Gonothecae not seen. Nematocysts of one category, heterotrichous microbasic euryteles (not seen discharged), 5.0-5.562.0-2.5 mm, bean-shaped.
The colony studied by Allman (1888) is badly preserved, but general dimensions and the analysis of the cnidome of remnant tissue, as well as the habit of the colony, could be studied. These characteristics are not different from those of C. abyssicola, corroborating Vervoort's (1966) decision.
Allman (1888: 40) described, as Cryptolaria flabellum, a new species of hydroid based on infertile material. His description is very poor in details: ''Colony attaining a height of about one inch; hydrocaulus rigid, rooted by a thick disc-like expansion, ramification in a single plane, and irregular. Hydrothecae alternate, distichous, very long and slender. Gonosome not known''. The species was considered well marked by Allman (1888: 40) because ''its long curved hydrothecae resemble slender lateral branches, while its rigid habit, and the fact of the ramification being all in one and the same plane, call to my mind the general aspect of certain Gorgonian Corals''. Nevertheless, the original description and figures of C. flabellum make it clear the species does not belong to the genus Cryptolaria. Indeed, Stechow (1923: 147) assigned most of the species of Cryptolaria described by Allman (1877Allman ( , 1888 to the genus Oswaldaria (presently considered a synonym of Acryptolaria), including Acryptolaria flabellum. This specific name was also quoted by Fraser (1944: 212) and Vervoort (1968: 99), both referring to Allman's material.
The binomen Cryptolaria flabellum is still adopted in a series of papers for the northern seas (namely Naumov 1960;Filatova and Barsanova 1964;Belousov 1975a-as Cryptolaria flabellata-and 1975b. The only taxonomic paper of this series, Naumov (1960), has the description and figures of material sampled in the Bering and Okhotsk Seas. Vervoort (1972) considered Naumov's material belonging to a new species distinct from C. flabellum, because of the hydrothecal length, the more dense sets of hydrothecae, the lack of the initial arrangement in slightly displaced pairs, and the extremely high number of distal hydrothecal renovations. Naumov's material seems to be similar to the type species of Cryptolarella abyssicola, except by the presence of the numerous renovations in the older (5basal) hydrothecae. However, in the absence of gonothecae in the Russian material (cf. Naumov 1960), there is even the possibility of Naumov's material being a species of Acryptolaria. Vervoort (1972) transferred Acryptolaria flabellum sensu Vervoort (1968) to the genus Cryptolarella. The description in Vervoort (1972) is based on fertile material collected from deep water off Peru, in the tropical eastern Pacific, during the Vema Expedition, for which the gonotheca was described (p 48, Figure 13a, b), undoubtedly indicating that it belongs to the genus Cryptolarella. We have re-studied part of this material, without gonothecae, deposited in the Nationaal Natuurhistorisch Museum (Leiden, The Netherlands), and observed the hydrothecal arrangement in many planes, a characteristic of Cryptolarella. Vervoort (1972) did not inspect Allman's type. We have also studied the type material of Cryptolaria flabellum [BMNH 1888.11.13.27;''Challenger'' St. 24, 18u389300N, 65u059300W, off Culebra Island, West Indies, 390 fms (5713 m); Allman 1888: 40] and confirmed the material is indeed an Acryptolaria species, as proposed by Fraser (1944) and Vervoort (1968), especially based on the alternate pattern of hydrothecal arrangement, different from that found in the genus Cryptolarella and in Vervoort's (1972) material.
As Vervoort's (1972) Cryptolarella is correctly assigned to this genus, it is important to consider whether it deserves a new name. The most characteristic feature of Vervoort's material is the very long free part of the hydrothecae (1.10-1.59 mm) especially if compared to the adnate part (0.86-1.075 mm). Vervoort (1972: 47) himself noticed the ''length depending on the number of renovations being present''. Measurements without considering hydrothecal renovations show another perspective: abcauline length 1.127-1.4 mm; free adcauline length 0.403-0.550 mm; adnate adcauline length 0.950-1.127 mm; adcauline length 1.497-1.530 mm; diameter at aperture 0.161-0.190 mm. Nevertheless, although the type specimen of C. abyssicola is smaller (free part 0.25-0.90 mm; adnate part encompassing Vervoort's material, 0.40-1.38 mm), there is a high variation of the free part, from 0.12 mm (type of C. diffusa) to 1.40 mm (C. abyssicola for the Tasmanian Sea; Vervoort 1966). The development of the free part may be a variable trait, greatly influenced by environmental conditions. The proportion adnate: free part of the hydrotheca (0.67-0.78) also overlaps with material already recorded as C. abyssicola, that reach 0.71 (C. abyssicola for the Tasmanian Sea; Vervoort 1966) and 0.77 (''C. humilis'' by Browne 1907 from the Bay of Biscay, see Vervoort 1966) (Table I). All other dimensions given by Vervoort (1972) are also similar to those of C. abyssicola. Therefore, we presently regard Cryptolarella flabellum sensu Vervoort (1972) as C. abyssicola.
The morphometric data of the recorded and studied material of Cryptolarella abyssicola reveals its highly variable dimensions (cf. Vervoort 1985: 286) (Table I). However, a closer examination of the holotype of the species shows that most of this variation is included in the range of the holotype variation. The most striking exception to these inclusions is the generally smaller size (namely length of free adcauline hydrothecal wall, diameter of hydrothecal aperture, maximum diameter of gonothecae, and diameter of gonothecae at aperture) of the holotype of C. diffusa, although some of these dimensions overlap. Other differences are the wider hydrothecal aperture in the holotype of C. humilis (this study) and of C. abyssicola from the Bay of Biscay (Vervoort 1985: 286), and the longer free part of the hydrothecae in C. abyssicola from the Tasman Sea (Vervoort 1966: 118-120, due to repeated renovations in those colonies) and Peru (Vervoort 1972: 47-49). Vervoort (1985: 286;probably following Millard 1975: 172) correlated the length of the adnate hydrothecal wall with depth, ''the largest dimensions being usually found in deep water material''. However, the variation of the dimensions in the holotype makes this unlikely.
Cryptolarella abyssicola is known from deep water; considered to be a ''true bathyal hydroid'' (Vervoort 1985: 294), it also inhabits abyssal bottoms. There are scattered records of the species for the Atlantic, Pacific, Indian, and Antarctic Oceans. Kramp (1951: 122) noted that in ''several other groups of marine animals we know that the abyssal species frequently have a very extensive geographical distribution''.  Ramil and Vervoort 1992; 4578 m from the Mid-Atlantic Ridge after Calder and Vervoort 1998). The species was found on rock (Kramp 1951), worm tubes and anthipathariids (Vervoort 1966).